Genome-Wide Identification and Expression Analysis of Phytosulfokine Peptide Hormone Genes in Camellia sinensis

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 <i>CsPSK</i> gene family in <i>Camellia sinensis</i>. In this study, we conducted a genome-wide identification and characterized 14 <i>CsPSK</i> genes in tea plants, which are unevenly distributed across seven chromosomes. <i>CsPSK</i> genes encode proteins ranging from 75 to 124 amino acids in length, all belonging to the PSK-α type and containing conserved PSK domains. A synteny analysis revealed that the expansion of the <i>CsPSK</i> gene family is primarily attributed to whole-genome duplication, with homology to <i>Arabidopsis thaliana PSK</i> genes. A promoter region analysis identified cis-regulatory elements related to hormone and stress responses. An expression profile analysis showed that <i>CsPSK</i> genes are highly expressed in roots, stems, flowers, and leaves, and are induced by both biotic and abiotic stresses. Furthermore, an RT-qPCR assay demonstrated that the expression levels of <i>CsPSK8</i>, <i>CsPSK9</i>, and <i>CsPSK10</i> are significantly upregulated following <i>Discula theae-sinensis</i> infection. These findings establish a basis for further research into the role of the Cs<i>PSK</i> gene family in tea plant disease resistance and underlying molecular mechanisms, offering valuable perspectives for developing novel antimicrobial peptides.