Greater than the sum of their parts: characterizing plant microbiomes at the community-level

•Each plant microbiome type differs predictably with its surrounding environment.•While most soil microbes are dormant, the bulk of rhizospheric microbes are active.•Plant microbiomes contribute to plant health by multiple mechanisms simultaneously. Specific subsets of microbes are capable of assembly into plant-associated communities that influence the fitness of both the host and the microbes. While there is a large spectrum of plant phenotypes cause by microbes, the microbial community members benefit from living in protected and nutrient rich plant-associated environments. Recent advances in ‘-omics’ technologies have provided researchers with the ability to identify and assign functions to even unculturable microbes inhabiting both above-ground and below-ground plant tissues. Thus, we are beginning to unravel the molecular mechanisms of microbiome assembly and activities that contribute to overall plant health, not only for individuals, but also at the community-level.