Transcriptional Activation of Pyoluteorin Operon Mediated by the LysR-Type Regulator PltR Bound at a 22 bp lys Box in Pseudomonas aeruginosa M18

Pseudomonas aeruginosa M18, a rhizosphere-isolated bacterial strain showing strong antifungal activity, can produce secondary metabolites such as phenazine-1-carboxylic acid and pyoluteorin (Plt). The LysR-type transcriptional regulator PltR activates the Plt biosynthesis operon pltLABCDEFG, the expression of which is induced by Plt. Here, we identified and characterized the non-conserved pltL promoter (pltLp) specifically activated by PltR and its upstream neighboring lys box from the complicated pltR–pltL intergenic sequence. The 22 bp palindromic lys box, which consists of two 9 bp complementary inverted repeats interrupted by 4 bp, was found to contain the conserved, GC-rich LysR-binding motif (T-N11-A). Evidence obtained in vivo from mutational and lacZ report analyses and in vitro from electrophoretic mobility shift assays reveals that the PltR protein directly bound to the pltLp region as the indispensable binding motif “lys box”, thereby transcriptionally activating the pltLp-driven plt operon expression. Plt, as a potential non-essential coinducer of PltR, specifically induced the pltLp expression and thus strengthened its biosynthetic plt operon expression

What Determines Successful Colonization and Expression of Biocontrol Traits at the Belowground Level?

Editor: Antonieta De Cal, Paloma Melgarejo, Naresh Magan.Plants and their associated microbial communities are continuously interacting. The consequences of this complex, multi-actor dialogue are of utmost relevance for the health and development of the plant holobiont. The plant-associated microbiota is a natural source of microorganisms with plant growth-promoting abilities, including biological control agents (BCA). Plant roots are the main entrance for soilborne phytopathogens, which are also components of the belowground plant-associated microbiota. Successful root colonization by BCA is thus key for effective biocontrol against these pathogens. Colonization and biocontrol are complex processes influenced by many (a)biotic factors. Upon colonization of the target niche, effective biocontrol is then the result of diverse modes of action that BCA may display, thereby eliminating pathogens’ propagules, reducing their number, or alleviating their deleterious effects. These mechanisms are not mutually exclusive and can operate either individually or in combination, varying in time and space. Inconsistencies usually observed in biocontrol effectiveness is a consequence of numerous (a)biotic and environmental factors affecting BCA performance. A more comprehensive knowledge of colonization processes and biocontrol modes of action of BCA, and that of the diverse factors influencing them, is now possible with the support of the currently-available -omics approaches. They will definitively offer a more holistic perspective that will help to overcome the lack of success sometimes observed when implementing biocontrol measures, particularly at the field scale.Our work is currently supported by grant AGL2016-75729-C2-1-R from the Spanish Ministerio de Economía, Industria y Competitividad/Agencia Estatal de Investigación, co-financed by the European Regional Development Fund (ERDF), and by the Horizon 2020 Project ‘Microbial Uptakes for Sustainable Management of Major Banana Pests and Diseases’ (MUSA; grant number 727624)