Coordinated regulation between jasmonic acid and abscisic acid mediates drought tolerance in sweetpotato

Drought is the main environmental factor limiting global crop yield in various abiotic stresses. Improving drought resistence of sweetpotato is necessary to ensure food security in the future climate scenarios. In this study, for Yanshu25 (Yan25, drought-tolerant cultivar), the genes related to jasmonic acid (JA) biosynthesis were significantly up-regulated by drought with relative higer endogenous JA content, while for Xushu32 (Xu32, drought-sensitive cultivar), the genes related to abscisic acid (ABA) biosynthesis were up-regulated by drought with relative higer endogenous ABA content. The coordinated regulation between JA and ABA on drought tolerance of sweetpotato was further carried using JA and ABA biosynthesis inhibitors--nordihydroguaiaretic acid (NDGA) or fluridone (FLU). Application of FLU or NDGA to drought-treated sweetpotato plants led to lower photosynthetic parameters and the activities of superoxide dismutase and peroxidase, and higher cell membrane damage under drought stress (D). For Xu32, under drought stress, FLU induced endogenous JA accumulation with lower expression level of JA signal transduction gene IbJAZ7, while NDGA did not affect ABA accumulation. FLU + JA recovered drought tolerance, as indicated by a significant increase of ABA content from D-FLU treatment, speculating that exogenous JA could promote endogenous ABA production. NDGA + ABA restored drought tolerance, as indicated by a significant up-regulation of JA and ABA contend from D treatment, speculating that endogenous ABA could also promote JA production and weaken NDGA inhibition. These results were in accordance with the expression trends of genes related to biosynthesis and signal transduction of JA and ABA. For Yan25, NDGA treatment increased leaf endogenous ABA content, and FLU treatment did not affect leaf JA accumulation. However, FLU + JA restored drought tolerance with higer ABA content and expressions of ABA-related genes. These results suggested that drought-sensitive sweetpotato was more dependent on ABA regulation pathway, and drought-tolerant sweetpotato was more dependent on JA regulation pathway under drought stress. In addition, there were positive feedback mechanisms of JA and ABA in sweetpotato in response to drought stress. Moreover, the function of IbAOS in sweetpotato roots was investigated and the results showed that IbAOS might improve drought tolerance by regulating JA biosynthesis. These results provided key information for further study of its role in tuberous root differentiation.