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Title: OVEREXPRESSION OF A NODULE-ENHANCED MALATE DEHYDROGENASE INCREASES NITROGEN FIXATION IN ALFALFA

Author
item DENTON, MATTHEW - UNIV OF MINNESOTA
item SCHULZE, JOACHIM - UNIV OF MINNESOTA
item TEMPLE, STEPHEN - UNIV OF MINNESOTA
item Russelle, Michael
item ALLAN, DEBORAH - UNIV OF MINNESOTA
item Samac, Deborah - Debby
item Vance, Carroll

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/8/2002
Publication Date: 8/8/2002
Citation: Denton, M.D., Schulze, J., Temple, S.J., Russelle, M.P., Allan, D., Samac, D.A., Vance, C.P. 2002. Overexpression of a nodule-enhanced malate dehydrogenase increases nitrogen fixation in alfalfa. American Society of Plant Biologists Annual Meeting. Available: http://Z16.133.76.127/pb2002/public/P60/1042.html.

Interpretive Summary:

Technical Abstract: Malate is crucial for symbiotic dinitrogen (N2) fixation, occurring in high concentrations in N2-fixing nodules as the major carbon source for bacteroid respiration. Malate also provides carbon skeletons for the assimilation of fixed nitrogen from ammonia into amino acids and is proposed to be involved in the regulation of the nodule oxygen diffusion barrier, important for the maintenance of nitrogenase. An alfalfa nodule-enhanced malate dehydrogenase (neMDH; EC 1.1.1.37) with high affinity for the reduction of oxaloacetate to malate, was overexpressed in transgenic alfalfa using the CaMV35S promoter. Overexpression of the transgene increased neMDH transcript abundance in leaves and roots. Western blots indicated that neMDH protein concentration was increased in root and leaf tissue of transgenic alfalfa. Experiments using 15N2 labeling confirmed that transformed alfalfa had significantly higher N2 fixation rates (0.406 nmol N2/hr/plant) than control plants (0.257 nmol N2/hr/plant). Enhancing the expression of genes involved in malic acid synthesis appears to be a suitable strategy to increase nitrogen fixation in legumes.