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POSTERS: Molecular plant-microbe interactions

Negative regulation of siderophore biosynthesis by a GATA transcription repressor in Alternaria alternata
Hsien-Che Lin - National Chung Hsing University and Academia Sinica, Taichung and Taipei, Taiwan. Pei-Ching Wu- National Chung Hsing University, Kuang-Ren Chung- National Chung Hsing University, Hsiao Chun Chen- National Chung Hsing University

Iron acquisition and storage in all cells must be carefully regulated to avoid iron-induced toxicity. Alternaria alternata produces a dimethyl coprogen siderophore to acquire iron from surrounding environment. The ability to acquire iron is also required for detoxification of reactive oxygen species and virulence. Genetic analysis reveals that a SreA gene encoding a GATA type transcription factor negatively regulates siderophore production. A. alternata strains lacking SreA (?sreA) increase siderophore production by 3.7-fold compared to wild type. ?sreA displays wild-type virulence in citrus, even though the mutant reduces 77% radial growth of wild type grown on PDA. An iron chelator and EDTA partially rescue mutant growth. ?sreA reduces 43% growth on minimal medium and slightly increases sensitivity to iron, potassium superoxide, and H2O2. However, ?sreA decreases sensitivity to diethyl maleate, rose Bengal, eosin Y, Congo red, and calcofluor white. The expression of SreA is induced by iron and repressed by H2O2, and negatively regulated by the oxidative stress-responsive transcription activator Yap1. Deletion of SreA leads to the increased expression of the genes involved in siderophore biosynthesis and transportation and reductive iron assimilation. EMSA reveals that the E.coli-expressed SreA protein could bind the promoter of the Nps6 gene encoding a nonribosomal peptide synthetase required for siderophore biosynthesis. Our results demonstrate that SreA plays a profound role in iron homeostasis and cellular sensitivity to xenobiotics.