Functional Study Of Arabidopsis Protein Phosphatase PP4 In Salt Resistance

Protein phosphorylation and dephosphorylation are crucial for regulation of plant development,growth and stress responses.Changes in phosphorylation status are one of the most common ways of adjusting the activity of proteins in signal transduction pathway.Arabidopsis PP4 was identified as a member of serine/threonine-specific PPP phosphatase family.PP4 catalytic subunits are conserved throughout eukaryotes,and PP4 was so important that could not be replaced by other protein phosphatases.There are two PP4 catalytic subunits in arabidopsis,named PPX1 and PPX2.Almost nothing is known about the function of PP4 in plant.It will make a big difference to study the function of PP4 in arabidopsis,which will broaden our view of protein phosphatase family.In recent years,many studies have shown that the family of phosphatase involved in stress-related processes.It raised a question of whether PP4 could also participate in plant abiotic stress response.In this study we used ppx1 and ppx2 mutants as parents in cross to breed to get the ppx1ppx2 double mutant.Based on the homozygous mutants and PP4-overexpressing transgenic lines,the salt resisitance of PP4 were analyzed.The results were shown as following:1.Protein phosphatase PP4 involved in plant salt stress response.The PP4 expression was detected by QPCR in wild-type seedlings under various abiotic stress,and we found that PP4 was strongly induced by salt stress.However ABA stress,drought stress or heat stress had not much effect on the expression of PP4.We speculated that PP4 was involved salt stress response in plant.2.The role of PP4 in salt stress response.Under salt stress,we investigated three salt stress related phenotypes including seed germination rate,root elongation and survival ratio.We found that ppx1 and ppx2 single mutants had no difference in phenotypes,however ppx1ppx2 double mutant and the over-expressing lines obviously increased the sensitivity to salt stress.3.PP4 expression patterns and its interacting protein.The results of GUS histochemical assay demonstrated that PP4 mainly expressed in root and stomatas.We also found that PP4 interacted with potassium sodium transporters HKT1.All in all,our studies showed that PP4 was strongly induced by the salt stress.The ppx1ppx2 double mutants and the PP4 over-expressing lines both exhibited salt-sensitive phenotypes.There was a interaction between PP4 and HKT1,which would further complete salt stress response network in plant.This study will make a great contribution to plant salt tolerant genetic engineering researches.