|Miller, Susan - Sue|
|Samac, Deborah - Debby|
Submitted to: Plant and Animal Genome VX Conference Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 1/15/2005
Publication Date: 1/15/2005
Citation: Miller, S.S., Liu, J., Graham, M., Fedorova, M., Bucciarelli, B., Catalano, C., Sherrier, J., Matsumoto, P., Samac, D.A., Gantt, S., Vance, C.P. 2005. Genome clustering of novel calcium binding proteins involved in root nodule symbiosis [abstract]. Plant and Animal Genome XIII Abstracts. Paper No. W-206, p. 49.
Technical Abstract: Changes in cellular calcium (Ca2+) concentrations, transduced by Ca2+ binding proteins, act as second messengers to affect plant growth and development. Analysis of the Medicago truncatula (Mt) EST database (www.tigr.org/tdb/mtgi/) revealed a unique set of calmodulin-like putative proteins (CaML1-6) that were expressed only in root nodules. Unlike typical calmodulins (CaMs), the novel nodule CaML proteins have N-terminal presequences and possess a variable number of Ca2+ binding EF-hands. Using recombinant CaML1 overexpressed in E. coli, we found that CaML proteins bind Ca2+. In situ hybridization and immulocalization studies showed nodule CaML mRNA and protein to be localized in the infected cells. The CaML protein is imported into the symbiosome space as evidenced by reporter gene activity of a CaML1::GFP chimeric gene and protein purification. To better understand the genomic arrangement, we isolated and characterized genes encoding Mt nodule CaMLs. Analysis of available BAC end sequences and PCR amplification of selected BAC clones showed that all six of the nodule CaML were clustered within a 150 kb region of the Mt genome. Also clustered in this region were two other nodulin genes, N25 and N22, and two putative R genes. Sequence similarity between N25 and CaMLs 1 and 2 indicate that an unequal recombination event between a progenitor CaM gene and N25 gave rise to the first nodule CaML gene. The data provide genetic and biochemical evidence for the first example of a plant gene being recruited for root nodule symbiosis.