Abstract
The basic leucine zipper (bZIP) transcription factor (TF) family, one of the largest and the most diverse TF families, is widely distributed across the eukaryotes. It has been described that the bZIP TFs play diverse roles in development, nutrient utilization, and various stress responses in fungi. However, little is known of the bZIP members in Cytospora chrysosperma, a notorious plant pathogenic fungus, which causes canker disease on over 80 woody plant species. In this study, 26 bZIP genes were systematically identified in the genome of C. chrysosperma, and two of them (named CcbZIP05 and CcbZIP23) significantly down-regulated in CcPmk1 deletion mutant (a pathogenicity-related mitogen-activated protein kinase) were selected for further analysis. Deletion of CcbZIP05 or CcbZIP23 displayed a dramatic reduction in fungal growth but showed increased hypha branching and resistance to cell wall inhibitors and abiotic stresses. The CcbZIP05 deletion mutants but not CcbZIP23 deletion mutants were more sensitive to the hydrogen peroxide compared to the wild-type and complemented strains. Additionally, the CcbZIP23 deletion mutants produced few pycnidia but more pigment. Remarkably, both CcbZIP05 and CcbZIP23 deletion mutants were significantly reduced in fungal virulence. Further analysis showed that CcbZIP05 and CcbZIP23 could regulate the expression of putative effector genes and chitin synthesis-related genes. Taken together, our results suggest that CcbZIP05 and CcbZIP23 play important roles in fungal growth, abiotic stresses response, and pathogenicity, which will provide comprehensive information on the CcbZIP genes and lay the foundation for further research on the bZIP members in C. chrysosperma.
Highlights
Introduction published maps and institutional affilTranscription factors (TFs) are involved in all kinds of biological processes, such as cellular growth, differentiation, and the response to environmental factors, through modulating the expression of downstream genes
The results showed that both CcbZIP05 and CcbZIP23 contribute to the fungal development, stress response, and pathogenicity of C. chrysosperma
The result showed responses, the fungal growths of the wild-type, ΔCcbZIP05/ΔCcbZIP23, that ∆CcbZIP23 mutants formed fewer pycnidia than wild-type and ∆CcbZIP23-1/C strains and (Figure 6D,E), while ∆CcbZIP05 mutants had no difference in the number of pycnidia compared with the wild-type (Figure S3). These results showed that CcbZIP05 and CcbZIP23 were involved in the fungal growth, and CcbZIP23 regulated the conidial production and pigment formation in C. chrysosperma
Summary
Transcription factors (TFs) are involved in all kinds of biological processes, such as cellular growth, differentiation, and the response to environmental factors, through modulating the expression of downstream genes. Their roles, including specific promoter sequences binding to transcriptional inhibition or activation, interaction with other TFs or molecular chaperones, as well as post-translational modifications, are crucial to regulating the transcription of target genes [1,2,3,4]. The bZIP proteins, widely distributed in eukaryotes, are regarded as one of the central regulators functioning in various biological processes in pathogenic fungi, such as fungal iations.
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