Transcriptome, metabolite profiling and functional genomics provide molecular insights into sweetpotato sprouting

Short dormancy period of sweetpotato (Ipomoea batatas) storage roots causes significant economic losses. To unravel the molecular mechanism of sweetpotato sprouting, a comparative transcriptome was performed using storage roots incubated under non-sprout (15 °C) and sprout favouring conditions (25 °C). Our analysis revealed that 7404 genes were differentially expressed between non-sprouting and sprouted storage roots incubated at 25 °C. Further, we observed that gibberellin (GA) biosynthesis gene IbGA3OXIDASE and abscisic acid (ABA) catabolism gene ABA 8'-HYDROXYLASE were upregulated by > 10-fold and > 40-fold, respectively, at the onset of sprouting. Metabolite profiling showed increased GA and cytokinin levels, but reduced ABA content in the sprout initials. Based on conserved expression patterns of phytohormone-related genes during sprouting in potato tubers and sweetpotato storage roots, two genes that were downregulated during sweetpotato sprouting - IbPYL4 (ABA receptor) and IbGA2OXIDASE (GA catabolic enzyme) - were independently overexpressed in potato. Transgenic potato plants overexpressing IbPYL4 or IbGA2OXIDASE exhibited low percentages of tuber sprouting and reduced sprout length. Furthermore, knockdown of the ABA 8'-HYDROXYLASE gene (ABA catabolism) significantly reduced sprout length in sweetpotato storage roots compared to wild-type plants. Overall, our study suggests that selective candidate genes (ABA 8'-HYDROXYLASE, IbPYL4, IbGA3OXIDASE, and IbGA2OXIDASE) could be targeted for developing sweetpotato genotypes with enhanced shelf-life.