Functional Analysis of Starch Metabolism in Plants

Abstract

In plants, starch is synthesized in leaves during the day-time from fixed carbon through photosynthesis and is mobilized at night to support continued respiration, sucrose export, and growth in the dark. The main crops where starch is biosynthesized and stored are corn, rice, wheat, and potatoes, and they are mainly used as food resources for humankind. There are many genes that are involved in starch biosynthesis from cytosol to storage organs in plants. ADP-glucose, UDP- glucose, and glucose-6-phosphate are synthesized catalyzed by UDP-invertase, AGPase, hexokinase, and P- hexose-isomerase in cytosol. Starch composed of amylopectin and amylose is synthesized by starch synthase, granule bound starch synthase, starch-branching enzyme, debranching enzyme, and pullulanase, which is primarily responsible for starch production in storage organs. Recently, it has been uncovered that structural genes are controlled by proteins derived from other genes such as transcription factors. To obtain more precise information on starch metabolism, the functions of genes and transcription factors need to be studied to understand their roles and functions in starch biosynthesis in plants. However, the roles of genes related to starch biosynthesis are not yet clearly understood. The papers of this special issue contain reviews and research articles on these topics and will be a useful resource for researchers involved in the quality improvement of starch storage crops.

Functional Haplotypes and Evolutionary Insight into the Granule-Bound Starch Synthase II (GBSSII) Gene in Korean Rice Accessions (KRICE_CORE)

“…The GBSSII reference gene region was adapted from Nipponbare. Others (1) : group of wild rice accessions other than Oryza nivara and Oryza rufipogon, Ins (2) : insertion, Del (3) : deletion, Dupl (4) : duplication, and DV (5) : different variation. Nineteen functional substitutions (nonsynonymous SNPs) were identified in the group of cultivated haplotypes (C_1-C_13) and were present in 162 temperate japonica, 18 tropical japonica, 6 indica, 3 aus, and 2 admixture rice accessions.…”

“…Highlighted alleles were minor alleles identified in their respective positions, Table S1: Summary of the 475 Korean rice accessions based on their different varietal types or ecotypes, Table S2: Pairwise estimates of genetic differentiation (F ST values) of the GBSSII gene between different subgroups of 475 Korean rice collections. Te_Japonica (1) : temperate japonica, Tr_Japonica (2) : tropical japonica, Table S3: Summary of average nucleotide diversity (π) and Tajima's D values within the GBSSII gene region of the 475 Korean rice accessions by means of different variety types, Table S4 S5: Phylogenetic tree for the orthologous genes GBSS1 and GBSSII. Scale bar indicates the proportion of sites changing along each branch.…”

“…Rice is a cereal grain in which the starch is mainly used as a food source for humans. Starch biosynthesis includes many enzymes, such as starch synthase, granule bound starch synthase (GBSS), starch-branching enzyme (SBE), debranching enzyme, and pullulanase, which synthesize amylose and amylopectin, the two main components of starch [1]. GBSS is the only enzyme that synthesizes amylose, which is a linear form of starch.…”

Insights into sugar metabolism during bilberry (Vaccinium myrtillus L.) fruit development

“…Glucose, fructose, and sucrose are classified as soluble sugars. Starch is a non‐soluble sugar that accumulates in storage organs, such as plastids in leaves, roots, stems, and fruits, and can be utilized only as a reserve energy source (Cho & Kang, 2020; Wang et al, 2013). In addition to being precursors for energy‐yielding processes, the soluble sugars have been identified as signaling molecules in various plant metabolic processes during fruit ripening (Jia et al, 2013) and are also known to be involved in stress and defense responses (Tauzin & Giardina, 2014).…”

“…The hexose interconversion reactions in these pathways are usually mediated by UDP‐glucose‐pyrophosphorylase (UDPG‐PP), phosphoglucoisomerase (PGI), and phosphoglucomutase (PGM) enzymes (Decker & Kleczkowski, 2019; Figure 1). Some studies have shown a correlation between insoluble starch accumulation and soluble sugar content in ripe fruits (Cho & Kang, 2020). However, the breakdown of starch by α‐ and β‐amylase could also contribute toward a significant increase in sugar content at later stages of fruit development (Souleyre et al, 2004).…”