Study On GFP Localization And Overexpression Of BAG Proteins In Arabidopsis Thaliana L.

BAG proteins are a kind of co-chaperones in mammals and play important roles in many physiological processes, including cell apoptosis, oncogenesis, neural differentiation, stress response and cell cycle. In Arabidopsis genome, there are seven genes encoding BAG proteins (AtBAG-1 through AtBAG-7). However the functions of these proteins are not clear. In this research, the functions of AtBAG-4 and AtBAG-7 were probed by GFP fusion subcellular localization and phenotype analysis of T-DNA insertion mutants and over-expression transgenic lines. The results are as follows.1. Subcellular localization. AtBAG-4 showed cytosolic localization, which is consistent with the bioinformatic prediction. AtBAG-7 is predicted to localized in the nucleus and endoplasmic reticulum while Brett Williams et al reported that AtBAG-7 was only localized in ER. However, our result showed that AtBAG-7 localized in both ER and nucleus.2. The previous study showed that atbag4 and hsp70 null mutants were more sensitive to salt stress than wild type plants (Col) and AtBAG-4 protein could physically interact with HSP70. We further crossed atbag4 with hsp70 and got the double mutants. The double mutants showed similar phenotype to hsp70 single mutant under salt stress. Biochemical activity assays showed that the in vitro chaperone activity of HSP70 was not affected by AtBAG-4 protein. Both AtBAG-4 and AtBAG-7 over-expression in Col increased tolerance to salt stress of transgenic plants. These results demonstrated that co-chaperone AtBAG-4 probably works as the scaffold of chaperone HSP70 and substrate interaction.3. In the research, the expression patterns of AtBAG-4, AtBAG-7 and HSP70 were further probed by promoter-GUS reporter system. The GUS staining results showed that all these genes are induced by salt stress, ultraviolet radiation, drought and low temperature, which were consistent with the results of RT-PCR analysis. The expression pattern that AtBAG-4 and AtBAG-7 are induced by different stresses is similar to that of other stress-induced genes. The results demonstrated that BAG proteins play important roles in stress response in Arabidopsis.