CHARACTERIZATION OF THE CALMODULIN GENE FAMILY IN WHEAT - STRUCTURE, CHROMOSOMAL LOCATION, AND EVOLUTIONARY ASPECTS

Calmodulin is a ubiquitous transducer of calcium signals in eukaryotes . In diploid plant species, several isoforms of calmodulin have been d escribed. Here, we report on the isolation and characterization of cal modulin cDNAs corresponding to 10 genes from hexaploid (bread) wheat ( Triticum aestivum). These genes encode three distinct calmodulin isofo rms; one isoform is novel in that it lacks a conserved calcium binding site. Based on their nucleotide sequences, the 10 cDNAs were classifi ed into four subfamilies. Using subfamily-specific DNA probes, calmodu lin genes were identified and the chromosomal location of each subfami ly was determined by Southern analysis of selected aneuploid lines. Th e data suggest that hexaploid wheat possesses at least 13 calmodulin-r elated genes. Subfamilies 1 and 2 mere both localized to the short arm s of homoeologous-group 3 chromosomes; subfamily 2 is located on all t hree homoeologous short arms (3AS, 3BS and 3DS), whereas subfamily 1 i s located only on 3AS and 3BS but not on 3DS. Further analysis reveale d that Aegilops tauschii, the presumed diploid donor of the D-genome o f hexaploid wheat, lacks a subfamily-1 calmodulin gene homologue, wher eas diploid species related to the progenitors of the A and B genomes do contain such genes. Subfamily 3 was localized to the short arm of h omoeologous chromosomes 2A, 2B and 2D, and subfamily 4 was mapped to t he proximal regions of 4AS, 4BL and 4DL. These findings suggest that t he calmodulin genes within each subfamily in hexaploid wheat represent homoeoallelic loci. Furthermore, they also suggest that calmodulin ge nes diversified into subfamilies before speciation of Triticum and Aeg ilops diploid species.