The Molecular Mechanism Of PLATZ2 In Regulating Salt Stress Response And Plant Growth In Arabidopsis Thaliana

Soil salinity is a worldwide problem that adversely affects plant growth and crop productivity.Plants also developed a large number of physiological and biochemical strategies to cope with salt stress.The salt overly sensitive(SOS)pathway is the most classical one,which mainly includes SOS1,SOS2,CBL4/SOS3 and CBL10/SCaBP8(SOS3-like calciumbinding protein 8).PLATZ as a new class of plant-specific zinc-dependent transcription factor,which was found in peas for the first time in 2001.Later researches have shown that PLATZs play important roles in regulating plant growth and abiotic stress responses.This study revealed the mechanism of PLATZ2in salt stress response.The main results are as follows:(1)The induced expression pattern of PLATZ2 was analyzed by RT-qPCR.The results showed that PLATZ2 was significantly up-regulated by high salt,mannitol,and abscisic acid,indicating that PLATZ2 may play important roles in salt stress,drought stress and ABA response.(2)The PLATZ2 overexpression lines and platz2/7 were used for phenotype analysis.The root length and fresh weight of PLATZ2 overexpression lines were significantly lower than that of WT,while the root length of platz2/7 was significantly longer than that of WT under salt stress.These results indicated that the redundant role of PLATZ2 and PLATZ7 in the negative regulation of plant salt stress response.(3)The subcellular localization of PLATZ2 was mainly in nucleus revealed by the35S::GFP-PLATZ2.And the GUS activity driven by CBL4/SOS3 promoter was inhibited by PLATZ2.These data indicated that PLATZ2 may function as a transcriptional repressor.(4)To study the regulation mechanism of PLATZ2,ChIP-qPCR and EMSA assays were conducted.The results indicated that PLATZ2 bound two regions of-582 to-383 bp and-172to-1 bp of the CBL4/SOS3 promoter,and the two regions-357 to-199 bp and-201 to-1 bp of the CBL10/SCaBP8 promoter in vivo and vitro.(5)To get the genetic evidence,transgenic lines CBL4(#11)and CBL10(#11)were generated by overexpressing CBL4/SOS3 and CBL10/SCaBP8 in PLATZ2 overexpression line(#11),respectively.Phenotypic analysis showed that CBL4(#11)and CBL10(#11)rescued the salt-sensitive and Na~+accumulation phenotype of PLATZ2 overexpression lines,indicating that PLATZ2 functioned upstream of CBL4/SOS3 and CBL10/SCaBP8.(6)Next,MYB32 was screened as an interaction protein from a yeast two-hybrid library.And the interaction between PLATZ2 and MYB32 were confirmed by Bi FC and pull-down assays.MYB32 interacts with PLATZ2 to inhibit the binding to the promoter of CBL4/SOS3 by each other.These results suggested that PLATZ2 interact with MYB32 to regulate the transcription of CBL4/SOS3 and CBL10/SCaBP8.(7)In addition,the germination rate of PLATZ2 overexpression lines were higher than that of WT under ABA treatment.The root length and fresh weight of PLATZ2 overexpression lines were lower than those of WT under normal conditions.The expression of EXP6 was inhibited in PLATZ2 overexpression lines and the GUS activity driven by EXP6 promoter was reduced by PLATZ2.These data indicated that PLATZ2 regulate Arabidopsis growth and ABA response.However,the regulation mechanism needs further investigation.