Partners in space: Discordant population structure between legume hosts and Rhizobium symbionts in their native range

To understand the coevolutionary dynamics of an interaction, theory suggests that we must study how genetic variation in both partners is structured in space. This is because, in coevolution, the spatial distribution of genetic variation in one species can both determine its ability to locally adapt to a partner species and also serve as an agent of selection acting on that partner species. Plant-microbe symbioses are ecologically and economically important, but broad-ranging dispersal and dynamic genome structure in bacteria present unique challenges for understanding spatial genetic processes in these systems. Here we study the model rhizobium Ensifer meliloti using a hierarchically structured sample of 191 strains from 21 sites in the native range and compare its population genetic structure to that of its host plant Medicago truncatula. We find that two of the three elements of the tripartite Ensifer genome lack a pattern of isolation by distance. Overall genetic variation across the symbiont genome is less spatially structured than that of its host, and variation in the two species is uncorrelated, indicating comparatively higher levels of gene flow among sampling sites in these bacterial symbionts relative to host plants. Taken together our results suggest that the spatial structure of genetic variation is impacted differently by the environment in the host and in the three symbiont genomic elements. This could lead to differing responses to selection not only between the host and symbiont, but also between the elements of the symbiont genome.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Plant Biology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2021

Author dc:creator

• Riley, Alexander

Contributors dc:contributor

• Heath, Katy D
• Marshall-Colon, Amy

• coevolution, mutualism, symbiosis, horizontal gene transfer, multipartite genome

Statement dc:rights

• Copyright 2020 Alexander Riley

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/109451

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/109451