Peroxin 14 tags peroxisomes and interacts with Nbr1 for pexophagy in the filamentous insect pathogenic fungus Beauveria bassiana

Abstract

Pexophagy is a main pathway for selective degradation of peroxisomes. However, the molecular mechanisms underlying pexophagy remain fragmented in the filamentous fungi. Herein, we described a complete pathway for pexophagy in the filamentous insect pathogenic fungus Beauveria bassiana. In B. bassiana, peroxin 14 (BbPex14) was a peroxisomal protein, and its loss did not completely abolish peroxisome biogenesis. The loss of BbPex14 blocked the importation of proteins with peroxisomal targeting signal type 1. ΔBbpex14 strain displayed the impaired phenotypes in vegetative growth, stress response, differentiation, and virulence. Notably, BbPex14 was required for pexophagy and interacted with BbNbr1 which was also involved in fungal stress response, development, and virulence. BbNbr1 sequentially interacted with autophagy-related protein 8 (Atg8) responsible for autophagosome biogenesis. BbNbr1 displayed dual association with peroxisome and autophagosome. Together, BbNbr1 act as a receptor recognizing the peroxisomal adaptor BbPex14 and translocates the targeted peroxisomes into autophagosomes. The Pex14-Nbr1-Atg8 pathway mediates pexophagy during development and stress response in B. bassiana. This investigation improves our understanding of the selective autophagy pathway in the filamentous fungi. Abbreviations: AA: amino acid; Atg: Autophagy-related gene; BiFC: bimolecular fluorescence complementation; Co-IP: co-immunoprecipitation; GFP: green fluorescent protein; HA: hemagglutinin; LT50: median lethal time; Nbr1: neighbor of BRCA1 gene 1; ROS: reactive oxygen species; SAR: receptors for selective autophagy;

Keywords

• pexophagy
• filamentous fungi
• insect pathogen
• vegetative growth
• stress resistance
• pathogenesis