Cytokinin-microbiome interactions regulate developmental functions

Background The interaction of plants with the complex microbial networks that inhabit them is important for plant health. While the reliance of plants on their microbial inhabitants for defense against invading pathogens is well documented, the acquisition of data concerning the relationships between plant developmental stage or aging, and microbiome assembly, is still underway. The plant hormone cytokinin (CK) regulates various plant growth and developmental processes. Here, examining the relationships between plant development and microbiome assembly, we observed developmental-age dependent changes in the phyllopshere microbiome. We show that age-related shifts in microbiome content vary based on content of, or sensitivity to, CK. Results We found a developmental age associated decline in microbial richness and diversity, accompanied by a decline in the presence of growth promoting and resistance inducing Bacilli in the phyllosphere. This decline was absent from CK-rich or CK-hypersensitive genotypes. Bacillus isolates we obtained from CK rich genotypes were found to alter the expression of developmental genes to support morphogenesis and alter the leaf developmental program when applied to seedlings, and enhance yield and agricultural productivity when applied to mature plants. Conclusions Our results support the notion that CK supports developmental functions in part via the bacterial community.

Automated summary

The interaction between plants and microbial communities is crucial for plant health. This study reveals that the composition of the phyllosphere microbiome is age-dependent in plants. The richness and diversity of the microbiome decrease as the plant ages, specifically in the presence of growth-promoting and resistance-inducing Bacilli. However, this decline is not observed in genotypes with high levels of the plant hormone cytokinin (CK). Furthermore, Bacillus isolates from CK-rich genotypes show the ability to alter gene expression and enhance yield and agricultural productivity. These results suggest that CK plays a role in supporting plant development through the modulation of the bacterial community.