Activation of catalase activity by a peroxisome-localized small heat shock protein Hsp17.6CⅡ

Plant catalases are important antioxidant enzymes and are indispensable for plant to cope with adverse environmental stresses. However, little is known how catalase activity is regulated especially at an organelle level. In this study, we identified that small heat shock protein Hsp17.6Cll （AT5GI2020） in- teracts with and activates catalases in the peroxisome of Arabidopsis thaliana. Although Hsp17.6Cll is classified into the cytosol-located small heat shock protein subfamily, we found that Hsp17.6ClI is located in the peroxisome. Moreover, Hsp17.6ClI contains a novel non-canonical peroxisome targeting signal 1 （PTS1）, QKL, 16 amino acids upstream from the C-terminus. The QKL signal peptide can partially locate GFP to peroxisome, and mutations in the tripeptide lead to the abolishment of this activity. In vitro catalase activity assay and holdase activity assay showed that Hsp17.6ClI increases CAT2 activity and prevents it from thermal aggregation. These results indicate that Hspl7.6ClI is a peroxisome-localized catalase chaperone. Overexpression of HsplK6II conferred enhanced catalase activity and tolerance to abiotic stresses in grabidopsis. Interestingly, overexpression of HspI7.6CII in catalase-deficient mutants, ncal-3 and cat2 cat3, failed to rescue their stress-sensitive phenotypes and catalase activity, suggesting that HsplT.6Cll-mediated stress response is dependent on NCA1 and catalase activity. Overall, we identified a novel peroxisome-located catalase chaperone that is involved in plant abiotic stress resis- tance by activating catalase activity.