Recruitment of novel calcium-binding proteins for root nodule symbiosis in Medicago truncatula.
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 Ca(2+)-binding gene for symbiotic purposes.
Liu
Junqi
J
Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota 55108, USA.
Miller
Susan S
SS
Graham
Michelle
M
Bucciarelli
Bruna
B
Catalano
Christina M
CM
Sherrier
D Janine
DJ
Samac
Deborah A
DA
Ivashuta
Sergey
S
Fedorova
Maria
M
Matsumoto
Peter
P
Gantt
J Stephen
JS
Vance
Carroll P
CP
D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000032:analysis* / Q000235:genetics / Q000502:physiology; D018745:Genome, Plant; D049452:Green Fluorescent Proteins / Q000032:analysis; D046913:Medicago truncatula / Q000166:cytology / Q000378:metabolism / Q000382:microbiology*; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000502:physiology; D009586:Nitrogen Fixation; D010802:Phylogeny; D010940:Plant Proteins / Q000032:analysis* / Q000235:genetics / Q000502:physiology; D018517:Plant Roots / Q000166:cytology / Q000378:metabolism / Q000382:microbiology; D011993:Recombinant Fusion Proteins / Q000032:analysis; D016415:Sequence Alignment; D013559:Symbiosis / Q000235:genetics* / Q000502:physiology
D002135:Calcium-Binding Proteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D002118:Calcium