Quorum Sensing and Plant-Induced Gene Expression in the Novel Group of Plant Beneficial and Environmental Burkholderia

Coutinho, Bruna Gonçalves (2014). Quorum Sensing and Plant-Induced Gene Expression in the Novel Group of Plant Beneficial and Environmental Burkholderia. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000efed

Abstract

The genus Burkholderia is composed of functionally diverse species and it can be divided into several groups. One of these, designated as the plant-beneficial-environmental (PBE) Burkholderia group, is formed by non-pathogenic species, which in most cases have been found to be associated with plants. It was previously established that members of the PBE group share an N-acyl-homoserine lactone (AHL) quorum-sensing (QS) system designated Bral/R that produces and responds to 3-oxo-C₁₄-HSL (OC14-HSL). In the present study, we further studied the Bral/R system in several members of the PBE group determining the AHL production profile as well its regulons. Major results include that different levels of AHLs are produced by different species and that the regulon is species specific. The biosynthesis of exopolysaccharide was the only common phenotype found to be regulated by Bral/R in several species of the PBE cluster. In addition, Bral/R was shown not to be important for plant nodulation by B. phymatum spp. nor for endophytic colonization and growth promotion of maize by B. phytofirmans PsJN. Moreover, the genome of the rice endophyte B. kururiensis M130 was sequenced and analysed in order to detect potential loci involved in its endophytic lifestyle and plant growth promotion. Two experimental approaches (plate screening of a transposon-promoter probe library and RNAseq) were then performed in order to identify loci that were regulated in response to plant macerate. The results indicated that B. kururiensis undergoes major regulatory changes affecting the expression of 27.7% of its protein coding genes. Interestingly, a great number of differentially expressed genes encode membrane transporters and secretion systems, which indicates that the exchange of molecules is an important aspect in planta. In addition, genes related to mobility, chemotaxis and adhesion were also over-represented suggesting recognition and an intimate interaction between bacteria and plant. This work highlights the close signalling taking place between plants and bacteria and helps us to understand the adaptation of an endophyte in planta.