Recruitment of novel calcium-binding proteins for root nodule symbiosis in Medicago truncatula

Junqi Liu, Susan S. Miller, Michelle Graham, Bruna Bucciarelli, Christina M. Catalano, D. Janine Sherrier, Deborah A. Samac, Sergey Ivashuta, Maria Fedorova, Peter Matsumoto, J. Stephen Gantt, Carroll P. Vance

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


Legume rhizobia symbiotic nitrogen (N2) fixation plays a critical role in sustainable nitrogen management in agriculture and in the Earth's nitrogen cycle. Signaling between rhizobia and legumes initiates development of a unique plant organ, the root nodule, where bacteria undergo endocytosis and become surrounded by a plant membrane to form a symbiosome. Between this membrane and the encased bacteria exists a matrix-filled space (the symbiosome space) that is thought to contain a mixture of plant- and bacteria-derived proteins. Maintenance of the symbiosis state requires continuous communication between the plant and bacterial partners. Here, we show in the model legume Medicago truncatula that a novel family of six calmodulin-like proteins (CaMLs), expressed specifically in root nodules, are localized within the symbiosome space. All six nodule-specific CaML genes are clustered in the M. truncatula genome, along with two other nodule-specific genes, nodulin-22 and nodulin-25. Sequence comparisons and phylogenetic analysis suggest that an unequal recombination event occurred between nodulin-25 and a nearby calmodulin, which gave rise to the first CaML, and the gene family evolved by tandem duplication and divergence. The data provide striking evidence for the recruitment of a ubiquitous Ca2+-binding gene for symbiotic purposes.

Original languageEnglish (US)
Pages (from-to)167-177
Number of pages11
JournalPlant physiology
Issue number1
StatePublished - May 2006


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