Genome-Wide Identification of the Oxidative Stress 3 (OXS3) Gene Family and Analysis of Its Expression Pattern During Ovule Development and Under Abiotic Stress in Cotton

<i>Oxidative Stress 3</i> (<i>OXS3</i>) encodes a plant-specific protein that makes great contributions to a plant's stress tolerance. However, reports on genome-wide identification and expression pattern analyses of OXS3 were only found for <i>Arabidopsis</i>, wheat, and rice. The genus <i>Gossypium</i> (cotton) serves as an ideal model for studying allopolyploidy. Therefore, two diploid species (<i>G. raimondii</i> and <i>G. arboreum</i>) and two tetraploid species (<i>G. hirsutum</i> and <i>G. barbadense</i>) were chosen in this study for a bioinformatics analysis, resulting in 12, 12, 22, and 23 OXS3 members, respectively. A phylogenetic tree was constructed using 69 cotton <i>OXS3</i> genes alongside 8 <i>Arabidopsis</i>, 10 rice, and 9 wheat genes, which were classified into three groups (Group 1-3). A consistent evolutionary relationship with the phylogenetic tree was observed in our structural analysis of the cotton <i>OXS3</i> genes and the clustering of six conserved motifs. Gene duplication analysis across the four representative <i>Gossypium</i> species suggested that whole-genome duplication, segmental duplication, and tandem duplication might play significant roles in the expansion of the <i>OXS3</i> gene family. Some existing elements responsive to salicylic acid (SA), jasmonic acid (JA), and abscisic acid (ABA) were identified by cis-regulatory element analysis in the promoter regions, which could influence the expression levels of cotton <i>OXS3</i> genes. Furthermore, the expression patterns of the <i>GhOXS3</i> gene were examined in different tissues or organs, as well as in developing ovules and fibers, with the highest expression observed in ovules. <i>GhOXS3</i> genes exhibited a more pronounced regulatory response to abiotic stresses, of which ten <i>GhOXS3</i> genes showed similar expression patterns under cold, heat, salt, and drought treatments. These observations were verified by quantitative real-time PCR experiments. These findings enhance our understanding of the evolutionary relationships and expression patterns of the <i>OXS3</i> gene family and provide valuable insights for the identification of vital candidate genes for trait improvement in cotton breeding.