Abstract
BackgroundStarch is the principle constituent of potato tubers and is of considerable importance for food and non-food applications. Its metabolism has been subject of extensive research over the past decades. Despite its importance, a description of the complete inventory of genes involved in starch metabolism and their genome organization in potato plants is still missing. Moreover, mechanisms regulating the expression of starch genes in leaves and tubers remain elusive with regard to differences between transitory and storage starch metabolism, respectively. This study aimed at identifying and mapping the complete set of potato starch genes, and to study their expression pattern in leaves and tubers using different sets of transcriptome data. Moreover, we wanted to uncover transcription factors co-regulated with starch accumulation in tubers in order to get insight into the regulation of starch metabolism.ResultsWe identified 77 genomic loci encoding enzymes involved in starch metabolism. Novel isoforms of many enzymes were found. Their analysis will help to elucidate mechanisms of starch biosynthesis and degradation. Expression analysis of starch genes led to the identification of tissue-specific isoenzymes suggesting differences in the transcriptional regulation of starch metabolism between potato leaf and tuber tissues. Selection of genes predominantly expressed in developing potato tubers and exhibiting an expression pattern indicative for a role in starch biosynthesis enabled the identification of possible transcriptional regulators of tuber starch biosynthesis by co-expression analysis.ConclusionsThis study provides the annotation of the complete set of starch metabolic genes in potato plants and their genomic localizations. Novel, so far undescribed, enzyme isoforms were revealed. Comparative transcriptome analysis enabled the identification of tuber- and leaf-specific isoforms of starch genes. This finding suggests distinct regulatory mechanisms in transitory and storage starch metabolism. Putative regulatory proteins of starch biosynthesis in potato tubers have been identified by co-expression and their expression was verified by quantitative RT-PCR.
Highlights
Starch is the principle constituent of potato tubers and is of considerable importance for food and non-food applications
It was shown that SS2 plays only a minor role in starch biosynthesis in tubers [43] which is in accordance with our expression analysis showing only a slightly higher expression in tubers compared to leaves being upregulated during tuber development
No studies have analyzed the roles of SS5 and SS6 in potato yet, but our gene expression data suggest a possible role for SS5 in potato tuber starch biosynthesis
Summary
Starch is the principle constituent of potato tubers and is of considerable importance for food and non-food applications. Starch accumulates during development and is stored over a long period of time It maintains the energy demand of the dormant tuber and fuels the outgrowth of new shoots after dormancy is broken. The glucosyl donor for starch biosynthesis in sink tubers is derived from sucrose which is transported via the phloem from the photosynthetically active leaf tissues to the developing tuber. Sucrose reaching the cytosol has to be converted to glucose 6-phosphate (G6P) which is subsequently imported into the amyloplast where it is further metabolized to ADP-Glc and starch. These differences give reasons to assume that different regulatory mechanisms operate in leaves and tubers
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