Preliminary Study Of The Function Of Type-one Protein Phosphatases Family In Arabidopsis

Protein phosphorylation is one of the most important and common regulatory mechanism that plays critical roles in the regulation of many cellular processes including cell cycle,cell growth,apoptosis and signal transduction pathways in Eukaryotes.Protein phosphatases 1(PP1s)are major members of serine threonine(Ser/Thr)protein phosphatases.In Arabidopsis,PPIs are referred to as type-one protein phosphatases(TOPPs).Previous studies indicated that TOPPs regulate blue light-dependent stomatal opening and embryonic development.In general,molecular mechanisms of TOPPs in regulating plant growth and development are not well studied.In this study,we found TOPP1-TOPP9 localized at the plasma membrane and in the nucleus through transient expression pattern of the tagged TOPPs in Nicotiana benthamiana leaves.The interaction between TOPP4 and PIN1 in vitro has,been reported by our laboratory.Using the yeast-two-hybrid assay,we found that TOPP1,TOPP3 and TOPP7 also can interact with PIN1 respectively.Analysis of the expression of each TOPP genes in T-DNA insertion homozygote mutants,we found that the expressions of all TOPP genes were decreased.It is notable that the expression levels of TOPP2,TOPP6 and TOPP7 reduced to zero compared with wild-type.But topps single mutants show similar phenotypes in growth to that of wild-type.In addition,the root response of topps mutants and wild-type were same under different concentrations of IAA treatment.Meanwhile,we also generated different double-mutants,triple-mutants,quadruple and penta mutants,and found that the phenotypes of these mutants were also like wild-type.The auxin sensitivity of the mutants and wild-type on root length in presence of different concentrations of IAA has no significant difference.The localizations of PIN2,PIN3 and PIN7 in root tip of topp2/4-2/6 and topp4-2/6/7 triple-mutants were not changed compared with wild-type.The expression of each TOPP genes in T-DNA insertion homozygote multiple mutants were same as the single mutants.It was presumed that TOPPs protein family has functional redundancy.When one or more genes of TOPPs are defective,other members of TOPPs will replace the function of the defective genes in order to maintain normal growth and development of plant.