Regulation Of Starch Metabolism Research Articles

Comparative analysis of the transcriptome during single-seed formation of Castanea henryi: regulation of starch metabolism and endogenous hormones

BackgroundIn seed plants, the ovule is the precursor to the seed. The process of ovule development and differentiation is regulated by multiple factors, including starch metabolism and endogenous hormones. Castanea henryi produces nuts with high nutritional value. However, the high proportion of empty buds restricts the commercial use of the tree. Previous studies have shown that the empty bud phenotype is closely related to ovule abortion. If none of the ovules in the ovary expand rapidly and develop in 7–8 weeks after pollination, an empty bud will form. Therefore, we studied the development and molecular mechanisms underlying single seed formation in C. henryi.ResultsWe found that 49 days after pollination (DAP) is a critical period for the formation of fertile and abortive ovules. The morphology and starch distribution of the fertile and abortive ovules differed significantly at 49 DAP. The fertile ovules were smooth and round in appearance, with a large amount of starch. In contrast, abortive ovules were smaller with only a small amount of starch. The embryo sac of the abortive ovule proceeded to develop abnormally, and the entire ovule lacked starch. We identified 37 candidate genes involved in metabolism with potential roles in the regulation of starch levels. Three ADP-glucose pyrophosphorylase (AGPase) genes, one granule-bound starch synthase (GBSS) gene, and two beta-amylase genes could affect starch accumulation. The levels of auxin, cytokinins, gibberellins, and jasmonic acid in fertile ovules were higher than those in abortive ovules. In addition, the levels of endogenous abscisic acid and salicylic acid in abortive ovules were higher than those in fertile ovules of the same age, consistent with the expression patterns of genes related to the synthesis of abscisic and salicylic acid and signal transduction. We identified and mapped the differentially expressed genes associated with hormone synthesis and signal transduction.ConclusionsThese results improve our general understanding of the molecular mechanisms underlying single seed development in C. henryi and the phenomenon of empty buds, providing directions for future research.

Rapid starch degradation in the wood of olive trees under heat and drought is permitted by three stress-specific beta amylases.

Carbon reserve use is a major drought response in trees, enabling tree survival in conditions prohibiting photosynthesis. However, regulation of starch metabolism under drought at the whole-tree scale is still poorly understood. To this end, we combined measurements of nonstructural carbohydrates (NSCs), tree physiology and gene expression. The experiment was conducted outside on olive trees in pots under 90d of seasonal spring to summer warming. Half of the trees were also subjected to limited water conditions for 28d. Photosynthesis decreased in dehydrating trees from 19 to 0.5µmolm-2 s-1 during the drought period. Starch degradation and mannitol production were a major drought response, with mannitol increasing to 71% and 41% out of total NSCs in shoots and roots, respectively. We identified the gene family members potentially relevant either to long-term or stress-induced carbon storage. Partitioning of expression patterns among β amylase and starch synthase family members was observed, with three β amylases possibly facilitating the rapid starch degradation under heat and drought. Our results suggest a group of stress-related, starch metabolism genes, correlated with NSC fluctuations during drought and recovery. The daily starch metabolism gene expression was different from the stress-mode starch metabolism pattern, where some genes are uniquely expressed during the stress-mode response.

Genes involved in the regulation of starch metabolism and defense response determine resistance in citrus against huanglongbing

Genes involved in the regulation of starch metabolism and defense response determine resistance in citrus against huanglongbing

Genome-wide analysis and phosphorylation sites identification of the 14-3-3 gene family and functional characterization of MeGRF3 in cassava.

The biological functionality of many members of the 14-3-3 gene family is regulated via phosphorylation at multiple amino acid residues. The specific phosphorylation-mediated regulation of these proteins during cassava root tuberization, however, is not well understood. In this study, 15 different 14-3-3 genes (designated MeGRF1 - 15) were identified within the cassava genome. Based upon evolutionary conservation and structural analyses, these cassava 14-3-3 proteins were grouped into ε and non-ε clusters. We found these 15 MeGRF genes to be unevenly distributed across the eight cassava chromosomes. When comparing the expression of these genes during different developmental stages, we found that three of these genes (MeGRF9, 12 and 15) were overexpressed at all developmental stages at 75, 104, 135, 182 and 267 days post-planting relative to the fibrous root stage, whereas two (MeGRF5 and 7) were downregulated during these same points. In addition, the expression of most MeGRF genes changed significantly in the early and middle stages of root tuberization. This suggests that these different MeGRF genes likely play distinct regulatory roles during cassava root tuberization. Subsequently, 18 phosphorylated amino acid residues were detected on nine of these MeGRF proteins. A phosphomimetic mutation at serine-65 in MeGRF3 in Arabidopsis thaliana (Arabidopsis) slightly influenced starch metabolism in these plants, and significantly affected the role of MeGRF3 in salt stress responses. Together these results indicate that 14-3-3 genes play key roles in responses to abiotic stress and the regulation of starch metabolism, offering valuable insights into the functions of these genes in cassava.

Transcriptome Analysis and Identification of Genes Associated with Starch Metabolism in Castanea henryi Seed (Fagaceae).

Starch is the most important form of carbohydrate storage and is the major energy reserve in some seeds, especially Castanea henryi. Seed germination is the beginning of the plant’s life cycle, and starch metabolism is important for seed germination. As a complex metabolic pathway, the regulation of starch metabolism in C. henryi is still poorly understood. To explore the mechanism of starch metabolism during the germination of C. henryi, we conducted a comparative gene expression analysis at the transcriptional level using RNA-seq across four different germination stages, and analyzed the changes in the starch and soluble sugar contents. The results showed that the starch content increased in 0–10 days and decreased in 10–35 days, while the soluble sugar content continuously decreased in 0–30 days and increased in 30–35 days. We identified 49 candidate genes that may be associated with starch and sucrose metabolism. Three ADP-glucose pyrophosphorylase (AGPase) genes, two nucleotide pyrophosphatase/phosphodiesterases (NPPS) genes and three starch synthases (SS) genes may be related to starch accumulation. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to validate the expression levels of these genes. Our study combined transcriptome data with physiological and biochemical data, revealing potential candidate genes that affect starch metabolism during seed germination, and provides important data about starch metabolism and seed germination in seed plants.

Structure and expression of barley starch phosphorylase genes

The function of starch phosphorylase has long been debated on the regulation of starch metabolism during the growth and development of plants. In this study, we isolated starch phosphorylase genes (Pho1 and Pho2) from barley, characterized their gene and protein structures, predicated their promoter's cis-elements and analyzed expression patterns. Multiple alignments of these genes showed that (1) both Pho1 and Pho2 genes possess 15 exons and 14 introns in all but three of the species analyzed, Aegilops tauschii (for Pho1 which contains 16 exons and 15 introns), potato (for Pho1b which contains 14 exons and 13 introns), and Triticum uraru (for Pho2 which contains 15 exons and 14 introns); (2) the exon-intron junctions of Pho1 and Pho2 flanking the ligand-binding sites are more conservative than the other regions. Analysis of protein sequences revealed that Pho1 and Pho2 were highly homologous except for two regions, the N terminal domain and the L78 insertion region. The results of real-time quantitative PCR (RT-qPCR) indicated that Pho2 is mainly expressed in germinating seeds, and the expression of Pho1 is similar to that of starch synthesis genes during seed development in barley. Microarray-based analysis indicated that the accumulation of Pho1 or Pho2 transcripts exhibited uniform pattern both in various tissues and various stages of seed development among species of barley, rice, and Arabidopsis. Pho1 of barley was significantly down-regulated under cold and drought treatments, and up-regulated under stem rust infection. Pho2 exhibited similar expression to Pho1 in barley. However, significant difference in expression was not detected for either Pho1 or Pho2 under any of the investigated abiotic stresses. In Arabidopsis, significant down-regulation was detected for Pho1 (PHS1) under abscisic acid (ABA) and for Pho2 (PHS2) under cold, salt, and ABA. Our results provide valuable information to genetically manipulate phosphorylase genes and to further elucidate their regulatory mechanism in the starch biosynthetic pathway.

A plastid-localized glycogen synthase kinase 3 modulates stress tolerance and carbohydrate metabolism.

Glycogen synthase kinase 3 (GSK-3) was originally identified as a regulator of glycogen synthesis in mammals. Like starch in plants, glycogen is a polymer of glucose, and serves as an energy and carbon store. Starch is the main carbohydrate store in plants. Regulation of starch metabolism, in particular in response to environmental cues, is of primary importance for carbon and energy flow in plants but is still obscure. Here, we provide evidence that MsK4, a novel Medicago sativa GSK-3-like kinase, connects stress signalling with carbon metabolism. MsK4 was found to be a plastid-localized protein kinase that is associated with starch granules. High-salt stress rapidly induced the in vivo kinase activity of MsK4. Metabolic profiling of MsK4 over-expressor lines revealed changes in sugar metabolism, including increased amounts of maltose, the main degradation product of starch in leaves. Plants over-expressing MsK4 showed improved tolerance to salt stress. Moreover, under high-salinity conditions, MsK4-over-expressing plants accumulated significantly more starch and showed modified carbohydrate content compared with wild-type plants. Overall, these data indicate that MsK4 is an important regulator that adjusts carbohydrate metabolism to environmental stress.

Regulation of Starch Metabolism in Arabidopsis Leaves

Starch is the main form by which plants store carbohydrate and is a major photosynthetic product in many species. Despite the importance of starch, there is still much more that needs to be learned about its synthesis and subsequent degradation. An article by [Smith et al. (2004)][1] applied the

Expression profiling of starch metabolism-related plastidic translocator genes in rice

The genes encoding the major putative rice plastidic translocators involved in the carbon flow related to starch metabolism were identified by exhaustive database searches. The genes identified were two for the triose phosphate/phosphate translocator (TPT), five for the glucose 6-phosphate/phosphate translocator (GPT) including putatively non-functional ones, four for the phosphoenolpyruvate/phosphate translocator (PPT), three for the putative ADP-glucose translocator (or Brittle-1 protein, BT1), two for the plastidic nucleotide transport protein (NTT), and one each for the plastidic glucose translocator (pGlcT) and the maltose translocator (MT). The expression patterns of the genes in various photosynthetic and non-photosynthetic organs were examined by quantitative real-time PCR. OsBT1-1 was specifically expressed in the seed and its transcript level tremendously increased at the onset of vigorous starch production in the endosperm, suggesting that the ADP-glucose synthesized in the cytosol is a major precursor for starch biosynthesis in the endosperm amyloplast. In contrast, all of the genes for OsTPT, OsPPT, and OsNTT were mainly expressed in source tissues, suggesting that their proteins play essential roles in the regulation of carbohydrate metabolism in chloroplasts. Substantial expression of the four OsGPT genes and the OspGlcT gene in both source and sink organs suggests that the transport of glucose phosphate and glucose is physiologically important in both photosynthetic and non-photosynthetic tissues. The present study shows that comprehensive analysis of expression patterns of the plastidic translocator genes is a valuable tool for the elucidation of the functions of the translocators in the regulation of starch metabolism in rice.

Mobilization of seed storage lipid by Arabidopsis seedlings is retarded in the presence of exogenous sugars

BackgroundSoluble sugar levels must be closely regulated in germinating seeds to ensure an adequate supply of energy and building materials for the developing seedling. Studies on germinating cereal seeds indicate that production of sugars from starch is inhibited by increasing sugar levels. Although numerous studies have focused on the regulation of starch metabolism, very few studies have addressed the control of storage lipid metabolism by germinating oilseeds.ResultsMobilization of storage lipid by germinating seeds of the model oilseed plant Arabidopsis thaliana (L.) Heynh. occurs at a greatly reduced rate in the presence of exogenous glucose or mannose, but not in the presence of equi-molar 3-O-methylglucose or sorbitol. The sugar-insensitive5-1/abscisic acid-insensitive4-101 (sis5-1/abi4-101) mutant is resistant to glucose inhibition of seed storage lipid mobilization. Wild-type seedlings become insensitive to glucose inhibition of storage lipid breakdown within 3 days of the start of imbibition.ConclusionsGrowth in the presence of exogenous glucose significantly retards mobilization of seed storage lipid in germinating seeds from wild-type Arabidopsis. This effect is not solely due to the osmotic potential of the media, as substantially higher concentrations of sorbitol than of glucose are required to exert significant effects on lipid breakdown. The inhibitory effect of glucose on lipid breakdown is limited to a narrow developmental window, suggesting that completion of some critical metabolic transition results in loss of sensitivity to the inhibitory effect of glucose on lipid breakdown.

MSS11, a novel yeast gene involved in the regulation of starch metabolism.

Expression of the STA1-3 glucoamylase genes, responsible for starch degradation in Saccharomyces cerevisiae, is down regulated by the presence of STA10. In order to elucidate the role of STA10 in the regulation of the glucoamylase system, a multicopy genomic library was constructed and screened for genes that enhanced growth of a STA2-STA10 S. cerevisiae strain on starch media. This screen allowed us to clone and characterize a novel activator gene of STA2 (and by extrapolation, STA1 and STA3), designated MSS11. A strain transformed with multiple copies of MSS11 exhibits increased levels of STA2 mRNA and, consequently, increased glucoamylase activity. Deletion of MSS11, located on chromosome XIII, results in media-dependent absence of glucoamylase synthesis. MSS11 has not been cloned previously and the encoded protein, Mss11p, is not homologous to any other known protein. An outstanding feature of Mss11p is that the protein contains regions of 33 asparagine residues interrupted by only three serine residues, and 35 glutamine residues interrupted by a single histidine residue. Epistasis studies showed that deletion of MSS11 abolishes the activation of STA2 caused by the over-expression of MSS10, a previously identified gene. In turn, it was found that deletion of MSS10 still allows activation of STA2 by over-expression of MSS11. Mss11p therefore appears to be positioned below Mss10p in a signal transduction pathway.

Relationship between Starch Accumulation and Activities of the Related Enzymes in the Leaf Sheath as a Temporary Sink Organ in Rice (Oryza sativa)

The starch stored temporarily in the leaf sheath of rice plants is translocated to the grain, contributing to the grain yield. In this paper, the relationship between starch accumulation and the activities of enzymes involved in the starch biosynthetic pathway in the leaf sheaths of rice plants was examined to elucidate the regulation mechanism of starch accumulation in the temporary sink organ. When the starch content was compared between different leaf sheath positions on the main stem, the 14th leaf sheath counted from the bottom, which elongated just before anthesis, showed about a four-fold higher value than the 10th leaf sheath. Among the enzymes involved in carbohydrate metabolism, the activity of starch branching enzyme (BE, EC2.4.1.18) was greatly higher in the 14th leaf sheath than in the 10th leaf sheath, while that of ADPglucose pyrophosphorylase (EC2.7.7.27) was similar between the two leaf sheaths. The starch content increased rapidly in the period around anthesis in the 12th and 14th leaf sheaths, but did not in the 10th and 11th leaf sheath. In the higher leaf sheath position, the activity of BE changed with noticeably similar trend to the starch content. Soluble starch synthase (SSS, EC2.4.1.21), granule-bound starch synthase (GBSS, EC2.4.1.21) and plastidial fructose- 1,6-bisphosphatase (FBPase, EC3.1.3.11) were also significantly correlated with the starch content. These results suggest that BE is involved in regulation of starch metabolism, possibly in collaboration with other enzymes such as SSS, GBSS and plastidial FBPase in temporary sink organs like the leaf sheath.

The regulation of starch metabolism by inorganic phosphate

Summary The effects of orthophosphate (Pi) on starch synthesis and degradation in the isolated intact spinach chloroplast are investigated. During CO2 fixation in the light increasing levels of Pi (0–1.0 mM), which have little effect on the rate of fixation, prolong the lag of starch synthesis and reduce its maximal rate from 14.5 to 6.8 μg-atom C incorporated into starch per milligram chlorophyll per hour. The label in dihydroxyacetone phosphate and other sugar phosphates, especially sedoheptulose-1,7-bis-phosphate, increases up to 10-fold under these conditions. Starch degradation in the dark is monitored in the chloroplast by following the breakdown of the 14C labeled starch. Pi concentrations in the order of 2.5–5.0 mM are optimal for starch mobilization at a rate of about 1 μg-atom C per milligram chlorophyll per hour.