Fungal pathogen hijacks phosphate signaling to promote pathogenicity

Weakening your opponent is an effective way to win a battle. A new paper by McCombe et al. shows that several pathogenic fungi weaken their plant hosts by disrupting their phosphate signaling pathways. Phosphate is indispensable for plant growth, as a component of ATP, nucleotides, phospholipids, and countless small molecules, so plants have complex systems for taking up and monitoring phosphate. Inositol pyrophosphate (PP-InsP) is a small, phosphate-rich molecule that serves as a measure of P sufficiency by interacting with key regulators to suppress the phosphate starvation response. McCombe et al. studied a class of effector proteins secreted by plant pathogens called Nudix (nucleoside-diphosphate linked to moiety X) proteins and found that they hydrolyze PP-InsP. Nudix genes are highly upregulated upon infection and knocking them out severely limits pathogen virulence. The authors initially looked at the interaction between Magnaporthe oryzae and rice, but found that Nudix effectors have similar properties in other pathogenic fungi (Colletotrichum spp.) acting on other plants. The authors confirmed that the PP-InsP hydrolase activity is required for the disease promotion by the Nudix proteins, and that they hydrolyze PP-InsP in plant cells and promote the starvation response, which may be sufficient to weaken the plant as it unnecessarily allocates energy to this pathway. However, the authors observe that the pathogen might also benefit nutritionally from the elevated intercellular P as the plant naively accumulates P. Furthermore, PP-InsPs have a role in activating jasmonate signaling, so lowering PP-InsP levels might additionally benefit the pathogen through suppressed defense signaling. This is a fascinating study showing once again that all is NOT fair in love and war. Have a look also at the accompanying Perspective by Caroline Gutjahr 10.1126/science.adw1568. (Summary by Mary Williams @PlantTeaching.bsky.social) Science 10.1126/science.adl5764