The Transcription Factor PsLBD42 Enhances Drought Tolerance Through Regulating the Fucosyltransferase PsFUT2 to Sustain Root Growth in Poplar.

Drought stress is a major abiotic factor that limits plant growth. While responses in the root system play a pivotal role in adapting to drought, the molecular mechanisms linking root development to drought tolerance remain poorly characterized in woody plants like Populus simonii. In this study, we found that the expression of a transcription factor in the lateral organ boundaries domain (LBD) family, PsLBD42, was highly upregulated under drought stress. Overexpression of PsLBD42 in poplar plants significantly improved drought tolerance, resulting in plants with a high photosynthesis rate, delayed leaf wilt, and improved root growth, but higher stomata conductance and transpiration than the wild-type. Silencing PsLBD42 inhibited root growth and decreased drought tolerance. A fucosyltransferase gene, PsFUT2, was identified as a potential target of PsLBD42 via RNA-seq analysis. Chromatin immunoprecipitation-qPCR (ChIP-qPCR), yeast one-hybrid, β-glucuronidase, and dual-luciferase assays demonstrated that PsLBD42 directly binds the promoter of PsFUT2 to positively regulate its expression. Under drought stress, overexpression of PsFUT2 in poplar roots improved root growth and enhanced drought tolerance, while an opposite result was observed in PsFUT2-silencing lines. Moreover, overexpression of PsFUT2 in the roots of PsLBD42-RNAi lines restored root development under drought stress in chimeric poplar plants. Collectively, our findings indicate that the PsLBD42-PsFUT2 module serves as a crucial pathway for regulating poplar root development in response to drought in poplar.