The transcription factor GRF1 enhances tolerance to Pi starvation through improving root development in poplar

Inorganic phosphorus (Pi) is an indispensable nutrient for plant growth and development. However, a significant portion of soil Pi is mineralized and becomes fixed in forms that are not readily available for plant uptake. In response to Pi deficiency, plants have evolved adaptive strategies to modify their root architecture, thereby optimizing Pi acquisition from the soil. However, the molecular mechanisms underpinning these responses in woody plants remain largely unexplored. In this study, we found that GROWTH-REGULATING FACTOR 1 (GRF1) expression is significantly and rapidly upregulated in both roots and leaves of poplar under Pi-limited conditions. Overexpression of GRF1 in poplar enhances root development and confers increased tolerance to Pi starvation stress, whereas poplars with knocked-down GRF1 exhibit opposite phenotypes. These results suggest that GRF1 positively influences these biological processes. Further analysis reveals that GRF1 interacts with GIF2 to up-regulate expression level of the auxin biosynthesis gene TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1, thereby promoting auxin content which in turn leads to modifications in root architecture under Pi deficiency for more Pi uptake. Our findings underscore the pivotal role of GRF1 in mediating root development under Pi starvation, provide novel insights into the molecular pathways involved in the Pi starvation response in woody species such as poplar, and offer potential targets for genetic engineering aimed at improving plant resilience to low Pi environments.