Regulatory mechanisms of exogenous GA3 application and identification of key genes related to salt tolerance in Populus davidiana × P. bolleana

Abstract

Gibberellins (GAs) are key plant growth regulators, but their regulatory mechanisms in woody plants remain to be explored. In this study, Populus davidiana × P. bolleana (Shanxin poplar) plants were treated with GA₃ for different times. The results revealed that exogenous GA₃ increased the fresh weight, stem internode length, plant height, stem diameter, chlorophyll content, and the width and length of leaves. Xylogenesis was enhanced under GA₃ treatment, as evidenced by the staining of transverse stem sections with toluidine blue, phloroglucinol-HCl, and calcofluor white. In addition, the total contents of endogenous GA, auxin, and cytokinin were increased. Furthermore, RNA-seq analysis indicated that 112, 2473, and 3773 genes were differentially expressed under GA₃ treatment for 0.5 h, 48 h, and 7 d. The differentially expressed genes (DEGs) were mainly related to plant hormone signal transduction, phenylpropanoid biosynthesis, diterpenoid biosynthesis, and photosynthesis processes. Further analysis suggested that GA₃ treatment enhanced plant biomass by regulating the expression of DEGs involved in cell elongation, xylem formation, and stress tolerance. Furthermore, our research has demonstrated that the overexpression of the DEGs MYB52 and bHLH71 can significantly enhance the salt tolerance of poplar plants by improving their capacity to scavenge reactive oxygen species (ROS). These findings provide insight into the regulatory mechanisms of GA₃ and identify the key genes associated with high salt tolerance in Shanxin poplar.