Showing papers in "Plant and Cell Physiology in 2002"
TL;DR: Results indicate that Hd 3a encodes a protein closely related to Arabidopsis FT and that the function and regulatory relationship with Hd1 and CO, respectively, of Hd3a and FT are conserved between rice (an SD plant) andArabidopsis (a long-day plant).
Abstract: ;Heading date 3a (Hd3a) has been detected as a heading-date-related quantitative trait locus in a cross between rice cultivars Nipponbare and Kasalath. A previous study revealed that the Kasalath allele of Hd3a promotes heading under short-day (SD) conditions. High-resolution linkage mapping located the Hd3a locus in a 20-kb genomic region. In this region, we found a candidate gene that shows high similarity to the FLOWERING LOCUS T (FT) gene, which promotes flowering in Arabidopsis. Introduction of the gene caused an early-heading phenotype in rice. The transcript levels of Hd3a were increased under SD conditions. The rice Heading date 1 (Hd1) gene, a homolog of CONSTANS (CO), has been shown to promote heading under SD conditions. By expression analysis, we showed that the amount of Hd3a mRNA is up-regulated by Hd1 under SD conditions, suggesting that Hd3a promotes heading under the control of Hd1. These results indicate that Hd3a encodes a protein closely related to Arabidopsis FT and that the function and regulatory relationship with Hd1 and CO, respectively, of Hd3a and FT are conserved between rice (an SD plant) and Arabidopsis (a long-day plant).
1,000 citations
TL;DR: A new unifying nomenclature is proposed that conveys an accurate description of the spectrum of biochemical activities that cumulative research has shown are catalyzed by xyloglucan endotransglucosylase/hydrolase (XTH).
Abstract: The polysaccharide xyloglucan is thought to play an important structural role in the primary cell wall of dicotyledons. Accordingly, there is considerable interest in understanding the biochemical basis and regulation of xyloglucan metabolism, and research over the last 16 years has identified a large family of cell wall proteins that specifically catalyze xyloglucan endohydrolysis and/or endotransglucosylation. However, a confusing and contradictory series of nomenclatures has emerged in the literature, of which xyloglucan endotransglycosylases (XETs) and endoxyloglucan transferases (EXGTs) are just two examples, to describe members of essentially the same class of genes/proteins. The completion of the first plant genome sequencing projects has revealed the full extent of this gene family and so this is an opportune time to resolve the many discrepancies in the database that include different names being assigned to the same gene. Following consultation with members of the scientific community involved in plant cell wall research, we propose a new unifying nomenclature that conveys an accurate description of the spectrum of biochemical activities that cumulative research has shown are catalyzed by these enzymes. Thus, a member of this class of genes/proteins will be referred to as a xyloglucan endotransglucosylase/hydrolase (XTH). The two known activities of XTH proteins are referred to enzymologically as xyloglucan endotransglucosylase (XET, which is hereby re-defined) activity and xyloglucan endohydrolase (XEH) activity. This review provides a summary of the biochemical and functional diversity of XTHs, including an overview of the structure and organization of the Arabidopsis XTH gene family, and highlights the potentially important roles that XTHs appear to play in numerous examples of plant growth and development.
716 citations
TL;DR: Results show that SRK2E plays an important role in ABA signaling in response to water stress, and it is demonstrated that two protein kinases, p44 and p42, were activated by ABA in Arabidopsis T87 cultured cells, and at least one protein kinase was activated not only by A BA but also by low humidity inArabidopsis plants.
Abstract: Protein phosphorylation has pivotal roles in ABA and osmotic stress signaling in higher plants. Two protein phosphatase genes, ABI1 and ABI2, are known to regulate these signaling pathways in Arabidopsis: The identity of ABA-activated protein kinases required for the ABA signaling, however, remains to be elucidated. Here we demonstrate that two protein kinases, p44 and p42, were activated by ABA in Arabidopsis T87 cultured cells, and at least one protein kinase, p44, was activated not only by ABA but also by low humidity in Arabidopsis plants. Analysis of T-DNA knockout mutants and biochemical analysis using a specific antibody revealed that the p44 is encoded by a SnRK2-type protein kinase gene, SRK2E. The srk2e mutation resulted in a wilty phenotype mainly due to loss of stomatal closure in response to a rapid humidity decrease. ABA-inducible gene expression of rd22 and rd29B was suppressed in srk2e. These results show that SRK2E plays an important role in ABA signaling in response to water stress.
554 citations
TL;DR: Current data points towards some CesA isoforms potentially being responsible for initiation or elongation of the recently identified sterol beta-glucoside primer within different cell types, e.g. those undergoing either primary or secondary wall cellulose synthesis.
Abstract: Modern techniques of gene cloning have identified the CesA genes as encoding the probable catalytic subunits of the plant CelS, the cellulose synthase enzyme complex visualized in the plasma membrane as rosettes. At least 10 CesA isoforms exist in Arabidopsis and have been shown by mutant analyses to play distinct role/s in the cellulose synthesis process. Functional specialization within this family includes differences in gene expression, regulation and, possibly, catalytic function. Current data points towards some CesA isoforms potentially being responsible for initiation or elongation of the recently identified sterol beta-glucoside primer within different cell types, e.g. those undergoing either primary or secondary wall cellulose synthesis. Different CesA isoforms may also play distinct roles within the rosette, and there is some circumstantial evidence that CesA genes may encode the catalytic subunit of the mixed linkage glucan synthase or callose synthase. Various other proteins such as the Korrigan endocellulase, sucrose synthase, cytoskeletal components, Rac13, redox proteins and a lipid transfer protein have been implicated to be involved in synthesizing cellulose but, apart from CesAs, only Korrigan has been definitively linked with cellulose synthesis. These proteins should prove valuable in identifying additional CelS components.
519 citations
TL;DR: A new model referred to as the "two-step branching and improper branch clearing model" is proposed to explain how amylopectin is synthesized, which emphasizes that two sets of reactions, alpha-1,6-branch formation and the subsequent alpha- 1,4-chain elongation, are fundamental to the construction of the cluster structure.
Abstract: Starch is made up of amylose (linear alpha-1,4-polyglucans) and amylopectin (alpha-1,6-branched polyglucans). Amylopectin has a distinct fine structure called multiple cluster structure and is synthesized by multiple subunits or isoforms of four classes of enzymes: ADPglucose pyrophosphorylase, soluble starch synthase (SS), starch branching enzyme (BE), and starch debranching enzyme (DBE). In the present paper, based on analyses of mutants and transgenic lines of rice in which each enzyme activity is affected, the contribution of the individual isoform to the fine structure of amylopectin in rice endosperm is evaluated, and a new model referred to as the "two-step branching and improper branch clearing model" is proposed to explain how amylopectin is synthesized. The model emphasizes that two sets of reactions, alpha-1,6-branch formation and the subsequent alpha-1,4-chain elongation, are catalyzed by distinct BE and SS isoforms, respectively, are fundamental to the construction of the cluster structure. The model also assesses the role of DBE, namely isoamylase or in addition pullulanase, to remove unnecessary alpha-1,6-glucosidic linkages that are occasionally formed at improper positions apart from two densely branched regions of the cluster.
481 citations
TL;DR: The results suggest that AS2 functions in the transcription of a certain gene(s) in plant nuclei and thereby controls the formation of a symmetric flat leaf lamina and the establishment of a prominent midvein and other patterns of venation.
Abstract: The ASYMMETRIC LEAVES2 (AS2) gene of Arabidopsis thaliana is involved in the establishment of the leaf venation system, which includes the prominent midvein, as well as in the development of a symmetric lamina. The gene product also represses the expression of class 1 knox homeobox genes in leaves. We have characterized the AS2 gene, which appears to encode a novel protein with cysteine repeats (designated the C-motif) and a leucine-zipper-like sequence in the amino-terminal half of the primary sequence. The Arabidopsis genome contains 42 putative genes that potentially encode proteins with conserved amino acid sequences that include the C-motif and the leucine-zipper-like sequence in the amino-terminal half. Thus, the AS2 protein belongs to a novel family of proteins that we have designated the AS2 family. Members of this family except AS2 also have been designated ASLs (AS2-like proteins). Transcripts of AS2 were detected mainly in adaxial domains of cotyledonary primordia. Green fluorescent protein-fused AS2 was concentrated in plant cell nuclei. Overexpression of AS2 cDNA in transgenic Arabidopsis plants resulted in upwardly curled leaves, which differed markedly from the downwardly curled leaves generated by loss-of-function mutation of AS2. Our results suggest that AS2 functions in the transcription of a certain gene(s) in plant nuclei and thereby controls the formation of a symmetric flat leaf lamina and the establishment of a prominent midvein and other patterns of venation.
363 citations
TL;DR: The biological roles of expansins are diverse, but can be related to the action of expansin to loosen cell walls, for example during cell enlargement, fruit softening, pollen tube and root hair growth, and abscission.
Abstract: Expansins are cell wall proteins that induce pH-dependent wall extension and stress relaxation in a characteristic and unique manner. Two families of expansins are known, named alpha- and beta-expansins, and they comprise large multigene families whose members show diverse organ-, tissue- and cell-specific expression patterns. Other genes that bear distant sequence similarity to expansins are also represented in the sequence databases, but their biological and biochemical functions have not yet been uncovered. Expansin appears to weaken glucan-glucan binding, but its detailed mechanism of action is not well established. The biological roles of expansins are diverse, but can be related to the action of expansins to loosen cell walls, for example during cell enlargement, fruit softening, pollen tube and root hair growth, and abscission. Expansin-like proteins have also been identified in bacteria and fungi, where they may aid microbial invasion of the plant body.
356 citations
TL;DR: A novel Myc-related bHLH transcription factor is identified, which physically associated with APRR1, which is similar in its amino acid sequence to PIF3, which has been identified as a phytochrome-interacting transcription factor.
Abstract: Several Arabidopsis genes have been proposed to encode potential clock-associated components, including the Myb-related CCA1 and LHY transcription factors and a member of the novel family of pseudo response regulators (APRR1/TOC1). We previously showed that mRNAs of the APRR1/TOC1 family of genes start accumulating after dawn rhythmically and sequentially at approximately 2 h intervals in the order: APRR9--> APRR7-->APRR5-->APRR3-->APRR1/TOC1. Here we constructed APRR1-overexpressing (APRR1-ox) plants, and examined certain circadian profiles for APRRs, CCA1, LHY, GI, CCR2, and CAB2. The free-running circadian rhythms of the APRR1/TOC1 family of genes, including APRR1, were dampened in APRR1-ox plants. In particular, the light-inducible expression of APRR9 was severely repressed in APRR1-ox plants, suggesting that there is a negative APRR1-->APRR9 regulation. The free-running robust rhythm of CAB2 was also dampened in APRR1-ox. The circadian profiles of potential clock-associated genes, CCA1, LHY, GI, and CCR2 were all markedly altered in APRR1-ox, each in characteristic fashion. To gain further insight into the molecular function of APRR1, we then identified a novel Myc-related bHLH transcription factor, which physically associated with APRR1. This protein (named PIL1) is similar in its amino acid sequence to PIF3, which has been identified as a phytochrome-interacting transcription factor. These results are discussed in relation to the current idea that APRR1 (TOC1) plays a role within, or close to, the Arabidopsis central oscillator.
252 citations
TL;DR: Rice (Oryza sativa L.) shows the highest tolerance to Al toxicity among small-grain cereal crops, however, the mechanisms and genetics responsible for its high Al tolerance are not yet well understood.
Abstract: Rice (Oryza sativa L.) shows the highest tolerance to Al toxicity among small-grain cereal crops, however, the mechanisms and genetics responsible for its high Al tolerance are not yet well understood. We investigated the response of rice to Al stress using the japonica variety Koshihikari in comparison to the indica variety Kasalath. Koshihikari showed higher tolerance at various Al concentrations than Kasalath. The Al content in root apexes was less in Koshihikari than in Kasalath, suggesting that exclusion mechanisms rather than internal detoxification are acting in Koshihikari. Al-induced secretion of citrate was observed in both Koshihikari and Kasalath, however, it is unlikely to be the mechanism for Al tolerance because there was no significant difference in the amount of citrate secreted between Koshihikari and Kasalath. Quantitative trait loci (QTLs) for Al tolerance were mapped in a population of 183 backcross inbred lines (BILs) derived from a cross of Koshihikari and Kasalath. Three putative QTLs controlling Al tolerance were detected on chromosomes 1, 2 and 6. Kasalath QTL alleles on chromosome 1 and 2 reduced Al tolerance but increased tolerance on chromosome 6. The three QTLs explained about 27% of the phenotypic variation in Al tolerance. The existence of QTLs for Al tolerance was confirmed in substitution lines for corresponding chromosomal segments.
251 citations
TL;DR: In vivo detection of (1)O(2) and O(2)(-*) by fluorescence quenching of two dansyl-based ROS sensors, the singlet oxygen specific DanePy and HO-1889NH, which is reactive to both singinglet oxygen and superoxide radicals.
Abstract: ;In order to understand the physiological functions of reactive oxygen species (ROS) generated in leaves, their direct measurement in vivo is of special importance. Here we report experiments with two dansyl-based ROS sensors, the singlet oxygen specific DanePy and HO-1889NH, which is reactive to both singlet oxygen and superoxide radicals. Here we report in vivo detection of 1 O 2 and O 2 – by fluorescence quenching of two dansyl-based ROS sensors, the 1 O2 specific DanePy and HO-1889NH, which was reactive with both 1 O2 and O2 – . The ROS sensors were administered to spinach leaves through a pinhole, and then the leaves were exposed to either excess photosynthetically active radiation or UV (280–360 nm) radiation. Microlocalization of the sensors’ fluorescence and its ROS-induced quenching was followed with confocal laser scanning microscopy and with fluorescence imaging. These sensors were specifically localized in chloroplasts. Quenching analysis indicated that the leaves exposed to strong light produced 1 O 2 , but hardly any O 2 – . On the other hand, the dominant ROS in UV-irradiated leaves was O2 – , while 1 O2 was minor.
244 citations
TL;DR: Kinetic and microscopic observations, using the intracellular fluorescent NO probe 4,5-diaminofluorescein-2 diacetate, both demonstrated that NO was produced within the cells in response to the addition of nitrite.
Abstract: Biological activity of nitric oxide (NO) production was investigated in the unicellular green alga Chlamydomonas reinhardtii. An NO specific electrode detected a rapid increase in signal when nitrite (NO(2)(-)) was added into a suspension of C. reinhardtii intact cells in the dark. The addition of KCN or the NO quencher bovine hemoglobin completely abolished the signal, verifying that the nitrite-dependent increase in signal is due to enzymatic NO production. L-arginine, the substrate for NO synthase, did not induce detectable NO production and the NOS inhibitor N(omega)-nitro-L-arginine showed no inhibitory effect on the nitrite-dependent production of NO. Illuminating cells showed a significant suppressive effect on NO production. When the photosynthetic electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea was present in the suspension, C. reinhardtii cells produced NO after the addition of nitrite even under illumination. Kinetic and microscopic observations, using the intracellular fluorescent NO probe 4,5-diaminofluorescein-2 diacetate, both demonstrated that NO was produced within the cells in response to the addition of nitrite. The Chlamydomonas mutant cc-2929, which lacks nitrate reductase (NR) activity, did not display any of the responses observed in the wild-type cells. The results presented here provide direct in vivo evidence to confirm that NR is involved in the nitrite-dependent NO production in the green alga.
TL;DR: Results showed that HgCl(2) consistently lowered g(i) and it is probable that the photosynthetic CO( 2) uptake across the plasma membrane of the mesophyll cells is facilitated by mercury-sensitive aquaporins.
Abstract: Experiments were conducted to examine whether mercury-sensitive aquaporins facilitate photosynthetic CO(2) diffusion across the plasma membrane of leaf mesophyll cells. Discs without abaxial epidermes from Vicia faba leaflets were treated with HgCl(2), an inhibitor of aquaporins. Hydraulic conductivity of the plasma membrane of these discs, measured as the weight loss of the discs in the 1 M sorbitol solution, was inhibited by sub-mM concentrations of HgCl(2) by 70 to 80%. Photosynthetic CO(2) fixation was also inhibited by the HgCl(2) treatment in a similar concentration range. When 0.3 mM HgCl(2) solution was fed to the V. faba leaflets with intact epidermes via the transpiration stream, the rate of photosynthesis on leaf area basis (A) measured at photosynthetically active photon flux density of 700 micromol m(-2) s(-1) and at leaf temperature of 25 degrees C, decreased by about 20 to 30% at any CO(2) concentration in the intercellular spaces (C(i)). However, when CO(2) concentration in the chloroplast stroma (C(c)) was calculated from fluorescence and gas exchange data and A was plotted against C(c), A at low C(c) concentrations did not differ before and after the treatment. The conductance for CO(2) diffusion from the intercellular spaces to the chloroplast stroma (g(i)) decreased to 40 and 30% of the control value, when the leaflets were fed with 0.3 mM and 1.2 mM HgCl(2), respectively. Similar results were obtained with leaves of Phaseolus vulgaris. Although effects of HgCl(2) were not specific, the present results showed that HgCl(2) consistently lowered g(i). It is, thus, probable that the photosynthetic CO(2) uptake across the plasma membrane of the mesophyll cells is facilitated by mercury-sensitive aquaporins.
TL;DR: The findings indicate that the shape, size, number and movement of peroxisomes in living cells are dynamic and changeable rather than uniform.
Abstract: Peroxisomes were visualized in living cells of various tissues in transgenic Arabidopsis by green fluorescent protein (GFP) through the addition of the peroxisomal targeting signal 1 (PTS1) or PTS2. The observation using confocal laser scanning microscopy revealed that the GFP fluorescence signals were detected as spherical spots in all cells of two kinds of transgenic plants. Immunoelectron microscopic analysis using antibodies against the peroxisomal marker protein, catalase, showed the presence of GFP in peroxisomes, confirming that GFP was correctly transported into peroxisomes by PTS1 or PTS2 pathways. It has been also revealed that peroxisomes are motile organelles whose movement might be caused by cytoplasmic flow. The movement of peroxisomes was more prominent in root cells than that in leaves, and divided into two categories: a relatively slow, random, vibrational movement and a rapid movement. Treatment with anti-actin and anti-tubulin drugs revealed that actin filaments involve in the rapid movement of peroxisomes. Moreover, abnormal large peroxisomes are present as clusters at the onset of germination, and these clusters disappear in a few days. Interestingly, tubular peroxisomes were also observed in the hypocotyl. These findings indicate that the shape, size, number and movement of peroxisomes in living cells are dynamic and changeable rather than uniform.
TL;DR: The results indicate that WWC functions as a starter of photosynthesis by generating DeltapH across thylakoid membranes for NPQ formation, supplying ATP for carbon assimilation, but WWC does not act to maintain a high NPQ, and PhiPSII is down-regulated by DeltAPH generated via the cyclic electron flow around PSI.
Abstract: Changes in chlorophyll fluorescence, P700(+)-absorbance and gas exchange during the induction phase and steady state of photosynthesis were simultaneously examined in rice (Oryza sativa L.), including the rbcS antisense plants. The quantum yield of photosystem II (PhiPSII) increased more rapidly than CO(2) assimilation in 20% O(2). This rapid increase in PhiPSII resulted from the electron flux through the water-water cycle (WWC) because of its dependency on O(2). The electron flux of WWC reached a maximum just after illumination, and rapidly generated non-photochemical quenching (NPQ). With increasing CO(2) assimilation, the electron flux of WWC and NPQ decreased. In 2% O(2), WWC scarcely operated and PhiPSI was always higher than PhiPSII. This suggested that cyclic electron flow around PSI resulted in the formation of NPQ, which remained at higher levels in 2% O(2). The electron flux of WWC in the rbcS antisense plants was lower, but these plants always showed a higher NPQ. This was also caused by the operation of the cyclic electron flow around PSI because of a higher ratio of PhiPSI/PhiPSII, irrespective of O(2) concentration. The results indicate that WWC functions as a starter of photosynthesis by generating DeltapH across thylakoid membranes for NPQ formation, supplying ATP for carbon assimilation. However, WWC does not act to maintain a high NPQ, and PhiPSII is down-regulated by DeltapH generated via the cyclic electron flow around PSI.
TL;DR: The phenotype of the Arabidopsis ped3 mutant indicated that the mutation in the PED3 gene inhibits the activity of fatty acid beta-oxidation, and Ped3p may contribute to the transport of fatty acids and their derivatives across the peroxisomal membrane.
Abstract: ;Glyoxysomes, a group of specialized peroxisomes, are organelles that degrade fatty acids by the combination of fatty acid -oxidation and glyoxylate cycle. However, the mechanism underlying the transport of the fatty acids across the peroxisomal membrane is still obscure in higher plant cells. We identified and analyzed the PED3 gene and its gene product, Ped3p. The phenotype of the Arabidopsis ped3 mutant indicated that the mutation in the PED3 gene inhibits the activity of fatty acid -oxidation. Ped3p is a 149-kDa protein that exists in peroxisomal membranes. The amino acid sequence of Ped3p had a typical characteristic for “full-size” ATP-binding cassette (ABC) transporter consisting of two transmembrane regions and two ATP-binding regions. This protein was divided into two parts, that had 32% identical amino acid sequences. Each part showed a significant sequence similarity with peroxisomal “half” ABC transporters so far identified in mammals and yeast. Ped3p may contribute to the transport of fatty acids and their derivatives across the peroxisomal membrane.
TL;DR: The sequence requirement of the ACGT-containing abscisic acid response element (ABRE) was determined as ACGTG G/T C, which matched very well with the consensus derived from sequence comparison of ABA-responsive promoters.
Abstract: The sequence requirement of the ACGT-containing abscisic acid response element (ABRE) was analyzed by systematically substituting the bases surrounding the ACGT-core of motif A, the principal ABRE of the rice gene, OSEM: This was done within the context of a 55-bp promoter fragment that minimally confers ABA-responsiveness to a heterologous promoter. Based on this analysis, the sequence requirement of the ACGT-containing ABRE was determined as ACGTG G/T C, which matched very well with the consensus derived from sequence comparison of ABA-responsive promoters.
TL;DR: Domain search analyses led to the classification of the Arabidopsis F-box proteins into at least 19 groups based on their domain structures, including Kelch repeats, LRRs and WD40 repeats, which are implicated in protein-protein interactions.
Abstract: ;F-box proteins regulate diverse cellular processes, including cell cycle transition, transcriptional regulation and signal transduction, by playing roles in Skp1p-cullin-Fbox protein (SCF) complexes or non-SCF complexes. F-box proteins are encoded by a large gene family. Our database search revealed that at least 568 F-box protein genes are present in the Arabidopsis thaliana (Arabidopsis) genome. Domain search analysis using SMART and Pfam-A databases revealed that 67 of the F-box proteins contained Kelch repeats and 29 contained leucine-rich repeats (LRRs). Interestingly only two F-box proteins contained WD40 repeats that are found in many F-box proteins of other organisms. Kelch repeats, LRRs and WD40 repeats are implicated in protein–protein interactions. This analysis also resulted in the finding of several unique functional domains; however, 448 of the F-box proteins did not contain any known domains. Therefore, these proteins were used to search the Pfam-B database to find novel domains, and three putative ones were found. These domain search analyses led us to classify the Arabidopsis F-box proteins into at least 19 groups based on their domain structures. Macro array analysis showed that several F-box protein genes are expressed in a tissue-specific manner.
TL;DR: Protein kinases and protein phosphatase were first identified as peroxisomal proteins suggesting that protein phosphorylation is one of the regulatory mechanisms in leaf peroxISomes.
Abstract: Leaf peroxisomes are present in greening cotyledons and contain enzymes of the glycolate pathway that functions in photorespiration. However, only a few leaf peroxisomal proteins, that is hydroxypyruvate reductase (HPR), glycolate oxidase (GO) and alanine:glyoxylate aminotransferase 1 (AGT1), have been characterized, and other functions in leaf peroxisomes have not been solved. To better understand the functions of leaf peroxisomes, we established a method to isolate leaf peroxisomes of greening cotyledons. We analyzed 53 proteins by MALDI-TOF MS and then identified 29 proteins. Among them, five proteins are related to the glycolate pathway, four proteins function in scavenging of hydrogen peroxide and additionally 20 novel leaf peroxisomal proteins were identified. In particular, protein kinases and protein phosphatase were first identified as peroxisomal proteins suggesting that protein phosphorylation is one of the regulatory mechanisms in leaf peroxisomes. Novel leaf peroxisomal proteins contained five PTS1-like proteins that have sequences where one amino acid is substituted with another one in PTS1 sequences. The PTS1 motif was suggested to have novel PTS1 sequences.
TL;DR: It is demonstrated that PGP1 plays a major role in the biosynthesis of phosphatidylglycerol in chloroplasts, and that phosphatidell cells with chloroplast particles are only found around vascular structures, whereas epidermal cells are enlarged but largely conserved.
Abstract: Phosphatidylglycerol is a ubiquitous phospholipid in the biological membranes of many organisms. In plants, phosphatidylglycerol is mainly present in thylakoid membranes and has been suggested to play specific roles in photosynthesis. Here, we have isolated two T-DNA tagged lines of Arabidopsis thaliana that have a T-DNA insertion in the PGP1 gene encoding a phosphatidylglycerolphosphate synthase involved in the biosynthesis of phosphatidylglycerol. In homozygous plants of the T-DNA tagged lines, the PGP1 gene was completely disrupted. The growth of these knockout mutants was dependent on the presence of sucrose in the growth medium, and these plants had pale yellow-green leaves. The leaves of the mutants had remarkably large intercellular spaces due to the reduction in the number of mesophyll cells. The development of chloroplasts in the leaf cells was severely arrested in the mutants. Mesophyll cells with chloroplast particles are only found around vascular structures, whereas epidermal cells are enlarged but largely conserved. The content of phosphatidylglycerol in the mutants was reduced to 12% of that of the wild type. These results demonstrate that PGP1 plays a major role in the biosynthesis of phosphatidylglycerol in chloroplasts, and that phosphatidylglycerol is essential for the development of thylakoid membranes in A. thaliana.
TL;DR: Results indicate that aquaporins in the root, especially the RsPIP2 group, may be a stress responsive type of aquaporin at least in the protein level.
Abstract: Aquaporins in the plasma and vacuolar membranes play a key role in the intercellular and intracellular water transport in plants. First, we quantitated the absolute amounts for mRNAs of eight aquaporin isoforms in hypocotyls of radish seedlings. Then, we investigated the effects of salt and water stresses (150 mM NaCl, 300 mM mannitol and 20% polyethylene glycol) and phytohormones (gibberellic acid, abscisic acid and brassinolide) on the mRNA and protein levels of aquaporins in the plasma membrane (RsPIP1-1, 1-2, 1-3, 2-1, 2-2 and 2-3) and vacuolar membrane (RsTIP1-1 and 2-1). The mRNA and protein levels of RsTIP1-1, RsTIP2-1, RsPIP1-1, RsPIP1-2 and RsPIP1-3 were comparatively constant. In contrast, mannitol treatment altered the mRNA levels of RsPIP2-1, RsPIP2-2 and RsPIP2-3 in roots. Immunoblot analysis showed that the RsPIP2-1 protein level was increased by NaCl treatment and decreased by treatment with mannitol and polyethylene glycol. Gibberellic acid and abscisic acid suppressed the levels of mRNAs of RsPIP2-1, RsPIP2-2 and RsPIP2-3 and the protein level of RsPIP2-1 in roots. On the other hand, the protein levels of RsPIP1-group members and RsTIPs were scarcely changed by these phytohormones. In the case of hypocotyls and cotyledons, the mRNA and protein levels of eight isoforms were not markedly affected by any treatment. These results indicate that aquaporins in the root, especially the RsPIP2 group, may be a stress responsive type of aquaporin at least in the protein level.
TL;DR: The expression patterns of the rice homolog of GI, OsGI, were similar to those of the Arabidopsis GI, suggesting the conservation of some mechanisms for the photoperiodic regulation of flowering between these two species.
Abstract: To better understand the molecular mechanisms of the photoperiodic regulation of rice, a short-day plant, we isolated 27 cDNAs that were differentially expressed in the photoperiod-insensitive se5 mutant from approximately 8,400 independent mRNA species by the use of a fluorescent differential display (FDD). For this screening, we isolated mRNAs at five different time points during the night and compared their expression patterns between se5 and the wild type. Of 27 cDNAs isolated, 12 showed diurnal expression patterns often associated with genes involved in the determination of the flowering time. In se5, expression of nine cDNAs was increased. Five of these cDNAs were up-regulated under SD, suggesting that they may promote flowering under SD. They included genes encoding a cDNA containing a putative NAC domain, the fructose-bisphosphate aldolase, and a protease inhibitor. Expression of three cDNAs was decreased in se5 but not photoperiodically regulated. These cDNAs included a rice homolog of Arabidopsis GIGANTEA (GI), lir1, and a gene for myo-inositol 1-phosphate synthase, all of which were previously shown to be under the control of circadian clocks. The expression patterns of the rice homolog of GI, OsGI, were similar to those of the Arabidopsis GI, suggesting the conservation of some mechanisms for the photoperiodic regulation of flowering between these two species.
TL;DR: Restoration of leaf size could not be explained solely on the basis of an increase in individual cell volume, thus suggesting that brassinosteroids play a dual role in regulating cell expansion and proliferation.
Abstract: ;The growth of leaves in the model plant, Arabidopsis thaliana (L.) Heynh., is determined by the extent of expansion of individual cells and by cell proliferation. Mutants of A. thaliana with known defects in the biosynthesis or perception of brassinosteroids develop small leaves. When the leaves of brassinosteroid-related mutants, det2 (deetiolated2 = cro1) and dwf1 (dwarf1 = cro2) were compared to wild-type plants, an earlier cessation of leaf expansion was observed; a detailed anatomical analysis further revealed that the mutants had fewer cells per leaf blade. Treatment of the det2 mutants with the brassinosteroid, brassinolide, reversed the mutation and restored the potential for growth to that of the wild type. Restoration of leaf size could not be explained solely on the basis of an increase in individual cell volume, thus suggesting that brassinosteroids play a dual role in regulating cell expansion and proliferation.
TL;DR: Peroxisome movement is most intense in elongated cells and those involved in long distance transport, suggesting that higher plants use cytoplasmic streaming to help transport vesicles and organelles over long distances.
Abstract: Here we examine peroxisomes in living plant cells using transgenic Arabidopsis thaliana plants expressing the green fluorescent protein (GFP) fused to the peroxisome targeting signal 1 (PTS1). Using time-lapse laser scanning confocal microscopy we find that plant peroxisomes exhibit fast directional movement with peak velocities approaching 10 microm s(-1). Unlike mammalian peroxisomes which move on microtubules, plant peroxisome movement is dependent on actin microfilaments and myosin motors, since it is blocked by treatment with latrunculin B and butanedione monoxime, respectively. In contrast, microtubule-disrupting drugs have no effect on peroxisome streaming. Peroxisomes were further shown to associate with the actin cytoskeleton by the simultaneous visualization of actin filaments and peroxisomes in living cells using GFP-talin and GFP-PTS1 fusion proteins, respectively. In addition, peroxisome budding was observed, suggesting a possible mechanism of plant peroxisome proliferation. The strong signal associated with the GFP-PTS1 marker also allowed us to survey cytoplasmic streaming in different cell types. Peroxisome movement is most intense in elongated cells and those involved in long distance transport, suggesting that higher plants use cytoplasmic streaming to help transport vesicles and organelles over long distances.
TL;DR: Results suggest that, during the early stage of caryopsis development, OsCIN1 is important for supplying a carbon source to developing filial tissues by cleaving unloaded sucrose in the apoplast.
Abstract: To establish the significance of cell wall invertase in grain filling of rice (Oryza sativa L.), we cloned a cDNA for a cell wall invertase from developing grains of rice. The cDNA, designated OsCIN1, contains an open reading frame of 1731 bp encoding a polypeptide of 577 amino acid residues. The deduced amino acid sequence showed typical features of the cell wall invertases, including a beta-fructosidase motif and a cysteine catalytic site, and shared 78.6 and 73.7% identity with maize cell wall invertases, Incw1 and Incw2, respectively. OsCIN1 is expressed in roots, in sink- and source-leaves, and in panicles. During the course of grain filling in the caryopses, OsCIN1 transcript is detectable only in the very early stage of their development, 1-4 d after flowering, when the cell wall invertase activity is the highest and the increase in caryopsis length is rapid. In situ localization of the mRNA revealed that OsCIN1 is expressed preferentially in the vascular parenchyma of the dorsal vein, integument and its surrounding cells, and is expressed weakly in the nucellar projection and nucellar epidermis. These results suggest that, during the early stage of caryopsis development, OsCIN1 is important for supplying a carbon source to developing filial tissues by cleaving unloaded sucrose in the apoplast.
TL;DR: Epigenetic modification of plant gene and transposon activity, which correlates with their methylation, is often heritable over many generations, allowing conventional genetic linkage analysis to identify the sequences affected in epigenetic variants.
Abstract: Epigenetic modification of plant gene and transposon activity, which correlates with their methylation, is often heritable over many generations. Such heritable properties allow conventional genetic linkage analysis to identify the sequences affected in epigenetic variants. Machinery controlling the establishment of the epigenetic state and role of the epigenetic controls in plant development are also discussed.
TL;DR: This review summarises recent literature on endo-beta-1,4-glucanases and their role in plant development and addresses the possible functions of membrane-anchored isoforms in the synthesis of cellulose.
Abstract: Recent studies have highlighted the involvement of membrane-anchored endo-beta-1,4-glucanases in cellulose biosynthesis in plants, suggesting that there are parallels with Agrobacterium tumefaciens and other bacteria which also require endo-beta-1,4-glucanases for cellulose synthesis. This review summarises recent literature on endo-beta-1,4-glucanases and their role in plant development and addresses the possible functions of membrane-anchored isoforms in the synthesis of cellulose.
TL;DR: Results suggest that MS1 protein is a nuclear signal molecule indispensable for pollen maturation, and identifies the Arabidopsis MALE STERILITY1 gene by transposon-mediated mutagenesis.
Abstract: We identified the Arabidopsis MALE STERILITY1 (MS1) gene by transposon-mediated mutagenesis. In the transposon-inserted allele ms1-8, normal immature microspores separated from tetrads, but their subsequent maturation was abnormal: the outer layer of the microspore was absent, and both the microspore and the tapetal layer gradually became vacuolated. Empty locules resulted. The MS1 gene was expressed only in the tapetal layer during a very short period when the microspores were packed as tetrads. By the time the microspores had separated, the gene was no longer expressed. MS1 was not expressed in microspores. MS1 encodes a protein with a PHD-finger motif characteristic of some transcriptional regulators. A fusion protein consisting of the N-terminus of MS1 and green fluorescent protein was localized in the nucleus. These results suggest that MS1 protein is a nuclear signal molecule indispensable for pollen maturation.
TL;DR: The result suggests that the level of the accD subunit is a determinant of ACCase levels, and that enzyme levels are in part controlled post-transcriptionally at thelevel of subunit assembly.
Abstract: Acetyl-CoA carboxylase (ACCase) in plastids is a key enzyme regulating the rate of de novo fatty acid biosynthesis in plants. Plastidic ACCase is composed of three nuclear-encoded subunits and one plastid-encoded accD subunit. To boost ACCase levels, we examined whether overexpression of accD elevates ACCase production. Using homologous recombination, we replaced the promoter of the accD operon in the tobacco plastid genome with a plastid rRNA-operon (rrn) promoter that directs enhanced expression in photosynthetic and non-photosynthetic organs, and successfully raised the total ACCase levels in plastids. This result suggests that the level of the accD subunit is a determinant of ACCase levels, and that enzyme levels are in part controlled post-transcriptionally at the level of subunit assembly. The resultant transformants grew normally and the fatty acid content was significantly increased in leaves, but not significantly in seeds. However, the transformants displayed extended leaf longevity and a twofold increase of seed yield over the control value, which eventually almost doubled the fatty acid production per plant of the transformants relative to control and wild-type plants. These findings offer a potential method for raising plant productivity and oil production.
TL;DR: It is concluded that P1-ZCr functions as a defense against oxidative stress by scavenging the highly toxic, lipid peroxide-derived alpha,beta-unsaturated aldehydes.
Abstract: P1-zeta-crystallin (P1-ZCr) is an oxidative stress-induced NADPH:quinone oxidoreductase in Arabidopsis thaliana, but its physiological electron acceptors have not been identified. We found that recombinant P1-ZCr catalyzed the reduction of 2-alkenals of carbon chain C-3-C-9 with NADPH. Among these 2-alkenals, the highest specificity was observed for 4-hydroxy-(2E)-nonenal (HNE), one of the major toxic products generated from lipid peroxides. (3Z)-Hexenal and aldehydes without alpha,beta-unsaturated bonds did not serve as electron acceptors. In the 2-alkenal molecules, P1-ZCr catalyzed the hydrogenation of alpha,beta-unsaturated bonds, but not the reduction of the aldehyde moiety, to produce saturated aldehydes, as determined by gas chromatography/mass spectrometry. We propose the enzyme name NADPH:2-alkenal alpha,beta-hydrogenase (ALH). A major portion of the NADPH-dependent HNE-reducing activity in A. thaliana leaves was inhibited by the specific antiserum against P1-ZCr, indicating that the endogenous P1-ZCr protein has ALH activity. Because expression of the P1-ZCr gene in A. thaliana is induced by oxidative stress treatments, we conclude that P1-ZCr functions as a defense against oxidative stress by scavenging the highly toxic, lipid peroxide-derived alpha,beta-unsaturated aldehydes.
TL;DR: Three genes homologous to water channels in the plasma membrane type subfamily from roots of barley seedlings were identified and competitive reverse transcription (RT)-PCR was applied in order to distinguish and to quantify their transcripts.
Abstract: We identified three genes homologous to water channels in the plasma membrane type subfamily from roots of barley seedlings. These genes were designated HvPIP2;1, HvPIP1;3, and HvPIP1;5 after comparison to Arabidopsis aquaporins. Competitive reverse transcription (RT)-PCR was applied in order to distinguish and to quantify their transcripts. The HvPIP2;1 transcript was the most abundant among the three in roots. Salt stress (200 mM NaCl) down-regulated HvPIP2;1 (transcript and protein), but had almost no effect on the expressions of HvPIP1;3, or HvPIP1;5. Approximately equal amounts of the transcripts of the three were detected in shoots, and salt stress enhanced the expression of HvPIP2;1 but not of HvPIP1;3, or HvPIP1;5. HvPIP2;1 protein was confirmed to be localized in the plasma membrane. Functional expression of HvPIP2;1 in Xenopus oocytes confirmed that HvPIP2;1 encoded an aquaporin that transports water. This water permeability was reduced by HgCl(2), which is a typical water channel inhibitor. This activity was not modified by some inhibitors against protein kinase and protein phosphatase.