A Plant Health View on Endohyphal Bacteria and Their Fungal Hosts

Abstract

Microbe-microbe interactions within the phytobiome, including those between endosymbiotic bacteria and their fungal hosts, influence plant health outcomes. Endohyphal bacteria (EHB) can modulate the virulence and survival of phytopathogenic fungi, making them both potential targets for fungal control and potential tools for exploring fungal biology. Fungal hosts may increase the fitness of bacterial symbionts, some of which act as plant pathogens themselves. These relationships can also result in an increase of microbially produced phytohormones, influencing the plant host and other symbioses. However, the functional outcome of EHB metabolites and mechanisms of change remain largely uninvestigated in most of the EHB-fungal relationships identified. Additionally, the morphological change experienced by some bacterial cells within fungi represents just one of the knowledge gaps in this field, with factors that determine bacterial and fungal partner specificity being another. Here, we compile studies of EHB from across diverse plant-associated microbes to provide a primer for EHB studies, considered through a phytobiomes lens, and comment on the directions for this emerging field.