Starch Synthesis Pathway Research Articles

Transcriptome-Based Spatiotemporal Analysis of Drought Response Mechanisms in Two Distinct Peanut Cultivars.

Drought tolerance varies among different peanut (Arachis hypogaea L.) cultivars. Here, drought responses of two cultivars, Huayu 22 (HY22) with drought tolerance and Fuhua 18 (FH18) with drought sensitivity, were compared at the morphological, physiological, biochemical, photosynthetic, and transcriptional levels. Drought stress caused wilting and curling of leaves, bending of stems, and water loss in both cultivars. There was an increase in malondialdehyde (MDA) content under prolonged drought stress, more so in FH18. But the levels of reactive oxygen species (H2O2) and lipid peroxidation were low in HY22. The activities of superoxide dismutase (SOD), peroxidase (POD), and glutathione reductase (GR) were considerably elevated, corresponding with rapid increases in the accumulation of soluble proteins, soluble sugars, and proline. Transcriptional sequencing showed gene expression varied seriously in HY22, which was upregulated in both stems of two cultivars, though downregulation was less pronounced in HY22. KEGG pathway analysis revealed significant enrichment in four leaf and six stem pathways. Additionally, core genes relating to photosynthesis, carbon fixation, proline synthesis, and sucrose and starch synthesis pathways were identified by correlation analysis. Those gene expressions were variously upregulated in stems of two cultivars, especially in HY22, giving a novel view of the shoot as a whole participating in stress response.

Genome-Wide Identification of microRNAs Associated with Starch Biosynthesis and Endosperm Development in Foxtail Millet.

Foxtail millet is one of the oldest crops, and its endosperm contains up to 70% of starch. Grain filling is an important starch accumulation process associated with foxtail millet yield and quality. However, the molecular mechanisms of grain filling in foxtail millet are relatively unclear. Here, we investigate the genes and regulated miRNAs associated with starch synthesis and metabolism in foxtail millet using high-throughput small RNA, mRNA and degradome sequencing. The regulation of starch synthesis and quality is carried out mainly at the 15 DAA to 35 DAA stage during grain filling. The DEGs between waxy and non-waxy foxtail millet were significant, especially for GBSS. Additionally, ptc-miR169i_R+2_1ss21GA, fve-miR396e_L-1R+1, mtr-miR162 and PC-5p-221_23413 regulate the expression of genes associated with the starch synthesis pathway in foxtail millet. This study provides new insights into the molecular mechanisms of starch synthesis and quality formation in foxtail millet.

Transcriptome-wide expression landscape and starch synthesis pathway co-expression network in sorghum.

The gene expression landscape across different tissues and developmental stages reflects their biological functions and evolutionary patterns. Integrative and comprehensive analyses of all transcriptomic data in an organism are instrumental to obtaining a comprehensive picture of gene expression landscape. Such studies are still very limited in sorghum, which limits the discovery of the genetic basis underlying complex agricultural traits in sorghum. We characterized the genome-wide expression landscape for sorghum using 873 RNA-sequencing (RNA-seq) datasets representing 19 tissues. Our integrative analysis of these RNA-seq data provides the most comprehensive transcriptomic atlas for sorghum, which will be valuable for the sorghum research community for functional characterizations of sorghum genes. Based on the transcriptome atlas, we identified 595 housekeeping genes (HKGs) and 2080 tissue-specific expression genes (TEGs) for the 19 tissues. We identified different gene features between HKGs and TEGs, and we found that HKGs have experienced stronger selective constraints than TEGs. Furthermore, we built a transcriptome-wide co-expression network (TW-CEN) comprising 35 modules with each module enriched in specific Gene Ontology terms. High-connectivity genes in TW-CEN tend to express at high levels while undergoing intensive selective pressure. We also built global and seed-preferential co-expression networks of starch synthesis pathways, which indicated that photosynthesis and microtubule-based movement play important roles in starch synthesis. The global transcriptome atlas of sorghum generated by this study provides an important functional genomics resource for trait discovery and insight into starch synthesis regulation in sorghum.

Transcriptomic and physiological analysis of the response of Spirodela polyrrhiza to sodium nitroprusside

BackgroundSpirodela polyrrhiza is a simple floating aquatic plant with great potential in synthetic biology. Sodium nitroprusside (SNP) stimulates plant development and increases the biomass and flavonoid content in some plants. However, the molecular mechanism of SNP action is still unclear.ResultsTo determine the effect of SNP on growth and metabolic flux in S. polyrrhiza, the plants were treated with different concentrations of SNP. Our results showed an inhibition of growth, an increase in starch, soluble protein, and flavonoid contents, and enhanced antioxidant enzyme activity in plants after 0.025 mM SNP treatment. Differentially expressed transcripts were analysed in S. polyrrhiza after 0.025 mM SNP treatment. A total of 2776 differentially expressed genes (1425 upregulated and 1351 downregulated) were identified. The expression of some genes related to flavonoid biosynthesis and NO biosynthesis was upregulated, while the expression of some photosynthesis-related genes was downregulated. Moreover, SNP stress also significantly influenced the expression of transcription factors (TFs), such as ERF, BHLH, NAC, and WRKY TFs.ConclusionsTaken together, these findings provide novel insights into the mechanisms of underlying the SNP stress response in S. polyrrhiza and show that the metabolic flux of fixed CO2 is redirected into the starch synthesis and flavonoid biosynthesis pathways after SNP treatment.

Genome-wide transcriptional responses to water deficit during seed development in Pisum sativum, focusing on sugar transport and metabolism.

Agriculture is particularly impacted by global changes, drought being a main limiting factor of crop production. Here, we focus on pea (Pisum sativum), a model legume cultivated for its seed nutritional value. A water deficit (WD) was applied during its early reproductive phase, harvesting plant organs at two key developmental stages, either at the embryonic or the seed-filling stages. We combined phenotypic, physiological and transcriptome analyses to better understand the adaptive response to drought. First, we showed that apical growth arrest is a major phenotypic indicator of water stress. Sugar content was also greatly impacted, especially leaf fructose and starch contents. Our RNA-seq analysis identified 2001 genes regulated by WD in leaf, 3684 genes in root and 2273 genes in embryonic seed, while only 80 genes were regulated during seed-filling. Hence, a large transcriptional reprogramming occurred in response to WD in seeds during early embryonic stage, but no longer during the later stage of nutritional filling. Biological processes involved in transcriptional regulation, carbon transport and metabolism were greatly regulated by WD in both source and sink organs, as illustrated by the expression of genes encoding transcription factors, sugar transporters and enzymes of the starch synthesis pathway. We then looked at the transcriptomic changes during seed development, highlighting a transition from monosaccharide utilization at the embryonic stage to sucrose transport feeding the starch synthesis pathway at the seed-filling stage. Altogether, our study presents an integrative picture of sugar transport and metabolism in response to drought and during seed development at a genome-wide level.

Telomere-to-telomere assembly of cassava genome reveals the evolution of cassava and divergence of allelic expression.

Cassava is a crucial crop that makes a significant contribution to ensuring human food security. However, high-quality telomere-to-telomere cassava genomes have not been available up to now, which has restricted the progress of haploid molecular breeding for cassava. In this study, we constructed two nearly complete haploid resolved genomes and an integrated, telomere-to-telomere gap-free reference genome of an excellent cassava variety, 'Xinxuan 048', thereby providing a new high-quality genomic resource. Furthermore, the evolutionary history of several species within the Euphorbiaceae family was revealed. Through comparative analysis of haploid genomes, it was found that two haploid genomes had extensive differences in linear structure, transcriptome features, and epigenetic characteristics. Genes located within the highly divergent regions and differentially expressed alleles are enriched in the functions of auxin response and the starch synthesis pathway. The high heterozygosity of cassava 'Xinxuan 048' leads to rapid trait segregation in the first selfed generation. This study provides a theoretical basis and genomic resource for molecular breeding of cassava haploids.

Evolutionary and expression analysis of starch synthase genes from Tartary buckwheat revealed the potential function of FtGBSSII‐4 and FtGBSSII‐5 in seed amylose biosynthesis

AbstractThe starch synthase has been identified well as a core enzyme in the starch biosynthesis pathway in monocots. However, only a few starch synthase genes (SSs) are known in dicots. Tartary buckwheat (Fagopyrum tataricum Gaertn.) is one of the dicots‐enriched starch in the seeds, but its starch synthesis pathway remains unclear. Here, 15 SS genes were identified in the Tartary buckwheat genome, including 5 granule‐bound starch synthase (GBSS) and 10 soluble starch synthase (SSS) genes. Evolutionary analysis showed that all FtGBSSs belonged to GBSSII, and its isoforms were more abundant than other dicots due to the segmental duplication events. Expression pattern analysis showed two GBSS genes (FtGBSSII‐4 and FtGBSSII‐5) and three SSS genes (FtSSII‐2, FtSSIII‐1, and FtSSIV‐2) were mainly expressed in seeds, indicating that they may be the dominant isoforms for the starch synthesis in Tartary buckwheat. Besides, 23 transcription factor genes out of 1073 were identified from 17 transcription factor families and highly expressed in seeds. Expression correlation analysis suggested that FtNF‐YB2 may be the promising regulators for FtSSs. These results provide new insights and a theoretical basis for understanding starch synthesis and regulation in Tartary buckwheat and other dicots.

Exogenous application of Bradyrhizobium japonicum AC20 enhances soybean tolerance to atrazine via regulating rhizosphere soil microbial community and amino acid, carbohydrate metabolism related genes expression

Atrazine is used to control broad-leaved weeds in farmland and has negative impacts on soybean growth. Legume-rhizobium symbiosis plays an important role in regulating abiotic stress tolerance of plants, however, the mechanisms of rhizobia regulate the tolerance of soybean to atrazine based on the biochemical responses of the plant-soil system are limited. In this experiment, Glycine max (L.) Merr. Dongnong 252, planted in 20 mg kg−1 of atrazine-contaminated soil, was inoculated with Bradyrhizobium japonicum AC20, and the plant growth, rhizosphere soil microbial diversity and the expression of the genes related to soybean carbon and nitrogen metabolism were assessed. The results indicated that strain AC20 inoculation alleviated atrazine-induced growth inhibition via increasing the contents of leghemoglobin and total nitrogen in soybean seedlings. The psbA gene expression level of the soybean seedlings that inoculated strain AC20 was 1.4 times than that of no rhizobium inoculating treatments. Moreover, the inoculated AC20 increased the abundance of Acidobacteria and Actinobacteria in soybean rhizosphere. Transcriptome analysis demonstrated that strain AC20 regulated the genes expression of amino acid metabolism and carbohydrate metabolism of soybean seedlings. Correlation analysis between 16S rRNA and transcriptome showed that strain AC20 reduced Planctomycetes abundance so as to down-regulated the expression of genes Glyma. 13G087800, Glyma. 12G005100 and Glyma.12G098900 involved in starch synthesis pathway of soybean leaves. These results provide available information for the rhizobia application to enhance the atrazine tolerate in soybean seedlings.

Cover Caption

September Online Cover: Characterization of lotus seed development; fresh weight, dry weight, and moisture content of developing seeds; optical microscope photographs of iodized slices of mature seed and rhizome; and Venn diagrams of differentially expressed genes, from “Differential expression involved in starch synthesis pathway genes reveal various starch characteristics of seed and rhizome in lotus (Nelumbo Nucifera)” by Fenglin Zhu, Han Sun, Jia Wang, Xingwen Zheng, Tao Wang, Ying Diao, and Zhongli Hu. p. 4250–4263.

Ectopic Expression of the Rice Grain-Size-Affecting Gene GS5 in Maize Affects Kernel Size by Regulating Endosperm Starch Synthesis.

Maize is one of the most important food crops, and maize kernel is one of the important components of maize yield. Studies have shown that the rice grain-size affecting gene GS5 increases the thousand-kernel weight by positively regulating the rice grain width and grain grouting rate. In this study, based on the GS5 transgenic maize obtained through transgenic technology with specific expression in the endosperm, molecular assays were performed on the transformed plants. Southern blotting results showed that the GS5 gene was integrated into the maize genome in a low copy number, and RT-PCR analysis showed that the exogenous GS5 gene was normally and highly expressed in maize. The agronomic traits of two successive generations showed that certain lines were significantly improved in yield-related traits, and the most significant changes were observed in the OE-34 line, where the kernel width increased significantly by 8.99% and 10.96%, the 100-kernel weight increased by 14.10% and 10.82%, and the ear weight increased by 13.96% and 15.71%, respectively; however, no significant differences were observed in the plant height, ear height, kernel length, kernel row number, or kernel number. In addition, the overexpression of the GS5 gene increased the grain grouting rate and affected starch synthesis in the rice grains. The kernels’ starch content in OE-25, OE-34, and OE-57 increased by 10.30%, 7.39%, and 6.39%, respectively. Scanning electron microscopy was performed to observe changes in the starch granule size, and the starch granule diameter of the transgenic line(s) was significantly reduced. RT-PCR was performed to detect the expression levels of related genes in starch synthesis, and the expression of these genes was generally upregulated. It was speculated that the exogenous GS5 gene changed the size of the starch granules by regulating the expression of related genes in the starch synthesis pathway, thus increasing the starch content. The trans-GS5 gene was able to be stably expressed in the hybrids with the genetic backgrounds of the four materials, with significant increases in the kernel width, 100-kernel weight, and ear weight. In this study, the maize kernel size was significantly increased through the endosperm-specific expression of the rice GS5 gene, and good material for the functional analysis of the GS5 gene was created, which was of great importance in theory and application.

Starch accumulation dynamics and transcriptome analysis of Chlorella sorokiniana during transition of sulfur nutritional status

Microalgae can effectively accumulate starch by using nutritional limitation methods in the context of bioalcohol fuel production. However, relatively few studies have focused on starch accumulation in microalgae and its molecular basis, especially under sulfur limitation conditions. In this study, the starch accumulation dynamics and physiological responses of Chlorella sorokiniana under sulfur starvation (SS) and sulfur replenishment (SR) conditions were investigated, and the genes involved in the transcriptional regulation were explored using RNA-seq. The starch content in C. sorokiniana cells significantly increased from 1.6% to 55.0% of dry weight within 24 h under SS conditions, and then, it decreased to 3.4% within 12 h after transition to SR conditions. However, cell growth was inhibited, and pigment content decreased under SS conditions. Using RNA-seq analysis, a total of 9720 differentially expressed genes (DEGs) induced by sulfur status were obtained. These genes were narrowed down to 454 starvation and replenishment cross-validated (SRV)-DEGs, among which 283 SRV-DEGs were significantly up-regulated and 171 SRV-DEGs were down-regulated under SS conditions, and returned to their previous state under SR conditions. The SRV-DEGs enriched in the sulfate metabolism pathway were all up-regulated under SS conditions after 6 h to speed up the sulfur metabolic cycle, and the transcriptional abundance of a sulfate transporter (SULTR4), cysteine synthase[O-acetylserine(thiol)-lyase] (OASTL), serine acetyltransferase (SAT), and methanethiol oxidase (SELENBP1) increased 8.6-fold, 12.6-fold, 8.7-fold, and 12.4-fold, respectively. Protein synthesis was correspondingly inhibited, which resulted in the reallocation of carbon and elevated the starch synthesis pathway, in which the expressions of glycogen branching enzyme (GBE) and starch synthase (SS) were up-regulated 12.0- and 3.0-fold, respectively. The fatty acid desaturase (FAD) and phosphatidic acid phosphatase (PAP) in the lipid synthesis pathway were strongly up-regulated 8.8- and 16.2-fold, respectively, indicating the competitive synthesis of lipids. The down-regulation of SRV-DEGs associated with carbon fixation, such as those in the Calvin cycle, possibly affected cell growth. The time-resolved transcriptional analysis identified the SRV-DEGs, revealing the underlying starch accumulation mechanism, as well as the relationship with cell growth and lipid synthesis.

Differential expression involved in starch synthesis pathway genes reveal various starch characteristics of seed and rhizome in lotus (Nelumbo Nucifera).

Lotus (Nelumbo nucifera) is one of the main aquatic vegetables in China. Its seed and rhizome are main edible parts which are rich in starch. Preliminary experiments of starch contents revealed that seed and rhizome expressed great differences in amylose and amylopectin contents. The rhizomes have higher amylopectin content, while the seeds have higher amylose content. In this study, we have estimated 16 varieties of lotus seeds and found that the amylose content of lotus seeds ranged from 30% to 50%, with an average amylose content of 43%, which showed high-amylose content characteristics. Morphological analysis of lotus seed shown that starch rapid accumulated in 20 DAF (day after fertilization) ∼ 26 DAF. Transcriptome of lotus seeds indicated that starch genes played an important role in seed development. Especially in 22 DAF, the genes which controlled amylose synthesis significantly increased, in contrast, the expression of amylopectin-related genes was stable and might limit the synthesis of amylopectin. We further analyzed the expression patterns of 11 key related genes between lotus seeds and rhizomes, and found that the expression of amylose-related genes to were higher in lotus seed, while the expression of genes related to amylopectin synthesis were higher in rhizome. This study provided a comprehensive research of molecular basis for starch in lotus seed and rhizome. Different expression among key genes during starch accumulation might be the principal cause of the differences in starch properties between seed and rhizome. PRACTICAL APPLICATION: Differential expression involved in starch synthesis pathway genes is the main reason for various starch characteristics of seed and rhizome in lotus. High amylose content in lotus seed is a valuable trait for developing functional food.

A Maize CBM Domain Containing the Protein ZmCBM48-1 Positively Regulates Starch Synthesis in the Rice Endosperm

Starch directly determines the grain yield and quality. The key enzymes participating in the process of starch synthesis have been cloned and characterized. Nevertheless, the regulatory mechanisms of starch synthesis remain unclear. In this study, we identified a novel starch regulatory gene, ZmCBM48-1, which contained a carbohydrate-binding module 48 (CBM48) domain. ZmCBM48-1 was highly expressed in the maize endosperm and was localized in the plastids. Compared with the wild type lines, the overexpression of ZmCBM48-1 in rice altered the grain size and 1000-grain weight, increased the starch content, and decreased the soluble sugar content. Additionally, the transgenic rice seeds exhibited an alterant endosperm cell shape and starch structure. Meanwhile, the physicochemical characteristics (gelatinization properties) of starch were influenced in the transgenic lines of the endosperm compared with the wild type seeds. Furthermore, ZmCBM48-1 played a positive regulatory role in the starch synthesis pathway by up-regulating several starch synthesis-related genes. Collectively, the results presented here suggest that ZmCBM48-1 acts as a key regulatory factor in starch synthesis, and could be helpful for devising strategies for modulating starch production for a high yield and good quality in maize endosperm.

Proteomic analysis of Euryale ferox Salisb seeds at different developmental stages

The development of plant seeds is accompanied by changes in their internal substances. The edible part of E. ferox is the seed, and starch and flavonoids are the storage substances and functional substances in E. ferox seeds respectively. Herein, four time points of seed development, including after flowering T10 (10 days), T20 (20 days), T30 (30 days) and T40 (40 days), were investigated by using iTRAQ technology. A total of 2809 differential proteins were identified. The enrichment analysis of differential proteins found that they were mainly enriched in starch synthesis pathways and flavonoid biosynthesis pathways. The key candidate enzymes for starch synthesis, APS (c54069), APL (c55730), SBE (c56416), SSS (c54912) and GBSS (c53181), were identified. At the same time,PAL (c50934), CHS (c49212), F3H (c35949) and ANS (c54610) may be key enzymes in flavonoid biosynthesis. In addition, the ABA signal transduction pathway was analyzed and it was identified that PYL3 (c54854) and ABI5 (c56122) are up-regulated from T10 to T40, and it is speculated that they play an important regulatory role in the development of E. ferox seeds. Together, these results reveals the dynamic changes during the development of E. ferox seeds, which will provide guidance for the study of the molecular mechanism of starch and flavonoids.

Genetic diversity analysis of Chinese fresh corn hybrids using SNP Chips

<p id="C3">China is a major fresh corn production and consumption country in the world. Assessment of genetic diversity and relationships among fresh corn hybrids in China has great benefit for hybrid identification and breed cultivation. In this study, an Illumina Maize 6K chip was employed to perform genome-wide scanning for the population structure and genetic distance of 385 fresh corn hybrids nationwide. The results showed that the average genetic diversity of 5067 SNP markers in 385 fresh corn hybrids was 0.406, with a range of 0.097-0.500. The average polymorphic information content (PIC) was 0.319, with a range of 0.092-0.375. The results of PCA and population genetic structure analysis revealed that the hybrids were mainly divided into three groups, which were non-sweet corn group (185 varieties), temperate sweet corn group (123 varieties), and tropical sweet corn group (77 varieties). The genetic distance between any two hybrids ranged from 0.132 to 0.472, with an average of 0.37. A total of 160 genome regions indicated strong population differentiation among different groups following <italic>F</italic>_ST analysis. Four key genes (<italic>sh2</italic>, <italic>su1</italic>, <italic>su2</italic>, and <italic>wx1</italic>) of starch synthesis pathway in maize grains were detected. Two candidate genes (<italic>sh2 </italic>and <italic>DGAT1-2</italic>) demonstrated different selection patterns in fresh corn groups and were validated using molecular markers. These results provide important theoretical guidance for the breeding and improvement of fresh corn varieties in China.

Sucrose synthases are not involved in starch synthesis in Arabidopsis leaves

Many plants accumulate transitory starch reserves in their leaves during the day to buffer their carbohydrate supply against fluctuating light conditions, and to provide carbon and energy for survival at night. It is universally accepted that transitory starch is synthesized from ADP-glucose (ADPG) in the chloroplasts. However, the consensus that ADPG is made in the chloroplasts by ADPG pyrophosphorylase has been challenged by a controversial proposal that ADPG is made primarily in the cytosol, probably by sucrose synthase (SUS), and then imported into the chloroplasts. To resolve this long-standing controversy, we critically re-examined the experimental evidence that appears to conflict with the consensus pathway. We show that when precautions are taken to avoid artefactual changes during leaf sampling, Arabidopsis thaliana mutants that lack SUS activity in mesophyll cells (quadruple sus1234) or have no SUS activity (sextuple sus123456) have wild-type levels of ADPG and starch, while ADPG is 20 times lower in the pgm and adg1 mutants that are blocked in the consensus chloroplastic pathway of starch synthesis. We conclude that the ADPG needed for starch synthesis in leaves is synthesized primarily by ADPG pyrophosphorylase in the chloroplasts.

Wheat E3 ubiquitin ligase TaGW2-6A degrades TaAGPS to affect seed size

TaGW2 has been identified as a key determinant of the grain weight in wheat (Triticum aestivum L.). In our previous study, we found that the grain size differs in Chinese Spring (CS) and its TaGW2-6A allelic variant (NIL31). In addition, the expression of the key starch biosynthesis enzyme gene TaAGPS differs significantly in the two materials. However, the underlying molecular mechanism associated with the action of TaGW2-6A has not been reported. In the present study, we found that TaGW2-6A-CS interacted with TaAGPS, whereas TaGW2-6A-NIL31 did not interact with it in vitro and in vivo. Furthermore, we found that the C-terminal LXLX domain (376–424 aa) of TaGW2-6A recognized TaAGPS. However, the TaGW2-6A allelic variant lacked this key interaction region due to premature translation termination. We also found that TaGW2-6A-CS can ubiquitinate TaAGPS and degrade it via the 26 S proteasome pathway. In addition, our analysis of the activity of ADP-glucose pyrophosphorylase (AGPase) indicated that the AGPase level in the endosperm cells was lower in CS than NIL31. Cytological observations demonstrated that the average number of starch granules and the average area of starch granules in endosperm cells were lower in CS than NIL31. The overexpression of TaAGPS positively regulated the seed size in transgenic Arabidopsis. Our findings provide novel insights into the molecular mechanism that allows TaGW2-6A-TaAGPS to regulate seed size via the starch synthesis pathway.

Starch biosynthesis in guard cells has features of both autotrophic and heterotrophic tissues.

The pathway of starch synthesis in guard cells (GCs), despite the crucial role starch plays in stomatal movements, is not well understood. Here, we characterized starch dynamics in GCs of Arabidopsis (Arabidopsis thaliana) mutants lacking enzymes of the phosphoglucose isomerase-phosphoglucose mutase-ADP-glucose pyrophosphorylase starch synthesis pathway in leaf mesophyll chloroplasts or sugar transporters at the plastid membrane, such as glucose-6-phosphate/phosphate translocators, which are active in heterotrophic tissues. We demonstrate that GCs have metabolic features of both photoautotrophic and heterotrophic cells. GCs make starch using different carbon precursors depending on the time of day, which can originate both from GC photosynthesis and/or sugars imported from the leaf mesophyll. Furthermore, we unravel the major enzymes involved in GC starch synthesis and demonstrate that they act in a temporal manner according to the fluctuations of stomatal aperture, which is unique for GCs. Our work substantially enhances our knowledge on GC starch metabolism and uncovers targets for manipulating GC starch dynamics to improve stomatal behavior, directly affecting plant productivity.

Combined RNA-seq and Phenotype Analysis Reveals a Potential Molecular Mechanism of the Difference in Grain Size of Naked Barley From the Qinghai–Tibetan Plateau

To understand the molecular mechanism controlling the size of barley grains, a number of traits were analyzed and RNA-seq was conducted on grains of two barley materials with a significant difference in thousand-grain weight (TGW) after flowering. The trait dataset delineates the dynamic changes in grain size after flowering, and it provides an understanding of the source of the difference in TGW. By comparing the transcripts of barley grains at several stages after flowering, we identified the gene expression characteristics and significantly enriched pathways in each stage. At the early stage of grain development, genes involved in fatty acid metabolism, plant hormone signal transduction, and pathways involved in cytoskeleton formation were significantly upregulated. At the later stage of grain development, genes involved in starch synthesis, glucose metabolism, and other pathways were significantly upregulated. Further, we used weighted gene coexpression network analysis (WGCNA) and correlation analysis of trait datasets to identify the coexpressed gene modules significantly associated with traits, such as grain length (GL), grain width (GW), and dry weight (DW). After comparing the modules with the differentially expressed gene (DEG) set, 12 candidate genes were selected, and among these, four genes were homologous to genes that regulate grain size in rice and other plants. The combined analysis identified many potential key regulatory factors that may control barley grain size and yield potential, thus providing new insights into the molecular mechanism of barley grain size.

Structure, function, and evolution of plant ADP-glucose pyrophosphorylase.

This review outlines research performed in the last two decades on the structural, kinetic, regulatory and evolutionary aspects of ADP-glucose pyrophosphorylase, the regulatory enzyme for starch biosynthesis. ADP-glucose pyrophosphorylase (ADP-Glc PPase) catalyzes the first committed step in the pathway of glycogen and starch synthesis in bacteria and plants, respectively. Plant ADP-Glc PPase is a heterotetramer allosterically regulated by metabolites and post-translational modifications. In this review, we focus on the three-dimensional structure of the plant enzyme, the amino acids that bind the regulatory molecules, and the regions involved in transmitting the allosteric signal to the catalytic site. We provide a model for the evolution of the small and large subunits, which produce heterotetramers with distinct catalytic and regulatory properties. Additionally, we review the various post-translational modifications observed in ADP-Glc PPases from different species and tissues. Finally, we discuss the subcellular localization of the enzyme found in grain endosperm from grasses, such as maize and rice. Overall, this work brings together research performed in the last two decades to better understand the multiple mechanisms involved in the regulation of ADP-Glc PPase. The rational modification of this enzyme could improve the yield and resilience of economically important crops, which is particularly important in the current scenario of climate change and food shortage.