Symbioses: Plant, Animal, and Microbe Interactions
Hirsch, Ann M. , Yu, Nicole , Ma, Natalie , Schwartz, Allison R. , De Hoff, P.L. .
The Chamaecrista fasciculata nitrogen-fixing symbiosis.
Chamaecrista fasciculata is one of few basal Caesalpinioid legumes that develops fully functional nodules in response to Rhizobium inoculation. Recent NSF support to S. Singer, G. May, S. Cannon, and J. Doyle has led to a transcriptome analysis of shoot, root, nodule and flower tissues to gain a better understanding of evolution in this genus. However, few detailed studies have been made of Chamaecrista nodule development although Naisbitt et al. (1) showed that some of the members of the genus produce nodules with persistent infection threads whereas others have symbiosomesóbacteroids enclosed with peribacteroid membranes. We studied C. fasciculata nodule formation following inoculation with the broad-host range Rhizobium NGR234 and confirmed that the bacteria were enclosed within symbiosomes. Even so, it was not obvious from these analyses whether the rhizobial infection process initiated in root hairs as is found in advanced legumes. Although infection threads were present in root hair cells, the threads aborted and did not enter the nodules. Yet, infection threads were found within the nodule proper. One explanation for this finding is that the rhizobia enter by crack entry and develop infection threads secondarily. To pursue this hypothesis further, we inoculated C. fasciculata seedlings with rhizobial strains specifically selected for this species and also with members of the genus Burkholderia, a beta-proteobacterial species that has been found to nodulate legumes. Interestingly, we found one Burkholderia species, deficient for the canonical nod gene complement, which is capable of entering C. fasciculata nodules.
(1) Naisbitt, T., E.K. James, and J.I. Sprent. 1991. New Phytol. 122:487-492.
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1 - UCLA, Department of MCD Biology and Molecular Biology Institute, 405 Hilgard Avenue, Los Angeles, CA, 90095-1606, USA
2 - University of California-Los Angeles, Access
3 - University of California-Los Angeles, Environmental Studies
4 - University of California-Los Angeles, Dept. of Molecular, Cell and Developmental Biology
Presentation Type: Oral Paper:Papers for Topics
Location: Wasatch B/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 8:45 AM