Symbiosis-specific expression of Rhizobium etli casA encoding a secreted calmodulin-related protein.
Symbiosis between Rhizobium and its leguminous host requires elaborate communication between the partners throughout the interaction process. A calmodulin-like protein, termed calsymin, was identified in Rhizobium etli; a calmodulin-related protein in a Gram-negative bacterium had not been described previously. Calsymin possesses three repeated homologous domains. Each domain contains two predicted EF-hand Ca(2+)-binding motifs. Ca(2+)-binding activity of calsymin was demonstrated on purified protein. R. etli efficiently secretes calsymin without N-terminal cleavage of the protein. The gene encoding calsymin, casA, is exclusively expressed during colonization and infection of R. etli with the host. Expression of casA is controlled by a repressor protein, termed CasR, belonging to the TetR family of regulatory proteins. Mutation of the casA gene affects the development of bacteroids during symbiosis and symbiotic nitrogen fixation.
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F. A. Janssens Laboratory of Genetics, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001, Heverlee, Belgium.
Schoeters
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Vanderleyden
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Michiels
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D000595:Amino Acid Sequence; D002135:Calcium-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D002147:Calmodulin / Q000096:biosynthesis / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D010944:Plants / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D012231:Rhizobium / Q000235:genetics / Q000378:metabolism; D013559:Symbiosis
D002135:Calcium-Binding Proteins; D002147:Calmodulin