Sucrose synthase gene PtSUS1 confers Pinellia ternata enhanced tuber yield and thermotolerance

Large scale cultivation of Pinellia ternata (Thunb.) Breit is the effective mean to address the disparity between the supply and demand of Pinelliae Rhizoma, the dried tuber of this medicinal plant. The cultivation of P. ternata is primarily threatened by high temperature that remains unsolved. Sucrose synthase (SUS) is important in regulating plant growth. However, the mechanism by which sucrose synthase in regulating plant thermotolerance is unclear. This study was undertaken to explore how sucrose synthase regulates heat resilience and tuber yield in P. ternata. Based on the expression profile data of PtSUSs, PtSUS1 was functionally characterized through overexpression in both Arabidopsis and P. ternata. PtSUS1, out of four PtSUS genes, showed a short-term heat-inducible expression. Transgenic Arabidopsis had enlarged seeds and showed more vigorous growth than did wild-type plants under high temperature conditions (P < 0.05). When PtSUS1 was overexpressed in P. ternata, enhanced tuber yield, larger bulbils, and increased thermotolerance were observed. These improvements are probably attributable to the increased synthase activity, improved cell wall properties and photosynthetic capacity, and lower reactive oxygen species accumulation (P < 0.05). Transgenic P. ternata showed reduced sucrose but increased UDP-glucose, ADP-glucose, cellulose and starch (P < 0.05). Transcriptome analysis showed that those genes associated with the LHC-II complex, PSII complex, cytochrome, LHC-I complex and ferredoxin-NADP reductase of light reactions in transgenics were significantly upregulated under both control and heat stress conditions. Modulation of sucrose synthase via overexpressing PtSUS1 boosted tuber yield and thermotolerance of P. ternata via maintaining photosynthesis homeostasis.