Symbiosis · Bacterial leaf symbiosis: what environmental factors influence it and does it drive host plant speciation

Bacterial leaf symbiosis: what environmental factors influence it and does it drive host plant speciation

Virtually all plants interact with endosymbiotic microorganisms that inhabit various plant organs. In general, plant-bacteria interactions can be beneficial, neutral, or detrimental to the host and may play a larger role in host fitness and survival. If a form of bacterial symbiosis beneficial to the plant partner is established, the fitness of the host plant can be improved by promoting growth through, among others, increased nutrient acquisition, by enhancing plant defence by means of secondary metabolites, or by other forms of antagonistic competition. It is known that associating with bacteria can be a trigger for adaptive radiation and the establishment of new species. This project’s overall goal is to investigate the long-term effect of symbiosis on diversification patterns. Over the course of million years, did plant-bacteria interactions contribute to the establishment of the current biodiversity on our planet? Specifically, in this project, we study a particular plant-bacteria interaction that is found in the Rubiaceae plant family (or coffee family) where several of its tropical lineages harbour non- pathological endophytic bacteria in their leaves. This specific form of interaction is currently known from hundreds of species in eight genera (around 5% of the species in the family). The current hypothesis regarding the function of this symbiosis is that the endophytes are involved in the biosynthesis of secondary metabolites that provide the host plants with chemical protection against herbivory. If bacterial leaf endophytes indeed provide their hosts with a short-term beneficial effect, they may be able to increase the evolutionary potential of their hosts, which will in turn be reflected in the long-term diversification rates. Because closely related plant species with and without endophytes exist, we are able to compare them to each other and investigate if associating with endophytes influences host plant evolution. A first objective was to elucidate the likely origin in time of bacterial leaf symbiosis, which indicated when the interaction has been established. A second objective was to investigate whether the presence of endophytes had an impact on the diversification rates of the host plants because the hypothesis is that lineages with endophytes will have deviating diversification rates as a result of the symbiosis.

Data: CORDIS, © European Union