How genes and the proteins they encode are differentially regulated in response to environmental and physiological changes is a central question in molecular biology. The genes and enzymes required for nitrate uptake and reduction in plants make up a tightly regulated pathway that responds to both internal and environmental signals including nitrate, light, circadian rhythms, hormones and CO2. This pathway plays a key role in plant growth and physiology because it (I) is required for the assimilation of nitrate, a vital source of nitrogen for plants, (II) consumes significant amounts of energy and (III) is integrally involved with other important processes such as photosynthesis, pH homeostasis and metabolite transport. In addition, nitrate assimilation serves as one of the primary processes that removes nitrate from the environment where it acts as a serious environmental and health hazard in water supplies. The long term objective of our work is to understand how the expression of genes in the nitrate assimilation pathway are regulated and coordinated in a multicellular organism that uses light as its primary source of energy. To accomplish our objective, structural genes of the nitrate assimilation pathway are being isolated and characterized and the regulatory mechanisms that control their expression and the activity of their products are being investigated. Plants defective in nitrate uptake and reduction due to mutations in nitrate transporter, nitrate reductase or molybdenum-pterin cofactor genes have been identified by selecting for mutants that are resistant to the herbicide chlorate. Three of these genes, a nitrate transporter and two nitrate reductase genes, have been cloned from Arabidopsis thaliana, a plant that offers key advantages for molecular and genetic studies. Additional genes and mutants will be sought to identify and isolate regulatory and nitrate transporter genes. The cis-acting regions responsible for the regulation of the nitrate reductase structural gene (NIA1) will be identified and characterized. The function and control of the recently discovered phosphorylation of nitrate reductase will be studied. Lastly, the function and regulation of the CHL1 nitrate transporter will be examined.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular Cytology Study Section (CTY)
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University of California San Diego
Schools of Arts and Sciences
La Jolla
United States
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Krouk, Gabriel; Ruffel, Sandrine; Gutierrez, Rodrigo A et al. (2011) A framework integrating plant growth with hormones and nutrients. Trends Plant Sci 16:178-82
Wang, Rongchen; Guan, Peizhu; Chen, Mingsheng et al. (2010) Multiple regulatory elements in the Arabidopsis NIA1 promoter act synergistically to form a nitrate enhancer. Plant Physiol 154:423-32
Krouk, Gabriel; Crawford, Nigel M; Coruzzi, Gloria M et al. (2010) Nitrate signaling: adaptation to fluctuating environments. Curr Opin Plant Biol 13:266-73