|Lara Flores, Miguel|
Submitted to: International Conference on Legume Genomics and Genetics
Publication Type: Abstract Only
Publication Acceptance Date: 12/7/2008
Publication Date: 12/7/2008
Citation: Lara Flores, M., Blanco, L., Silvente, S., Gaona, Y., Vance, C.P., Reddy, P.M. 2008. Coordination between carbon and nitrogen metabolism in nitrogen fixing bean nodules [abstract]. IV International Conference on Legume Genomics and Genetics, December 7-12, 2008, Puerto Vallarta, Mexico. Abstract No. L11. p. 22. Interpretive Summary:
Technical Abstract: A cDNA clone of asparagine synthetase (AS) called PvNAS2 and two different cDNA clones of PvNADH-GOGAT were isolated from bean nodules. Southern blot analysis indicated that a small gene family encodes AS. Northern analysis demonstrated that PvNAS2 expression is induced in nodules during the early days of nitrogen fixation. Investigations with the PvNAS2 promoter gusA fusion revealed that the expression of PvNAS2 is solely localized to vascular traces and outer cortical cells, but never detected in the central nitrogen-fixing zone of the nodule. Each clone of PvNADH-GOGAT-I (7.4 kb) and PvNADH-GOGAT-II (7.0 kb), represents a unique gene in the bean genome. PvNADH-GOGAT-II expression is higher than PvNADH-GOGAT-I during nodule development. In situ hybridization and promoter expression analyses demonstrated that the NADH-GOGAT-I and –II genes are differentially expressed in bean nodules. Regulation studies of these three enzymes revealed that PvNAS2 expression is downregulated when carbon availability is reduced and the addition of glucose resulted in its induction, leading to the increased asparagine production and in the reduction of ureide content in nodules. Expression of PvNADH-GOGAT-I, but not PvNADH-GOGAT-II, is strongly inhibited by ureides. Since in bean the symbiotically assimilated nitrogen is transported from nodules to the shoot in the form of ureides, this result indicated that ammonia assimilation in bean nodules takes place through glutamine synthetase and PvNADH-GOGAT-II but not PvNADH-GOGAT-I. In light of the above results, a model is proposed in which a favorable environment is created for the efficient transfer of the amido group of glutamine for the synthesis of ureide in bean nodule.