Metabolite and light regulation of metabolism in plants: lessons from the study of a single biochemical pathway

Abstract We are using molecular, biochemical, and genetic approaches to studythe structural and regulatory genes controlling the assimilation ofinorganic nitrogen into the amino acids glutamine, glutamate, aspar-tate and asparagine. These amino acids serve as the principal nitrogen-transport amino acids in most crop and higher plants including Arabi-dopsis thaliana . We have begun to investigate the regulatory mechan-isms controlling nitrogen assimilation into these amino acids in plantsusing molecular and genetic approaches in Arabidopsis . The synthesisof the amide amino acids glutamine and asparagine is subject to tightregulation in response to environmental factors such as light and tometabolic factors such as sucrose and amino acids. For instance, lightinduces the expression of glutamine synthetase (GLN2) and repressesexpression of asparagine synthetase (ASN1) genes. This reciprocalregulation of GLN2 and ASN1 genes by light is reflected at the levelof transcription and at the level of glutamine and asparagine biosyn-thesis. Moreover, we have shown that the regulation of these genes isalso reciprocally controlled by both organic nitrogen and carbonmetabolites. We have recently used a reverse genetic approach tostudy putative components of such metabolic sensing mechanisms inplants that may be conserved in evolution. These components includean