Genome-Wide Identification and Functional Analysis of the GUX Gene Family in Eucalyptus grandis

Xylan, one of the most important structures and polysaccharides, plays critical roles in plant development, growth, and defense responses to pathogens. Glucuronic acid substitution of xylan (GUX) functions in xylan sidechain decoration, which is involved in a wide range of physiological processes in plants. However, the specifics of GUXs in trees remain unclear. In this study, the characterization and evolution of the GUX family genes in E. grandis, a fast-growing forest tree belonging to the Myrtaceae family, were performed. A total of 23 EgGUXs were identified from the E. grandis genome, of which all members contained motif 2, 3, 5, and 7. All GUX genes were phylogeneticly clustered into five distinct groups. Among them, EgGUX01~EgGUX05 genes were clustered into group III and IV, which were more closely related to the AtGUX1, AtGUX2, and AtGUX4 members of Arabidopsis thaliana known to possess glucuronyltransferase activity, while most other members were clustered into group I. The light-responsive elements, hormone-responsive elements, growth and development-responsive elements, and stress-responsive elements were found in the promoter cis-acting elements, suggesting the expression of GUX might also be regulated by abiotic factors. RNA-Seq data confirmed that EgGUX02, EgGUX03, and EgGUX10 are highly expressed in xylem, and EgGUX09, EgGUX10, and EgGUX14 were obviously responses to abiotic stresses. The results of this paper will provide a comprehensive determination of the functions of the EgGUX family members, which will further contribute to understanding E. grandis xylan formation.