BcWRKY22 Activates BcCAT2 to Enhance Catalase (CAT) Activity and Reduce Hydrogen Peroxide (H2O2) Accumulation, Promoting Thermotolerance in Non-Heading Chinese Cabbage (Brassica campestris ssp. chinensis)

Abstract

WRKY transcription factors (TFs) participate in plant defense mechanisms against biological and abiotic stresses. However, their regulatory role in heat resistance is still unclear in non-heading Chinese cabbage. Here, we identified the WRKY-IIe gene <i>BcWRKY22</i>(<i>BraC09g001080.1</i>), which is activated under high temperatures and plays an active role in regulating thermal stability, through transcriptome analysis. We further discovered that the BcWRKY22 protein is located in the nucleus and demonstrates transactivation activity in both the yeast and plant. Additionally, our studies showed that the transient overexpression of <i>BcWRKY22</i> in non-heading Chinese cabbage activates the expression of catalase 2 (<i>BcCAT2</i>), enhances CAT enzyme activity, and reduces Hydrogen Peroxide (H₂O₂) accumulation under heat stress conditions. In addition, compared to its wild-type (WT) counterparts, <i>Arabidopsis thaliana</i> heterologously overexpresses <i>BcWRKY22</i>, improving thermotolerance. When the <i>BcWRKY22</i> transgenic root was obtained, under heat stress, the accumulation of H₂O₂ was reduced, while the expression of catalase 2 (<i>BcCAT2</i>) was upregulated, thereby enhancing CAT enzyme activity. Further analysis revealed that BcWRKY22 directly activates the expression of <i>BcCAT2</i> (<i>BraC08g016240.1</i>) by binding to the W-box element distributed within the promoter region of <i>BcCAT2</i>. Collectively, our findings suggest that BcWRKY22 may serve as a novel regulator of the heat stress response in non-heading Chinese cabbage, actively contributing to the establishment of thermal tolerance by upregulating catalase (CAT) activity and downregulating H₂O₂ accumulation via <i>BcCAT2</i> expression.