Silencing of the Mycorrhiza-Inducible Phosphate Transporter TaPT3-2D in Wheat Enhances Pathogen Susceptibility and Impairs Arbuscular Mycorrhizal Symbiosis

The interplay between phosphate (Pi) signaling and defense pathways is crucial for plant fitness, yet its molecular basis, particularly in wheat, remains poorly understood. Here, we functionally characterized the plasma membrane-localized high-affinity phosphate transporter TaPT3-2D and demonstrated its essential roles in Pi uptake, arbuscular mycorrhizal (AM) symbiosis, and fungal disease resistance. Quantitative analyses showed that TaPT3-2D expression was strongly induced by AM colonization (165-fold increase) and by infection with Bipolaris sorokiniana (54-fold increase) and Gaeumannomyces tritici (15-fold increase). In contrast, virus-induced gene silencing (VIGS) of TaPT3-2D reduced Pi uptake and mycorrhizal colonization. Moreover, TaPT3-2D-silenced plants exhibited increased susceptibility to biotrophic, hemibiotrophic, and necrotrophic fungi, accompanied by reduced expression of pathogen-related genes. The simultaneous impairment of Pi uptake, AM symbiosis, and defense responses in silenced plants indicates that TaPT3-2D functionally couples these processes. Functional complementation assays in low-Pi medium further revealed that TaPT3-2D partially rescued defective Pi uptake in mutant MB192 yeast, supporting its role as a high-affinity phosphate transporter. Collectively, these results identify TaPT3-2D as both a key regulator of individual pathways and as a molecular link connecting Pi homeostasis, symbiotic signaling, and disease resistance in wheat.