Enhanced Vitamin C Production Mediated by an ABA-Induced PTP-Like Nucleotidase Improves Drought Tolerance of Arabidopsis and Maize.

Abscisic acid (ABA) is a key phytohormone that mediates environmental stress responses. Vitamin C, or L-ascorbic acid (AsA), is the most abundant antioxidant against stress damages in plant. How ABA and AsA signaling pathways interact in stress responses remains elusive. In this study, we characterized a previously unidentified gene, PTPN (PTP-like Nucleotidase). Arabidopsis PTPN (AtPTPN) was expressed in multiple tissues and upregulated by ABA and drought treatments. Atptpn mutants were hyposensitive to ABA but hypersensitive to drought stresses, while plants with enhanced expression of AtPTPN showed opposite phenotypes to Atptpn. Overexpressing maize PTPN (ZmPTPN) promoted, while knock-down ZmPTPN inhibited plant drought tolerance, indicating conserved and positive roles of PTPN in plant drought tolerance. AtPTPN and ZmPTPN released Pi by hydrolyzing GDP/GMP/dGMP/IMP/dIMP. AtPTPN positively regulated AsA production via endogenous Pi contents control. Overexpression of VTC2, the rate-limiting synthetic enzyme in AsA biosynthesis, promoted AsA production and plant drought tolerance, which is largely dependent of AtPTPN activity. We further demonstrated that the heat shock transcription factor HSFA6a directly bound AtPTPN promoter and activated AtPTPN expression. Genetic interaction assays showed that AtPTPN was required for HSFA6a to regulate ABA and drought responses. Our data indicate a PTPN-mediated crosstalk between ABA signaling and AsA biosynthesis pathways that positively control plant drought tolerance.