Genome wide characterization and expression profiling of protein disulfide isomerase (PDI) gene family members in watermelon under cold stress.

Abstract

BACKGROUND: Protein Disulfide Isomerases (PDIs) are essential molecular chaperones that guide proteins to fold correctly by forming disulfide bonds, which are essential for protein stability and helping plants cope with stress. However, PDIs in watermelon (Citrullus lanatus) have not been explored. OBJECTIVE: This study focused on identifying and analyzing the PDI gene family in watermelon, with particular attention to their functions during exposure to cold stress. METHODS: Sixteen Citrullus lanatus PDI (ClPDI) genes were identified and analyzed for their evolutionary relationships, gene structure, regulatory elements, gene duplications, conserved motifs, miRNA targets, phosphorylation sites, and predicted 3D protein models. Gene expression under cold stress was examined in tolerant (SW66) and sensitive (PPI526233) watermelon genotypes. In addition, antioxidant enzyme activities were assessed. RESULTS: All sixteen ClPDI genes were distributed across nine watermelon chromosomes and contained thioredoxin domains, forming ten evolutionary clusters. One gene duplication event was identified within watermelon, along with fifteen orthologous relationship shared with Arabidopsis and rice. Promoter analysis revealed common abiotic stress related regulatory elements. Expression analysis showed that twelve of the sixteen ClPDI genes were upregulated (≥ 2 fold) in the tolerant genotype under cold stress, with ClPDI6, ClPDI8, and ClPDI15 exhibiting ≥ 100 fold induction. Antioxidant enzyme activities were higher in the tolerant genotype than in the sensitive genotype following cold stress. CONCLUSION: The study highlights the important role of the PDI gene family in watermelon under cold stress and suggests that enhanced antioxidant activity may help maintain a favorable redox environment for proper PDI function. These findings provide potential molecular targets for improving cold stress tolerance in watermelon.