The Studies On Arabidopsis Thaliana Co-chaperone Mutants Of Fes1a Bag6 And Fes1a Hop1 Hop2

HSP70s play an important role in the heat-induced stress tolerance of plants.However,effective HSP70 function requires the assistance of many co-chaperones.BAG6 and Fes1 A are HSP70 binding proteins or co-chaperones,which is critical for Arabidopsis thaliana thermotolerance.To date,little is known about how these plant co-chaperones interact and perform their function cooperatively.In this study,we first determined the subcellular location of BAG6.As indicated by fluorescence signal distribution of the BAG6-GFP in subcellular as well as by the western-blot result of BAG6 in purified nuclei and vacuolar fractions,we determined that BAG6 is a nuclear localization protein rathen than a suggested vacuolar-associated protein.By assessed the thermotolerance of a fes1 a bag6 double mutant,we found that the fes1 a bag6 double mutant showed a significant increase in thermotolerance,compared to fes1 a.However,calmodulin inhibitors diminished this enhanced thermotolerance in the fes1 a bag6double mutant.In addition,we found that the IQ motif in BAG6 was essential for effective BAG6 performance.Since BAG6 is localized in the nucleus,the signal transduction is likely to involve nuclear calcium signaling.Moreover,our result indicted that the regulation of fes1 a by BAG6 and the regulation of fes1 a by TBP depended on totally different signaling pathways.Hop is the other co-chaperone of HSP70.In a previous study,it was found that any of hop single mutants was insensitive to salt,but hop1 hop2 double mutant exhibited a salt-sensitive phenotype.Also,fes1 a was sensitive to salt stress only upon more than 125 m M Na Cl stress during its germination stage.In this experiment,we found that the fes1 a hop1 hop2 triple mutant considerably increased its salt sensitivity.75 m M Na Cl was enough to impede its growth of the triple mutant,compared to wild type.However,the fes1 a hop1 hop2 triple mutant,hop1 hop2 double mutant and fes1 a all grew as normally as wild type on MS medium.Thus,we suggest that Fes1 A and Hops cooperatively carry out their function in salt tolerance of Arabidopsis.The main innovations of this study were presented as follows:1.IQ motif is essential to effective performance of BAG6.2.Calmodulin is involvedin signal transduction.3.BAG6 is localized in the nucleus.4.the regulation of fes1 a by BAG6 or TBP depended on totally different signaling pathways.5.Fes1 A and Hops cooperatively carry out their function in salt tolerance of Arabidopsis.