GSK3 ‐Like Kinase SlBIN2 , a Negative Regulator of BR ‐Signaling Influences Cold Stress Response in Tomato Through Transcriptional Regulation

ABSTRACT In plants, BIN2 is a well‐known member of GSK3, a major negative regulator of brassinosteroid (BR) signaling. GSK3s play a vital role in the abiotic stress response in plants, regulating salinity stress responses and influencing heat and drought resistance. To evaluate the impact of cold stress on tomato , SlBIN2.1‐ overexpressing and SlBIN2‐ knockout lines were exposed to cold stress alongside WT. The expression of genes encoding enzymes involved in enzymatic activity, including Cu/Zn SOD , POD1, and CAT1, was increased in the knockout lines, thereby improving the activity of these enzymes. On the other hand, the expression of these genes was comparatively lower in the SlBIN2.1 ‐OE lines and, hence, reduced enzymatic activity. MDA and H 2 O 2 were highly accumulated in overexpressed lines, while proline content was increased in the knockout lines compared to other plants. Expression of cold‐related genes, including CBF1 , CBF2 , CBF3 , NCED1, and NCED2, was upregulated in the knockout lines compared to both overexpressed and WT plants. Transcriptomic data show that core pathways related to cold response were negatively regulated in SlBIN2.1‐ OE and, hence, decreased cold stress tolerance in tomato. Overall, SlBIN2 knockout improves cold stress response in tomato by regulating enzymatic activity and expression of cold‐related genes.