H+-Pyrophosphatase VP1 Enhances Low Phosphorus Tolerance by Interacting With the Auxin Influx Carrier AUX1 in Wheat.

Phosphorus (P) is an essential macronutrient for crop growth, and its deficiency significantly limits wheat productivity, thereby underscoring the importance of improving phosphorus use efficiency (PUE) for global food security. Although proton-pyrophosphatase (Type I H⁺-pyrophosphatase, VP1, H⁺-PPases) plays critical roles in plant responses to abiotic stresses, the molecular mechanisms underlying its function in wheat (Triticum aestivum L.) under low-phosphorus (LP) stress remain largely unexplored. Elymus dahuricus, a wild forage grass species, exhibits notable resistance to diverse environmental stresses. In the present study, a VP1-like gene from Elymus dahuricus (EdVP1) was introduced into wild-type (WT) wheat cultivar Shimai366 (SHI366). Two-year field trials conducted under LP conditions demonstrated that overexpression of EdVP1 significantly increased spike number per meter, grain yield, phosphorus harvest index (PHI), and phosphorus use efficiency (PUE). Specifically, transgenic lines OE13 and OE28 exhibited average yield increases of 14.25% and 15.65%, respectively, relative to WT plants over two consecutive years, accompanied by improved photosynthetic rates and chlorophyll content during the grain-filling stage. Additionally, P concentrations in the roots of transgenic lines were significantly elevated compared to SHI366. Subsequent assays under phosphorus-deficient conditions confirmed substantial improvements in both biomass accumulation and root system architecture (RSA) in the transgenic lines. Physiological analyses further demonstrated reduced accumulation of reactive oxygen species (ROS) and enhanced activities of antioxidant enzymes in these lines. Collectively, these findings indicate that the VP1 gene from Elymus dahuricus markedly enhances wheat tolerance to P deficiency. To elucidate the underlying mechanisms of VP1-like genes in wheat, the endogenous plasma membrane (PM) H⁺-PPases gene TaVP1 (TraesCS7D02G507600), which exhibits the closest evolutionary relationship and highest sequence homology with EdVP1 among grass species, was identified and found to be upregulated in EdVP1 transgenic wheat. TaVP1 expression was predominantly localized in roots and was strongly induced by P-deficient and auxin (IAA) treatment. Notably, auxin levels were significantly increased in the roots of transgenic lines, concomitant with upregulated expression of the auxin influx carrier gene TaAUX1 (TraesCS3B02G401000). Both in vivo and in vitro assays demonstrated a direct interaction between TaVP1 and TaAUX1 at the plasma membrane. Furthermore, factors associated with downstream auxin transport and response, along with the key phosphate starvation transcription factor TaPHR1, exhibit an upregulated expression pattern in the transgenic lines. Taken together, these results reveal a novel mechanism by which H⁺-PPase enhances tolerance to phosphorus deficiency in wheat through crosstalk with auxin signaling pathways.