Genome-wide identification and expression analysis of PUB genes in cotton
Abstract Background: U-box gene is gene of ubiquitin ligase, which contain U-box domain. Plant U-box gene (PUB) plays an important role in the response to stresses, but less reports about PUBs in cotton were issued. Therefore research of PUBs in cotton will be of great importance and necessity to study the mechanism of tolerance-resistance of the cotton. Results: In this study, we identified 93, 96, 185 and 208 PUBs from the three sequenced cotton species G. raimondii (D5), G. arboreum (A2), G. hirsutum (AD1) and G. arbadense (AD2), respectively. Subcellular localization analysis showed that the PUBs in cotton were distributed in various parts of the cells, mainly in the nucleus. The PUBs in cotton were divided into six subfamilies (A-F) by phylogenetic analysis, and intron/exon structure was comparatively conserved within the subfamily. Location analysis showed cotton PUBs were unevenly anchored on all the chromosomes varying from 1 to 14. It was found that there are 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 between A2 and D5, through multiple sequence alignment, but that the tandem duplication region of A2 or D5 was not found. It was also found that, there were 105, 14 and 17 homologous gene pairs in intra-subgenome of At and Dt, At subgenome, Dt subgenome of allotetraploid cotton, respectively. Among the PUBs family, totally 106, 116, 85 and 81 homologous gene pairs were found in A2-At, A2-Dt, D5-At and D5-Dt. Function analysis of GhPUB85A and GhPUB45D showed they positively responded the abiotic stresses, but the expression patterns were different. Besides, although the expressions of these two homologous genes were similar, their contributions were different when responding to stresses, showing different response differences to abiotic stresses and function division of two subgenomes of G. hirsutum. Conclusion: This study provided the genome-wide identification, structure, evolution and expression analysis of PUBs in cotton, and the results showed that the PUBs was highly conserved in evolutionary history of cotton. All PUB genes were involved in response to abiotic stresses at varying degrees.