The role of autophagy in Cryphonectria hypovirus 1 (CHV1) infection in Cryphonectria parasitica.

The interaction between Cryphonectria parasitica, the causal agent of chestnut blight, and Cryphonectria hypovirus 1 (CHV1) results in fungal hypovirulence associated with alterations of fungal development, reduced sporulation and pigmentation, accumulation of cytosolic vesicles. The role of these vesicles is to support CHV1 maintenance and replication, but the origin of these compartments is still under debate. Due to the phylogenetic proximity between CHV1 and poliovirus, which induces autophagosome proliferation in infected cells, we decided to explore the involvement of autophagy in vesicle accumulation and virus replication in CHV1-infected mycelium. We are studying the autophagy dynamic in CHV1-infected Cryphonectria expressing GFP-CpAtg8. Atg8 is the fungal orthologue of the mammalian LC3, an essential protein for autophagosome formation which is considered a reliable autophagosome marker. In CHV1-free hyphae, GFP-CpAtg8 distribution was mostly cytosolic, but in presence of CHV1 we observed a punctate distribution of fluorescence which is compatible with the binding of GFP-CpAtg8 with autophagosome membranes. The induction of autophagy is also supported by the observed increase of accumulation of GFP-CpAtg8 in presence of CHV1 compared with virus-free mycelium which could be due to an activation of gene transcription and/or to protein stabilization. Overall our results seem to confirm the activation of autophagy by CHV1. We are now testing through various approaches if CHV1 is able to induce autophagosomes proliferation to support its own replication or if this is an effect of fungal defense against hypovirus infection.