Penicillium digitatum is the most common cause of postharvest decay in citrus fruits around the world. Previous studies revealed that the bZIP gene family plays crucial roles in development, stress adaptation, and pathogenicity in fungi. However, little is known about the bZIP genes in P. digitatum. In this study, we systematically identified the bZIP family in 23 Penicillium species and analyzed their evolutionary relationships. We found that gene loss and gene duplication shaped the evolution of the Penicillium bZIP family. P. digitatum experienced 3 bZIP gene loss events, but with no gene duplication. We subsequently characterized the biological functions of one important member, PdatfA in P. digitatum by constructing the deletion mutant. Results showed that ΔPdatfA exhibited a moderate growth defect, reduced pigmentation, and slightly increased resistance to fungicides iprodione and fludioxonil. However, ΔPdatfA displayed similar rot symptoms to that of the wild-type. The ΔPdatfA mycelia were not affected in response to oxidative stress while its conidia showed enhanced resistance due to the upregulation of catalases. Our results provide new insights into the evolution and functions of the bZIP gene family in Penicillium.

BACKGROUND:Fusarium head blight (FHB) is a devastating disease of cereal crops worldwide mainly caused by Fusarium graminearum. Due to the unavailability of FHB-resistant wheat cultivars, chemical fungicide application is currently the most effective approach for controlling FHB now. In the last few years, a novel cyanoacrylate fungicide, phenamacril, has been widely used in China for FHB disease management. In previous studies, we identified that myosin I (FgMyo1) is the target of phenamacril and is essential for mycotoxin deoxynivalenol (DON) biosynthesis and fungal growth. However, the regulation of FgMYO1 gene expression is still largely unknown. RESULTS:In this study, we identified a b-ZIP transcription factor, FgTfmI, which regulates the mRNA expression of FgMYO1 upon phenamacril treatment. The FgTfmI directly binds to the promoter region of FgMYO1, and is required for the upregulation of FgMYO1 in response to phenamacril treatment. The deletion mutant of FgTFMI (ΔFgTfmI) displayed a slight growth defect, while it showed hypersensitivity to phenamacril, but not to other tested fungicides. FgTfmI also contributed to DON biosynthesis and the infection process in planta. CONCLUSIONS:The transcription factor FgTfmI plays an important role in regulating transcription of the genes involved in phenamacril tolerance, DON biosynthesis and virulence in F. graminearum. © 2019 Society of Chemical Industry.

Cellulase production in filamentous fungi is largely regulated at the transcriptional level, and several transcription factors have been reported to be involved in this process. In this study, we identified ClrC, a novel transcription factor in cellulase production in Penicillium oxalicum. ClrC and its orthologs have a highly conserved basic leucine zipper (bZIP) DNA binding domain, and their biological functions have not been explored. Deletion of clrC resulted in pleiotropic effects, including altered growth, reduced conidiation and increased sensitivity to oxidative and cell wall stresses. In particular, the clrC deletion mutant ΔclrC showed 46.1% ± 8.1% and 58.0% ± 8.7% decreases in production of filter paper enzyme and xylanase activities in cellulose medium, respectively. In contrast, 57.4% ± 10.0% and 70.9% ± 19.4% increased production of filter paper enzyme, and xylanase was observed in the clrC overexpressing strain, respectively. The transcription levels of major cellulase genes, as well as two cellulase transcriptional activator genes, clrB and xlnR, were significantly downregulated in ΔclrC, but substantially upregulated in clrC overexpressing strains. Furthermore, we observed that the absence of ClrC reduced full induction of cellulase expression even in the clrB overexpressing strain. These results indicated that ClrC is a novel and efficient engineering target for improving cellulolytic enzyme production in filamentous fungi.

Colletotrichum gloeosporioides is an important pathogen of anthracnose, which is able to infect numerous crops in tropical and subtropical regions, causing great economic losses. To investigate the fungal response to host-generated reactive oxygen species (ROS), we cloned and characterized the CgAP1 gene of C. gloeosporioides. CgAP1 encoded a bZIP transcription factor which had a bZIP DNA-binding domain and two cysteine-rich domains structurally and functionally related to Saccharomyces cerevisiae YAP1. Deletion of CgAP1 in C. gloeosporioides resulted in increasing sensitivity to HO, changes in cell wall integrity and loss of pathogenicity. To understand the regulatory network of CgAP1, RNA sequencing was used to identify differentially expressed genes in the CgAP1 mutant. It was shown that several genes involved in ROS detoxification and cell wall integrity were affected by CgAP1. Moreover, CgAP1 was also involved in many biological processes especially ribosome, cellular transport and amino acid metabolism. In conclusion, CgAP1 is an important transcription factor involved in oxidative stress, cell wall integrity and pathogenicity in C. gloeosporioides.

is a soilborne, hemibiotrophic phytopathogenic fungus that causes Fusarium crown rot and Fusarium head blight in wheat. The basic leucine zipper proteins (bZIPs) are evolutionarily conserved transcription factors that play crucial roles in a range of growth and developmental processes and the responses to biotic and abiotic stresses. However, the roles of bZIP transcription factors remains unknown in . In this study, a bZIP transcription factor Fpkapc was identified to localize to the nucleus in . A mutant strain (Δ) was constructed to determine the role of Fpkapc in growth and pathogenicity of . Transcriptomic analyses revealed that many genes involved in basic metabolism and oxidation-reduction processes were downregulated, whereas many genes involved in metal iron binding were upregulated in the Δ strain, compared with the wild type (WT). Correspondingly, the mutant had severe growth defects and displayed abnormal hyphal tips. Conidiation in the mutant was reduced, with more conidia in smaller size and fewer septa than in the WT. Also, relative to WT, the Δ strain showed greater tolerance to ion stress, but decreased tolerance to HO. The mutant caused smaller disease lesions on wheat and barley plants, but significantly increased gene expression, compared with the WT. In summary, Fpkapc plays multiple roles in governing growth, development, stress responses, and virulence in .

In phytopathogenic fungi, the HOG MAPK pathway has roles in osmoregulation, fungicide sensitivity, and other processes. The ATF1/CREB-activating transcription factor Atf1 is a regulator that functions downstream of the HOG MAPK pathway. Here, we identified a gene, designated CsAtf1, that encodes a bZIP transcription factor in Colletotrichum siamense, which is the main pathogen that causes Colletotrichum leaf fall disease in rubber trees in China. CsAtf1 localizes to the nucleus. Its mRNA expression correlates positively with that of CsPbs2 and CsHog1 in the HOG MAPK pathway in response to activator (anisomycin), inhibitor (SB203580) and fludioxonil treatments. The CsAtf1 deletion mutant showed slightly retarded mycelial growth, small conidia, slow spore germination, and abnormal appressorium formation. This mutant showed the increased spore germination rate after fludioxonil treatment and more resistance to the fungicide fludioxonil than did the wild-type fungus. However, unlike deletion of Pbs2 or Hog1, which resulted in greater sensitivity to osmotic stress, the CsAtf1 deletion induced slightly increased resistance to osmotic stress and the cell wall stress response. The ΔCsAtf1 strain also exhibited significantly reduced virulence on rubber tree leaves. These data revealed that CsAtf1 plays a key role in the regulation of fludioxonil sensitivity and in pathogenicity regulation in C. siamense.