Pan-Genome Identification and Expression Analysis of Lipoxygenase Genes in Cucumber

Lipoxygenase (LOX) is a dioxygenase that contains non-heme iron and plays a crucial role in regulating plant growth and development, signal transduction, and responses to both biotic and abiotic stresses. In this study, we identified 24 CsLOXs from the pan-genome of 12 cucumber ( Cucumis sativus L.) accessions, with most CsLOX proteins exhibiting amino acid variations. To elucidate their functions, we examined the phylogenetic relationships, gene structures, conserved domains, promoter cis-elements, and collinearity of the 24 CsLOXs from the newly updated genome version 4.0 of ‘Chinese Long 9930’. The results indicated that CsLOXs can be categorized into three subfamilies: 9-LOX, Type I 13-LOX, and Type II 13-LOX. Additionally, promoter analysis revealed that the promoters of CsLOXs contain various cis-elements related to stress and hormone responses. The expression of CsLOXs demonstrated tissue specificity, with each CsLOX expressed in at least one tissue, and six CsLOXs expressed across all tissues. Furthermore, in the transcriptome data of cucumber responses to heat, cold, powdery mildew (PM), downy mildew (DM), and gray mold (GM) stresses, eight, four, eight, eight, and four CsLOXs exhibited differential expression, respectively. Notably, CsLOX22 responded to heat, cold, DM, and GM stresses. Our results provided a reference for further exploring the functions of CsLOXs in cucumber.