# Causes and consequences of bacterial local adaptation via MGEs in the plant microbiome

## TL;DR

This paper explores how mobile genetic elements in plant-associated bacteria help or hinder their adaptation to specific niches and affect plant hosts.

## Contribution

The paper synthesizes how large MGEs both promote and constrain bacterial local adaptation in the plant microbiome.

## Key findings

- MGEs provide rapid, niche-specific fitness advantages to bacteria.
- Fitness conflicts between MGEs and host genomes can constrain bacterial adaptation.
- MGEs influence the expansion or contraction of plant niches through bacterial interactions.

## Abstract

Adaptations that enable plant‐associated bacteria to fill disparate niches comprise a critical component of microbial diversity. Genes that confer locally adaptive bacterial traits, ranging from heavy metal resistance to pathogen or symbiont infectivity, often reside within mobile genetic elements (MGEs) that can move between genomes. While MGEs may speed microbial adaptation, they also have selfish fitness interests and potentially separate evolutionary trajectories from their host genome. MGEs can also impose physiological burdens and be limited in the transmissibility of function across hosts, which likely constrains bacterial local adaptation. Given these constraints, the prevalence of adaptive loci on potentially exploitative MGEs poses a dilemma: how do fitness conflicts and alignments between MGEs and the main replicon shape bacterial local adaptation and impact plant hosts? We synthesize research on ways MGEs confer rapid, niche‐specific fitness advantages to bacteria, identify factors that promote or constrain bacterial adaptation, and highlight MGE impacts on plants. We focus on large, self‐transmissible MGEs (islands, plasmids, and prophages; though we expect relevance to other MGEs as well) to better understand how MGEs bolster yet constrain bacterial local adaptation. We specifically explore the role of MGEs in shaping bacteria that themselves play a role in expanding or contracting the plant niche.