Whole-Genome Identification of the Kunitz Trypsin Inhibitor (CaKTI) Gene Family in Capsicum annuum and Its Response to Verticillium dahliae Infection

Verticillium wilt caused by Verticillium dahliae poses a severe threat to pepper (Capsicum annuum) production worldwide. Kunitz trypsin inhibitors (KTIs) play crucial roles in plant disease resistance, yet research on the CaKTI gene family in pepper, especially regarding its regulatory functions in resistance to V. dahliae, remains limited. In this study, members of the CaKTI gene family were systematically identified in the pepper genome, followed by comprehensive analyses of their physicochemical properties, phylogeny, chromosomal localization, conserved motifs, cis-acting elements in promoters, and expression profiles. A total of 22 CaKTI genes were identified, all harboring the beta-trefoil_STI superfamily domain. They were unevenly distributed across four chromosomes, with evident tandem duplication events, and exhibited tissue-specific and developmental stage-specific expression patterns. In the Verticillium-resistant pepper cultivar, five candidate CaKTI genes (CaKTI9, CaKTI6, CaKTI17, CaKTI18, and CaKTI22) were significantly induced and upregulated, particularly in roots, and their expression might be modulated by the methyl jasmonate signaling pathway. This study reveals the molecular features, evolutionary conservation, and defense-associated expression patterns of CaKTI genes in pepper and provides a preliminary exploratory basis for future research on disease resistance and molecular breeding.