Genome-wide identification and expression analysis of PUB genes in cotton

Abstract

Background: The U-box gene encodes a ubiquitin ligase that contain U-box domain. The plant U-box gene (PUB) plays an important role in the response to stress, but few reports about PUBs in cotton were available. Therefore research on PUBs is of great importance and is a necessity when studying the mechanism of stress tolerance in cotton. Results: In this study, we identified 93, 96, 185 and 208 PUBs from four sequenced cotton species G. raimondii (D5), G. arboreum (A2), G. hirsutum (AD1) and G. barbadense (AD2), respectively. Prediction analysis of subcellular localization showed that the PUBs in cotton were widely distributed in cells, but primarily in the nucleus. The PUBs in cotton were divided into six subfamilies (A-F) on the basis of phylogenetic analysis, and the intron/exon structure was comparatively conserved within each subfamily. Location analysis showed that cotton PUBs were unevenly anchored on all chromosomes, varying from 1 to 14 per chromosome. Through multiple sequence alignment, 3 tandem duplications and 28 segmental duplications in cotton genome D5, 2 tandem duplications and 25 segmental duplications in A2, and 143 homologous gene pairs shared in A2 and D5 were found; however no tandem duplication region in A2 or D5 was found. Additionally, 105, 14 and 17 homologous gene pairs were found in the intra-subgenome of At and Dt, the At subgenome and the Dt subgenome of allotetraploid cotton, respectively. Functional analysis of GhPUB85A and GhPUB45D showed that these genes positively responded to abiotic stresses, but the expression patterns were different. In addition, although the expression levels of these two homologous genes were similar, their contributions were different when responding to stresses, specifically showing different responses to abiotic stresses and functional differences between the two subgenomes of G. hirsutum. Conclusion: This study reports the genome-wide identification, structure, evolution and expression analysis of PUBs in cotton, and the results showed that the PUBs were highly conserved throughout the evolutionary history of cotton. All PUB genes were involved in response to abiotic stresses (including those genes induced by salt, drought, hot and cold) to varying degrees.