The CgATG16 Was Involved in Growth, Development and Virulence Through Autophagy Modulation in the Rubber Tree Anthracnose Fungus Colletotrichum gloeosporioides

<i>Colletotrichum gloeosporioides</i> causes rubber tree anthracnose and leads to serious loss in natural rubber production. Autophagy is a highly conserved process to maintain nutrient recycling and plays important roles in growth, development and pathogenicity in plant pathogenic fungi. The process of autophagy is modulated by a series of autophagy-related (ATG) genes. ATG16 is a subunit of the ATG12-ATG5-ATG16 complex which functions in a manner analogous to an E3-like enzyme which is essential for autophagosome formation. However, the function of the ATG16 homolog in <i>C. gloeosporioides</i> remains unknown. In this study, the ATG16 homolog of <i>C. gloeosporioides</i> was identified and named as CgATG16. The expression level of <i>CgATG16</i> was particularly higher in conidium, germination, appressorium, and the early stage of infection, and significantly induced by nutritional deficiency. Absence of <i>CgATG16</i> led to slower colony growth, decreased conidia production and germination rate, longer germ tube cells, lower appressorium formation rate and impaired pathogenicity to rubber tree leaves. Absence of <i>CgATG16</i> resulted in lower melanin content with decreased expression of polyketide synthase gene <i>CgPKS1</i> and scytalone dehydratase gene <i>CgSCD1</i>. Moreover, absence of <i>CgATG16</i> also led to the universal autophagy marker ATG8-GFP failing to enter into the vacuoles in mycelium and during appressorium development with a significantly reduced autophagosome number. Both rapamycin and cyclic adenosine monophosphate (cAMP) partially restored the appressorium formation ability in <i>CgATG16</i> knockout mutant. Absence of <i>CgATG16</i> increased the activity of target of rapamycin (TOR) kinase and decreased the content of cAMP. These data suggest that CgATG16 contributes to the pathogenicity of <i>C. gloeosporioides</i> to the rubber tree by regulating the mycelium growth, melanin synthesis and the formation of invasion structure, and this process is related to autophagy mediated by TOR and cAMP signaling.