Liangcheng Du, and
First, second, and fifth authors: College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China/Key Laboratory of Integrated Management of Crop Diseases and Pests (Nanjing Agricultural University), Ministry of Education, P. R. China; third author: International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149, Trieste, Italy; and fourth author: Department of Chemistry, University of Nebraska-Lincoln, Lincoln 68588.
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Accepted for publication 27 September 2013.
Lysobacter enzymogenes is a ubiquitous plant-associated and environmentally friendly bacterium emerging as a novel biological control agent of plant disease. This bacterium produces diverse antifungal factors, such as lytic enzymes and a secondary metabolite (heat-stable antifungal factor [HSAF]) having antifungal activity with a novel structure and mode of action. The regulatory mechanisms for biosynthesis of antifungal factors is largely unknown in L. enzymogenes. The solo LuxR proteins have been shown to be widespread, playing important roles in plant-associated bacteria. Here, we cloned and studied a solo LuxR protein, LesR, from L. enzymogenes strain OH11. Overexpression but not deletion of lesR significantly impaired HSAF biosynthesis levels and antimicrobial activities but did not show visible effect on production of major lytic enzymes. Overexpression of lesR also led to remarkably accelerated cell aggregation and induced production of a melanin-like pigment in L. enzymogenes; these two phenotypes are mediated by the diffusible factor cell-to-cell signaling system of L. enzymogenes. The C-terminus helix-turn-helix domain was shown to be critical for several lesR-controlled functions. Overall, our study provides the first example of the roles and mechanisms of a solo LuxR protein in a plant-associated L. enzymogenes.
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