Rhizosphere microbes influence host circadian clock function

The circadian clock is an important determinant of individual fitness that is entrained by local conditions. In addition to known abiotic inputs that entrain the circadian clock, individual pathogenic soil bacteria affect the circadian period of plant hosts. Yet, in nature, plants interact with diverse microbial communities including hundreds to thousands of microbial taxa, and the effect of these communities on clock function remains unclear. In Arabidopsis thaliana, we used diverse rhizosphere inoculates and both wild-type and clock mutant genotypes to test the effect of complex rhizosphere microbial communities on the host circadian clock. Host plants with an intact rhizosphere microbiome expressed a circadian period that was closer to 24 hrs in duration and significantly shorter (by 60 minutes on average) relative to plants grown with a disrupted microbiome. Wild-type host genotypes differed significantly in clock sensitivity to microbiome treatments, where the effect was most pronounced in the Landsberg erecta genotype and least in the Columbia genotype. Rhizosphere microbes collected from a host genotype with a short-period phenotype (toc1-21) and used as inoculate significantly shortened the long-period phenotype of the ztl-1 clock mutant genotype. The results indicate that complex rhizosphere microbial communities significantly affect host clock function.