Premium
Control and host‐dependent activation of insect toxin expression in a root‐associated biocontrol pseudomonad
Author(s) -
PéchyTarr Maria,
Borel Naomi,
Kupferschmied Peter,
Turner Vincent,
Binggeli Olivier,
Radovanovic Dragica,
Maurhofer Monika,
Keel Christoph
Publication year - 2013
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/1462-2920.12050
Subject(s) - biology , toxin , mcherry , mutant , microbiology and biotechnology , pseudomonas fluorescens , regulator , repressor , spodoptera littoralis , gene , gene expression , bacteria , green fluorescent protein , genetics , botany , pest analysis , noctuidae
Summary P seudomonas fluorescens CHA 0 is a root‐associated biocontrol agent that suppresses soil‐borne fungal diseases of crops. Remarkably, the pseudomonad is also endowed with systemic and oral activity against pest insects which depends on the production of the insecticidal Fit toxin. The toxin gene ( fitD ) is part of a virulence cassette encoding three regulators ( FitF , FitG , FitH ) and a type I secretion system ( FitABC‐E ). Immunoassays with a toxin‐specific antibody and transcriptional analyses involving fitG and fitH deletion and overexpression mutants identified LysR family regulator FitG and response regulator FitH as activator and repressor, respectively, of Fit toxin and transporter expression. To visualize and quantify toxin expression in single live cells by fluorescence microscopy, we developed reporters which in lieu of the native toxin protein express a fusion of the Fit toxin with red fluorescent mCherry . In a wild‐type background, expression of the mCherry ‐tagged Fit toxin was activated at high levels in insect hosts, i.e. when needed, yet not on plant roots or in batch culture. By contrast, a derepressed fitH mutant expressed the toxin in all conditions. P . fluorescens hence can actively induce insect toxin production in response to the host environment, and FitH and FitG are key regulators in this mechanism.