Plants associate closely with some soil microorganisms and engage with them in beneficial relationships near the root surface. It is expected that beneficial microbes can support plants to be resilient to stresses in the environment, such as drought. However, it is not well understood how microbes are recruited to the root during stress or which members of the diverse soil microbial community are most responsive during stress. This research will investigate how microorganisms respond to plant hormones that signal stress. Understanding the dynamic relationships between soil microbes and plants during stress is important for anticipating, and potentially managing, expected changes in plant performance given environmental and land-use changes. This project will assess how soil microorganisms alter their growth and activities when exposed to plant hormones, quantify how the molecules released from roots change during stress and assess the responses of microbes to those changes, and determine how members of soil microbial communities collectively respond to plant stress signals in natural and controlled environments. This work has broad significance for understanding plant resilience, with expected outcomes of national interest for agriculture and land management, food and energy security, sustainability, and general soil health. It will also benefit society by providing quantitative scientific workforce training and community outreach at Michigan State University's Science Festival and other public campus events. <br/><br/>The objective of the research is to understand the rules of assembly and function of the rhizosphere microbiome given exposure to plant hormones that signal stress. For plants, root microbiome recruitment and assembly is facilitated through the soil, which provides the physical, chemical, and biological context for plant-microbiome engagement. Soil harbors a rich reservoir of microbial diversity, but up to 80% of microorganisms in soil are dormant and have inaccessible functional potential. When plants are stressed, they release metabolites into the soil that could serve as signals to microorganisms. This research aims to: 1) uncover bacterial responses in growth and resuscitation to stress phytohormones; 2) to quantify microbial community dynamics and interactions given plant stress signals; and 3) to identify members of complex soil microbial communities that resuscitate and assemble to the rhizosphere during stress. A multi-scale approach will be used that combines in vivo quantification of bacterial responses to phytohormones, synthetic microbiome construction and manipulation, and in situ experiments of rhizosphere microbiome dynamics in soil. This research is expected to decipher rules governing microbiome dynamics when plants are stressed. A foundational understanding of the interactions between plants, microorganisms and the environment will facilitate management of microbiomes towards desired functions, and will support goals towards sustainable agriculture and food and energy security.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.