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

Area of Science:

• Molecular biology
• Cell biology
• Mycology

Background:

• The vacuole degrades cellular cargo via endocytosis and autophagy.
• The retromer complex mediates cargo retrieval from endosomes, preventing premature degradation.
• The role of retromer in regulating vacuolar proteases during autophagy is not well understood.

Purpose of the Study:

• To investigate the function of the retromer complex in regulating the vacuolar proteolytic system during autophagy in Magnaporthe oryzae.
• To determine if retromer influences the delivery and activity of vacuolar proteases essential for autophagic substrate degradation.

Main Methods:

• Utilized genetic deletion mutants of retromer components (e.g., MoVps35) and vacuolar proteases (MoPrb1, MoPep4) in M. oryzae.
• Employed fluorescence microscopy to track the localization of vacuolar proteases (e.g., MoPrb1-GFP).
• Assessed autophagy flux through mutation of catalytic residues of MoPrb1 and observed fungal development and pathogenicity.

Main Results:

• Retromer complex components, including MoVps35, are required for the delivery of vacuolar proteases (MoPrb1) to the vacuole lumen.
• Deletion of retromer components or MoPrb1 impairs autophagy flux, conidiation, and plant infection.
• MoVps35 interacts with MoPep4, and loss of MoPep4 affects micro-autophagy (pexophagy).

Conclusions:

• The retromer complex plays a critical role in regulating both macro- and micro-autophagy in M. oryzae.
• Retromer ensures the delivery of essential vacuolar proteases, like MoPrb1 and MoPep4, for efficient cargo degradation.
• This pathway is vital for fungal development, pathogenicity, and overall cellular homeostasis.