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A Single Mutation in the oprF mRNA Leader Confers Strict Translational Control by the Gac/Rsm System in Pseudomonas fluorescens CHA0

Alvarez Crespo, María Cecilia, Valverde, Claudio
Current microbiology 2009 v.58 no.2 pp. 182-188
Pseudomonas fluorescens, crops, cucumbers, cultivars, messenger RNA, mutants, mutation, nucleotide sequences, plant pathogenic fungi, porins, roots, secondary metabolites, tomatoes
The rhizobacterium Pseudomonas fluorescens CHA0 is able to antagonize fungal phytopathogens on a variety of crop plants, mainly due to the production of secondary metabolites that are coordinately upregulated by the global regulatory Gac/Rsm cascade. The two-component system GacS/GacA activates transcription of the three small regulatory RNAs RsmX, RsmY, and RsmZ, which counteract translational repression of target mRNAs by RsmA and RsmE proteins. In a search for novel Gac/Rsm targets based on the minimal sequence on mRNA leaders required for RsmA/RsmE control, the leader region of the major porin OprF emerged as a candidate. Although an isogenic CHA0 oprF mutant showed a reduced ability to attach to cucumber and tomato roots, suggesting a role for OprF in root colonization as a requisite for pathogen antagonism, a translational oprF'-'lacZ fusion was weakly regulated by Gac/Rsm despite its high sequence similarity to the hcnA leader. A single base substitution put the modified oprF 5'-UTR under strict control by Gac/Rsm. The results highlight the subtle sequence requirements of Gac/Rsm targets.