Showing papers on "Endosperm published in 2006"
TL;DR: It is shown that the cyp707a1 mutant accumulated ABA to higher levels in dry seeds than the cyP707a2 mutant, and each CYP707A gene plays a distinct role during seed development and postgermination growth.
Abstract: Endogenous abscisic acid (ABA) levels are regulated by both biosynthesis and catabolism of the hormone. ABA 8′-hydroxylase is considered to be the key catabolic enzyme in many physiological processes. We have previously identified that four members of the Arabidopsis (Arabidopsis thaliana) CYP707A gene family (CYP707A1 to CYP707A4) encode ABA 8′-hydroxylases, and that the cyp707a2 mutants showed an increase in ABA levels in dry and imbibed seeds. In this study, we showed that the cyp707a1 mutant accumulated ABA to higher levels in dry seeds than the cyp707a2 mutant. Expression analysis showed that the CYP707A1 was expressed predominantly during mid-maturation and was down-regulated during late-maturation. Concomitantly, the CYP707A2 transcript levels increased from late-maturation to mature dry seed. Phenotypic analysis of single and double cyp707a mutants indicates that the CYP707A1 is important for reducing ABA levels during mid-maturation. On the other hand, CYP707A2 is responsible for the regulation of ABA levels from late-maturation to germination. Moreover, CYP707A1 and CYP707A3 were also shown to be involved in postgermination growth. Spatial expression analysis suggests that CYP707A1 was expressed predominantly in embryo during mid-maturation, whereas CYP707A2 expression was detected in both embryo and endosperm from late-maturation to germination. Our results demonstrate that each CYP707A gene plays a distinct role during seed development and postgermination growth.
476 citations
TL;DR: Functional and expression analyses have revealed that At NCED6 and AtNCED9 are required for ABA biosynthesis during seed development, and demonstrate that ABA synthesized in both the endosperm and the embryo participates in the hormonal balance that controls seed dormancy and germination.
Abstract: Summary
The cleavage of 9-cis-epoxycarotenoids to xanthoxin, catalyzed by 9-cis-epoxycarotenoid dioxygenases, is considered to be the key regulatory step of abscisic acid (ABA) biosynthesis. In Arabidopsis, genes for these enzymes form a multigene family with nine members, only five of which are thought to be involved in ABA production. In contrast to the prominent function of AtNCED3 in stress responses, the physiological and developmental role of the other 9-cis-epoxycarotenoid dioxygenases (NCEDs) remain unknown. Our functional and expression analyses have revealed that AtNCED6 and AtNCED9 are required for ABA biosynthesis during seed development. Reverse genetic analysis showed that ABA levels were reduced in Atnced6 and Atnced9 mutant seeds. In addition, transgenic plants overexpressing the AtNCED6 gene overproduced ABA. In accordance with mutant phenotypes, both AtNCED6 and AtNCED9 exhibited seed-specific expression. Detailed cytological studies were carried out, either by using transcriptional fusions of the promoter with GUS and GFP reporter genes, or by in situ hybridization. Expression of AtNCED6 was observed exclusively in the endosperm during seed development, that of AtNCED9 in both embryo and endosperm at mid-development. In addition to reduced ABA levels, Atnced6 and Atnced9 mutant seeds were also resistant to paclobutrazol, a gibberellin biosynthesis inhibitor. Although seeds of single mutants were still dormant, reduced dormancy was observed in the Atnced6 Atnced9 double-mutant seeds. These demonstrate that ABA synthesized in both the endosperm and the embryo participates in the hormonal balance that controls seed dormancy and germination.
417 citations
TL;DR: It is strongly suggested that amylopectin chains are synthesized by the coordinated actions of SSI, SSIIa, and SSIIIa isoforms.
Abstract: Four starch synthase I (SSI)-deficient rice (Oryza sativa) mutant lines were generated using retrotransposon Tos17 insertion. The mutants exhibited different levels of SSI activities and produced significantly lower amounts of SSI protein ranging from 0% to 20% of the wild type. The mutant endosperm amylopectin showed a decrease in chains with degree of polymerization (DP) 8 to 12 and an increase in chains with DP 6 to 7 and DP 16 to 19. The degree of change in amylopectin chain-length distribution was positively correlated with the extent of decrease in SSI activity in the mutants. The structural changes in the amylopectin increased the gelatinization temperature of endosperm starch. Chain-length analysis of amylopectin in the SSI band excised from native-polyacrylamide gel electrophoresis/SS activity staining gel showed that SSI preferentially synthesized DP 7 to 11 chains by elongating DP 4 to 7 short chains of glycogen or amylopectin. These results show that SSI distinctly generates DP 8 to 12 chains from short DP 6 to 7 chains emerging from the branch point in the A or B1 chain of amylopectin. SSI seemingly functions from the very early through the late stage of endosperm development. Yet, the complete absence of SSI, despite being a major SS isozyme in the developing endosperm, had no effect on the size and shape of seeds and starch granules and the crystallinity of endosperm starch, suggesting that other SS enzymes are probably capable of partly compensating SSI function. In summary, this study strongly suggested that amylopectin chains are synthesized by the coordinated actions of SSI, SSIIa, and SSIIIa isoforms.
357 citations
TL;DR: How seed anatomy, light, and plant-to-plant variation influence the content and measurement of oil in Arabidopsis seeds is described to establish a reference data set on the fatty acid composition and distribution of mass and oil between tissues of Arabdopsis seeds that should help to predict the applicability of results obtained withArabidopsis to other oilseeds.
353 citations
TL;DR: It is concluded that the single cell endosperm layer plays an active role in the regulation of seed germination in Arabidopsis and that ABA signaling mutants demonstrate the spatial specificity of ABA action in Seed germination.
Abstract: Regulation of seed germination requires coordinate action by the embryo and surrounding endosperm. We used Arabidopsis thaliana to establish the relative roles of embryo and endosperm in the control of seed germination and seedling establishment. We previously showed that endospermic oil reserves are used postgerminatively via gluconeogenesis to fuel seedling establishment and that lipid breakdown is repressed by abscisic acid (ABA) in embryo but not endosperm tissues. Here, we use RNA amplification to describe the transcriptome of the endosperm and compare the hormone responses of endosperm and embryo tissues. We show that the endosperm responds to both ABA and gibberellin but that ABA in particular regulates nuclear but not plastid-encoded photosynthetic gene expression in the embryo. We also show that ABA INSENSITIVE4 (ABI4) expression is confined to the embryo, accounts for the major differences in embryo response to ABA, and defines a role for ABI4 as a repressor of lipid breakdown. Furthermore, ABI5 expression in the endosperm defines a second region of altered ABA signaling in the micropylar endosperm cap. Finally, embryo and endosperm ABA signaling mutants demonstrate the spatial specificity of ABA action in seed germination. We conclude that the single cell endosperm layer plays an active role in the regulation of seed germination in Arabidopsis.
342 citations
TL;DR: It is proposed that Lepidium is an emerging Brassicaceae model system for endosperm weakening and that the complementary advantages of Lepidium and Arabidopsis can be used in parallel experiments to investigate the molecular mechanisms of endos sperm weakening.
Abstract: The endosperm is a barrier for radicle protrusion of many angiosperm seeds. Rupture of the testa (seed coat) and rupture of the endosperm are two sequential events during the germination of Lepidium sativum L. and Arabidopsis thaliana (L.) Heyhn. Abscisic acid (ABA) specifically inhibits the endosperm rupture of these two closely related Brassicaceae species. Lepidium seeds are large enough to allow the direct measurement of endosperm weakening by the puncture force method. We found that the endosperm weakens prior to endosperm rupture and that ABA delays the onset and decreases the rate of this weakening process in a dose-dependent manner. An early embryo signal is required and sufficient to induce endosperm weakening, which afterwards appears to be an organ-autonomous process. Gibberellins can replace this embryo signal; de novo gibberellin biosynthesis occurs in the endosperm and weakening is regulated by the gibberellin/ABA ratio. Our results suggest that the control of radicle protrusion during the germination of Brassicaceae seeds is mediated, at least in part, by endosperm weakening. We propose that Lepidium is an emerging Brassicaceae model system for endosperm weakening and that the complementary advantages of Lepidium and Arabidopsis can be used in parallel experiments to investigate the molecular mechanisms of endosperm weakening.
299 citations
TL;DR: It is found that unfertilized endosperm developed, suggesting that a previously unrecognized positive signal from the fertilization of the egg cell initiates proliferation of the central cell.
Abstract: Double fertilization of the egg cell and the central cell by one sperm cell each produces the diploid embryo and the typically triploid endosperm and is one of the defining characteristics of flowering plants (angiosperms). Endosperm and embryo develop in parallel to form the mature seed, but little is known about the coordination between these two organisms. We characterized a mutation of the Arabidopsis thaliana Cdc2 homolog CDC2A (also called CDKA;1), which has a paternal effect. In cdc2a mutant pollen, only one sperm cell, instead of two, is produced. Mutant pollen is viable but can fertilize only one cell in the embryo sac, allowing for a genetic dissection of the double fertilization process. We observed exclusive fertilization of the egg cell by cdc2a sperm cells. Moreover, we found that unfertilized endosperm developed, suggesting that a previously unrecognized positive signal from the fertilization of the egg cell initiates proliferation of the central cell.
267 citations
TL;DR: Data suggest that FEM111/AGL80 functions as a transcription factor within the central cell gene regulatory network and controls the expression of downstream genes required for central cell development and function.
Abstract: During plant reproduction, the central cell of the female gametophyte becomes fertilized to produce the endosperm, a storage tissue that nourishes the developing embryo within the seed. The molecular mechanisms controlling the specification and differentiation of the central cell are poorly understood. We identified a female gametophyte mutant in Arabidopsis thaliana , fem111 , that is affected in central cell development. In fem111 female gametophytes, the central cell9s nucleolus and vacuole fail to mature properly. In addition, endosperm development is not initiated after fertilization of fem111 female gametophytes. fem111 contains a T-DNA insertion in AGAMOUS-LIKE80 ( AGL80 ). FEM111/AGL80 is a member of the MADS box family of genes that likely encode transcription factors. An AGL80–green fluorescent protein fusion protein is localized to the nucleus. Within the ovule and seed, FEM111/AGL80 is expressed exclusively in the central cell and uncellularized endosperm. FEM111/AGL80 expression is also detected in roots, leaves, floral stems, anthers, and young flowers by real-time RT-PCR. FEM111/AGL80 is required for the expression of two central cell–expressed genes, DEMETER and DD46 , but not for a third central cell–expressed gene, FERTILIZATION-INDEPENDENT SEED2 . Together, these data suggest that FEM111/AGL80 functions as a transcription factor within the central cell gene regulatory network and controls the expression of downstream genes required for central cell development and function.
206 citations
TL;DR: Gene expression patterns covering over 10,000 seed-expressed sequences were analyzed by macroarray technology in maternal tissue and filial endosperm and embryo during barley seed development from anthesis until late maturation to suggest that PCD in the pericarp is mediated by distinct classes of proteases and is under the hormonal control of both jasmonic acid (JA) and ethylene via ethylene-responsive element binding protein (EREBP) transcription factors (TFs).
Abstract: Gene expression patterns covering over 10,000 seed-expressed sequences were analyzed by macroarray technology in maternal tissue (mainly pericarp) and filial endosperm and embryo during barley seed development from anthesis until late maturation. Defined sets of genes showing distinct expression patterns characterized both tissue type and major developmental phases. The analysis focused on regulatory networks involved in programmed cell death (PCD) and abscisic acid (ABA)-mediated maturation. These processes were similar in the different tissues, but typically involved the expression of alternative members of a common gene family. The analysis of co-expressed gene sets and the identification of cis regulatory elements in orthologous rice gene 'promoter' regions suggest that PCD in the pericarp is mediated by distinct classes of proteases and is under the hormonal control of both jasmonic acid (JA) and ethylene via ethylene-responsive element binding protein (EREBP) transcription factors (TFs). On the other hand, PCD in endosperm apparently involves only the ethylene pathway, but employs distinct gene family members from those active in the pericarp, and a different set of proteases and TFs. JA biosynthetic genes are hardly activated. Accordingly, JA levels are high in the pericarp but low in the endosperm during middle and late developmental stages. Similarly, genes acting in the deduced ABA biosynthetic pathway and signaling network differ between endosperm and embryo. ABA in the endosperm appears to exert an influence over storage product synthesis via SNF1 kinase. In the embryo, ABA seems to influence the acquisition of desiccation tolerance via ABA response element binding factors, but the data also suggest the existence of an ABA-independent but interactive pathway acting via the dehydration-responsive element binding (DREB) 2A TF.
189 citations
TL;DR: This work has shown that the endosperm mediates a maternal input that is based on memory of the transcriptional states of imprinted genes, which is crucial for harmonious seed growth.
173 citations
TL;DR: Evidence is presented that the debranching enzyme isoamylase 3 (ISA3) acts at the surface of the starch granule, but in its absence soluble branched glucans are debranched in the stroma via limit dextrinase.
TL;DR: Results suggest that the presence of the transgenes did not significantly alter gene expression and that, at this level of investigation, transgenic plants could be considered substantially equivalent to untransformed parental lines.
Abstract: Detailed global gene expression profiles have been obtained for a series of transgenic and conventionally bred wheat lines expressing additional genes encoding HMW (high molecular weight) subunits of glutenin, a group of endosperm-specific seed storage proteins known to determine dough strength and therefore bread-making quality. Differences in endosperm and leaf transcriptome profiles between untransformed and derived transgenic lines were consistently extremely small, when analysing plants containing either transgenes only, or also marker genes. Differences observed in gene expression in the endosperm between conventionally bred material were much larger in comparison to differences between transgenic and untransformed lines exhibiting the same complements of gluten subunits. These results suggest that the presence of the transgenes did not significantly alter gene expression and that, at this level of investigation, transgenic plants could be considered substantially equivalent to untransformed parental lines.
TL;DR: Dissection and analysis of mature Brassica seeds showed that the trihydroxy C18:1 fatty acid was found mainly in the embryo, while ferulate, fatty alcohols and C22 and C24 species were specific to the seed coat plus endosperm.
TL;DR: Although single-mutant swn plants did not show any defects, swn mutations enhanced the mea mutant phenotype in producing autonomous seeds, and MEA and SWN perform partially redundant functions in controlling the initiation of endosperm development before fertilization in Arabidopsis.
Abstract: In Arabidopsis, a complex of Polycomb-group (PcG) proteins functions in the female gametophyte to control the initiation of seed development. Mutations in the PcG genes, including MEDEA (MEA) and FERTILIZATION-INDEPENDENT SEED 2 (FIS2), produce autonomous seeds where endosperm proliferation occurs in the absence of fertilization. By using a yeast two-hybrid screen, we identified MEA and a related protein, SWINGER (SWN), as SET-domain partners of FIS2. Localization data indicated that all three proteins are present in the female gametophyte. Although single-mutant swn plants did not show any defects, swn mutations enhanced the mea mutant phenotype in producing autonomous seeds. Thus, MEA and SWN perform partially redundant functions in controlling the initiation of endosperm development before fertilization in Arabidopsis.
TL;DR: The results highlight the role of the amyloplast as a starch-storing organelle that fulfills a spectrum of biosynthetic needs of the parent tissue and demonstrates the advantage of using isolated organelles in proteomic studies.
Abstract: By contrast to chloroplasts, our knowledge of amyloplasts—organelles that synthesize and store starch in heterotrophic plant tissues—is in a formative stage. While our understanding of what is considered their primary function, i.e. the biosynthesis and degradation of starch, has increased dramatically in recent years, relatively little is known about other biochemical processes taking place in these organelles. To help fill this gap, a proteomic analysis of amyloplasts isolated from the starchy endosperm of wheat seeds (10 d postanthesis) has been conducted. The study has led to the identification of 289 proteins that function in a range of processes, including carbohydrate metabolism, cytoskeleton/plastid division, energetics, nitrogen and sulphur metabolism, nucleic acid-related reactions, synthesis of various building blocks, proteinrelated reactions, transport, signalling, stress, and a variety of other activities grouped under ‘miscellaneous’. The function of 12% of the proteins was unknown. The results highlight the role of the amyloplast as a starch-storing organelle that fulfills a spectrum of biosynthetic needs of the parent tissue. When compared with a recent proteomic analysis of whole endosperm, the current study demonstrates the advantage of using isolated organelles in proteomic studies.
TL;DR: The temporal and spatial appearance of key polysaccharides in the cell walls of early developing endosperm of barley, prior to aleurone differentiation is reported.
Abstract: Barley endosperm begins development as a syncytium where numerous nuclei line the perimeter of a large vacuolated central cell. Between 3 and 6 days after pollination (DAP) the multinucleate syncytium is cellularized by the centripetal synthesis of cell walls at the interfaces of nuclear cytoplasmic domains between individual nuclei. Here we report the temporal and spatial appearance of key polysaccharides in the cell walls of early developing endosperm of barley, prior to aleurone differentiation. Flowering spikes of barley plants grown under controlled glasshouse conditions were hand-pollinated and the developing grains collected from 3 to 8 DAP. Barley endosperm development was followed at the light and electron microscope levels with monoclonal antibodies specific for (1→3)-β-d-glucan (callose), (1→3,1→4)-β-d-glucan, hetero-(1→4)-β-d-mannans, arabino-(1→4)-β-d-xylans, arabinogalactan-proteins (AGPs) and with the enzyme, cellobiohydrolase II, to detect (1→4)-β-d-glucan (cellulose). Callose and cellulose were present in the first formed cell walls between 3 and 4 DAP. However, the presence of callose in the endosperm walls was transient and at 6 DAP was only detected in collars surrounding plasmodesmata. (1→3,1→4)-β-d-Glucan was not deposited in the developing cell walls until approximately 5 DAP and hetero-(1→4)-β-d-mannans followed at 6 DAP. Deposition of AGPs and arabinoxylan in the wall began at 7 and 8 DAP, respectively. For arabinoxylans, there is a possibility that they are deposited earlier in a highly substituted form that is inaccessible to the antibody. Arabinoxylan and heteromannan were also detected in Golgi and associated vesicles in the cytoplasm. In contrast, (1→3,1→4)-β-d-glucan was not detected in the cytoplasm in endosperm cells; similar results were obtained for coleoptile and suspension cultured cells.
TL;DR: Results indicate that sucrose synthase plays an important role in sugar metabolism during sucrose accumulation in the coffee fruit.
Abstract: Sucrose metabolism and the role of sucrose synthase were investigated in the fruit tissues (pericarp, perisperm, and endosperm) of Coffea arabica during development. Acid invertase, sucrose phosphate synthase, and sucrose synthase activities were monitored and compared with the levels of sucrose and reducing sugars. Among these enzymes, sucrose synthase showed the highest activities during the last stage of endosperm and pericarp development and this activity paralleled closely the accumulation of sucrose in these tissues at this stage. Carbon partitioning in fruits was studied by pulse–chase experiments with 14 C-sugars and revealed high rates of sucrose turnover in perisperm and endosperm tissues. Additional feeding experiments with 14 CO2 showed that leaf photosynthesis contributed more to seed development than the pericarp in terms of photosynthate supply to the endosperm. Sugar analysis, feeding experiments, and histological studies indicated that the perisperm plays an important role in this downloading process. It was observed that the perisperm presents a transient accumulation of starch which is degraded as the seed develops. Two full-length cDNAs (CaSUS1 and CaSUS2) and the complete gene sequence of the latter were also isolated. They encode sucrose synthase isoforms that are phylogenetically distinct, indicating their involvement in different physiological functions during cherry development. Contrasting expression patterns were observed for CaSUS1 and CaSUS2 in perisperm, endosperm, and pericarp tissues: CaSUS1 mRNAs accumulated mainly during the early development of perisperm and endosperm, as well as during pericarp growing phases, whereas those of CaSUS2 paralleled sucrose synthase activity in the last weeks of pericarp and endosperm development. Taken together, these results indicate that sucrose synthase plays an important role in sugar metabolism during sucrose accumulation in the coffee fruit.
TL;DR: In this article, the FIS Polycomb group (PcG) proteins are used to restrict endosperm proliferation by imprinting the maternal alleles of FIS target genes.
Abstract: Seed development in flowering plants is initiated by the fusion of two male gametes with two female gametes—the egg cell and the central cell—which leads to the formation of an embryo and an endosperm, respectively. Fertilization-independent seed formation is actively repressed by the FERTILIZATION-INDEPENDENT SEED (FIS) Polycomb group (PcG) proteins, an evolutionarily conserved class of proteins that ensures the stable transmission of developmental decisions. The FIS proteins act together in a complex and modify their target genes by applying repressive methylation on histone H3 lysine 27. In addition to its function before fertilization, the FIS complex restricts endosperm proliferation. This function is likely to be achieved by imprinting the maternal alleles of FIS target genes. However, imprinting in the endosperm is controlled not only by the FIS complex but also by DNA methylation, and the interconnections between these two processes are now being investigated.
TL;DR: It is proposed that loading the scutellar phloem in germinating wheat seeds can proceed by symplasmic and apoplasmic pathways, the latter facilitated by SUT activity.
Abstract: Three homeologous genes encoding a sucrose (Suc) transporter (SUT) in hexaploid wheat (Triticum aestivum), TaSUT1A, 1B, and 1D, were expressed in germinating seeds, where their function is unknown All three TaSUT1 proteins were confirmed to be capable of transporting both Suc and maltose by complementation tests with the SUSY7/ura3 yeast (Saccharomyces cerevisiae) mutant strain The role of Suc transporters in germinating grain was examined by combining in situ hybridization, immunolocalization, fluorescent dye tracer movement, and metabolite assays TaSUT1 transcript and SUT protein were detected in cells of the aleurone layer, scutellar epidermis, scutellar ground cells, and sieve element-companion cell complexes located in the scutellum, shoot, and root Ester loading of the membrane-impermeable fluorescent dye carboxyfluorescein into the scutellum epidermal cells of germinating seeds showed that a symplasmic pathway connects the scutellum to the shoot and root via the phloem However, the scutellar epidermis provides an apoplasmic barrier to solute movement from endosperm tissue Measurements of sugars in the root, shoot, endosperm, and scutellum suggest that, following degradation of endosperm starch, the resulting hexoses are converted to Suc in the scutellum Suc was found to be the major sugar present in the endosperm early in germination, whereas maltose and glucose predominate during the later stage It is proposed that loading the scutellar phloem in germinating wheat seeds can proceed by symplasmic and apoplasmic pathways, the latter facilitated by SUT activity In addition, SUTs may function to transport Suc into the scutellum from the endosperm early in germination and later transport maltose
TL;DR: The physical, chemical and physiological changes in the embryo, endosperm and testa, as well as the interactions between these tissues all contribute to successful germination, and hypotheses to explain global mechanisms of seed germination are examined.
Abstract: The chemical energy synthesized during photosynthesis as carbohydrates, lipids and proteins accumulates in seeds and provides a food source for animals. Seeds are also important genetic delivery systems essential for sustainable agriculture and environmental control. Genetic information in elite cultivars of crop species accumulated during breeding programs is distributed in the form of seeds. Ensuring successful germination and seedling establishment is a significant first step in agricultural production. The molecular and biochemical mechanisms of seed germination are not fully understood. Our knowledge of the interactions between the embryo, endosperm and testa has been advanced through tomato seed research, a model system for seed germination research. Recent discoveries using Arabidopsis thaliana have provided additional information about the molecular and genetic mechanisms of seed dormancy and germination. Genes expressed during seed development determine the size, shape and chemical properties of mature seeds and affect seed dormancy. In imbibed seeds, genes associated with hormone biosynthesis and degradation play critical roles in radicle emergence. The physical, chemical and physiological changes in the embryo, endosperm and testa, as well as the interactions between these tissues all contribute to successful germination. Recent literature on seed science research needs to be compiled to provide a clear picture for seed germination. Hypotheses to explain global mechanisms of seed germination are examined in this review.
TL;DR: It is demonstrated that the MYBGA–GARE interaction affects sugar feedback control in balanced energy production during seedling growth and insight is provided into the control mechanisms of tissue-specific regulation of α-amylase expression by sugar and GA signaling interference.
Abstract: Expression of α-amylase genes during cereal grain germination and seedling growth is regulated negatively by sugar in embryos and positively by gibberellin (GA) in endosperm through the sugar response complex (SRC) and the GA response complex (GARC), respectively. We analyzed two α-amylase promoters, αAmy3 containing only SRC and αAmy8 containing overlapped SRC and GARC. αAmy3 was sugar-sensitive but GA-nonresponsive in both rice (Oryza sativa) embryos and endosperms, whereas αAmy8 was sugar-sensitive in embryos and GA-responsive in endosperms. Mutation of the GA response element (GARE) in the αAmy8 promoter impaired its GA response but enhanced sugar sensitivity, and insertion of GARE in the αAmy3 promoter rendered it GA-responsive but sugar-insensitive in endosperms. Expression of the GARE-interacting transcription factor MYBGA was induced by GA in endosperms, correlating with the endosperm-specific αAmy8 GA response. αAmy8 became sugar-sensitive in MYBGA knockout mutant endosperms, suggesting that the MYBGA–GARE interaction overrides the sugar sensitivity of αAmy8. In embryos overexpressing MYBGA, αAmy8 became sugar-insensitive, indicating that MYBGA affects sugar repression. α-Amylase promoters active in endosperms contain GARE, whereas those active in embryos may or may not contain GARE, confirming that the GARE and GA-induced MYBGA interaction prevents sugar feedback repression of endosperm α-amylase genes. We demonstrate that the MYBGA–GARE interaction affects sugar feedback control in balanced energy production during seedling growth and provide insight into the control mechanisms of tissue-specific regulation of α-amylase expression by sugar and GA signaling interference.
TL;DR: Five putative rice (Oryza sativa) proteins that share characteristic motifs with previously described plant KRPs are identified and spatial and temporal transcript detection in developing seeds suggests that Orysa;KRP1 plays an important role in the exit from the mitotic cell cycle during rice grain formation.
Abstract: Kip-related proteins (KRPs) play a major role in the regulation of the plant cell cycle. We report the identification of five putative rice (Oryza sativa) proteins that share characteristic motifs with previously described plant KRPs. To investigate the function of KRPs in rice development, we generated transgenic plants overexpressing the Orysa;KRP1 gene. Phenotypic analysis revealed that overexpressed KRP1 reduced cell production during leaf development. The reduced cell production in the leaf meristem was partly compensated by an increased cell size, demonstrating the existence of a compensatory mechanism in monocot species by which growth rate is less reduced than cell production, through cell expansion. Furthermore, Orysa;KRP1 overexpression dramatically reduced seed filling. Sectioning through the overexpressed KRP1 seeds showed that KRP overproduction disturbed the production of endosperm cells. The decrease in the number of fully formed seeds was accompanied by a drop in the endoreduplication of endosperm cells, pointing toward a role of KRP1 in connecting endocycle with endosperm development. Also, spatial and temporal transcript detection in developing seeds suggests that Orysa;KRP1 plays an important role in the exit from the mitotic cell cycle during rice grain formation.
TL;DR: The data suggest an important role for apoplastic cleavage of sucrose throughout the duration of seed development; and, of the two isoforms, the INCW2 appears to control metabolic flux of sugar utilization in the developing endosperm.
Abstract: We show here that the total invertase activity in developing seeds of maize is due to two cell wall invertase (CWI) genes, Incw1 and Incw2 (Mn1). Our previous results have shown that loss-of-function mutations at the Mn1 locus lead to the miniature-1 (mn1) seed phenotype, marked by a loss of >70% of seed weight at maturity. The mn1 seed mutant is, however, non-lethal presumably because it retains a residual low level, ∼1%, of the total CWI activity relative to the Mn1 endosperm throughout seed development. Evidence here shows that the residual activity in the mn1 mutant is encoded by the Incw1 gene. RNA level analyses, especially quantitative real-time PCR studies, showed significant spatial and temporal heterogeneity in the expression of the two CWI genes in the developing endosperm. The Mn1-encoded Incw2 transcripts were seen at the highest levels in the basal region (the sugar unloading zone) during the early phase of cell division and elongation in the endosperm. In contrast, the highest levels of Incw1 transcripts were seen in the storage phase in both the upper (storage cells) and the lower parts of the endosperm. Protein and enzyme level analyses, however, appeared to show a lack of concordance with the RNA level of expression in both the Mn1 and mn1 endosperms, indicating a possibility of post-transcriptional control in the expression of these two genes. Collectively, the data suggest an important role for apoplastic cleavage of sucrose throughout the duration of seed development; and, of the two isoforms, the INCW2 appears to control metabolic flux of sugar utilization in the developing endosperm.
TL;DR: Using expression analysis, the role of the sucrose transporter OsSUT1 during germination and early growth of rice seedlings has been examined in detail, over a time-course ranging from 1 d to 7 d post-imbibition.
Abstract: Using expression analysis, the role of the sucrose transporter OsSUT1 during germination and early growth of rice seedlings has been examined in detail, over a time-course ranging from 1 d to 7 d post-imbibition. Unlike the wheat orthologue, TaSUT1, which is thought to be directly involved in sugar transfer across the scutellar epithelium, OsSUT1 is not expressed in the scutellar epithelial cell layer of germinating rice and is, therefore, not involved in transport of sugars across the symplastic discontinuity between the endosperm and the embryo. OsSUT1 expression was also absent from the aleurone cells, indicating it is not involved in the transport of sucrose in this cell layer during germination. However, by 3 d post-imbibition, OsSUT1 was present in the companion cells and sieve elements of the scutellar vascular bundle, where it may play a role in phloem loading of sucrose for transport to the developing shoot and roots. This sucrose is most likely sourced from hexoses imported from the endosperm. In addition, sucrose may be remobilized from starch granules which are present at a high density in the scutellar ground tissues surrounding the vasculature and at the base of the shoot. OsSUT1 was also present in the coleoptile and the first and second leaf blades, where it was localized to the phloem along the entire length of these tissues, and was also present within the phloem of the primary roots. OsSUT1 may be involved in retrieval of sugars from the apoplasm in these tissues.
TL;DR: A systematic comparison of the proteomes of zygotic embryos, somatic embryos grown in liquid medium containing 30 or 60 g l−1 sucrose, germinating embryos of both types and endosperm in order to obtain novel insights into seed and germination physiology is obtained.
Abstract: In the horticulturally important ornamental species Cyclamen persicum Mill., somatic embryogenesis is an efficient vegetative propagation method and the development of artificial seeds is an ultimate aim. This study aims at a systematic comparison of the proteomes of zygotic embryos, somatic embryos grown in liquid medium containing 30 or 60 g l−1 sucrose, germinating embryos of both types and endosperm in order to obtain novel insights into seed and germination physiology. Using high resolution two-dimensional isoelectric focussing/sodium dodecylsulfate polyacrylamide gel electrophoresis (2D IEF/SDS PAGE), 74% of the proteins expressed in zygotic embryos were found in similar abundance in somatic embryos grown in 60 g l−1 sucrose. Somatic embryos grown in 30 g l−1 sucrose accumulated fewer protein species than those grown in 60 g l−1. Selected proteins were identified following mass spectrometry (nano-LC-MS/MS). Four enzymes involved in glycolysis (UDP-glucose pyrophosphorylase, fructose bisphosphate aldolase, triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase GAPDH) were specifically induced in somatic embryos. 11S globulin proteins identified by MS were present in high levels in somatic embryos, zygotic embryos and endosperm, whereas 7S globulins were detected mainly in endosperm and zygotic embryos. These are the first storage proteins identified in C. persicum. Xyloglucans are known to be another group of seed storage compounds in C. persicum. Interestingly, xyloglucan endotransglycosylases were found to be highly expressed in endosperm tissue. We discuss the physiological implications of these observations.
TL;DR: The time course and pattern of deposition of the ( 1→3) and (1→3),(1→4)-β-glucans and AX in the endosperm cell walls of wheat during grain development was studied using specific antibodies.
Abstract: Arabinoxylans (AX) and (1→3),(1→4)-β-glucans are major components of wheat endosperm cell walls. Their chemical heterogeneity has been described but little is known about the sequence of their deposition in cell walls during endosperm development. The time course and pattern of deposition of the (1→3) and (1→3),(1→4)-β-glucans and AX in the endosperm cell walls of wheat (Triticum aestivum L. cv. Recital) during grain development was studied using specific antibodies. At approximately 45°D (degree-days) after anthesis the developing walls contained (1→3)-β-glucans but not (1→3),(1→4)-β-glucans. In contrast, (1→3),(1→4)-β-glucans occurred widely in the walls of maternal tissues. At the end of the cellularization stage (72°D), (1→3)-β-glucan epitopes disappeared and (1→3),(1→4)-β-glucans were found equally distributed in all thin walls of wheat endosperm. The AX were detected at the beginning of differentiation (245°D) in wheat endosperm, but were missing in previous stages. However, epitopes related to AX were present in nucellar epidermis and cross cells surrounding endosperm at all stages but not detected in the maternal outer tissues. As soon as the differentiation was apparent, the cell walls exhibited a strong heterogeneity in the distribution of polysaccharides within the endosperm.
TL;DR: The results show that both embryo/endosperm and maternal factors contribute to germination inhibition at supraoptimal temperatures in Arabidopsis and confirm the role of ABA in thermoinhibition of seed germination and a link between seed physiological dormancy and response to high temperature.
Abstract: Temperature is a primary environmental cue for seed germination of many weeds and vegetables. To investigate the mechanism of germination regulation by temperature, we selected five high temperature (thermoinhibition)-resistant germination mutants (TRW lines) from 20,000 T-DNA insertion lines of Arabidopsis. Segregation analyses indicated that each of the five lines had single locus recessive mutations. The seeds of TRW134-15 and TRW187 showed reduced sensitivity to ABA and also to the gibberrellin biosynthesis inhibitor, paclobutrazol. Genetic and nucleotide sequencing analyses indicated that TRW187 is a new allele of abi3 (abi3-14). TRW71-1 exhibited a maternal effect for both thermoinhibition-resistant and transparent testa phenotypes, and genetic analysis revealed that the mutation was allelic to tt7 (tt7-4 sib). Interestingly, the seeds of reduced dormancy mutants rdo1, rdo2, rdo3 and rdo4 were also thermoinhibition tolerant, and all the TRW seeds showed reduced dormancy. Like rdo3, TRW13-1 had shorter siliques and slightly shorter stems than the wild type. The mutation of TRW13-1 was mapped to the bottom arm of chromosome 1 where rdo3 has also been mapped, but the two mutants are not allelic. We designated TRW13-1 as thermoinhibition-resistant germination 1 (trg1). We also mapped the ABA-insensitive mutation of TRW134-15 to the bottom arm of chromosome 5 and named it trg2. These results show that both embryo/endosperm and maternal factors contribute to germination inhibition at supraoptimal temperatures in Arabidopsis. In addition, we confirm the role of ABA in thermoinhibition of seed germination and a link between seed physiological dormancy and response to high temperature.
TL;DR: The pattern of expression of genes for caffeine synthesis during growth is roughly related to the in situ synthesis of caffeine from adenine nucleotides, although exceptions were found in the very early and later stages of fruit growth.
TL;DR: Transient expression experiments in co-bombarded developing endosperms and in barley aleurone layers demonstrated that HvMYBS3 trans-activated transcription both from Itr1 and Amy6.4 promoters was demonstrated, in contrast with a previously reported seed-expressed R1MYB, HvMCB1.
Abstract: The SHAQKYF R1MYB transcription factor (TF) HvMYBS3 from barley is an activator of gene expression both during endosperm development and in aleurone cells upon seed germination. Its mRNA was detected as early as 10 days after flowering in developing barley endosperm, with a peak at 18 days, and in aleurone cells at 8 h after water imbibition, as shown by Northern blot and in situ hybridization analyses. The HvMYBS3 protein expressed in bacteria binds to oligonucleotides containing a GATA core derived from the promoters of: (i) the developing endosperm gene Itr1 (5'-GATAAGATA-3') encoding trypsin inhibitor BTI-CMe, and (ii) the post-germinating aleurone gene Amy6.4 (5'-TATCCAC-3'/5'-GTGGATA-3') encoding a high-pI alpha-amylase. Transient expression experiments in co-bombarded developing endosperms and in barley aleurone layers demonstrated that HvMYBS3 trans-activated transcription both from Itr1 and Amy6.4 promoters, in contrast with a previously reported seed-expressed R1MYB, HvMCB1, which was an activator of Itr1 and a transcriptional repressor of the Amy6.4 gene. In the yeast three-hybrid system, the HvMYBS3 protein formed a ternary complex with BPBF and BLZ2, two important seed TFs. However, no binary interactions could be detected between HvMYBS3 and BLZ2 or between HvMYBS3 and BPBF.