Elucidating molecular mechanisms by which seeds respond to environmental factors

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Plant hormones are low abundant signal molecules, which significantly influence a variety of processes in plant growth and development. Functional genomics research in cereals has revealed that key genetic loci for yield production and stress responses selected by the classical breeding include a series of hormone metabolism and signaling genes. The plant hormone metabolism is regulated by a number of environmental factors and plays an important role in tuning plant growth in response to changing environment. Current challenge in plant biology and biotechnology is to understand how plants sense the environmental factors and alter the plant hormone metabolism. The Nambara research group studies how plants control cellular concentrations of the plant hormone levels with a focus on abscisic acid (ABA) metabolism. We use Arabidopsis seed germination as a model system, because seeds have sophisticated mechanisms to sense environmental conditions. Mature, dry seeds contain all the components required to resume the plant’s life cycle in an appropriate environment. The seeds sense water, nutrients, temperature, after-ripening, and light to determine if the appropriate germination environment exists, and a change in these external cues alters plant hormone metabolism and signaling, which determine whether seeds germinate or remain dormant. The proposed research aims to elucidate the molecular mechanisms by which seeds sense environmental signals and regulate plant hormone metabolism, with a focus on how nitrate regulates ABA catabolism and seed germination. Nitrate is a major nitrogen source existing in soil and influences plant growth and development as a nutrient and as a signal. As a nutrient, nitrate is assimilated to ammonium and then incorporated into amino acids. As a signal, low nitrate concentration causes rapid reprogramming of genome-wide gene expression, even in mutants defective in nitrate assimilation. Nitrate promotes seed germination in many plant species. The effect of nitrate on germination can be observed in mutants defective in nitrate assimilation. This indicates that it acts as a signal to stimulate germination. My research group previously reported that nitrate activates ABA catabolism and reduces ABA, an inhibitor of germination. Despite recent identification of essential genes for nitrate sensing and signal transduction, the molecular mechanisms by which nitrate regulates ABA catabolism remain largely unknown. The overall goal of this grant is to investigate the molecular and cellular mechanisms involved in nitrate regulation of ABA metabolism and seed germination. My research group has recently identified the novel factor regulating these processes during Arabidopsis seed germination. We will elucidate the molecular function of the regulators in nitrate signaling in seeds. Stable crop yield under nitrate limited condition is a key target for plant biotechnology, because sustainable agricultural practices must limit expensive and potentially polluting nitrate inputs. Our basic research will help to gain a novel solution to increase crop yield and decrease crop losses.