Genome-wide identification, phylogenetic and expressional analysis of the UXS gene family in cotton

Background: UDP-glucuronate decarboxylase (UXS) is an enzyme in plants and participates in cell wall noncellulose. Previous research suggested that cotton GhUXS gene regulated the conversion of non-cellulosic polysaccharides and modulates their composition in plant cell walls, showing its possible cellular function determining the quality of cotton fibers. Here, we performed evolutionary, phylogenetic, and expressional analysis of UXS genes from cottons and other selected plants. Results: By exploring the sequenced cotton genomes, we identified 10, 10, 18, and 20 UXSs genes in Gossypium raimondii , Gossypium arboretum , Gossypium hirsutum and Gossypium barbadense , and retrieved their homologs from other representative plants, including 5 dicots, 1 monocot, 5 green alga, 1 moss, and 1 lycophyte. Phylogenetic analysis suggested that UXS genes could be divided into four subgroups and members within each subgroup shared similar exon-intron structures, motif and subcellular location. Notably, gene colinearity information indicates 100% constructed trees to have aberrant topology, and helps determine and use corrected phylogeny. In spite of conservative nature of UXS, during the evolution of Gossypium , UXS genes were subjected to significant positive selection on key evolutionary nodes. Expression profiles derived from RNA-seq data showed distinct expression patterns of GhUXS genes in various tissues and different development. Most of GhUXS gene expressed highly at 10, 20 and 25 DPA (day post anthesis) of fibers. Real-time quantitative PCR analysis GhUXS genes expressed highly at 20 DPA or 25 DPA. Conclusions: UXS is relatively conserved in plants and significant positive selection affects cotton UXS evolution. The comparative genome-wide identification and expression profiling would lay an important foundation to understanding the biological functions of UXS gene family in cotton species and other plants.