Brassinosteroid‐Mediated BraSERKs Regulation and Antioxidant Defense Enhancement Confer Cd/Zn Stress Tolerance in Chinese Cabbage

Somatic embryogenesis receptor kinases (SERKs) are pivotal regulators of plant development and stress adaptation, known to integrate multiple signaling pathways, including brassinosteroid (BR)‐mediated responses to coordinately modulate stress‐related gene expression. While SERKs participate in biotic/abiotic stress regulation, their roles in heavy metal (HM) stress responses and BR‐mediated transcriptional control under HM exposure remain unexplored. Therefore, we systematically identified 20 BraSERK genes in Chinese cabbage ( Brassica rapa subsp. Pekinensis), revealing conserved domain architectures and stress‐responsive expression patterns. Three BraSERK members ( BraSERK9 , 12 , and 17 ) exhibited significant induction under Cd/Zn stress. The potential regulatory roles of BR on Chinese cabbage exposed to Cd/Zn stress were investigated in this study by exogenous spraying of 24‐epibrassinolide (EBR). The results showed that EBR could significantly increase total chlorophyll content, reduce Zn/Cd translocation, increase antioxidant capacity, and thus attenuate Cd/Zn‐induced toxicity. Moreover, EBR dynamically regulated BraSERKs expression in a tissue‐ and metal‐specific manner, potentiating BraSERK12/17 induction in Zn‐stressed shoots while suppressing BraSERK9 . Our findings suggest that BraSERKs may contribute to BR‐mediated HM adaptation, while EBR appears to play a dual protective role through both direct phytoprotection and potential modulation of SERK pathway activity under Cd/Zn co‐stress conditions. This study advances our understanding of BR‐mediated metal tolerance in crops, offering potential strategies to mitigate HM toxicity through targeted SERK pathway modulation.