Understanding Starch Metabolism in Pea Seeds towards Tailoring Functionality for Value-Added Utilization

Starch is the most abundant storage carbohydrate and a major component in pea seeds, accounting for about 50% of dry seed weight. As a by-product of pea protein processing, current uses for pea starch are limited to low-value, commodity markets. The globally growing demand for pea protein poses a great challenge for the pea fractionation industry to develop new markets for starch valorization. However, there exist gaps in our understanding of the genetic mechanism underlying starch metabolism, and its relationship with physicochemical and functional properties, which is a prerequisite for targeted tailoring functionality and innovative applications of starch. This review outlines the understanding of starch metabolism with a particular focus on peas and highlights the knowledge of pea starch granule structure and its relationship with functional properties, and industrial applications. Using the currently available pea genetics and genomics knowledge and breakthroughs in omics technologies, we discuss the perspectives and possible avenues to advance our understanding of starch metabolism in peas at an unprecedented level, to ultimately enable the molecular design of multi-functional native pea starch and to create value-added utilization.

Localization of planteose hydrolysis during seed germination of Orobanche minor

Root parasitic weeds of the Orobanchaceae, such as witchweeds (Striga spp.) and broomrapes (Orobanche and Phelipanche spp.), cause serious losses in agriculture worldwide. No practical method to control these parasitic weeds has been developed to date. Understanding the characteristic physiological processes in the life cycles of root parasitic weeds is particularly important to identify specific targets for growth modulators. In our previous study, planteose metabolism was revealed to be activated soon after the perception of strigolactones in germinating seeds of O. minor. Nojirimycin inhibited planteose metabolism and impeded seed germination of O. minor, indicating that planteose metabolism is a possible target for root parasitic weed control. In the present study, we investigated the distribution of planteose in dry seeds of O. minor by matrix-assisted laser desorption/ionization—mass spectrometry imaging. Planteose was detected in tissues surrounding—but not within—the embryo, supporting its suggested role as a storage carbohydrate. Biochemical assays and molecular characterization of an α-galactosidase family member, OmAGAL2, indicated the enzyme is involved in planteose hydrolysis in the apoplast around the embryo after the perception of strigolactones to provide the embryo with essential hexoses for germination. These results indicated that OmAGAL2 is a potential molecular target for root parasitic weed control.

Inactivating histone deacetylase HDA promotes longevity by mobilizing trehalose metabolism

Histone acetylations are important epigenetic markers for transcriptional activation in response to metabolic changes and various stresses. Using the high-throughput SEquencing-Based Yeast replicative Lifespan screen method and the yeast knockout collection, we demonstrate that the HDA complex, a class-II histone deacetylase (HDAC), regulates aging through its target of acetylated H3K18 at storage carbohydrate genes. We find that, in addition to longer lifespan, disruption of HDA results in resistance to DNA damage and osmotic stresses. We show that these effects are due to increased promoter H3K18 acetylation and transcriptional activation in the trehalose metabolic pathway in the absence of HDA. Furthermore, we determine that the longevity effect of HDA is independent of the Cyc8-Tup1 repressor complex known to interact with HDA and coordinate transcriptional repression. Silencing the HDA homologs in C. elegans and Drosophila increases their lifespan and delays aging-associated physical declines in adult flies. Hence, we demonstrate that this HDAC controls an evolutionarily conserved longevity pathway.

ELONGATED HYPOCOTYL 5 mediates blue light-induced starch degradation in tomato

Starch is the major storage carbohydrate in plants, and its metabolism in chloroplasts depends mainly on light. However, the mechanism through which photoreceptors regulate starch metabolism in chloroplasts is unclear. In this study, we found that the cryptochrome 1a (CRY1a)-mediated blue light signal is critical for regulating starch accumulation by inducing starch degradation through the HY5 transcription factor in the chloroplasts in tomato. cry1a mutants and HY5-RNAi plants accumulated more starch and presented lower transcript levels of starch degradation-related genes in their leaves than did the wild-type (WT) plants. Blue light significantly induced the transcription of starch degradation-related genes in the wild-type and CRY1a- or HY5-overexpressing plants but had little effect in the cry1a and HY5-RNAi plants. Dual-luciferase assays, electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP)-qPCR revealed that HY5 could activate the starch degradation-related genes PWD, BAM1, BAM3, BAM8, MEX1 and DPE1 by directly binding to their promoters. Silencing of HY5 and these starch degradation-related genes in CRY1a-overexpressing plants led to increased accumulation of starch and decreased accumulation of soluble sugars. These findings presented here not only deepen our understanding of how light control starch degradation and sugar accumulation but also allow us to explore potential targets for improving crop quality.

Down-regulation of the Genome Uncoupled 4 Retards Starch Biosynthesis in Rice

BackgroundStarch is the major storage carbohydrate in rice, with essential physical functions for plant growth. The starch biosynthesis in rice employs the cooperation of nucleus and plastid, which requires regulation of the signals from nucleus to plastid. However, the plastid-to-nucleus retrograde signals for starch biosynthesis is partly mediated by tetrapyrrole intermediates, i.e., heme, but the underlying mechanism is largely unknown. In previous studies, we revealed that the Genome Uncoupled 4 (OsGUN4) mutation in rice have been revealed to greatly affect tetrapyrrole intermediates but retain a high photosynthetic capacity. ResultsHere, we further found that down-regulation of OsGUN4 promoted to accumulate sucrose but reduce the total starch, attributing to abnormal performance of metabolisms and enzyme activities of starch biosynthesis in leaves of gun4epi. Besides, the exogenous sucrose led to induced starch synthesis but reduced sucrose contents in wild-type, while norflurazon(NF) treatments could eliminate or weaken these inductions. Nevertheless, no changes were detectedbetween check and sucrose treatments in the gun4epi,whereas NF treatment enhanced the trends of increased sucrose but reduced starch,suggesting the roles of OsGUN4 on balance of photosynthesis and starch biosynthesis. Dynamic activity changes of starch biosynthetic enzymes were in accordance with the contents of carbon metabolites. Moreover, RNA sequencing revealed that a great deal DEGs were associated with starch metabolic pathways, with 62 genes being up-regulated and 25 down-regulated in gun4epi. Many genes involved in starch biosynthesis performed down-regulated expression, including the transcription factor of bZIP58 and its target genes of OsBEIIb and OsSSI, which are vital for the formation of amylopectin and starch granules, while displayed up-regulatedexpression of OsSSIIIa and OsGBSSI that promotes the formation of amylose. ConclusionIn conclusion, these findings confirm that OsGUN4 play regulatory roles on biosynthetic genes and enzyme activity in starch biosynthesis.

Enhancement of Characteristics and Potential Applications of Amylases: A Brief Review

Starch is the major storage carbohydrate of plant products. Amylases are the group of enzymes hydrolyzes starch and related polymers to smaller oligosaccharides and less amount of monosaccharide. Microbes are the major sources of amylases, exploited for large scale production in different industries. Recently, protein engineering has been applied to improve the structural and physicochemical properties of the enzyme for its potential applications. Amylases are mostly used for liquefaction of starch in the purpose of glucose, maltose, and high fructose containing syrup preparation, malto-oligosaccharides production, desizing, production of bio-fuel, detergent preparation, waste management, and preparation of digestive aids.

Draft Genome Sequence of the Biofuel-Relevant Microalga Desmodesmus armatus

A draft genome of 906 scaffolds of 115.8 Mb was assembled for Desmodesmus armatus, a diploid, lipid- and storage carbohydrate-accumulating microalga proven relevant for large-scale, outdoor cultivation, and serves as a model alga platform for improving photosynthetic efficiency and carbon assimilation for next-generation bioenergy production.

Selection and subsequent physiological characterisation of industrial Saccharomyces cerevisiae strains during continuous growth at sub- and- supra optimal temperatures

A phenotypic screening of 12 industrial yeast strains and the well-studied laboratory strain CEN.PK113-7D at cultivation temperatures between 12 °C and 40 °C revealed significant differences in maximum growth rates and temperature tolerance. Two Saccharomyces cerevisiae strains, one performing best at sub-, and the other at supra-optimal temperatures, plus the laboratory strain, were selected for further physiological characterization in well-controlled bioreactors. The strains were grown in anaerobic chemostats, at a fixed specific growth rate of 0.03 h-1 and sequential batch cultures at 12, 30, and 39 °C. We observed significant differences in biomass and ethanol yields on glucose, biomass protein and storage carbohydrate contents, and biomass yields on ATP between strains and cultivation temperatures. Increased temperature tolerance coincided with higher energetic efficiency of cell growth, indicating that temperature intolerance is a result of energy wasting processes, such as increased turnover of cellular components (e.g. proteins) due to temperature induced damage.

Comparative transcriptomics reveals the difference in early endosperm development between maize with different amylose contents

In seeds, the endosperm is a crucial organ that plays vital roles in supporting embryo development and determining seed weight and quality. Starch is the predominant storage carbohydrate of the endosperm and accounts for ∼70% of the mature maize kernel weight. Nonetheless, because starch biosynthesis is a complex process that is orchestrated by multiple enzymes, the gene regulatory networks of starch biosynthesis, particularly amylose and amylopectin biosynthesis, have not been fully elucidated. Here, through high-throughput RNA sequencing, we developed a temporal transcriptome atlas of the endosperms of high-amylose maize and common maize at 5-, 10-, 15- and 20-day after pollination and found that 21,986 genes are involved in the programming of the high-amylose and common maize endosperm. A coexpression analysis identified multiple sequentially expressed gene sets that are closely correlated with cellular and metabolic programmes and provided valuable insight into the dynamic reprogramming of the transcriptome in common and high-amylose maize. In addition, a number of genes and transcription factors were found to be strongly linked to starch synthesis, which might help elucidate the key mechanisms and regulatory networks underlying amylose and amylopectin biosynthesis. This study will aid the understanding of the spatiotemporal patterns and genetic regulation of endosperm development in different types of maize and provide valuable genetic information for the breeding of starch varieties with different contents.