Colletotrichum spp. is ranked in the top 10 plant fungal pathogens and serves as a model for the study of hemibiotrophic pathogens, but its molecular mechanisms of pathogenesis remain largely unknown. Among species of Colletotrichum , C. fructicola causes anthracnose disease on more than 50 plants, such as pears, apples, and the important, edible-oil plant Camellia oleifera .

Camellia oleifera is one of the most valuable woody edible-oil crops, and anthracnose seriously afflicts its yield and quality. We recently showed that the CfSnt2 regulates the pathogenicity of Colletotrichum fructicola, the dominant causal agent of anthracnose on C. oleifera. However, the molecular mechanisms of CfSnt2-mediated pathogenesis remain largely unknown. Here, we found that CfSnt2 is localized to the nucleus to regulate the deacetylation of histone H3. The further transcriptomic analysis revealed that CfSnt2 mediates the expression of global genes, including most autophagy-related genes. Furthermore, we provided evidence showing that CfSnt2 negatively regulates autophagy and is involved in the responses to host-derived ROS and ER stresses. These combined functions contribute to the pivotal roles of CfSnt2 on pathogenicity. Taken together, our studies not only illustrate how CfSnt2 functions in the nucleus, but also link its roles on the autophagy and responses to host-derived stresses with pathogenicity in C. fructicola.

Anthracnose is a common disease found in Camellia oleifera producing areas across China, whose primary pathogen is Colletotrichum fructicola. We previously revealed that autophagy is essential for the pathogenicity of C. fructicola. However, the function of ubiquitin–proteasome system (UPS), which is a parallel protein degradation pathway to autophagy, remains elusive. Here, we report that CfRad6, an E2 conjugating enzyme in UPS, interacts with three putative E3 ubiquitin ligases, namely CfRad18, CfUbr1, and CfBre1. Importantly, we presented evidence showing that CfRad6 negatively regulates autophagy, revealing the first link between UPS and autophagy in pathogenic fungi. Targeted gene deletion showed that CfRad6 is involved in growth and conidiation. We further found that the ΔCfrad6 mutant is defective in appressoria formation and responses to environmental stresses. These combined effects, along with the abnormal autophagy level, lead to the pathogenicity defects of the ΔCfrad6 mutant. Taken together, our study indicates the pleiotropic functions of CfRad6 in the development and pathogenicity of C. fructicola.

Camellia oleifera is the native economic edible oil tree in China and anthracnose occurs commonly in its producing areas. We previously found that ubiquitin-like CfAtg8-related autophagy is essential for the pathogenicity of Colletotrichum fructicola, the major pathogen of anthracnose on C. oleifera. The aim of this study is to further elucidate the roles of autophagy in the pathogenesis of C. fructicola. Based on BLAST_P analysis and reverse genetics, we identified the central hub of another ubiquitin-like system, CfAtg5, and characterized its functions in C. fructicola. As suspected, we found that CfAtg5 is required for autophagy, both in MM-N and H₂O₂ induction conditions. Targeted gene deletion of CfATG5 revealed that CfAtg5 is involved in growth and conidiation. We further found that the ∆Cfatg5 mutant is defective in appressorium formation and in responses to cell wall integrity and oxidative stresses. The combined effects, together with the abolished autophagy, result in the pathogenicity defects of the ∆Cfatg5 mutant. Our study further illustrates the importance of normal autophagy in the physiology and pathogenicity of C. fructicola, and offers a potential target in the development of new anthracnose control strategies.

Camellia oleifera is a native woody oil plant in southern China and is infected with anthracnose wherever it is grown. We previously identified Colletotrichum fructicola as the major causal agent of anthracnose on C. oleifera and found that CfAtg8 regulates the pathogenicity and development of C. fructicola. Here, we revealed that CfAtg4 interacts with CfAtg8, contributing to the formation of autophagosomes. The CfAtg8^1–160 allele, which only contains 1–160 amino acids of the CfAtg8, partially recovered the autophagosome numbers and autophagy defects of the ΔCfatg4 mutant. Consequently, these recoveries resulted in the restoration of the defects of the ΔCfatg4 mutant in growth and responses to different external stresses, albeit to an extent. Importantly, we illustrated the critical roles of CfAtg8^1–160 in appressoria formation, and pathogenicity. Collectively, our findings provide new insights into the importance of the interaction between CfAtg8 and CfAtg4 in the growth, autophagy and pathogenicity of the phytopathogenic fungi.

Camellia oleifera is an important economic woody oil plant in many Asian countries, and the anthracnose caused by Colletotrichum fructicola is prevalent in its cultivation regions, causing significant losses annually. We previously found that CfGcn5-mediated H3 acetylation governs virulence of C. fructicola. To further elucidate the regulatory mechanism of CfGcn5, we carried out mass spectrometry analysis for CfGcn5-interacting proteins and identified CfAda3 protein for functional analysis. We found that CfAda3 was mainly localized in nucleus and cooperated with CfGcn5 to acetylate H3K18 for global gene transcription. Targeted gene deletion revealed that CfAda3 is involved in growth and conidiation. Similar to ΔCfgcn5 mutant, the ΔCfada3 mutant is defective in conidial germination, appressorial formation, autophagy, and in the response to environmental stresses. These combined effects result in its non-virulence on C. oleifera. In addition, we provided evidence showing that both NLS region and ADA3 domain are required for the localization and function of CfAda3. Moreover, we indicated that the interaction with CfGcn5 is essential but not sufficient for the normal localization and full function of CfAda3. Taken together, our studies not only illustrate the prominent roles of CfAda3 in growth, development, and virulence but also highlight how CfAda3 functions together with CfGcn5 in C. fructicola.