Circadian interactions between plants and microorganisms

Life on Earth evolved in environmental conditions that fluctuate with a daily cycle. Organisms from all kingdoms of life, including plants and their associated microorganisms, harbour circadian clocks as an adaptation to these environmental changes. We review the involvement of circadian clocks in associations between plants and microbes, focusing first on mechanisms of specific circadian clock-regulated plant-microbe interactions. We then discuss more general ecological and evolutionary consequences of clock regulation of plant-microbe interactions and argue that circadian clocks can choreograph complex plant-microbe community interactions across multiple levels of biological organisation. We also discuss the difficulties in determining the precise nature of interactions in such communities, for both individual rhythmic interactions and the emergent rhythmic properties of these communities. An understanding of the regulation of these interactions by circadian clocks is likely to have implications for crop performance, fertiliser and pesticide use, soil and ecosystem health, biogeochemical cycling, and the impacts of global warming.