Quorum Sensing in the Rhizosphere

Abstract

The rhizosphere is a biologically and chemically rich and diverse environment that arises through the interplay between host plant and the microorganisms that inhabit this space. The diverse microorganisms which call this region home are crucial players in determining the success and failure of the scaffold (i.e., host plant) they inhabit. Rhizosphere interactions can impact agricultural yields, disease resistance, nutrient utilization, nutrient uptake, ecological robustness, and secondary metabolite production. How this mixture of cues and signals directs the actions of potentially deleterious or beneficial microbial associations with host plants is crucial to improving agricultural yields, food safety, and our general understanding of terrestrial ecology. Frequently, symbiotic microorganisms (both pathogenic and mutualistic) within the rhizosphere tightly regulate phenotypic switching to behaviors that are relevant to their host plants based on population density, a phenomenon known as quorum sensing (QS). QS has emerged as a crucial regulatory strategy for rhizosphere behaviors such as nitrogen fixation, as well as biofilm and virulence factor production. Here we review a variety of known QS mechanisms, how biotic and abiotic factors influence QS size and persistence, the effectiveness of QS at the root surface, and provide relevant examples of QS microorganisms within the rhizosphere. We also explore how host plants have evolved to detect and respond to QS signals, as well as the potential significance of this discovery. Finally, we consider how to integrate QS processes into existing models for biotic and abiotic cycles also present at the rhizosphere.