Poster: Plant-symbiont interactions

Abs # 579: Identification and characterization of novel calcium binding proteins in the symbiosome space of M. truncatula nodules

Presenter:	Liu, Junqi , liuxx162@tc.umn.edu
Authors	Liu, Junqi  (A)   Miller, Sue  (D)   Bucciarelli, Bruna  (D)   Fedorova, Maria  (A)   Matsumoto, Peter  (A)   Graham, Michelle  (B)   Sherrier, Janine  (E)   Samac, Deborah  (C)   Gannt, Steve  (B)   Vance, Carroll  (A) (D)
Affiliations:	(A): Department of Agronomy and Plant Genetics, University of Minnesota (B): Plant Biology, University of Minnesota (C): Plant Pathology, University of Minnesota (D): USDA-ARS, Plant Science Research Unit (E): Department of Plant and Soil Sciences, University of Delaware

Calcium is a key messenger and has been implicated in the mediation of a variety of signaling processes including the symbiotic legume-rhizobium interaction. Calmodulins (CaMs) are the prevalent calcium sensor and Ca ²⁺ /CaM complex can regulate the function of diverse proteins, such as transcription factors, metabolic enzymes and ion channels. The specificity and subcellular nature of calcium signaling remains largely unclear. Analysis of the transcriptome in Medicago truncatula root nodules revealed a group of nodule specific transcripts encoding calmodulin-like proteins, designated as NodCaMs (for nodule specific calmodulin-like proteins). Unlike typical calmodulins (CaM) with four EF hands, these NodCaMs only have two to three EF hands. All NodCaMs are predicted to possess an N-terminal signal peptide. We have proven that fusion NodCaMs bind calcium in vitro. We also found that two of the NodCaM genes are located 2.5kb from each other in tandem orientation. A NodCaM promoter was fused to GUS and EGFP coding region and used in the transformation of Medicago sativa. Cellular expression pattern of NodCaMs correlates with the process of nodule development. Both in situ hybridization and GUS staining showed that NodCaM expression was strong in infected cells whereas little to no expression was observed in uninfected cells in mature nodules. In addition, antibody raised against NodCaM fusion protein recognized the native NodCaMs in the symbiosome space. The subcellular localization was further confirmed by the MS/MS analysis of symbiosome space protein fraction. Taken together the genomics, biochemical, histological and molecular data, these NodCaMs seem to represent a novel class of calcium sensors located in the symbiosome space with functions specific to root nodules.