Laboratory of Plant Systematics
Benny Lemaire
Co-evolution in bacteriophilous Psychotria (Rubiaceae)
Introduction
Bacterial nodules in roots are widely distributed among legumes and other families of angiosperms. Bacterial leaf nodulation on the other hand is less common. Bacterial leaf symbiosis has been reported in the monocot family Dioscoreaceae and in two eudicot families, i.e. Myrsinaceae and Rubiaceae of which the latter family have received the most attention.
Rubiaceae have the largest number of species with bacterial leaf nodules, found in three genera, i.e. Pavetta (ca. 250 species), Psychotria (ca. 80 species) and Sericanthe (11 species). Recent work has concentrated on physiological aspects of the symbiosis in Psychotria. The presence of the endosymbiont seems obligatory for the survival of the Psychotria host plant. Loss of the bacteria showed a clear effect on the hormone metabolism of the plant. This interaction combined with a closed symbiotic cycle leads to the hypothesis that both partners diversified together resulting in cospeciation.
Scientific Goals
Testing this hypothesis using modern phylogenetic analysis will contribute to our knowledge in the evolution of bacterial leaf symbiosis in Psychotria. Nuclear and chloroplast markers will be used to infer phylogenetic relationships within Psychotria and the bacterial endosymbionts. Using the resulting topologies, the degree of coevolution between symbiont and host will be investigated. Furthermore, the phylogeny will be calibrated using the available fossil record in order to date the origin of bacterial leaf symbiosis in Psychotria. The results of this research will undoubtedly improve our scientific knowledge about this fascinating symbiotic interaction between plants and bacteria.
This doctoral research project is supported with a financial grant from the Institute for the Promotion of Innovation by Science and Technology in Flanders (IWT).
