Genome-Wide Identification and Salt Stress Response Analysis of the COMT Gene Family in Poncirus trifoliata

Caffeic acid O-methyltransferase (COMT) serves as a crucial rate-limiting enzyme within the melatonin biosynthesis pathway and is involved in various primary and secondary metabolic processes, significantly contributing to plant growth, development, and stress response. Nevertheless, a comprehensive characterization of the COMT gene family in citrus species, particularly with regard to its functional roles under salinity stress, remains unavailable. In the current study, we identified 47 COMT loci from the Poncirus trifoliata genome, and these genes were observed to be non-uniformly scattered across seven chromosomes. The majority of these genes are predicted to localize within the Golgi apparatus and nucleus. Each PtrCOMT gene contains between 2 and 19 exons and 1 and 18 introns, and they are categorized into four groups based on phylogenetic analysis. Collinearity analysis uncovered three intraspecific collinear gene pairs in Poncirus trifoliata. Three orthologous collinear pairs were detected between P. trifoliata and Arabidopsis thaliana, and one pair between P. trifoliata and Oryza sativa. Additionally, the promoter regions of PtrCOMT genes were found to contain 23 distinct cis-acting regulatory elements. Expression analysis indicated tissue-specific expression patterns, with higher expression levels observed in roots. Furthermore, qRT-PCR profiling detected increased expression of multiple candidate PtrCOMT genes upon high-salt treatment, hinting that members of this family may be implicated in plant salt stress regulatory processes. Overall, these findings provide a foundation for further investigation into the functional roles of PtrCOMT genes in response to salt stress.