XagR, a LuxR Homolog, Contributes to the Virulence of Xanthomonas axonopodis pv. glycines to Soybean

• Published in: Molecular plant-microbe interactions Vol. 25; no. 8; pp. 1104 - 1117
• Main Authors: Chatnaparat, Tiyakhon, Prathuangwong, Sutruedee, Ionescu, Michael, Lindow, Steven E.
• Format: Journal Article
• Language: English
• Published: St. Paul, MN APS Press 01.08.2012; The American Phytopathological Society
• Subjects: Adhesins; adhesion; Bacterial Adhesion - genetics; Bacterial plant pathogens; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Base Sequence; Biological and medical sciences; Feedback; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; gene overexpression; genes; Genome, Bacterial; Glycine; Glycine max; Glycine max - microbiology; Host-Pathogen Interactions - genetics; Infection; Inoculation; Leaves; Molecular Sequence Data; mutants; Mutation; Pathogens; Phytopathology. Animal pests. Plant and forest protection; Plant diseases; Plant Diseases - microbiology; Plant Leaves - microbiology; Plant protection; Post-transcription; Proteolysis; Rain; rainfall simulation; Regulon; Repressor Proteins - metabolism; Soybeans; topical application; Trans-Activators - metabolism; Transcription; Virulence; Virulence - genetics; Xanthomonas axonopodis; Xanthomonas axonopodis - pathogenicity; Xanthomonas axonopodis pv. glycines; Pseudomonadales; Plant pathogen; Xanthomonas axonopodis; Virulence; Glycine max; Grain legume; Plant; Leguminosae; Dicotyledones; Angiospermae; Bacteria; Pseudomonadaceae; Spermatophyta
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/MPMI-01-12-0008-R

A novel luxR homolog, termed XagR, in Xanthomonas axonopodis pv. glycines, the cause of soybean pustule, controls expression of pip, yapH, and at least 77 other genes. Although XagR and Pip are required for full virulence of X. axonopodis pv. glycines to soybean, constitutive overproduction of XagR suppresses infection. The xagR-dependent induction of pip occurs in planta only 2 days or more after inoculation. Although the transcription of xagR appears constitutive, XagR accumulates only in cells that have colonized soybean plants for more than 2 days suggesting that some components produced during the infection process mediate post-transcriptional control, likely by protecting XagR from proteolytic degradation. XagR modulates the adhesiveness of the pathogen during the infection process by suppressing the adhesin YapH. Although yapH mutants incite more infections of soybean leaves than the wild-type strain when topically applied under dry conditions, the mutant causes fewer infections when leaves are subject to simulated rain events after inoculation. Likewise, yapH mutants and cells in which XagR was overexpressed exhibited much more egress from infected leaves than the wild-type strain. Thus, XagR differentially modulates expression of a variety of genes during the infection process in response to feedback from plant molecules elaborated during infection to coordinate processes such as invasion, infection, and cell egress needed to complete the disease cycle.