Genome-wide characterization and expression analysis of the aldehyde dehydrogenase (ALDH) gene superfamily under abiotic stresses in cotton

In plants, aldehyde dehydrogenases (ALDHs) function as 'aldehyde scavengers' by removing reactive aldehydes and thus play important roles in stress responses. To date, 30 ALDHs have been identified in Gossypium raimondii, whereas ALDHs have not been studied in Gossypium arboreum or in tetraploid cotton. In this study, we identified 30, 59 and 59 aldehyde dehydrogenase (ALDH) genes from G. arboreum, G. hirsutum and G. barbadense, respectively. Gene structure analysis revealed that members of the same family exhibit similar exon-intron structures and structural domains, and all members of the ALDH18 family possess a distinct AA-kinase domain. Synteny analysis showed that segmental and tandem duplications have played an important role in the expansion and evolution of ALDHs in cotton. Phylogenetic and synteny analysis between G. arboreum and G. raimondii demonstrated that all GaALDHs and GrALDHs are orthologous and that most GaALDHs are located in syntenic blocks corresponding to those of G. raimondii, implying that these genes appeared before the divergence of G. arboreum and G. raimondii and that no expansion of the ALDH superfamily has occurred in these two cotton species. Quantitative real-time PCR analysis revealed that the majority of GaALDHs and GhALDHs are up-regulated under conditions of high salinity and drought, indicating that these genes may be stress responsive. The findings of this study, based on genome-wide identification of ALDHs in Gossypium and analysis of their evolution and expression, provide a foundation for further analysis of ALDHs and suggest potential target genes for improving stress resistance in cotton.