A Preliminary Study Of Arabidopsis Auxiliary Molecular Chaperones Bag6 And Hop

Fes1A,Bag,and Hop are all Hsp70 co-chaperones of Arabidopsis.Our previous results indicated that knockout of AtFes1 a led to Arabidopsis defect in heat tolerance.But,the further mutant of Bag6 in atfes1 a could reduce the thermal sensitivity of atfes1 a.Bag6 acts as a suppressor of atfes1 a.In this experiment,the author studied whether the C-terminal and IQ domains are the essential to AtBag6 supperssor whose knockout led to an increase of thermotoleranc in atfes1 a.By studying the thermotolerance of the double mutant of atbag6::atfes1a,the authors found that the C-terminus of AtBag6 is its important functional domain.In addition,expression of the IQ motif-mutated AtBag6(abbreviated as AtBag6-IQ)did not correct the thermotolerance defect in atfes1 a.Since the protein expression level of AtBag6-IQ in OE-Bag6-IQ transgenic lines was lower than that of AtBag6 in WT,it is not yet possible to determine whether the IQ motif is an essential domain for Bag6.Hop is a co-chaperone of Hsp70.Hop gene family has three genes(Hop1,Hop2,and Hop3).We obtained the mutants of three individual Hop genes and further bred double and triple mutants of the three individual Hop genes.With these muntants,we determinated their tolerances to various stress.The results of salt stress experiments showed that the phenotypes of the three individual hop mutants were all identical to that of wild-type(WT),but the three-mutant of hop1/2/3 and the double mutant of hop1::hop2 showed more sensitive phenotypes upon salt stress compared to WT.We also evaluated the high-temperature sensitivity of the triple mutant of hop1/2/3.Undergoing the heat stress at 35°C for for 7 days,the hop1/2/3 mutant seedlings showed more severe damaged phenotype than that WT plant,indicating that Hop genes are involved in Arabidopsis thermotolerance.In addition,after the treatment at 4°C for 10 days,the phenotype of the hop1/2/3 mutant presented no difference from WT.Interestingly,the result of dithiothreitol and tunicamycin treatments indicated that Hop genes are not involved in the endoplasmic reticulum stress,which is different from the previous report.