scispace - formally typeset
Search or ask a question

Showing papers on "Endosperm published in 2003"


Journal ArticleDOI
TL;DR: For the first time, tools for global analyses of starch biosynthesis are available for cereal crops, and are heralded by the draft sequence of the rice genome.

508 citations


Journal ArticleDOI
TL;DR: The data indicate that SUSIBA2 binds to the SURE elements in the barley iso1 promoter as an activator and demonstrate the involvement of a WRKY protein in carbohydrate anabolism.
Abstract: SURE (sugar responsive) is a cis element in plant sugar signaling. The SURE element was reported first for potato, in which it confers sugar responsiveness to the patatin promoter. A SURE binding transcription factor has not been isolated. We have isolated a transcription factor cDNA from barley and purified the corresponding protein. The transcription factor, SUSIBA2 (sugar signaling in barley), belongs to the WRKY proteins and was shown to bind to SURE and W-box elements but not to the SP8a element in the iso1 promoter. Nuclear localization of SUSIBA2 was demonstrated in a transient assay system with a SUSIBA2:green fluorescent protein fusion protein. Exploiting the novel transcription factor oligodeoxynucleotide decoy strategy with transformed barley endosperm provided experimental evidence for the importance of the SURE elements in iso1 transcription. Antibodies against SUSIBA2 were produced, and the expression pattern for susiba2 was determined at the RNA and protein levels. It was found that susiba2 is expressed in endosperm but not in leaves. Transcription of susiba2 is sugar inducible, and ectopic susiba2 expression was obtained in sugar-treated leaves. Likewise, binding to SURE elements was observed for nuclear extracts from sugar-treated but not from control barley leaves. The temporal expression of susiba2 in barley endosperm followed that of iso1 and endogenous sucrose levels, with a peak at ∼12 days after pollination. Our data indicate that SUSIBA2 binds to the SURE elements in the barley iso1 promoter as an activator. Furthermore, they show that SUSIBA2 is a regulatory transcription factor in starch synthesis and demonstrate the involvement of a WRKY protein in carbohydrate anabolism. Orthologs to SUSIBA2 were isolated from rice and wheat endosperm.

494 citations


Journal ArticleDOI
TL;DR: It is demonstrated that Sus plays a rate-limiting role in the initiation and elongation of the single-celled fibers and that suppression of Sus only in the maternal seed tissue represses fiber development without affecting embryo development and seed size.
Abstract: Cotton is the most important textile crop as a result of its long cellulose-enriched mature fibers. These single-celled hairs initiate at anthesis from the ovule epidermis. To date, genes proven to be critical for fiber development have not been identified. Here, we examined the role of the sucrose synthase gene (Sus) in cotton fiber and seed by transforming cotton with Sus suppression constructs. We focused our analysis on 0 to 3 days after anthesis (DAA) for early fiber development and 25 DAA, when the fiber and seed are maximal in size. Suppression of Sus activity by 70% or more in the ovule epidermis led to a fiberless phenotype. The fiber initials in those ovules were fewer and shrunken or collapsed. The level of Sus suppression correlated strongly with the degree of inhibition of fiber initiation and elongation, probably as a result of the reduction of hexoses. By 25 DAA, a portion of the seeds in the fruit showed Sus suppression only in the seed coat fibers and transfer cells but not in the endosperm and embryo. These transgenic seeds were identical to wild-type seeds except for much reduced fiber growth. However, the remaining seeds in the fruit showed Sus suppression both in the seed coat and in the endosperm and embryo. These seeds were shrunken with loss of the transfer cells and were <5% of wild-type seed weight. These results demonstrate that Sus plays a rate-limiting role in the initiation and elongation of the single-celled fibers. These analyses also show that suppression of Sus only in the maternal seed tissue represses fiber development without affecting embryo development and seed size. Additional suppression in the endosperm and embryo inhibits their own development, which blocks the formation of adjacent seed coat transfer cells and arrests seed development entirely.

443 citations


Journal ArticleDOI
TL;DR: The results demonstrate that seed abortion in the medea mutant is largely mediated by deregulated expression of the type I MADS-box gene PHE1, consistent with the proposed function of the FIS genes as transcriptional repressors.
Abstract: The Polycomb-group (PcG) proteins MEDEA, FERTILIZATION INDEPENDENT ENDOSPERM, and FERTILIZATION INDEPENDENT SEED2 regulate seed development in Arabidopsis by controlling embryo and endosperm proliferation. All three of these FIS-class proteins are likely subunits of a multiprotein PcG complex, which epigenetically regulates downstream target genes that were previously unknown. Here we show that the MADS-box gene PHERES1 (PHE1) is commonly deregulated in the fis-class mutants. PHE1 belongs to the evolutionarily ancient type I class of MADS-box proteins that have not yet been assigned any function in plants. Both MEDEA and FIE directly associate with the promoter region of PHE1, suggesting that PHE1 expression is epigenetically regulated by PcG proteins. PHE1 is expressed transiently after fertilization in both the embryo and the endosperm; however, it remains up-regulated in the fis mutants, consistent with the proposed function of the FIS genes as transcriptional repressors. Reduced expression levels of PHE1 in medea mutant seeds can suppress medea seed abortion, indicating a key role of PHE1 repression in seed development. PHE1 expression in a hypomethylated medea mutant background resembles the wild-type expression pattern and is associated with rescue of the medea seed-abortion phenotype. In summary, our results demonstrate that seed abortion in the medea mutant is largely mediated by deregulated expression of the type I MADS-box gene PHE1.

435 citations


Journal ArticleDOI
TL;DR: It is established that msi1 mutant gametophytes initiate endosperm development in the absence of fertilization at a high penetrance and that MSI1 has an essential function in the correct initiation and progression of seed development.
Abstract: Seed development in angiosperms initiates after double fertilization, leading to the formation of a diploid embryo and a triploid endosperm. The active repression of precocious initiation of certain aspects of seed development in the absence of fertilization requires the Polycomb group proteins MEDEA (MEA), FERTILIZATION-INDEPENDENT ENDOSPERM (FIE) and FERTILIZATION-INDEPENDENT SEED2. Here we show that the Arabidopsis WD-40 domain protein MSI1 is present together with MEA and FIE in a 600 kDa complex and interacts directly with FIE. Mutant plants heterozygous for msi1 show a seed abortion ratio of 50% with seeds aborting when the mutant allele is maternally inherited, irrespective of a paternal wild-type or mutant MSI1 allele. Further more, msi1 mutant gametophytes initiate endosperm development in the absence of fertilization at a high penetrance. After pollination, only the egg cell becomes fertilized, the central cell starts dividing prior to fertilization, resulting in the formation of seeds containing embryos surrounded by diploid endosperm. Our results establish that MSI1 has an essential function in the correct initiation and progression of seed development.

421 citations


Journal ArticleDOI
TL;DR: In this paper, the expression of the soybean ferritin gene under the control of the glutelin promoter in rice has proven to be effective in enhancing grain nutritional levels, not only in brown grains but also in polished grains.

387 citations


Journal ArticleDOI
TL;DR: Genetic ablation of PA-accumulating cells targeted by the BAN promoter fused to BARNASE led to the formation of normal plants that produced viable yellow seeds, which had no obvious defects in endosperm and embryo development.
Abstract: Anthocyanidin reductase encoded by the BANYULS (BAN) gene is the core enzyme in proanthocyanidin (PA) biosynthesis. Here, we analyzed the developmental mechanisms that regulate the spatiotemporal expression of BAN in the developing Arabidopsis seed coat. PA-accumulating cells were localized histochemically in the inner integument (seed body and micropyle) and pigment strand (chalaza). BAN promoter activity was detected specifically in these cells. Gain-of-function experiments showed that an 86-bp promoter fragment functioned as an enhancer specific for PA-accumulating cells. Mutations in regulatory genes of PA biosynthesis abolished BAN promoter activity (transparent testa2 [tt2], tt8, and transparent testa glabra1 [ttg1]), modified its spatial pattern (tt1 and tt16), or had no influence (ttg2), thus revealing complex regulatory interactions at several developmental levels. Genetic ablation of PA-accumulating cells targeted by the BAN promoter fused to BARNASE led to the formation of normal plants that produced viable yellow seeds. Importantly, these seeds had no obvious defects in endosperm and embryo development.

375 citations


Journal ArticleDOI
TL;DR: The high temperature regimens reduced the relativ el evels of transcripts for starch synthase more than the other starch biosynthetic enzymes.

287 citations


Journal ArticleDOI
TL;DR: It is proposed that two independent gain-of-function events associated with insertions into the promoter of the Y1 gene and upregulation of expression in endosperm have been incorporated into yellow maize.
Abstract: We investigated the effects of human selection for yellow endosperm color, representing increased carotenoid content, on two maize genes, the Y1 phytoene synthase and PSY2, a putative second phytoene synthase. Multiple polymorphic sites were identified at Y1 and PSY2 in 75 white and yellow maize inbred lines. Many polymorphic sites showed strong association with the endosperm color phenotype at Y1, but no detectable association was found at PSY2. Nucleotide diversity was equivalent for whites and yellows at PSY2 but was 19-fold less in yellows than in whites at Y1, consistent with the white ancestral state of the gene. The strong sequence haplotype conservation within yellows at Y1 and a significant, negative Tajima's D both verified positive selection for yellow endosperm. We propose that two independent gain-of-function events associated with insertions into the promoter of the Y1 gene and upregulation of expression in endosperm have been incorporated into yellow maize.

273 citations


Journal ArticleDOI
TL;DR: Reduction of seed size in haikuresults from coordinated reduction of endosperm size, embryo proliferation, and cell elongation of the maternally derived integument is presented, providing further evidence for a control of integument development mediated by endOSperm-derived signals.
Abstract: In flowering plants, maternal seed integument encloses the embryo and the endosperm, which are both derived from double fertilization. Although the development of these three components must be coordinated, we have limited knowledge of mechanisms involved in such coordination. The endosperm may play a central role in these mechanisms as epigenetic modifications of endosperm development, via imbalance of dosage between maternal and paternal genomes, affecting both the embryo and the integument. To identify targets of such epigenetic controls, we designed a genetic screen in Arabidopsis for mutants that phenocopy the effects of dosage imbalance in the endosperm. The two mutants haiku 1 and haiku 2 produce seed of reduced size that resemble seed with maternal excess in the maternal/paternal dosage. Homozygous haiku seed develop into plants indistinguishable from wild type. Each mutation is sporophytic recessive, and double-mutant analysis suggests that both mutations affect the same genetic pathway. The endosperm of haiku mutants shows a premature arrest of increase in size that causes precocious cellularization of the syncytial endosperm. Reduction of seed size in haiku results from coordinated reduction of endosperm size, embryo proliferation, and cell elongation of the maternally derived integument. We present further evidence for a control of integument development mediated by endosperm-derived signals.

263 citations


Journal ArticleDOI
TL;DR: Endosperm development appears to be predominantly under epigenetic controls that might be linked with its evolutionary origin, and is controlled maternally by chromatin-remodeling complexes.

Journal ArticleDOI
TL;DR: The endosperm starch from the sbe1 mutant had aLower onset concentration for urea gelatinization and a lower onset temperature for thermo-gelatinization compared with the wild type, indicating that the genetic modification of amylopectin fine structure is responsible for changes in physicochemical properties of sbe 1 starch.
Abstract: We have isolated a starch mutant that was deficient in starch-branching enzyme I (BEI) from the endosperm mutant stocks of rice (Oryza sativa) induced by the treatment of fertilized egg cells with N-methyl-N-nitrosourea. The deficiency of BEI in this mutant was controlled by a single recessive gene, tentatively designated as starch-branching enzyme mutant 1 (sbe1). The mutant endosperm exhibited the normal phenotype and contained the same amount of starch as the wild type. However, the mutation apparently altered the fine structure of amylopectin. The mutant amylopectin was characterized by significant decrease in both long chains with degree of polymerization (DP) ≥ 37 and short chains with DP 12 to 21, marked increase in short chains with DP ≤ 10 (A chains), and slight increase in intermediate chains with DP 24 to 34, suggesting that BEI specifically synthesizes B1 and B2–3 chains. The endosperm starch from the sbe1 mutant had a lower onset concentration for urea gelatinization and a lower onset temperature for thermo-gelatinization compared with the wild type, indicating that the genetic modification of amylopectin fine structure is responsible for changes in physicochemical properties of sbe1 starch.

Journal ArticleDOI
01 Feb 2003-Planta
TL;DR: Results demonstrate that deregulation of endosperm AGP increases overall plant sink strength, leading to larger, more productive plants in a manner similar to that in wheat having similar genetic modification.
Abstract: In this work we test the hypothesis that yield of rice ( Oryza sativa L.) can be enhanced by increasing endosperm activity of ADP-glucose pyrophosphorylase (AGP), a key enzyme in starch biosynthesis. The potential for increases in yield exist because rice initiates more seeds than are taken to maturity and possesses excess photosynthetic capacity that could be utilized if there were more demand for assimilate. Following an approach already shown to be successful in wheat, experiments were designed to increase demand for assimilate by increasing the capacity for starch synthesis in endosperm. This was accomplished by transforming rice with a modified maize AGP large subunit sequence ( Sh2r6hs) under control of an endosperm-specific promoter. This altered subunit confers upon AGP decreased sensitivity to allosteric inhibition by inorganic phosphate (Pi) and enhanced heat stability, potentially leading to higher AGP activity in vivo. The Sh2r6hs transgene increased AGP activity in developing endosperm by 2.7-fold in the presence of Pi. Increases in AGP activity in transgenic seeds compared with controls were maximal between 10-15 days after anthesis. Starch content of individual seeds at harvest was not increased, but seed weight per plant and total plant biomass were each increased by more than 20%. Increased endosperm AGP activity thus stimulates setting of additional seeds and overall plant growth rather than increasing yield of seeds already set. Results demonstrate that deregulation of endosperm AGP increases overall plant sink strength, leading to larger, more productive plants in a manner similar to that in wheat having similar genetic modification.

Journal ArticleDOI
TL;DR: The influence of high temperature during grain filling on the protein composition of bread wheat evaluated by proteomic tools was determined and 37 proteins were identified as significantly changed by heat treatment.
Abstract: High temperatures during grain filling have been reported to be one of the factors that can affect the dough properties and quality characteristics of wheat. Responses to high temperature have been related to changes in protein composition at both quantitative and qualitative levels. The present study was conducted to determine the influence of high temperature during grain filling on the protein composition of bread wheat evaluated by proteomic tools. Plants were grown in the field and transferred to cabinets soon after flowering. They were subjected to two thermal regimes 18 degrees C/10 degrees C (day/night) and 34 degrees C/10 degrees C. Total proteins were extracted from control grains and treated plants at three different post-anthesis stages. The proteins were separated by two-dimensional gel electrophoresis and analysed by Melanie 3 software. Of the total number of mature wheat grain proteins, 37 were identified as significantly changed by heat treatment. Analysis by matrix-assisted laser desorption/ionization mass spectrometry and tandem mass spectrometry coupled with database searching allowed the characterization of 25 heat-induced proteins and only one heat-decreased protein spot. To learn more about the function of the identified proteins, we examined their expression during treatment.

Journal ArticleDOI
TL;DR: It is proposed that βGlu not only helps defend seeds against pathogens, but is also a key factor in regulating coat-imposed dormancy and germination of seeds in response to environmental and hormonal cues.
Abstract: Glucanase (� Glu) expression in seeds plays important roles in the regulation of seed germination, dormancy and in the defence against seed pathogens. A thick � -1,3-glucan layer is typical for the seed envelope of cucurbitaceous species, confers seed semipermeability and is degraded during germination. In many species with coat-imposed dormancy, the seed envelope confers a physical constraint to radicle emergence. In the solanaceous species, the micropylar endosperm and testa have this function, and endosperm weakening appears to be a prerequisite for germination. Class IGlu is transcriptionally induced in the micropylar endosperm of tobacco, tomato and other solanaceous seeds just prior to radicle emergence. � Glu induction and germination are tightly linked in response to plant hormones and environmental factors, e.g. they are both promoted by gibberellins and inhibited by abscisic acid (ABA). Sense and antisense transformation of tobacco reveals two sites ofGlu action: after-ripening-mediated release of testa-imposed dormancy and endosperm rupture during germination. The use of an ABA-inducible chimeric sense-transgene resulted in overexpression of class IGlu in seeds and provided direct evidence that � Glu contributes to endosperm rupture. A model integratingGlu, seed dormancy, after-ripening and germination is presented, and possible mechanisms for � Glu action are discussed. It is proposed thatGlu not only helps defend seeds against pathogens, but is also a key factor in regulating coat-imposed dormancy and germination of seeds in response to environmental and hormonal cues.

Journal ArticleDOI
TL;DR: Results indicate that AGL15 is involved in support of development in an embryonic mode and localization to the nuclei supports a role in gene regulation during this phase of the life cycle.
Abstract: The MADS domain protein AGL15 (AGAMOUS-Like 15) has been found to preferentially accumulate in angiosperm tissues derived from double fertilization (i.e. the embryo, suspensor, and endosperm) and in apomictic, somatic, and microspore embryos. Localization to the nuclei supports a role in gene regulation during this phase of the life cycle. To test whether AGL15 is involved in the promotion and maintenance of embryo identity, the embryogenic potential of transgenic plants that constitutively express AGL15 was assessed. Expression of AGL15 was found to enhance production of secondary embryos from cultured zygotic embryos, and constitutive expression led to long-term maintenance of development in this mode. Ectopic accumulation of AGL15 also promoted somatic embryo formation after germination from the shoot apical meristem of seedlings in culture. These results indicate that AGL15 is involved in support of development in an embryonic mode.

Journal ArticleDOI
TL;DR: The temporal and spatial association of HvCWINV1 and HvSTP1 expression indicates that hexoses liberated by the invertase within the endospermal cavity are taken up by the transporter to be delivered into the central uncellularised space of theendosperm to supply mitotically active endosperm cells with hexoses.
Abstract: To analyse carbohydrate metabolism and its role during early seed development of barley we characterised genes encoding two cell wall-bound invertases (HvCWINV1 and HvCWINV2) and two putative hexose transporter-like genes (HvSTP1 and HvSTP2). No typical vacuolar invertase gene could be identified. Instead, a gene encoding sucrose:fructan 6-fructosyltransferase (HvSF6FT1), an enzyme with soluble acid invertase activity, was isolated and characterised. Furthermore, enzyme activities and sugar levels were measured. HvSF6FT1-mRNA levels and acid soluble invertase activity are highest in the maternal pericarp 1-2 days after flowering (DAF). HvSF6FT1 is strongly expressed in regions flanking the main vascular bundle and to a lower extent in filial endospermal transfer cells, which persist until maturity and never accumulate starch. In contrast, cell wall-bound invertase HvCWINV2 is expressed early in development mainly in the style region and later on in pericarp areas which transiently accumulate starch and undergo degradation later in development. The hexose transporter HvSTP2 shows a temporal and spatial expression pattern similar to HvCWINV2. Transcripts of HvCWINV1 have been localised within the first row of endospermal cells and in the outermost area of the nucellar projection as well as in endospermal transfer cells before starch filling; the same regions of the endosperm are labelled with a hexose transporter HvSTP1-probe. HvSTP1 is expressed at very low levels within the pericarp but much higher in the syncytial endosperm at 3 DAF and in endospermal transfer cells 7 DAF. The temporal and spatial association of HvCWINV1 and HvSTP1 expression indicates that hexoses liberated by the invertase within the endospermal cavity are taken up by the transporter to be delivered into the central uncellularised space of the endosperm to supply mitotically active endosperm cells with hexoses. The results are discussed and compared with published data on the role of soluble sugars as signal molecules in seed developmental processes.

Journal ArticleDOI
TL;DR: A possible physiological role of sugars in the germination of sorghum seeds is discussed, as compared to the control the level of glucose and sucrose was higher in embryos and endosperm after stress treatments.
Abstract: The effect of various abiotic stresses on germination rate, growth and soluble sugar content in Sorghum bicolor (L.) Moench cv. CSH 6 seed embryos and endosperm during early germination was investigated. Under stress conditions germination, water potential and tissue water content decreased markedly. Subsequently, this reduction resulted in marked decreases in fresh weight both in embryos and endosperm. Conversely, a substantial increase in dry weight was observed. Furthermore, a considerable increase in the sugar contents in both embryo and endosperm was detected. The fructose level was always higher than glucose and sucrose in response to various stresses. However, as compared to the control the level of glucose and sucrose was higher in embryos and endosperm after stress treatments. Based upon these results a possible physiological role of sugars in the germination of sorghum seeds is discussed.

Journal ArticleDOI
TL;DR: It is suggested that the responsiveness of placenta to whole-plant stress factors and of endosperm to indirect factors may play key roles in determining the threshold for kernel abortion.
Abstract: The early post-pollination phase of maize (Zea mays) development is particularly sensitive to water deficit stress. Using cDNA microarray, we studied transcriptional profiles of endosperm and placenta/pedicel tissues in developing maize kernels under water stress. At 9 d after pollination (DAP), placenta/pedicel and endosperm differed considerably in their transcriptional responses. In placenta/pedicel, 79 genes were significantly affected by stress and of these 89% were up-regulated, whereas in endosperm, 56 genes were significantly affected and 82% of these were down-regulated. Only nine of the stress-regulated genes were in common between these tissues. Hierarchical cluster analysis indicated that different sets of genes were regulated in the two tissues. After rewatering at 9 DAP, profiles at 12 DAP suggested that two regulons exist, one for genes responding specifically to concurrent imposition of stress, and another for genes remaining affected after transient stress. In placenta, genes encoding recognized stress tolerance proteins, including heat shock proteins, chaperonins, and major intrinsic proteins, were the largest class of genes regulated, all of which were up-regulated. In contrast, in endosperm, genes in the cell division and growth category represented a large class of down-regulated genes. Several cell wall-degrading enzymes were expressed at lower levels than in controls, suggesting that stress delayed normal advance to programmed cell death in the central endosperm. We suggest that the responsiveness of placenta to whole-plant stress factors (water potential, abscisic acid, and sugar flux) and of endosperm to indirect factors may play key roles in determining the threshold for kernel abortion.

Journal ArticleDOI
TL;DR: This is the first report of using nonantibiotic pmi driven by a novel promoter in generating transgenic indica rice for possible future use in human nutrition.
Abstract: Vitamin-A deficiency (VAD) is a major malnutrition problem in South Asia, where indica rice is the staple food. Indica-type rice varieties feed more than 2 billion people. Hence, we introduced a combination of transgenes using the biolistic system of transformation enabling biosynthesis of provitamin A in the endosperm of several indica rice cultivars adapted to diverse ecosystems of different countries. The rice seed-specific glutelin promoter (Gt-1 P) was used to drive the expression of phytoene synthase (psy), while lycopene beta-cyclase (lcy) and phytoene desaturase (crtI), fused to the transit peptide sequence of the pea-Rubisco small subunit, were driven by the constitutive cauliflower mosaic virus promoter (CaMV35S P). Transgenic plants were recovered through selection with either CaMV35S P driven hph (hygromycin phosphotransferase) gene or cestrum yellow leaf curling virus promoter (CMP) driven pmi (phophomannose isomerase) gene. Molecular and biochemical analyses demonstrated stable integration and expression of the transgenes. The yellow colour of the polished rice grain evidenced the carotenoid accumulation in the endosperm. The colour intensity correlated with the estimated carotenoid content by spectrophotometric and HPLC analysis. Carotenoid level in cooked polished seeds was comparable (with minor loss of xanthophylls) to that in non-cooked seeds of the same transgenic line. The variable segregation pattern in T1 selfing generation indicated single to multiple loci insertion of the transgenes in the genome. This is the first report of using nonantibiotic pmi driven by a novel promoter in generating transgenic indica rice for possible future use in human nutrition.

Journal ArticleDOI
TL;DR: The maize FIE2 and sorghum FIE proteins form a monophyletic group, sharing a closer relationship to each other than to the FIE1 protein, suggesting that maize fie genes originated from two different ancestral genomes.
Abstract: Two maize genes with predicted translational similarity to the Arabidopsis FIE (Fertilization-Independent Endosperm) protein, a repressor of endosperm development in the absence of fertilization, were cloned and analyzed. Genomic sequences of fie1 and fie2 show significant homology within coding regions but none within introns or 5′ upstream. The fie1 gene is expressed exclusively in the endosperm of developing kernels starting at ∼6 days after pollination. fie1 is an imprinted gene showing no detectable expression of the paternally derived fie1 allele during kernel development. Conversely, fie2 is expressed in the embryo sac before pollination. After pollination, its expression persists, predominantly in the embryo and at lower levels in the endosperm. The paternal fie2 allele is not expressed early in kernel development, but its transcription is activated at 5 days after pollination. fie2 is likely to be a functional ortholog of the Arabidopsis FIE gene, whereas fie1 has evolved a distinct function. The maize FIE2 and sorghum FIE proteins form a monophyletic group, sharing a closer relationship to each other than to the FIE1 protein, suggesting that maize fie genes originated from two different ancestral genomes.

Journal ArticleDOI
TL;DR: The results indicate that the isoamylase1 is essential for amylopectin biosynthesis in rice endosperm, and that alteration of the iso amylase activity is an effective means to modify the physicochemical properties and granular structure of starch.
Abstract: This is the first report on regulation of the isoamylase1 gene to modify the structure of amylopectin and properties of starch by using antisense technology in plants. The reduction of isoamylase1 protein by about 94% in rice endosperm changed amylopectin into a water-insoluble modified amylopectin and a water-soluble polyglucan (WSP). As compared with wild-type amylopectin, the modified amylopectin had more short chains with a degree of polymerization of 5-12, while their molecular sizes were similar. The WSP, which structurally resembled the phytoglycogen in isoamylase-deficient sugary-1 mutants, accounted for about 16% of the total alpha-polyglucans in antisense endosperm, and it was distributed throughout the whole endosperm unlike in sugary-1 mutant. The reduction of isoamylase activity markedly lowered the gelatinization temperature from 54 to 43 degrees C and the viscosity, and modified X-ray diffraction pattern and the granule morphology of the starch. The activity of pullulanase, the other type of starch debranching enzyme, in the antisense endosperm was similar to that in wild-type, whereas it is deficient in sugary-1 mutants. These results indicate that the isoamylase1 is essential for amylopectin biosynthesis in rice endosperm, and that alteration of the isoamylase activity is an effective means to modify the physicochemical properties and granular structure of starch.

Journal ArticleDOI
Mei Guo1, Mary Rupe1, Olga N. Danilevskaya1, Xiaofeng Yang1, Zihua Hu1 
TL;DR: A novel imprinted gene no-apical-meristem (NAM) related protein1 (nrp1) that was expressed only in the endosperm and regulated by gene-specific imprinting is discovered, which may play an important role inendosperm development.
Abstract: We have taken a genomic approach to examine global gene expression in the maize endosperm in relation to dosage and parental effects. Endosperm of eight hybrids generated by reciprocal crosses and their seven inbred parents were sampled at three developmental stages: 10, 14, and 21 days after pollination (DAP). These samples were subjected to GeneCalling, an open-ended mRNA-profiling technology, which simultaneously analyzes thousands of genes. Results indicated that the overall level of gene expression in the maize endosperm was dosage-dependent, that is, the gene expression was proportional to the parental genome contribution of 2n maternal : 1n paternal. However, approximately 8% of the genes deviated from such allelic additive expression and exhibited differential expression in hybrids of reciprocal crosses, resembling either maternally or paternally expressed genes. There were more genes with maternal-like expression (MLE) than those with paternal-like expression (PLE). Allele-specific expression analysis of four selected genes using the WAVE denaturing HPLC (dHPLC) system revealed several mechanisms responsible for the deviation from the allelic additive expression in the hybrid endosperm: heterochronic allelic variation, allelic variation in the level of expression, and genomic imprinting. We discovered a novel imprinted gene no-apical-meristem (NAM) related protein1 (nrp1) that was expressed only in the endosperm and regulated by gene-specific imprinting. The nrp1 gene, a putative transcriptional factor, may play an important role in endosperm development.

Journal ArticleDOI
TL;DR: A comparison of grain-filling in C3 and C4 cereals suggests that rice has structural features allied to C3 cereals, such as wheat, but with significant differences.
Abstract: The endosperm and embryo that constitute the filial tissues of rice caryopsis are isolated from the maternal tissues by the absence of any symplastic continuity. Nutrients are transported to the endosperm through a single ovular vascular trace present on the ventral side of the ovary. Initially solute enters through the chalaza into the nucellar projection and then into the endosperm. At later stages transport occurs through the nucellar epidermis, centripetally towards the endosperm. The cell walls of the nucellar epidermis are provided with rib-like thickenings. A comparison of grain-filling in C3 and C4 cereals suggests that rice has structural features allied to C3 cereals, such as wheat, but with significant differences.

Journal ArticleDOI
TL;DR: Despite different life-cycles, both flowering plants and multicellular animals have evolved complex sensing mechanisms that act after fertilization as 'quality checks' on reproduction, and that detect chromosome dosage and the parent of origin for specific genes.
Abstract: Continuous development, the absence of a germline, flexible and reversible cellular differentiation, and the existence of haploid and diploid generations — both of which express genes — are characteristics that distinguish plants from animals. Because these differences alter the impact of mutations, animals and plants experience varied selection pressures. Despite different life-cycles, both flowering plants and multicellular animals have evolved complex sensing mechanisms that act after fertilization as 'quality checks' on reproduction, and that detect chromosome dosage and the parent of origin for specific genes. Although flowering plant embryos escape such surveillance in vitro, embryo success in the seed often depends on a healthy endosperm — a nutritive tissue that is produced by a second fertilization event in which maternal and paternal gene contributions can be monitored immediately after fertilization and throughout development.

Journal ArticleDOI
TL;DR: In this short review, attention is focused on the synthesis of the soluble substrate for starch synthesis, ADPglucose (ADPG), and the role of metabolite transporters in mediating its delivery to the site of starch synthesis.
Abstract: The biosynthesis of starch is the major determinant of yield in cereal grains. In this short review, attention is focused on the synthesis of the soluble substrate for starch synthesis, ADPglucose (ADPG). Consideration is given to the pathway of ADPG production, its subcellular compartmentation, and the role of metabolite transporters in mediating its delivery to the site of starch synthesis. As ADPG is an activated sugar, the dependence of its production on respiration, changes which occur during development, and the constraints which ATP production may place on carbon partitioning into different end-products are discussed.

Journal ArticleDOI
TL;DR: It is concluded that the dominant cause of seed abortion in the diploid A. thaliana × tetraploid Arabidopsis arenosa cross is parental genomic imbalance, and manipulation of DNA methylation can be sufficient to erect hybridization barriers.
Abstract: The success or failure of interspecific crosses is vital to evolution and to agriculture, but much remains to be learned about the nature of hybridization barriers. Several mechanisms have been proposed to explain postzygotic barriers, including negative interactions between diverged sequences, global genome rearrangements, and widespread epigenetic reprogramming. Another explanation is imbalance of paternally and maternally imprinted genes in the endosperm. Interspecific crosses between diploid Arabidopsis thaliana as the seed parent and tetraploid Arabidopsis arenosa as the pollen parent produced seeds that aborted with the same paternal excess endosperm phenotype seen in crosses between diploid and hexaploid A. thaliana. Doubling maternal ploidy restored seed viability and normal endosperm morphology. However, substituting a hypomethylated tetraploid A. thaliana seed parent reestablished the hybridization barrier by causing seed abortion and a lethal paternal excess phenotype. We conclude from these findings that the dominant cause of seed abortion in the diploid A. thaliana x tetraploid A. arenosa cross is parental genomic imbalance. Our results also demonstrate that manipulation of DNA methylation can be sufficient to erect hybridization barriers, offering a potential mechanism for speciation and a means of controlling gene flow between species.

Journal ArticleDOI
TL;DR: In situ hybridization experiments reveal that the sal1 gene is ubiquitously expressed in vegetative as well as zygotic grain tissues, with no difference being detected between aleurone cells and starchy endosperm cells.
Abstract: A microscopy-based screen of a large collection of maize Mutator (Mu) transposon lines identified the supernumerary aleurone layers 1-1 (sal1-1) mutant line carrying up to seven layers of aleurone cells in defective kernel endosperm compared with only a single layer in wild-type grains. Normal, well filled endosperm that is homozygous for the sal1-1 mutant allele contains two to three layers of aleurone cells. Cloning of the sal1 gene was accomplished by using Mu tagging, and the identity of the cloned gene was confirmed by isolating an independent sal1-2 allele by reverse genetics. Homozygous sal1-2 endosperm has two to three layers of aleurone cells in normal, well filled grains. In situ hybridization experiments reveal that the sal1 gene is ubiquitously expressed in vegetative as well as zygotic grain tissues, with no difference being detected between aleurone cells and starchy endosperm cells. Northern blot analysis failed to detect the sal1-2 transcript in leaves of homozygous plants, suggesting that the allele is a true sal1 knockout allele. The sal1 gene encodes a homologue of the human Chmp1 gene, a member of the conserved family of the class E vacuolar protein sorting genes implicated in membrane vesicle trafficking. In mammals, CHMP1 functions in the pathway targeting plasma membrane receptors and ligands to lysosomes for proteolytic degradation. Possible roles for the function of the sal1 gene in aleurone signaling, including a defect in endosome trafficking, are discussed.

Journal ArticleDOI
TL;DR: The induction of a modified sexual reproduction program in AI cells may enable the manifestation of apomixis in Hieracium, indicating that sexuality and apomixedis are interrelated pathways that share regulatory components.
Abstract: Seed formation in flowering plants requires meiosis of the megaspore mother cell (MMC) inside the ovule, selection of a megaspore that undergoes mitosis to form an embryo sac, and double fertilization to initiate embryo and endosperm formation. During apomixis, or asexual seed formation, in Hieracium ovules, a somatic aposporous initial (AI) cell divides to form a structurally variable aposporous embryo sac and embryo. This entire process, including endosperm development, is fertilization independent. Introduction of reproductive tissue marker genes into sexual and apomictic Hieracium showed that AI cells do not express a MMC marker. Spatial and temporal gene expression patterns of other introduced genes were conserved commencing with the first nuclear division of the AI cell in apomicts and the mitotic initiation of embryo sac formation in sexual plants. Conservation in expression patterns also occurred during embryo and endosperm development, indicating that sexuality and apomixis are interrelated pathways that share regulatory components. The induction of a modified sexual reproduction program in AI cells may enable the manifestation of apomixis in Hieracium.

Journal ArticleDOI
TL;DR: It is suggested that the decreased activity of starch branching enzyme reduces the branching frequency of the branches of amylopectin, which results in the increased amount of long chains ofAmylopECTin of endosperm in rice grain at high temperature.