*Article* **Characterization of AtBAG2 as a Novel Molecular Chaperone**

**Chang Ho Kang 1,\*, Jae Hyeok Lee 1, Yeon-Ju Kim 2, Cha Young Kim 3, Soo In Lee 4, Jong Chan Hong <sup>1</sup> and Chae Oh Lim 1,\***


**Abstract:** Bcl-2-associated anthanogene (BAG) family proteins regulate plant defense against biotic and abiotic stresses; however, the function and precise mechanism of action of each individual BAG protein are not yet clear. In this study, we investigated the biochemical and molecular functions of the *Arabidopsis thaliana* BAG2 (AtBAG2) protein, and elucidated its physiological role under stress conditions using mutant plants and transgenic yeast strains. The T-DNA insertion *atbag2* mutant plants were highly susceptible to heat shock, whereas transgenic yeast strains ectopically expressing *AtBAG2* exhibited outstanding thermotolerance. Moreover, a biochemical analysis of GST-fused recombinant proteins produced in bacteria revealed that AtBAG2 exhibits molecular chaperone activity, which could be attributed to its BAG domain. The relevance of the molecular chaperone function of AtBAG2 to the cellular heat stress response was confirmed using yeast transformants, and the experimental results showed that overexpression of the *AtBAG2* sequence encoding only the BAG domain was sufficient to impart thermotolerance. Overall, these results suggest that the BAG domain-dependent molecular chaperone activity of AtBAG2 is indispensable for the heat stress response of Arabidopsis. This is the first report demonstrating the role of AtBAG2 as a sole molecular chaperone in Arabidopsis.

**Keywords:** BAG (Bcl-2-associated anthanogene) family proteins; abiotic stress; molecular chaperone
