Wood forming tissue-specific expression of PaTyDC4 promotes xylem differentiation and lignin deposition during secondary growth and confers drought tolerance in Populus

Abstract

Tyrosine decarboxylase (TyDC) converts tyrosine to tyramine and plays a crucial role in secondary metabolite reactions, development, and stress responses in plants. Currently, the biological role of TyDC proteins from trees is unknown. This study provided evidence showing that poplar PaTyDC4 functions in wood development and drought stress response. PaTyDC4 is preferentially expressed in wood-forming cells in stems. Overexpression of PaTyDC4 in poplars under the control of a xylem-specific promoter resulted in an increase in the ratio of xylem to phloem width, vessel cell area, and lignin accumulation in the stems. Biochemical assays revealed that PaTyDC4 is a component of the PaC3H17-PaMYB199 module-mediated pathway. In poplar stems, PaTyDC4 expression was directly suppressed by PaMYB199, which was attenuated by the interaction between PaC3H17 and PaMYB199. In addition, PaTyDC4 overexpression lines showed stronger drought tolerance than the wild-type lines, with higher photosynthetic capacity and lower levels of H2O2. These results indicate that PaTyDC4 promotes xylem differentiation and lignin deposition during secondary growth and confers drought tolerance. Our findings may be useful for the genetic modification of biomass and drought resistance in trees.