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Reference : UMR9198-PETMER-001
Workplace : GIF SUR YVETTE
Date of publication : Monday, June 29, 2020
Scientific Responsible name : Tatiana Timtchenko
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
Ménage à Trois: The fitness landscape of the plant endophyte and phytophagous insect symbiont Burkholderia insecticola.
Diverse soil-resident Burkholderia can colonize rhizospheres and plants but the molecular mechanisms enabling them to do so remain largely unknown. We have previously shown the power of a combined RNA-seq transcriptome and Tn-seq approach to identify at a full genome scale the functions of B. insecticola required to colonize the insect host. In this project, the PhD student will use the Tn-seq approach to identify the functions required for soil and plant colonization. In the future, also RNA-seq experiments on the same sample types could be performed. Combined with the insect data set, a full description will be obtained of the fitness landscape of this bacterium in all of its known lifestyles. This will allow to compare gene functions required in these environments, which will be useful from
a fundamental perspective to understand similitudes and differences between these three different ecological niches for this bacterium. The study will furthermore offer a starting point for targeted interference with insect symbiosis as a pest control strategy while at the same time maintain or even improve the colonization capabilities of plants.
Many bacteria of the genus Burkholderia are very potent Plant-Growth Promoting Rhizobacteria (PGPR). Burkholderia can enhance plant biomass production as well as resistance against biotic and abiotic stresses. However, several species are also symbionts of phytophagous insects stimulating growth, development and fecundity of these insects, which are serious crop pests. Thus, these bacteria can be a double-edged sword for use in agriculture. The soil bacterium Burkholderia insecticola is the symbiont of the bean bug Riptortus pedestris, an insect pest of soybean and other legumes, provoking crop losses by damaging seeds, rendering them unusable for
consumption. Preliminary data confirm that this Burkholderia species can also efficiently colonize the rhizosphere of soybean plants and even infect the cortical root cells of rice plants. Thus, B. insecticola, soybean plants and bean bug insects seem to be involved in a ménage à trois in which each is interacting tightly with the other two members, either in a mutualistic, commensal or
pathogenic relationship. In recent years, we have developed in ongoing research many different approaches to unravel the molecular mechanisms of the
B. insecticola-bean bug interaction, in both the insect and in the bacteria. However, the other aspects of the lifestyle of this bacterium, its survival in the soil and the colonization of plants, are under-investigated. In this PhD project, it is proposed to investigate further in detail the capacity of the strain to colonize soils and plants and to identify the involved bacterial fitness determinants.
In more general terms, soil and rhizosphere bacteria have important functions in soil processes and in promoting plant growth and immunity. These functions are intensively studied. The genetic requirements of bacteria that enable them to colonize roots are also relatively well-studied, however those required for survival in soils are not very well known. This project will highlight the latter two issues.
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