THE LUXR FAMILY TRANSCRIPTIONAL REGULATOR RFIA PLAY AN INDISPENSABLE ROLE IN PSEUDOMONAS CORRUGATA VIRULENCE ON TOMATO

Molecular studies on Pseudomonas corrugata, causal agent of tomato pith necrosis, are limited only to a few aspects. An important role is attributed to phytotoxic and antimicrobial cationic lipodepsipeptides. In a previous study we isolated the pcoI/pcoR N-acyl homoserine lactone (AHL) quorum sensin...

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Published in:Journal of plant pathology 2009-12, Vol.91 (4), p.S4.35-S4.35
Main Authors: Licciardello, G, Bertani, I, Steindler, L, Bella, P, Strano, C, Venturi, V, Catara, V
Format: Article
Language:English
Subjects:
Bacillus megaterium
Lycopersicon esculentum
Pseudomonas corrugata
Rhodotorula pilimanae
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Summary:Molecular studies on Pseudomonas corrugata, causal agent of tomato pith necrosis, are limited only to a few aspects. An important role is attributed to phytotoxic and antimicrobial cationic lipodepsipeptides. In a previous study we isolated the pcoI/pcoR N-acyl homoserine lactone (AHL) quorum sensing (QS) system which, as assessed by mutant derivatives, has an important role in virulence and in vitro antagonistic activity. Here we describe a gene, rfiA, coding for a transcriptional regulator belonging to the LuxR family located downstream the pcoI gene. RT-PCR analysis revealed that rfiA is directly linked to QS by co-transcription with pcol. In the downstream region of pcoI-rfiA, a RND (Resistance Nodulation System) transport system which is directly regulated by RfiA was identified. We found that pcol, pcoR and rfiA knock-out mutant culture filtrates are unable to inhibit the growth of Rhodotorula pilimanae and Bacillus megaterium, usually used to detect the LDP production. Moreover, time course monitoring revealed that both AHLs and LDPs are produced at high bacterial population cell densities. The role of RfiA in the development of disease symptoms in tomato was demonstrated by the absence of necrosis in stem pith tissues of plants inoculated with its mutant, as compared to those inoculated with the wild-type strain. Our data strongly suggest that P. corrugata QS regulates LPDs production through the transcriptional activator RfiA which then regulates the transcription of genes responsible for toxin production and secretion.
ISSN:1125-4653