Genome wide identification, characterization of upstream protein kinases involving CBF dependent pathway and antioxidant enzyme analysis in Watermelon (Citrullus lanatus) under brassinosteroid and cold treatment

Brassinosteroids (BRs) are steroidal plant hormones involved in regulation of physiological and molecular processes to ameliorate various biotic and abiotic stresses. Exogenous application of BRs to improve stress tolerance in plants has recently become a high research priority. The involvement of these steroidal hormones in upregulation of stress-related defense genes and their cross talk with other metabolic pathways like CBF dependent and independent pathways are gaining importance. In this study, the primary and master regulator protein kinases (PKs) e.g. BRASSINOSTEROID INSENSITIVE1 (BRI) and BR SIGNALING KINASES (BSK) were analysed. Initially, ClaBRI-ClaBSK gene families were identified and characterized after RT-PCR analysis under cold treatment (CT). These findings were subsequently confirmed in the cold-sensitive lines (PI526233 and SW54) under BRs and cold simultaneous treatment (BRs + CT). Additionally, bio-physiochemical properties, phylogenetic analysis, gene structure, cis element identification and chromosome localization were also analyzed. The activities of superoxide dismutase (SOD), peroxidase (POD) was significantly increased in tolerant and sensitive lines under both treatments (CT and BRs + CT) as compared to sensitive lines under only CT treatment while the electrolyte leakage (EL) was observed to be opposite to these enzymes’ activities for same treatments. In RT-PCR results, the genes ClaBRI2 , ClaBSK1 , ClaBSK4 and ClaBSK8 showed positive expressions in case of same treatments mentioned above. Furthermore, the upregulation of ClaHDA6 (positive regulator of cold tolerance) and the downregulation of ClaBIN2 (negative regulator of cold tolerance) in earlier times impart the significance of the present study. These results suggest that BRs application may contribute to improved cold stress tolerance in watermelon.