Functional analysis of CfSnf1 in the development and pathogenicity of anthracnose fungus Colletotrichum fructicola on tea-oil tree

Gene Family Expansion during the Adaptation of Colletotrichum gloeosporioides to Woody Plants

Gene gains/losses during evolution are critical for the adaptation of organisms to new environments or hosts. However, it remains unknown whether gene family expansions facilitated the adaptation of phytopathogenic fungi to woody plants. In this study, we compared the newly sequenced genome of the Colletotrichum gloeosporioides strain CFCC80308 with the genomes of two other C. gloeosporioides strains, Cg-14 and Lc-1, isolated from Persea americana and Liriodendron leaves, respectively. The genes in the expanded families, which were associated with plant surface signal recognition, encoded various proteins, including glycosyde hydrolases (GHs) and cytochrome P450. Interestingly, there was a substantial increase in the number of GH family genes in CFCC80308. Specifically, there were 368 enriched genes in the GH families (e.g., GH1, GH3, GH10, GH12, GH15, GH16, GH17, GH18, GH25, GH32, GH53, GH61, GH76, and GH81); the expression levels of these genes were highly up-regulated during the infection of poplar trees. Additionally, the GH17 family was larger in CFCC80308 than in C. gloeosporioides strains Cg-14 and Lc-1. Furthermore, the expansion of the MP65-encoding gene family during the adaptation of Colletotrichum species to woody plants was consistent with the importance of gene gains/losses for the adaptation of organisms to their environments. This study has clarified how C. gloeosporioides adapted to woody plants during evolution.

Sucrose non-fermenting protein kinase gene UvSnf1 is required for virulence in Ustilaginoidea virens

Rice false smut caused by Ustilaginoidea virens is becoming one of the most devastating diseases in rice production areas in the world. Revealing U. virens potential pathogenic mechanisms provides ideas for formulating more effective prevention and control strategies. Sucrose non-fermenting 1 (Snf1) protein kinase plays a critical role in activating transcription and suppressing gene expression, as well as in cellular response to various stresses, such as nutrient limitation. In our study, we identified the Snf1 homolog UvSnf1 and analyzed its biological functions in U. virens. The expression level of UvSnf1 was dramatically up-regulated during invasion, indicating that UvSnf1 may participate in infection. Phenotypic analyses of UvSnf1 deletion mutants revealed that UvSnf1 is necessary for hyphae growth, spore production, and virulence in U. virens. Moreover, UvSnf1 promotes U. virens to use unfavorable carbon sources when the sucrose is insufficient. In addition, deletion of UvSnf1 down-regulates the expression of the cell wall-degrading enzymes (CWDEs) genes under sucrose limitation conditions in U. virens. Further analyses showed that CWDEs (UvCut1 and UvXyp1) are not only involved in growth, spore production, and virulence but are also required for the utilization of carbon sources. In conclusion, this study demonstrates that UvSnf1 plays vital roles in virulence and carbon source utilization in U. virens, and one of the possible mechanisms is playing a role in regulating the expression of CWDE genes.

Cell Wall Integrity Mediated by CfCHS1 Is Important for Growth, Stress Responses and Pathogenicity in Colletotrichum fructicola

Camellia oleifera, a woody plant that produces edible oil, is indigenous to China. The devastating disease of anthracnose inflicts significant financial losses on Ca. oleifera. The primary causative agent of anthracnose on Ca. oleifera is Colletotrichum fructicola. Chitin, a pivotal constituent of fungal cell walls, assumes a critical function in their proliferation and maturation. To study the biological functions of chitin synthase 1(Chs1) in C. fructicola, the CfCHS1 gene knockout mutants, ∆Cfchs1-1 and ∆Cfchs1-2, and their complementary strain, ∆Cfchs1/CfCHS1, of C. fructicola were generated. Our results showed that the colony diameters of wild-type and complement-strain ∆Cfchs1/CfCHS1, mutant ∆Cfchs1-1 and ∆Cfchs1-2 cultured on the CM and MM medium were 5.2, 5.0, 2.2 and 2.4 cm and 4.0, 4.0, 2.1 and 2.6 cm, respectively, which were significantly smaller for the mutant than for the wild type and complement strain; the inhibition rates on the CM medium supplemented with H₂O₂, DTT, SDS and CR were 87.0% and 88.5%, 29.6% and 27.1%, 88.0% and 89.4%, and 41.7% and 28.7%, respectively, for the mutant strains, ∆Cfchs1-1 and ∆Cfchs1-2, which were significantly higher than those for the other two strains; the rate of hyphal tips with CFW fluorescence in ∆Cfchs1-1 and ∆Cfchs1-2 was 13.3% and 15.0%, which was significantly lower than those for the other two strains; the mutant strains, ∆Cfchs1-1 and ∆Cfchs1-2, lost the ability to produce conidia; the mutant strains showed weaker pathogenicity on wounded and unwounded Ca. oleifera leaves than the wild type and complement strain. The findings of this study suggest that CfChs1 plays a crucial role in the growth and development, stress responses, and pathogenicity of C. fructicola. Thus, this gene could be a potential target for developing novel fungicide.

Identification of Camellia oleifera WRKY transcription factor genes and functional characterization of CoWRKY78

Camellia oleifera Abel is a highly valued woody edible oil tree, which is endemic to China. It has great economic value because C. oleifera seed oil contains a high proportion of polyunsaturated fatty acids. C. oleifera anthracnose caused by Colletotrichum fructicola, poses a serious threat to C. oleifera growth and yield and causes the benefit of the C. oleifera industry to suffer directly. The WRKY transcription factor family members have been widely characterized as vital regulators in plant response to pathogen infection. Until now, the number, type and biological function of C. oleifera WRKY genes are remains unknown. Here, we identified 90 C. oleifera WRKY members, which were distributed across 15 chromosomes. C. oleifera WRKY gene expansion was mainly attributed to segmental duplication. We performed transcriptomic analyses to verify the expression patterns of CoWRKYs between anthracnose-resistant and -susceptible cultivars of C. oleifera. These results demonstrated that multiple candidate CoWRKYs can be induced by anthracnose and provide useful clues for their functional studies. CoWRKY78, an anthracnose-induced WRKY gene, was isolated from C. oleifera. It was significantly down-regulated in anthracnose-resistant cultivars. Overexpression of CoWRKY78 in tobacco markedly reduced resistance to anthracnose than WT plants, as evidenced by more cell death, higher malonaldehyde content and reactive oxygen species (ROS), but lower activities of superoxide dismutase (SOD), peroxidase (POD), as well as phenylalanine ammonia-lyase (PAL). Furthermore, the expression of multiple stress-related genes, which are associated with ROS-homeostasis (NtSOD and NtPOD), pathogen challenge (NtPAL), and pathogen defense (NtPR1, NtNPR1, and NtPDF1.2) were altered in the CoWRKY78-overexpressing plants. These findings increase our understanding of the CoWRKY genes and lay the foundation for the exploration of anthracnose resistance mechanisms and expedite the breeding of anthracnose-resistant C. oleifera cultivars.

Detection and Quantification of Anthracnose Pathogen Colletotrichum fructicola in Cultivated Tea-Oil Camellia Species from Southern China Using a DNA-Based qPCR Assay

Tea-oil Camellia species as edible-oil producing trees are widely cultivated in southern China. Camellia anthracnose that is mainly caused by Colletotrichum fructicola is a major disease of tea-oil trees. However, rapid detection and precise quantification of C. fructicola in different Camellia species that are crucial for the fundamental study of this pathosystem and effective disease management remain largely unexplored. Here, we developed a sensitive, rapid, and accurate method for quantifying C. fructicola growth in different Camellia species using a quantitative PCR assay. Amplified C. fructicola DNA using ITS-specific primers is relatively compared with the amplification of Camellia oleifera using the TUB gene. We determined that the fungal growth is tightly associated with the disease development in Ca. oleifera following C. fructicola infection in a time-course manner. This assay is highly sensitive, as fungal growth was detected in six different inoculated tea-oil Camellia species without visible disease lesion symptoms. Additionally, this method was validated by quantifying the Camellia anthracnose in orchards that did not show any disease symptoms. This assay enables the rapid, highly sensitive, and precise detection and quantification of C. fructicola growth in different tea-oil Camellia species, which will have a practical application for early diagnosis of anthracnose disease under asymptomatic conditions in Camellia breeding and field and will facilitate the development of tea-oil trees and C. fructicola interaction as a mold system to study woody plant and fungal pathogens interaction.

Genomic and genetic advances of oiltea-camellia (Camellia oleifera)

Oiltea-camellia (C. oleifera) is a widely cultivated woody oil crop in Southern China and Southeast Asia. The genome of oiltea-camellia was very complex and not well explored. Recently, genomes of three oiltea-camellia species were sequenced and assembled, multi-omic studies of oiltea-camellia were carried out and provided a better understanding of this important woody oil crop. In this review, we summarized the recent assembly of the reference genomes of oiltea-camellia, genes related to economic traits (flowering, photosynthesis, yield and oil component), disease resistance (anthracnose) and environmental stress tolerances (drought, cold, heat and nutrient deficiency). We also discussed future directions of integrating multiple omics for evaluating genetic resources and mining key genes of important traits, and the application of new molecular breeding and gene editing technologies to accelerate the breeding process of oiltea-camellia.

Overexpression of dihydroflavonol 4-reductase (CoDFR) boosts flavonoid production involved in the anthracnose resistance

The outbreak of anthracnose caused by Colletotrichum spp. represents a devastating epidemic that severely affects oil tea (Camellia oleifera) production in China. However, the unknown resistance mechanism to anthracnose in C. oleifera has impeded the progress of breeding disease-resistant varieties. In this study, we investigated the physiological responses of resistant and susceptible lines during C. gloeosporioides infection. Our results showed that the accumulation of malondialdehyde (MDA), catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) in both disease-resistant and susceptible lines increased by C. gloeosporioides infection. Also, disease-resistant lines exhibited lower MDA, but higher POD, SOD, and CAT activities compared to susceptible lines. The accumulation of flavonoids in both resistant and susceptible C. oleifera leaves increased following C. gloeosporioides infection, and the increase was greater in resistant lines. Further, we identified and functionally characterized the dihydroflavonol 4-reductase (CoDFR) from the resistant C. oleifera line. We showed that the full-length coding sequence (CDS) of CoDFR is 1044 bp encoding 347 amino acids. The overexpression of CoDFR in tobacco altered the expression of flavonoid biosynthetic genes, resulting in an increased flavonoid content in leaves. CoDFR transgenic tobacco plants exhibited increased anthracnose resistance. Furthermore, the transgenic plants had higher salicylic acid content. These findings offer potential insights into the pivotal role of CoDFR involved in flavonoid-mediated defense mechanisms during anthracnose invasion in resistant C. oleifera.

The CfMcm1 Regulates Pathogenicity, Conidium Germination, and Sexual Development in Colletotrichum fructicola

Glomerella leaf spot (GLS), caused by Colletotrichum fructicola, is a severe disease worldwide on apple, causing defoliation, leaf and fruit spot, and substantial yield loss. However, little is known about its molecular mechanisms of pathogenesis. Previous transcriptome analysis revealed that a transcription factor, CfMcm1, was induced during leaf infection. In the present work, expression pattern analysis verified that the CfMcm1 gene was strongly expressed in conidia and early infection. Phenotypic analysis revealed that the gene deletion mutant ΔCfMcm1 lost pathogenicity to apple leaves by inhibiting conidial germination and appressorium formation. In addition to appressorium-mediated pathogenicity, ΔCfMcm1 colonization and hyphal extension in wounded apple fruit was also reduced, and conidial germination mode and conidial color were altered. ΔCfMcm1 displayed impairment of cell wall integrity and response to stress caused by oxidation, osmosis, and an acid environment. Furthermore, the deletion mutant produced fewer and smaller perithecia and no ascospores. In contrast, melanin deposition in mycelia of ΔCfMcm1 was strengthened. Further comparative transcriptome and quantitative PCR analysis revealed that CfMcm1 modulated expression of genes related to conidial development (CfERG5A, CfERG5B, CfHik5, and CfAbaA), appressorium formation (CfCBP1 and CfCHS7), pectin degradation (CfPelA and CfPelB), sexual development (CfMYB, CfFork, CfHMG, and CfMAT1-2-1), and melanin biosynthesis (CfCmr1, CfPKS1, CfT4HR1, CfTHR1, and CfSCD1). Our results demonstrated that CfMcm1 is a pivotal regulator possessing multiple functions in pathogenicity, asexual and sexual reproduction, and melanin biosynthesis.

The CfSnt2-Dependent Deacetylation of Histone H3 Mediates Autophagy and Pathogenicity of Colletotrichum fructicola

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.

Histone Acetyltransferase CfGcn5-Mediated Autophagy Governs the Pathogenicity of Colletotrichum fructicola

Camellia oleifera is a woody edible-oil plant in China, and anthracnose occurs wherever it is grown, causing serious losses each year. We previously identified that the histone acetyltransferase CfGcn5 orchestrates growth, development, and pathogenicity in Colletotrichum fructicola, the major causal agent of anthracnose on C. oleifera. To elucidate the underlying mechanism, we conducted a transcriptome analysis and found that CfGcn5 is mainly involved in ribosomes, catalytic and metabolic processes, primary metabolism, and autophagy. In addition, we provided evidence showing that CfGcn5 serves as an autophagy repressor to mediate the expression of many autophagy-related genes (ATG) and undergoes degradation during autophagy. Moreover, we found that the CfATG8 and CfATG9 gene-deletion mutants had defects in mitosis and autophagy, resulting in their decreased appressoria formation rates and lower turgor pressure. These combined effects caused the failure of their appressoria functions and caused defects on their pathogenicity, revealing the importance of autophagy in pathogenicity. Taken together, our study illustrates that the autophagy repressor CfGcn5 undergoes degradation in order to regulate autophagy-dependent pathogenicity in C. fructicola.

The Retromer Subunit CfVps29 Is Involved in the Growth, Development, and Pathogenicity of Colletotrichum fructicola

Camellia oleifera is an edible oil tree species native to China. Anthracnose is a common disease of Ca. oleifera, which reduces the production of the trees and brings huge economic losses. We have previously identified the fungus Colletotrichum fructicola as the major pathogen of anthracnose in Ca. oleifera. The retromer complex participates in the intracellular retrograde transport of the cargos from the endosome to the trans-Golgi network in the eukaryotes. Vacuolar protein sorting 29 is a subunit of the retromer complex. Targeted CfVPS29 gene deletion revealed that CfVps29 is involved in growth, conidiation, and the response to cell wall stress. We further found that the ΔCfvps29 mutant was minimally pathogenic to Ca. oleifera leaves, as a result of its defect in appressorium formation. This study illustrated the crucial functions of CfVps29 in the development, cell wall stress response, and pathogenicity of C. fructicola and, therefore, identified it as a potential fungicide target for the control of anthracnose.

Recent progress on harm, pathogen classification, control and pathogenic molecular mechanism of anthracnose of oil-tea

Oil tea (Camellia oleifera), mainly used to produce high-quality edible oil, is an important cash crop in China. Anthracnose of oil tea is a considerable factor that limits the yield of tea oil. In order to effectively control the anthracnose of oil tea, researchers have worked hard for many years, and great progress has been made in the research of oil tea anthracnose. For instance, researchers isolated a variety of Colletotrichum spp. from oil tea and found that Colletotrichum fructicola was the most popular pathogen in oil tea. At the same time, a variety of control methods have been explored, such as cultivating resistant varieties, pesticides, and biological control, etc. Furthermore, the research on the molecular pathogenesis of Colletotrichum spp. has also made good progress, such as the elaboration of the transcription factors and effector functions of Colletotrichum spp. The authors summarized the research status of the harm, pathogen types, control, and pathogenic molecular mechanism of oil tea anthracnose in order to provide theoretical support and new technical means for the green prevention and control of oil tea anthracnose.

H3K4 Methyltransferase CfSet1 Is Required for Development and Pathogenesis in Colletotrichum fructicola

Tea-oil tree (Camellia oleifera Abel.) is a unique woody edible oil species in China. Anthracnose is the common disease of Ca. oleifera, which affected the production and brought huge economic losses. Colletotrichum fructicola is the dominant pathogen causing Ca. oleifera anthracnose. The gene CfSET1 was deleted and its roles in development and pathogenicity of C. fructicola were studied. Our results show that this protein participated in the growth, conidiation, appressorium formation, and pathogenicity of this fungal pathogen. Our results help us understand the mechanisms of pathogenesis in C. fructicola and suggest CfSet1 as a potential target for the development of new fungicide.

Snf1 Kinase Differentially Regulates Botrytis cinerea Pathogenicity according to the Plant Host

The Snf1 kinase of the glucose signaling pathway controls the response to nutritional and environmental stresses. In phytopathogenic fungi, Snf1 acts as a global activator of plant cell wall degrading enzymes that are major virulence factors for plant colonization. To characterize its role in the virulence of the necrotrophic fungus Botrytis cinerea, two independent deletion mutants of the Bcsnf1 gene were obtained and analyzed. Virulence of the Δsnf1 mutants was reduced by 59% on a host with acidic pH (apple fruit) and up to 89% on hosts with neutral pH (cucumber cotyledon and French bean leaf). In vitro, Δsnf1 mutants grew slower than the wild type strain at both pH 5 and 7, with a reduction of 20–80% in simple sugars, polysaccharides, and lipidic carbon sources, and these defects were amplified at pH 7. A two-fold reduction in secretion of xylanase activities was observed consequently to the Bcsnf1 gene deletion. Moreover, Δsnf1 mutants were altered in their ability to control ambient pH. Finally, Δsnf1 mutants were impaired in asexual sporulation and did not produce macroconidia. These results confirm the importance of BcSnf1 in pathogenicity, nutrition, and conidiation, and suggest a role in pH regulation for this global regulator in filamentous fungi.

The SNARE Protein CfVam7 Is Required for Growth, Endoplasmic Reticulum Stress Response, and Pathogenicity of Colletotrichum fructicola

The tea-oil tree Camellia oleifera is native to China and is cultivated in many parts of southern China. This plant has been grown for over 2,000 years, mainly for its high-quality cooking oil. Anthracnose is the main disease of tea-oil tree and results in a huge loss annually. Colletotrichum fructicola is a major pathogen causing anthracnose on tea-oil tree. In a previous study, we characterized that the bZIP transcription factor CfHac1 controlled the development and pathogenicity of C. fructicola. Here, we identified and characterized the function of CfVAM7 gene, which was significantly downregulated at the transcriptional level in the ΔCfhac1 strain under dithiothreitol stress. Targeted gene deletion revealed that CfVam7 is important in growth, pathogenicity, and responses to endoplasmic reticulum-related stresses. Further analysis revealed that CfVam7 is required for appressorium formation and homotypic vacuole fusion, which are important for fungal pathogen invasion. Cytological examinations revealed that CfVam7 is localized to vacuole membranes in the hyphal stage. The Phox homology (PX) and SNARE domains of CfVam7 were indispensable for normal cellular localization and biological function. Taken together, our results suggested that CfVam7-mediated vacuole membrane fusion promotes growth, stress response, and pathogenicity of C. fructicola.

The Molecular Mechanisms of Phytophthora infestans in Response to Reactive Oxygen Species Stress

Reactive oxygen species (ROSs) are critical for the growth, development, proliferation, and pathogenicity of microbial pathogens; however, excessive levels of ROSs are toxic. Little is known about the signaling cascades in response to ROS stress in oomycetes such as Phytophthora infestans, the causal agent of potato late blight. Here, P. infestans was used as a model system to investigate the mechanism underlying the response to ROS stress in oomycete pathogens. Results showed severe defects in sporangium germination, mycelium growth, appressorium formation, and virulence of P. infestans in response to H₂O₂ stress. Importantly, these phenotypes mimic those of P. infestans treated with rapamycin, the inhibitor of target of rapamycin (TOR, 1-phosphatidylinositol-3-kinase). Strong synergism occurred when P. infestans was treated with a combination of H₂O₂ and rapamycin, suggesting that a crosstalk exists between ROS stress and the TOR signaling pathway. Comprehensive analysis of transcriptome, proteome, and phosphorylation omics showed that H₂O₂ stress significantly induced the operation of the TOR-mediated autophagy pathway. Monodansylcadaverine staining showed that in the presence of H₂O₂ and rapamycin, the autophagosome level increased in a dosage-dependent manner. Furthermore, transgenic potatoes containing double-stranded RNA of TOR in P. infestans (PiTOR) displayed high resistance to P. infestans. Therefore, TOR is involved in the ROS response and is a potential target for control of oomycete diseases, because host-mediated silencing of PiTOR increases potato resistance to late blight.

The Histone Acetyltransferase CfGcn5 Regulates Growth, Development, and Pathogenicity in the Anthracnose Fungus Colletotrichum fructicola on the Tea-Oil Tree

The tea-oil tree (Camellia oleifera Abel.) is a commercial edible-oil tree in China, and anthracnose commonly occurs in its plantations, causing great losses annually. We have previously revealed that CfSnf1 is essential for pathogenicity in Colletotrichum fructicola, the major pathogen of anthracnose on the tea-oil tree. Here, we identified CfGcn5 as the homolog of yeast histone acetyltransferase ScGcn5, which cooperates with ScSnf1 to modify histone H3 in Saccharomyces cerevisiae. Targeted gene deletion revealed that CfGcn5 is important in fungi growth, conidiation, and responses to environmental stresses. Pathogenicity assays indicated that CfGcn5 is essential for C. fructicola virulence both in unwounded and wounded tea-oil tree leaves. Further, we found that CfGcn5 is localized to the nucleus and this specific localization is dependent on both NLS region and HAT domain. Moreover, we provided evidence showing that the nuclear localization is essential but not sufficient for the full function of CfGcn5, and the NLS, HAT, and Bromo domains were proven to be important for normal CfGcn5 functions. Taken together, our studies not only illustrate the key functions of CfGcn5 in growth, development, and pathogenicity but also highlight the relationship between its locations with functions in C. fructicola.

Transcription Factor CfSte12 of Colletotrichum fructicola Is a Key Regulator of Early Apple Glomerella Leaf Spot Pathogenesis

Glomerella leaf spot (GLS), caused by Colletotrichum fructicola, is a rapidly emerging disease leading to defoliation, fruit spot, and storage fruit rot on apple in China. Little is known about the mechanisms of GLS pathogenesis. Early transcriptome analysis revealed that expression of the zinc finger transcription factor Ste12 gene in C. fructicola (CfSte12) was upregulated in appressoria and leaf infection. To investigate functions of CfSte12 during pathogenesis, we constructed gene deletion mutants (ΔCfSte12) by homologous recombination. Phenotypic analysis revealed that CfSte12 was involved in pathogenesis of nonwounded apple fruit and leaf, as well as wounded apple fruit. Subsequent histological studies revealed that loss of pathogenicity by ΔCfSte12 on apple leaf was expressed as defects of conidium germination, appressorium development, and appressorium-mediated penetration. Further RNA sequencing-based transcriptome comparison revealed that CfSte12 modulates the expression of genes related to appressorium function (e.g., genes for the tetraspanin PLS1, Gas1-like proteins, cutinases, and melanin biosynthesis) and candidate effectors likely involved in plant interaction. In sum, our results demonstrated that CfSte12 is a key regulator of early apple GLS pathogenesis in C. fructicola In addition, CfSte12 is also needed for sexual development of perithecia and ascospores.IMPORTANCE Glomerella leaf spot (GLS) is an emerging fungal disease of apple that causes huge economic losses in Asia, North America, and South America. The damage inflicted by GLS manifests in rapid necrosis of leaves, severe defoliation, and necrotic spot on the fruit surface. However, few studies have addressed mechanisms of GLS pathogenesis. In this study, we identified and characterized a key pathogenicity-related transcription factor, CfSte12, of Colletotrichum fructicola that contributes to GLS pathogenesis. We provide evidence that the CfSte12 protein regulates many important pathogenic processes of GLS, including conidium germination, appressorium formation, appressorium-mediated penetration, and colonization. CfSte12 also impacts development of structures needed for sexual reproduction which are vital for the GLS disease cycle. These results reveal a key pathogenicity-related transcription factor, CfSte12, in C. fructicola that causes GLS.