Discovery of a Novel Signal that Enhances Germination and Seedling Growth

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Plant hormones control how and when plants grow, and how plants react to their environment. Manipulating plant hormones with chemical and genetic tools has been instrumental in the green revolution; a deeper understanding of how hormones control plant growth will likely fuel future advances in agriculture. In this project, biological sensors will be developed to detect a recently recognized plant hormone called strigolactone, and an unknown molecule in plants (KL) that controls seed germination, seedling growth, and leaf shape. The biological sensors will be used in this project to purify KL, which may be a novel hormone, and to identify genes that produce it. Discovery of KL may lead to the development of new agrichemicals or genetic modifications that promote uniform seed germination and seedling vigor, thus increasing crop yields. Strigolactone sensors will be useful tools for plant breeders to more easily develop crops with altered strigolactone levels, which can in turn influence the fertilizer requirements of crops and their susceptibility to weeds. Undergraduate students and a postdoctoral researcher will be trained in research skills and scientific communication, leading to enhancement of the scientific workforce. Research discoveries will be communicated to the public through journal publications, press releases, news articles, and local speaking opportunities.Karrikins are compounds found in smoke that promote seed germination after fire and enhance seedling vigor. The karrikin signaling pathway is highly similar to the strigolactone signaling pathway, suggesting common ancestry. A receptor that is necessary for karrikin responses, KARRIKIN INSENSITIVE 2 (KAI2), has been identified, but karrikins are unlikely to be its native ligand. The aims of this project are to (1) develop sensitive and specific biological assays to detect the unknown KAI2 ligand (KL) and strigolactones, (2) identify genes involved in KL biosynthesis, and (3) highly purify KL from plant extracts as a steppingstone toward its identification. Biological sensors for karrikins/KL and strigolactones based on transcriptional or proteolytic responses will be engineered. These bioassays will be used in genetic screens to identify KL-deficient mutants. Finally, bioassay-guided fractionation will be used to isolate KL in small molecule extracts from plants. The discovery of KL and KL biosynthesis genes will catalyze a new field of research in plant biology that impacts the understanding of seed dormancy, seedling photomorphogenesis, and leaf development. It will also provide insights into the ancestral function of the KAI2 signaling mechanism in basal land plants, which later duplicated and evolved to mediate growth control by strigolactones.