Molecular regulation of functions of Pseudomonas protegens by primary metabolites in the rhizosphere: Systematic analyses and applications to agriculture.

Pseudomonas protegens and related strains exert protective effects in plants by producing a wide range of secondary metabolites and extracellular enzymes that contribute to the suppression of plant pathogens in the rhizosphere. Our genomic and metabolomic studies on P. protegens demonstrated that intracellular low-molecular-weight effectors, such as guanosine tetraphosphate, fumarate, and γ-aminobutyrate, function as important signals in niche adaptation to plant roots. Extra- and intracellular levels of fumarate and succinate correlated with the regulation of secondary metabolism. We then investigated the involvement of exogenous amino acids in plant protection by P. protegens against Pythium damping off and root rot in cucumber. Among the amino acids tested, glutamate exerted positive effects on the efficacy of plant protection by P. protegens. The promoter activities of genes involved in the regulation of functions were characterized in detail, and we noted the dose-dependent regulation of functions in response to exogenous glutamate. In this mini-review, we introduce our previous findings on pseudomonads in terms of effective and ecological applications of this bacterium. The effective regulation of root-colonizing pseudomonads in the rhizosphere using extracellular signals that affect biocontrol activity will lead to advances in research on plant-microbe interactions.