Retromer Regulates Macro- and Micro-Autophagy via Distinct Vacuolar Proteases in the Rice Blast Fungus.

The vacuole degrades and recycles endocytic and autophagic cargos, while the retromer complex sorts cargos from the endosomes to the trans-Golgi network or the plasma membrane, thus preventing unnecessary vacuolar degradation. However, whether the retromer complex regulates vacuolar proteolytic system during autophagic substrate degradation remains unclear. This study demonstrates that the retromer complex regulates both general and selective autophagy by ensuring the delivery of vacuolar protease(s) into the vacuole lumen in the rice blast fungus Magnaporthe oryzae. The central retromer subunit, MoVps35, transports the serine protease MoPrb1 from the endosomes to the vacuole lumen. Deletion of MoVPS35 or any other retromer component prevents the transport of MoPrb1-GFP into the vacuole lumen. Consistently, ΔMoprb1 mutant shows similar defects as the retromer mutants, including failure of autophagy-dependent conidiation and plant infection. Additionally, mutation of the catalytic residues of MoPrb1 (Asp 192, His 224 and Ser 390) reduces autophagy flux. Furthermore, MoVps35 also interacts with another aspartyl protease MoPep4 via MoPrb1. Loss of MoPEP4 leads to abnormal micro-autophagy (pexophagy) but not to fungal development and pathogenicity. Overall, this study demonstrates a crucial role of the retromer complex in the regulation of macro- and micro-autophagy by different vacuolar proteases in M. oryzae.