Autophagy safeguards conidial environmental persistence in filamentous fungi

Conidiation mechanism confers filamentous fungus efficient dispersal and survival in natural habitats. However, the mechanisms that regulate conidial lifespan and persistence remain enigmatic. We recently revealed that autophagy functions as a sub-cellular mechanism essential for conidial longevity and vitality after maturation in Beauveria bassiana. Significantly, BbApe4 (B. bassiana aspartyl aminopeptidase) contributes to conidial persistence and recovery from dormancy. There are two isoforms for BbAtg8 (B. bassiana autophagy-related protein 8), BbAtg8-α and BbAtg-β. BbApe4 is translocated into vacuoles via its direct binding to BbAtg8-α (hereafter called BbAtg8), which occurs during conidial germination and hyphal growth. The specific interaction between BbAtg8 and BbApe4 is crucial for vacuolar targeting and functionality of BbApe4 and dependent on the autophagic function of BbAtg8. We named the BbApe4-BbAtg8 pathway as simplified cytoplasm-to-vacuole pathway (sCvt) due to the absence of the autophagy receptors that characterize classic yeast Cvt pathway. These findings demonstrate that autophagy acts as a physiological mechanism for fungal survival in nature and highlight the diversity in autophagy-related pathways for vacuolar targeting of hydrolase between fungi. Abbreviations: Bb: Beauveria bassiana; ATG: autophagy-related gene; AIM: Atg8-family interacting motif; Cvt pathway: cytoplasm-to-vacuole targeting pathway; Ape4: aspartyl aminopeptidase.