Genome-Wide Identification of PSK Gene Family and Effects of Abscisic Acid (ABA) in Regulating Antioxidant Activity and ROS Signaling Under Drought Stress in Brassica napus

Phytosulfokine (PSK) is a tyrosine-sulfated pentapeptide found throughout the plant kingdom, playing key roles in plant growth, development, and responses to biotic and abiotic stresses. However, there is still a lack of a comprehensive analysis of the BnPSK gene family in Brassica napus. In this study, we conducted a genome-wide identification and characterized 19 BnPSK genes in oil seed plants, which are unevenly distributed across both sub-genomes (A and C). BnPSK proteins ranged from 77 to 99 amino acids (BnPSK3c and BnPSK3d) in length, all belonging to the PSK-α type and containing conserved PSK domains. Synteny analysis revealed that the expansion of the BnPSK gene family is primarily attributed to whole genome duplication, with homology to Arabidopsis thaliana PSK genes. A promoter region analysis identified cis-acting elements related to hormone and stress responses. An expression profile analysis showed that BnPSK genes are highly expressed in roots, leaves, petals, and pollens and are induced by both abiotic stresses and phytohormone application. Furthermore, RT-qPCR assay demonstrated that the expression levels of BnPSK4c, BnPSK5a, and BnPSK5b were significantly enhanced under drought stress (3~5-fold) both in plant roots and leaves following ABA application. Lastly, the application of ABA induced antioxidant activity including SOD, POD, CAT and APX (2~5-fold) and their corresponding genes (3~5-fold), and altered the ROS-signaling in rapeseed plants; also, strong evidence of mitigating drought stress was present. These findings establish a basis for further research into the role of the BnPSK gene family in oilseed plant tolerance against drought stress and underlying molecular mechanisms, offering valuable perspectives for developing novel peptides.