| Protein phosphatase and dephosphorylation have an important role for post-translational modification that controls many regulatory circuits by modulating the conformation,activity,localization and stability of substrate proteins.Some protein phosphatases perform specifical function through regulatory subunits binding catalytic engine to locate in target site of cell.In the PPP family,protein partners bring specificity to the PPP engines.Protein phosphatase TOPP4 and PP2A both belong to the PPP family,which are sequence and structurally related and maintain an identical catalytic mechanism and partial function.Here,we studied the relationship between TOPP4 and PP2A,and found that they have a similar expression pattern.When the vector that contained TOPP4 gene driven by PP2A promoter was ectopically expressed in topp4-1 and rcn1,it could partially recover the phenotype of the two mutants.On the contrary,when the vector that contained PP2A gene driven by TOPP4 promoter was ectopically expressed in topp4-1 and rcn1,it could also partially recover the two mutants.Furthermore,the yeast two-hybrid analysis demonstrated that TOPP4 and PP2A A could interact in vivo.Accordingly,PP2A A could be regulated TOPP4.Protein phosphatase PP2A plays a very important role in root gravitropism.The rcn1 mutant which is a loss-of-function mutation in one of the A regulatory subunits of PP2A A1 showed curled main root and defective root gravitropism.We also studied the root gravitropism of topp4-1 and found that it was more sensitive than that in wild type.Further study reveled that amyloplasts was reduced in topp4-1,and some related genes were also decreased in the mutant.We found auxin lateral transport was faster in topp4-1 compared with wild type by observing the distribution of DR5:GFP in root tip.We speculated that asymmetric distribution of auxin could be the main reason for sensitivity of gravitropism of topp4-1. |
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