APS Abstracts of Presentations

Evidence that the SyrF regulatory protein directly controls the syr-syp genes dedicated to phytotoxin production by Pseudomonas syringae
Presenter: N. Wang, Texas A&M University, College Station, TX, USA
Co-Author(s): S. Lu, Mississippi State University, MS, USA; A. Records, Texas A&M University, College Station, TX, USA; D. Gross, Texas A&M University, College Station, TX, USA
Phytopathology 95:S109

The production of syringomycin and syringopeptin by P. syringae pv. syringae is controlled by the salA and syrF regulatory genes. The objective of this study was to test the hypothesis that SyrF, which is a member of the LuxR regulatory protein family and controlled by SalA, directly binds to the promoter regions of the syr-syp genes and operons involved in toxin synthesis and secretion. Microarray analysis with 70-mer oligonucleotides established that all the syr-syp genes belong to the salA/syrF regulon. Bioinformatic analyses showed that syr-syp genes and operons share high similarity in the promoter regions. The 10/35 promoter regions of operons III and IV were defined based on deletion and site-directed mutagenesis analyses of sypA::uidA and syrB1::uidA reporters with GUS assays. A conserved motif, GACAGACGC, around the 35 region, was identified for all the individual genes and operons. Gel shift analysis demonstrated that the overexpressed and purified MBP-SyrF, but not the MBP-SalA fusion protein, bound to the upstream region of syrB1. In vitro cross-linking experiments followed by Western blotting analysis indicated that both proteins form dimers or trimers. These results revealed that the SyrF regulatory protein is critical to expression of the syr-syp gene clusters and directly binds to the promoter regions of syr-syp genes and operons.

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