Dissecting Drivers of Root Microbiome Composition.

Plant-associated microbial communities promote plant health by: improving nutrient acquisition, producing plant growth hormones, and protecting plants from abiotic and biotic stress. While agricultural biotechnology companies work to translate microbial mechanisms of plant growth promotion into biological products for crop yield improvement, there remain opportunities to understand plant-microbe and microbe-microbe relationships to facilitate increased consistency and widespread success of these biological products. Among key traits of successful biological products are robust colonization and reliable activity despite significant microbial competition and a sophisticated plant immune system. Rather than define mechanisms to augment plant productivity, these studies explore potential host-mediated and microbe-mediated mechanisms gating the transition from bulk soil to rhizosphere and finally into the internal root microbiome. Although the mechanisms of plant microbiome assembly are complicated and interweaving, massive parallel sequencing of plant grown in natural soils and synthetic communities composed of a well-defined mixture of bacterial root isolates has uncovered common activities associated with robust colonizers of the root microbiome. Further, these approaches have identified critical chemicals produced by plant and microbes to restrict root endosphere microbiome membership. Together, the studies described here begin to define the orchestration of multiple selective mechanisms to control root microbiome membership.