Comparative Analysis, Characterization and Evolutionary Study of Dirigent Gene Family in Cucurbitaceae and Expression of Novel Dirigent Peptide against Powdery Mildew Stress

Dirigent (DIR) proteins are induced under various stress conditions and involved in sterio- and regio-selective coupling of monolignol. A striking lack of information about dirigent genes in cucurbitaceae plants underscores the importance of functional characterization. In this study, 112 DIR genes were identified in six species, and 61 genes from major cultivated species were analyzed. DIRs were analyzed using various bioinformatics tools and complemented by expression profiling. Phylogenetic analysis segregated the putative DIRs into six distinctively known subgroups. Chromosomal mapping revealed uneven distribution of genes, whereas synteny analysis exhibited that duplication events occurred during gene evolution. Gene structure analysis suggested the gain of introns during gene diversification. Gene ontology (GO) enrichment analysis indicates the participation of proteins in lignification and pathogen resistance activities. We also determined their organ-specific expression levels in three species revealing preferential expression in root and leaves. Furthermore, the number of CmDIR (CmDIR1, 6, 7 and 12) and ClDIR (ClDIR2, 5, 8, 9 and 17) genes exhibited higher expression in resistant cultivars after powdery mildew (PM) inoculation. In summary, based on the expression and in-silico analysis, we propose a role of DIRs in disease resistance mechanisms.