Abstract
BackgroundCyperus esculentus is unique in that it can accumulate significant amounts of oil, starch and sugar as major storage reserves in tubers with high tuber yield and therefore considered as a novel model to study carbon allocation into different storage reserves in underground sink tissues such as tubers and roots. Sucrose (Suc) plays a central role in control of carbon flux toward biosynthesis of different storage reserves; however, it remains unclear for the molecular mechanism underlying Suc metabolism in underground oil-rich storage tissues. In the present study, a comprehensive transcriptome analysis of C. esculentus oil tuber compared to other plant oil- or carbohydrate-rich storage tissues was made for the expression patterns of genes related to the Suc metabolism.ResultsThe results revealed some species-specific features of gene transcripts in oil tuber of C. esculentus, indicating that: (i) the expressions of genes responsible for Suc metabolism are developmentally regulated and displayed a pattern dissimilar to other plant storage tissues; (ii) both of Suc breakdown and biosynthesis processes might be the major pathways associated with Suc metabolism; (iii) it was probably that Suc degradation could be primarily through the action of Suc synthase (SUS) other than invertase (INV) during tuber development. The orthologs of SUS1, SUS3 and SUS4 are the main SUS isoforms catalyzing Suc breakdown while the vacuolar INV (VIN) is the leading determinant controlling sugar composition; (iv) cytosolic hexose phosphorylation possibly relies more on fructose as substrate and uridine diphosphate glucose pyrophosphorylase (UGP) plays an important role in this pathway; (v) it is Suc-phosphate synthase (SPS) B- and C-family members rather than SPS A that are the principal contributors to SPS enzymes and play crucial roles in Suc biosynthesis pathway.ConclusionsWe have successfully identified the Suc metabolic pathways in C. esculentus tubers, highlighting several conserved and distinct expressions that might contribute to sugar accumulation in this unique underground storage tissue. The specific and differential expression genes revealed in this study might indicate the special molecular mechanism and transcriptional regulation of Suc metabolism occurred in oil tubers of C. esculentus.
Highlights
Cyperus esculentus is unique in that it can accumulate significant amounts of oil, starch and sugar as major storage reserves in tubers with high tuber yield and considered as a novel model to study carbon allocation into different storage reserves in underground sink tissues such as tubers and roots
Suc metabolism plays a central role in control of carbon flux toward biosynthesis of different storage reserves including starch, oil, sugar, and protein in sink tissues such as seeds, fruits, tubers, stems, bulbs, meristems and flowers [16]
Sucrose accumulation in developing tubers of C. esculentus Compared to other common plants that rich in oil or starch or sugars in their sink organs, the portion of sugars on fresh weight (FW) in mature tubers of C. esculentus is relatively high among the storage reserves, in which it is higher than those of oil plants and even greater than some carbohydrate-rich fruit, root and tuber crops such as grape, sugar beet, sweet potato and potato (Table 1)
Summary
Cyperus esculentus is unique in that it can accumulate significant amounts of oil, starch and sugar as major storage reserves in tubers with high tuber yield and considered as a novel model to study carbon allocation into different storage reserves in underground sink tissues such as tubers and roots. Sucrose (Suc) plays a central role in control of carbon flux toward biosynthesis of different storage reserves; it remains unclear for the molecular mechanism underlying Suc metabolism in underground oil-rich storage tissues. Suc metabolism plays a central role in control of carbon flux toward biosynthesis of different storage reserves including starch, oil, sugar, and protein in sink tissues such as seeds, fruits, tubers, stems, bulbs, meristems and flowers [16]
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