title: Benzoxazinoids in root exudates of maize attract Pseudomonas putida to the rhizosphere.
abstract: Benzoxazinoids, such as 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA), are secondary metabolites in grasses. In addition to their function in plant defence against pests and diseases above-ground, benzoxazinoids (BXs) have also been implicated in defence below-ground, where they can exert allelochemical or antimicrobial activities. We have studied the impact of BXs on the interaction between maize and Pseudomonas putida KT2440, a competitive coloniser of the maize rhizosphere with plant-beneficial traits. Chromatographic analyses revealed that DIMBOA is the main BX compound in root exudates of maize. In vitro analysis of DIMBOA stability indicated that KT2440 tolerance of DIMBOA is based on metabolism-dependent breakdown of this BX compound. Transcriptome analysis of DIMBOA-exposed P. putida identified increased transcription of genes controlling benzoate catabolism and chemotaxis. Chemotaxis assays confirmed motility of P. putida towards DIMBOA. Moreover, colonisation essays in soil with Green Fluorescent Protein (GFP)-expressing P. putida showed that DIMBOA-producing roots of wild-type maize attract significantly higher numbers of P. putida cells than roots of the DIMBOA-deficient bx1 mutant. Our results demonstrate a central role for DIMBOA as a below-ground semiochemical for recruitment of plant-beneficial rhizobacteria during the relatively young and vulnerable growth stages of maize.
authors.affiliation: Centre for Sustainable Soils and Grassland Systems, Rothamsted Research, Harpenden, Hertfordshire, United Kingdom. andy.neal@rothamsted.ac.uk
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Neal
authors.forename: Shakoor
authors.initials: S
authors.lastname: Ahmad
authors.forename: Ruth
authors.initials: R
authors.lastname: Gordon-Weeks
authors.forename: Jurriaan
authors.initials: J
authors.lastname: Ton
mesh_terms: D048588:Benzoxazines / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D018517:Plant Roots / Q000737:chemistry / Q000378:metabolism*; D016958:Pseudomonas putida / Q000235:genetics / Q000502:physiology*; D058441:Rhizosphere; D059467:Transcriptome; D003313:Zea mays / Q000737:chemistry / Q000378:metabolism* / Q000382:microbiology*
chemical_list: D048588:Benzoxazines