Evolutionary Characterization of tubulin Gene Family in the Desert Biomass Willow (Salix psammophila) and Expression of the β-tubulin Gene SpsTUB10 during Different Stresses

Abstract

Microtubules, polymerized from α-tubulin (TUA) and β-tubulin (TUB) monomers, play a pivotal role in shaping plant morphogenesis according to developmental and environmental cues. Salix psammophila C. Wang & C. Y. Yang is an important shrub plant in sand-fixing afforestation in arid regions, with three significantly distinct plant types shaped under various environments, namely, upright, intermediate, and scattered types. However, how tubulin genes respond to the developmental and environmental signs in S. psammophila has been far less studied. Here, based on RNA-seq, Sanger sequencing, and real-time PCR (RT-PCR) data, we analyzed the phylogeny of tubulins and their expression profiles in S. psammophila among the three plant types. Furthermore, we analyzed the genetic structure and expression pattern of SpsTUB10 in S. psammophila under various abiotic stress treatments. In total, we identified 26 SpsTubulin genes in S. psammophila. The homologous alignment and phylogenetic analysis revealed that these SpsTubulin genes can be classified into two groups, corresponding to the TUA and TUB genes. The expression profiles of these SpsTubulin genes in various organs showed that most SpsTubulin genes were mainly expressed in the root. SpsTUB10 is a member of the TUB IIa group, consisting of two intros and three exons. The SpsTUB10 protein contains a typical GTPase domain and a C-terminal domain, with α-helix and random coil dominant in the secondary and tertiary structures. The RT-PCR results of SpsTUB10 showed an extremely significant difference in expression levels among the root and stem-developing organs between the upright and scattered types, and the transcript level of SpsTUB10 had a significantly negative correlation with the crown-height ratio. Under different treatments, we found that cold, osmotic stress, and short daylight could significantly increase SpsTUB10 expression levels compared to those in the controls, thereby supporting the positive role of SpsTUB10 in stress-induced responses. These results will provide evidence for the SpsTubulin genes’ response to the developmental and environmental cues in S. psammophila.