Developmental and Structural Section
Hirsch, Ann M. , Ou, Patricia C. , Tran, Huong , Yoshimatsu, Kei , Lum, Michelle R. , De Hoff, P.L. , Fujishige, Nancy .
Symbiosis in the Caesalpinioid Legumes, Chamaecrista fasciculata and Gleditsia triacanthos.
The nitrogen-fixing mutualism between rhizobia and legumes is one of the best-studied interactions between plants and bacteria. Two major groups of rhizobia, 1) alpha-proteobacteria, i.e. the family Rhizobiaceae (alpha-rhizobia), and 2) certain beta-proteobacteria, Burkholderia and Cupriavidus (beta-rhizobia), inhabit legume root nodules, converting inert atmospheric nitrogen into ammonia, which is assimilated by plants into proteins and nucleic acids. Surprisingly, little is known about the interactions with alpha-rhizobia for the Caesalpinioid legumes, the most basal of the three sub-classes of the legume family, and nothing is known about beta-rhizobial interactions. Although more than 80% of Mimosoid and Papilionoid legumes nodulate, less than 30% of the Caesalpinioid species form nodules. Thus, they represent a transition from non-nodulating to nodulating legumes and can help tease out the evolutionary origins of nodule formation. Chamaecrista fasciculata is one of the few Caesalpinioid legumes that nodulates; it forms indeterminate nodules, but Gleditsia triacanthos is non-nodulating. Both species establish mycorrhizal associations, but so far few studies have been made of this important symbiotic interaction in either species. Because of the strong developmental and evolutionary connection between nodulation and mycorrhization (see Hirsch, Lum, and Downie, 2001. Plant Physiol. 127: 1484-1492), we are investigating the details of both symbiotic interactions in these two basal legumes. We have already cloned one of the genes common to the Nod-/Myc- pathway from G. triacanthos, and are developing a hairy root transformation system to test the function of this gene by RNAi.
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1 - UCLA, Dept. of MCD Biology and Mol Biol Institute, 405 Hilgard Avenue, Los Angeles, California, 90095, USA
2 - Univ. Calif. Los Angeles, Department of Mol, Cell & Develop Biology, 405 Hilgard Avenue, Los Angeles, Calif., 90095-1606, USA
3 - Loyola Marymount University, Dept. of Biology, 1 LMU Drive, Los Angeles, Calif., 90045, USA
4 - UCLA, Molecular Biology Institute, Los Angeles, CA, 90095, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 28th, 2008
Time: 8:45 AM