A matter of hierarchy: Activation of orfamide production by the posttranscriptional Gac-Rsm cascade of Pseudomonas protegens CHA0 through expression upregulation of the two dedicated transcriptional regulators

PATRICIO SOBRERO; ANDRES MUZLERA; JULIETA FRESCURA; EDGARDO JOFRÉ; CLAUDIO VALVERDE

Environmental Microbiology Reports

Wiley Online Library

Año: 2017 vol. 9 p. 599 - 611

1758-2229

 In this work, wesurveyed the genome of P. protegensCHA0 in order to identify novel mRNAs possibly under the control of the Gac-Rsmcascade that might, for their part, serve to elucidate as-yet-unknown functionsinvolved in the biocontrol of plant pathogens and/or in cellular processesrequired for fitness in natural environments. In view of the experimentalevidence from former studies on the Gac-Rsm cascade, we developed acomputational screen supported by a combination of sequence, structural, andevolutionary constraints that led to a dataset of 43 potential novel mRNAtargets. We then confirmed several mRNA targets experimentally and next focusedon two of the respective genes that are physically linked to the orfamide biosyntheticgene cluster and whose predicted open-reading frames resembled cognate LuxR-typetranscriptional regulators of cyclic lipopeptide clusters in relatedpseudomonads. In this report, we demonstrate that in strain CHA0, orfamideproduction is stringently dependent on a functional Gac-Rsm cascade and that bothmRNAs encoding transcriptional regulatory proteins are under direct translationalcontrol of the RsmA/E proteins. Our results have thus revealed a hierarchicalcontrol over the expression of orfamide biosynthetic genes with the final transcriptionalcontrol subordinated to the global Gac-Rsm posttranscriptional regulatorysystem.