The mitotic exit mediated by small GTPase Tem1 is essential for the pathogenicity of Fusarium graminearum

Nucleoside Diphosphate Kinase FgNdpk Is Required for DON Production and Pathogenicity by Regulating the Growth and Toxisome Formation of Fusarium graminearum

Nucleoside diphosphate kinases (NDPKs) are nucleotide metabolism enzymes that play different physiological functions in different species. However, the roles of NDPK in phytopathogen and mycotoxin production are not well understood. In this study, we showed that Fusarium graminearum FgNdpk is important for vegetative growth, conidiation, sexual development, and pathogenicity. Furthermore, FgNdpk is required for deoxynivalenol (DON) production; deletion of FgNDPK downregulates the expression of DON biosynthesis genes and disrupts the formation of FgTri4-GFP-labeled toxisomes, while overexpression of FgNDPK significantly increases DON production. Interestingly, FgNdpk colocalizes with the DON biosynthesis proteins FgTri1 and FgTri4 in the toxisome, and coimmunoprecipitation (Co-IP) assays show that FgNdpk associates with FgTri1 and FgTri4 in vivo and regulates their localizations and expressions, respectively. Taken together, these data demonstrate that FgNdpk is important for vegetative growth, conidiation, and pathogenicity and acts as a key protein that regulates toxisome formation and DON biosynthesis in F. graminearum.

A feedback regulation of FgHtf1-FgCon7 loop in conidiogenesis and development of Fusarium graminearum

The transcription factor FgHtf1 is important for conidiogenesis in Fusarium graminearum and it positively regulates the expression of the sporulation-related gene FgCON7. However, the regulatory mechanism underlying its functions is still unclear. The present study intends to uncover the functional mechanism of FgHtf1 in relation to FgCon7 in F. graminearum. We demonstrated that FgCON7 serves as a target gene for FgHtf1. Interestingly, FgCon7 also binds the promoter region of FgHTF1 to negatively regulate its expression, thus forming a negative-feedback loop. We demonstrated that FgHtf1 and FgCon7 have functional redundancy in fungal development. FgCon7 localizes in the nucleus and has transcriptional activation activity. Deletion of FgCON7 significantly reduces conidia production. 4444 genes were regulated by FgCon7 in ChIP-Seq, and RNA-Seq revealed 4430 differentially expressed genes in FgCON7 deletion mutant, with CCAAT serving as a consensus binding motif of FgCon7 to the target genes. FgCon7 directly binds the promoter regions of FgMSN2, FgABAA, FgVEA and FgSMT3 genes and regulates their expression. These genes were found to be important for conidiogenesis. To our knowledge, this is the first study that unveiled the mutual regulatory functions of FgCON7 and FgHTF1 to form a negative-feedback loop, and how the loop mediates sporulation in F. graminearum.

Antifungal and elicitor activities of p-hydroxybenzoic acid for the control of aflatoxigenic Aspergillus flavus in kiwifruit

Aspergillus flavus not only reduces kiwifruit production but also synthesizes carcinogenic aflatoxins, resulting in a relevant threat to human health. p-Hydroxybenzoic acid (pHBA) is one of the most abundant phenolics in kiwifruit. In this study, pHBA was found to reduce A. flavus mycelial growth by blocking the fungal mitotic exit network (MEN) and cytokinesis and to inhibit the biosynthesis of aflatoxins B1 and B2. The application of pHBA promoted the accumulation of endogenous pHBA and induced oxidative stress in A. flavus-infected kiwifruit, resulting in an increase in H2O2 content and catalase (CAT) and superoxide dismutase (SOD) activities. Preventive and curative treatments with 5 mM pHBA reduced A. flavus advancement by 46.1% and 68.0%, respectively. Collectively, the antifungal and elicitor properties of pHBA were examined for the first time, revealing new insights into the role of pHBA in the defense response of kiwifruit against A. flavus infection.

PdStuA Is a Key Transcription Factor Controlling Sporulation, Hydrophobicity, and Stress Tolerance in Penicillium digitatum

Penicillium digitatum has become one of the main pathogens in citrus due to its high spore production and easy spread. In this study, the function of the APSES transcription factor StuA in P. digitatum was characterized, and the results indicated that it was involved in conidium and conidiophore development. No conidiophores were observed in the mycelium of the ∆PdStuA mutant that had grown for two days, while an abnormal conidiophore was found after another two days of incubation, and only small thin phialides as well as a very small number of spores were formed at the top of the hyphae. Moreover, it was observed that the ∆PdStuA mutant showed various defects, such as reduced hydrophobicity and decreased tolerance to cell wall inhibitors and H2O2. Compared to the original P. digitatum, the colony diameter of the ∆PdStuA mutant was not significantly affected, but the growth of aerial hyphae was obviously induced. In in vivo experiments, the spore production of the ∆PdStuA mutant grown on citrus fruit was remarkably decreased; however, there was no significant difference in the lesion diameter between the mutant and original strain. It could be inferred that less spore production might result in reduced spread in citrus, thereby reducing the green mold infection in citrus fruit during storage. This study provided a gene, PdStuA, which played key role in the sporulation of P. digitatum, and the results might provide a reference for the molecular mechanisms of sporulation in P. digitatum.