MoOrp-mediated PtdIns4P transportation is essential for autophagy and pathogenicity in Magnaporthe oryzae

Macroautophagy/autophagy is essential to the pathogenicity of Magnaporthe oryzae. Phosphatidylinositol-4-phosphate (PtdIns4P) is a key lipid involved in the autophagy process. Recent studies have shown that the PtdIns4P pool on autophagic membranes is crucial to autophagosome biogenesis and fusion with the vacuole; however, the mechanism regulating the PtdIns4P levels on autophagic membranes is still unclear. Here, we report that two oxysterol-binding protein-related proteins, MoOrp1 and MoOrp2, required for the pathogenicity in M. oryzae, function as PtdIns4P transporters to modulate the autophagy process. We found that simultaneous knockout of MoORP1 and MoORP2 genes (△Moorp1–2) led to a range of defects in autophagy-related infection processes, including lipid degradation and autophagic cell death in conidia, generation of appressorial turgor pressure required for host penetration, and growth of infectious hyphae in plant cells. Autophagy flux assays of the △Moorp1–2 strain revealed a prominent deficiency in autophagosome formation and fusion with the vacuole. Molecular analyses showed that both MoOrp1 and MoOrp2 could bind PtdIns4P and be recruited to the autophagosome by interacting with MoAtg8. Disruption of the two MoORP genes impeded the autophagy-induced PtdIns4P accumulation on the autophagosome and vacuolar membrane. Disturbance of the molecular features vital for PtdIns4P-binding activity in MoOrp1 and MoOrp2 abolished their function in autophagy and pathogenicity. Hence, our study uncovers new roles of the Atg8 protein and highlights the significance of the MoOrp-mediated PtdIns4P translocation in regulating autophagy and pathogenicity in M. oryzae.Abberivations: Atg: autophagy related; BiFC: bimolecular fluorescence complementation; CHOL: cholesterol; CM: complete medium; CL: cardiolipin; Co-IP: co-immunoprecipitation; DAG: diacylglycerol; FDA: fluorescein diacetate; GABARAP: GABA type A receptor-associated protein; GFP: green fluorescent protein; hpi: hours post inoculation; IH: invasive hypha; LDs: lipid droplets; MM-N: minimum medium minus nitrogen; Mo: Magnaporthe oryzae; ORPs: oxysterol-binding protein-related proteins; OSBP: oxysterol-binding protein; ORD: OSBP-related domain; PAS: phagophore assembly site; PA: phosphatidic acid; PS: phosphatidylserine; PE: phosphatidylethanolamine; PC: phosphatidylcholine; PG: phosphatidylglycerol; PtdIns: phosphatidylinositol; PIs: phosphoinositides; PtdIns4Ks: phosphatidylinositol 4-kinases; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns4P: phosphatidylinositol-4-phosphate; PtdIns(3,5)P2: phosphatidylinositol-3,5-bisphosphate; PtdIns(4,5)P2: phosphatidylinositol-4,5-bisphosphate; PM: plasma membrane; SM: sphingomyelin; ST: sulfatide; TG: triglyceride; TOR: target of rapamycin; YFP: yellow fluorescent protein.