| Drought is one of the main abiotic stresses that affect the normal growth and development of plants.With global warming,drought is a major bottleneck of agricultural development,and threatens the food security of the world.Due to the immovability,plants have evolved a unique set of protection mechanisms to resist abiotic stresses in the long-term evolution process.It is of great significance to analyze the mechanism of plant response to drought stress.Abscisic acid(ABA)is a key phytohormone and growth mediation agent of plants.Previous studies have shown that ABA regulats the plant response to drought stress.Ascorbic acid(As A)is the main antioxidant in plants,which is beneficial to eliminate the oxidative damage caused by abiotic stresses and helps plants to resist abiotic stresses.Although many studies have reported that ABA and As A are involved in the regulation of abiotic stress responses,it is still unknown whether and how ABA signaling pathway and As A pathway interact with each other in response to drought stress.In this study,we screened the drought phenotypes of ～140 T-DNA insertion mutants of genes encoding Arabidopsis phosphatases with unknown function.Of these,we found a drought sensitive mutant,and cloned the candidate gene At PTPN(PTP-like Nucleutidase).Phylogenetic analysis showed that PTPN was highly conserved in different plant species,suggesting that PTPN may have important biological functions.Arabidopsis PTPN(At PTPN)was expressed in multiple tissues and upregulated by ABA and drought treatments.Compared with wild-type,Atptpn mutants were hyposensitive to ABA but hypersensitive to drought stress.Expressing of At PTPN in Atptpn mutant could restore the ABA insensitive and drought sensitive phenotypes of Atptpn mutant,while enhanced expression of At PTPN promoted the sensitivity of plants to ABA and tolerance of these plants to drought stress.Based on sequence alignment,we found and cloned the homologous gene Zm PTPN,which has the highest similarity with At PTPN in maize genome(the amino acid sequence of Zm PTPN is 72% indentical to that of At PTPN).Overexpression of Zm PTPN could improve the drought resistance of maize seedling.Knocking-down the expression of Zm PTPN,inhibited drought tolerance of maize seedings.These results demonstrated that PTPN has conserved and positive roles in drought tolerance.In order to further analyze the molecular mechanism of PTPN regulating plant drought tolerance,the substrate of PTPN was screened.Through substrate screening,we found that PTPN protein could hydrolyze the nucleotides,including GDP / GMP / d GMP / IMP / d IMP,to release Pi,demonstrating its nucleotidase activity.VTC2 is a rate-limiting synthetic enzyme in As A biosynthesis.Our study showed that At PTPN could regulate the As A synthesis pathway by control “local Pi” levels,and then affect As A production in plants.Overexpression of VTC2 significantly increased As A levels and enhanced drought resistance of plants,which was partly depended on At PTPN activity.These results suggested that VTC2 and At PTPN have genetic interaction in As A biosynthesis and response to drought stress.Through yeast one hybrid screening,we identified the heat shock transcription factor HSFA6 a that directly binds to the HSE(heat shock factor binding element)site of the At PTPN promoter and activates At PTPP expression.Genetic interaction analysis showed that At PTPN was required for HSFA6 a to regulate ABA and drought responses.In summary,we found a new drought-resistant gene At PTPN in this study.On one hand,HSFA6 a mediated the response of At PTPN gene to ABA;on the other hand,as a nucleotidase,At PTPN regulates the biosynthesis of As A.Our data indicate an At PTPNmediated crosstalk between ABA signaling and As A biosynthesis pathways that positively control plant drought tolerance.The discovery of At PTPN gene and the analysis of its drought resistance mechanism provide new genetic resources and theoretical basis for crop drought resistance breeding. |
