The Alternaria alternata StuA transcription factor interacting with the pH-responsive regulator PacC for the biosynthesis of host-selective toxin and virulence in citrus

Yanan Chen; Yingzi Cao; Chen Jiao; Xuepeng Sun; Yunpeng Gai; Zengrong Zhu; Hongye Li

doi:10.1128/spectrum.02335-23

Microbiology Spectrum (Dec 2023)

The Alternaria alternata StuA transcription factor interacting with the pH-responsive regulator PacC for the biosynthesis of host-selective toxin and virulence in citrus

Yanan Chen,
Yingzi Cao,
Chen Jiao,
Xuepeng Sun,
Yunpeng Gai,
Zengrong Zhu,
Hongye Li

Affiliations

Yanan Chen: The Key Laboratory of Molecular Biology of Crop Pathogens and Insects of Ministry of Agriculture, The Key Laboratory of Biology of Crop Pathogens and Insects of Zhejiang Province, Institute of Biotechnology, Zhejiang University , Hangzhou, China
Yingzi Cao: The Key Laboratory of Molecular Biology of Crop Pathogens and Insects of Ministry of Agriculture, The Key Laboratory of Biology of Crop Pathogens and Insects of Zhejiang Province, Institute of Biotechnology, Zhejiang University , Hangzhou, China
Chen Jiao: The Key Laboratory of Molecular Biology of Crop Pathogens and Insects of Ministry of Agriculture, The Key Laboratory of Biology of Crop Pathogens and Insects of Zhejiang Province, Institute of Biotechnology, Zhejiang University , Hangzhou, China
Xuepeng Sun: Collaborative Innovation Center for Efficient and Green Production of Agriculture in Mountainous Areas of Zhejiang Province, College of Horticulture Science, Zhejiang Agriculture & Forestry University , Hangzhou, China
Yunpeng Gai: The Key Laboratory of Molecular Biology of Crop Pathogens and Insects of Ministry of Agriculture, The Key Laboratory of Biology of Crop Pathogens and Insects of Zhejiang Province, Institute of Biotechnology, Zhejiang University , Hangzhou, China
Zengrong Zhu: The Key Laboratory of Molecular Biology of Crop Pathogens and Insects of Ministry of Agriculture, The Key Laboratory of Biology of Crop Pathogens and Insects of Zhejiang Province, Institute of Biotechnology, Zhejiang University , Hangzhou, China
Hongye Li: The Key Laboratory of Molecular Biology of Crop Pathogens and Insects of Ministry of Agriculture, The Key Laboratory of Biology of Crop Pathogens and Insects of Zhejiang Province, Institute of Biotechnology, Zhejiang University , Hangzhou, China

DOI: https://doi.org/10.1128/spectrum.02335-23
Journal volume & issue: Vol. 11, no. 6

Abstract

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ABSTRACT The tangerine pathotype of Alternaria alternata produces a host-selective toxin termed Alternaria citri toxin (ACT). The molecular mechanisms underlying the global regulation and biosynthesis of ACT remain unknown. In the present study, the function of an APSES transcription factor StuA was investigated. StuA was shown to be required for ACT biosynthesis and fungal virulence. StuA was found, for the first time, to physically interact with a pH-responsive transcription regulator PacC using yeast two-hybrid, bimolecular fluorescence complementation, and GST pull-down assays. Functional analyses revealed that StuA and PacC regulate the expression of genes involved in toxin biosynthesis and virulence. Mutation of stuA via targeted gene deletion or silencing pacC yielded fungal strains that decreased the expression of seven toxin biosynthetic genes (ACCT) and toxin production. EMSA analyses revealed that PacC could bind to the promoters of ACTT6 encoding an enoyl-CoA hydratase and ACTTR encoding an ACT pathway-specific transcription factor. Site-directed mutagenesis of five potential protein kinase A (PKA) phosphorylation sites in StuA revealed that none of the sites was involved in ACT production, indicating that the function of StuA in the regulation of ACT gene expression is not dependent on phosphorylation. Overall, our results confirmed that PacC is one of the key regulators interacting with StuA for the biosynthesis of ACT. Environmental pH may play a decisive role during A. alternata pathogenesis. Our results also revealed a previously unrecognized (StuA-PacC)→ACTTR module for the biosynthesis of ACT in A. alternata. IMPORTANCE In this study, we used Alternaria alternata as a biological model to report the role of StuA in phytopathogenic fungi. Our findings indicated that StuA is required for Alternaria citri toxin (ACT) biosynthesis and fungal virulence. In addition, StuA physically interacts with PacC. Disruption of stuA or pacC led to decreased expression of seven toxin biosynthetic genes (ACCT) and toxin production. PacC could recognize and bind to the promoter regions of ACTT6 and ACTTR. Our results revealed a previously unrecognized (StuA-PacC)→ACTTR module for the biosynthesis of ACT in A. alternata, which also provides a framework for the study of StuA in other fungi.

Published in Microbiology Spectrum

ISSN: 2165-0497 (Online)
Publisher: American Society for Microbiology
Country of publisher: United States
LCC subjects: Science: Microbiology
Website: https://journals.asm.org/journal/spectrum

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