Abstract
Autophagy is a degradation system in the cell, involved in the turnover of cellular components, development, differentiation, immune responses, protection against pathogens, and cell death. Autophagy is induced by nutrient starvation, in which cytoplasmic components and organelles are digested via vacuoles/lysosomes. In this study, by using electron microscopy, we observed that hypovirus CHV1-EP713 infection of Cryphonectria parasitica, the causative agent of chestnut blight disease, caused proliferation of autophagic-like vesicles. This phenomenon could be mimicked by treating the wild-type strain of the fungus EP155 with the autophagy induction drug rapamycin. Some of the hypovirulence-associated traits, including reduced pigmentation and conidiation, were also observed in the rapamycin-treated EP155. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) revealed that genes involved in autophagy were up-regulated in expression. Deletion of cpatg8, a gene encoding a homolog of ATG8 in Saccharomyces cerevisiae, resulted in attenuation of virulence and reduction in sporulation, as well as accumulation of the double-stranded viral RNA. Furthermore, virus-encoded p29 protein was found to co-localize with CpATG8, implying that the viral protein may interfere with the function of CpATG8. Taken together, these findings show that cpatg8 can be regulated by the hypovirus and is required for virulence and development of the fungus and accumulation of viral dsRNA in chestnut blight fungus.
Highlights
Autophagy is a conserved cellular process of eukaryotic cells that degrades intracellular protein complexes and organelles in the vacuole or lysosome (Klionsky et al, 2016; Liu et al, 2016; Yin et al, 2016)
We used an electron microscope to compare the subcellullar structure of the wild-type strain EP155 and virus-infected strain EP155/CHV1-EP713 and found that the number of vesicles was increased in the cytoplasm by more than 3-fold following virus infection (Figure 1)
Loss of cpatg8 leads to the inhibited autophagy in C. parasitica (Figure 4), suggesting that cpatg8 is essential for autophagy in this fungus
Summary
Autophagy is a conserved cellular process of eukaryotic cells that degrades intracellular protein complexes and organelles in the vacuole or lysosome (Klionsky et al, 2016; Liu et al, 2016; Yin et al, 2016). Autophagy has diverse physiological functions in the regulation of energy and nutrient metabolism, organelle quality control, removing misfolded proteins (Yin et al, 2016), and the development of filamentous fungi (Khan et al, 2012; Voigt and Pöggeler, 2013b; Liu et al, 2016). In Fusarium graminearum, FgATG8 was found to function in the formation of aerial mycelium and formation of reproductive structures, nutritional use of storage lipid droplets, and infection (Josefsen et al, 2012)
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