Collaborative Research: Root-to-Shoot Communication via the bps Signal

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Drought causes dramatic reductions in agricultural yields. An important step toward mitigating drought-associated losses is to fully understand how perception of drought causes reduced growth, and its associated impacts on agricultural production. The earliest perception of drought occurs as roots encounter dry soil, and the resulting whole-plant responses are believed to arise from a mobile chemical signal that moves from roots to shoots. The Sieburth lab has discovered a highly conserved gene family that regulates production of a root-to-shoot signal that is sufficient to induce drought responses. The goal of this research is to identify this signaling molecule. The Sieburth and Dilkes labs will use metabolomic, genetic, and gene expression based approaches. This combination of strategies should chemically identify the mobile signal and establish its relationship to other known components of root-to-shoot signaling. Knowing the chemical identity of the root-to-shoot signal could lead to development of new agricultural practices that promote greater food security.Plants drought responses include synthesis of abscisic acid (ABA) in the shoots, and decreased growth rates. Because most drought responses are measured in shoots, whereas the plant root is believed to initially detect drought conditions, scientists have long postulated a mobile root-to-shoot chemical signal that coordinates drought responses. The bypass1 (bps1) mutant of Arabidopsis has a growth-arrest phenotype caused by a graft-transmissible signal over-produced in bps1 roots. Transcriptomics and hormone measurements demonstrated that this mobile compound is sufficient to induce ABA synthesis in wild-type shoots, and genetic analyses demonstrated that growth arrest is independent of ABA. This project's goal is chemical identification of this over-produced compound. Experiments will use previously established extraction methods, fractionation by Ultra Performance Liquid Chromatography, and analysis by mass spec. Other experiments will use a labeled precursor and precursor analogs; these will clarify the structural components of the precursor that are required in the active product, and time-resolved assays using the labeled precursor should prove informative for its biosynthetic pathway. In addition, bps1 and wild type root transcriptomes will be compared, and reverse genetic analyses will be carried out to test whether differentially expressed genes are necessary to produce the mobile compound. Finally, bps1 mutants will be generated in another plant species, and its metabolome analyzed; this experiment will test the hypothesis that this drought-induced root-to-shoot compound is the same in different plant species. Diverse undergraduates and high-school students will be trained through this grant; broad outreach to under-represented groups includes interaction with local community colleges.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.