Genome-wide characterization and CGMMV-responsive expression profiling of the pathogenesis-related protein 1 gene family in watermelon

Watermelon (Citrullus lanatus) is an economically important fruit crop worldwide, yet its production is severely threatened by cucumber green mottle mosaic virus (CGMMV), which causes substantial yield losses and compromises fruit quality. Pathogenesis-related (PR) proteins are integral components of plant defense, with the PR1 family representing one of the most conserved and extensively characterized groups of defense-related proteins. Although the PR1 gene family has been characterized in numerous plant species, its composition and role in watermelon in response to CGMMV infection remain largely unexplored. In this study, 19 PR1 genes were identified in the watermelon genome (cv. 97103) through genome-wide identification. These ClPR1s were classified into three subgroups (Group II - Grour IV) by phylogenetic analysis, and were found to be unevenly distributed on 5 chromosomes. In addition, these ClPR1s contained one CAP or CAP superfamily domain, and 78.95% ClPR1s were intronless. The main cis-acting elements in the ClPR1 promoters were predicted to respond to hormone signaling, stress responses, and transcription factor binding, particularly MYB and MYC recognition sites. The expression pattern revealed that ClPR1s ClPR1s were expressed in various tissues and that their expression was induced by CGMMV. CGMMV infection triggered tissue- and genotype-specific induction of ClPR1s ( ClPR1-1 , ClPR1-2 , ClPR1-6 , and ClPR1-15 ), as well as the differentially expressed ClPR1s ( ClPR1-1 , ClPR1-6 , and ClPR1-15 ) between CGMMV-resistance (PI) and CGMMV-sensitive (ZK) watermelon may play important roles in the response to CGMMV infection. While ClPR1-2 was strongly induced at the early infection stage in leaves. Furthermore, transcription factor binding-site prediction identified ERF family transcription factor as potential upstream regulators of CGMMV-inducible ClPR1 genes, and exogenous ETH treatment significantly enhanced the expression of specific ClPR1 genes. These findings suggest that ETH signaling may be involved in transcriptional regulation of ClPR1 gene during the watermelon response to CGMMV infection. This study provides comprehensive insights into the ClPR1s ClPR1s gene family and pinpoints candidate genes for further investigations into the function of ClPR1s in the response of watermelon to CGMMV infection.