Sinapoylglucose: malate sinapoyltransferase SNG1 negatively regulates drought resistance by crosstalk with abscisic acid signaling in Arabidopsis.

Drought stress has a profound impact on yield, with massive repercussions for agricultural production. In addition to ABA, the central hormone controlling the plant response to drought, secondary metabolites also play important functions in drought stress; however, the precise nature of their roles is still obscure. Metabolomics analysis of ABA- and PEG-treated Arabidopsis wild-type (WT) seedlings as well as ABA signal transduction mutants snrk-triple (snrk2.2 snrk2.3 snrk2.6) and pyl-quadruple (pyr1 pyl1 pyl2 pyl4) identified a number of drought-related metabolites. Specifically, we observed differences in the levels of sinapic acid and quercetin. To assess the function of sinapoyl esters in the regulation of drought stress, we characterized the sinapoylglucose accumulator 1 (sng1) mutant, deficient in the conversion of sinapoylglucose (SG) to sinapoylmalate (SM), resulting in high endogenous levels of SG and low SM levels. sng1 mutants showed increased drought resistance compared to WT plants. RNA-sequencing of sng1 and WT rosette leaves before and after dehydration revealed differentially expressed genes related to cuticle synthesis, anthocyanin biosynthesis, leaf senescence and ABA response. Consistently, phenotypic analysis of the sng1 mutant showed increased cuticle synthesis, wax crystal deposition, anthocyanin accumulation, leaf senescence, ABA responsiveness and stomatal closure compared to WT plants. We propose that the deficiency of SM and accumulation of SG in sng1 mutants may affect the metabolic flow of sinapoyl esters to activate multiple biological processes whose combined action enhances drought resistance. Our findings shed light on the secondary metabolites regulatory network in response to drought stress in Arabidopsis.