GA20ox orchestrates distinct roles in cambium and xylem development via gibberellin and auxin signaling in poplar

Gibberellin 20-oxidase (GA20ox) is a key enzyme of gibberellin (GA) biosynthesis. Its involvement during secondary growth in trees is incompletely understood. In this study, we generated transgenic poplar for xylem-specific knockdown of PagGA20ox3/4 by RNAi interference (RNAi). The RNAi transgenic plants were dwarfed and showed reduction in stem diameter, xylem width, number of cambial cell layers, fiber length, and cell wall thickness. Transgenic wood had decreased lignin content and increased cellulose/hemicellulose contents compared to wildtype wood. RNA-seq and RT-qPCR analyses revealed that in the GA20ox transgenic plants the genes involved in cambial cell division, xylem secondary cell wall (SCW) biosynthesis, and hormone signaling were differentially expressed. Metabolite profiling revealed that perturbation of PagGA20ox3/4 disrupted auxin homeostasis. Our study demonstrates the role of GA in cambial activity and xylem cell wall thickening and also suggests that GA may regulate wood formation through affecting auxin signaling. This work provides a xylem-specific strategy for manipulating GA20ox genes to improve wood properties. • Xylem-specific GA20ox manipulation improves poplar biomass quality/yield. • Perturbation of GA20ox affects cambial activity and xylem cell wall biosynthesis. • GA20ox is involved in cell wall chemical composition in poplar. • GA20ox mediates auxin homeostasis, coordinating GA-auxin crosstalk during poplar wood formation.