Molecular cloning of the wheat CK2alpha gene and detection of its linkage with Vrn-A1 on chromosome 5A.

The casein kinase CK2 is one of the major multifunctional protein kinases in cells that is expressed ubiquitously and is essential for survival. The alpha-subunit of CK2 is thought to be involved in light-regulated gene expression and rhythmic expression of genes by circadian rhythm in plants. The rice chromosome-3 region containing the photoperiod-response Hd6 gene, an orthologue of the CK2alpha genes of Arabidopsis and maize, is in synteny with the wheat chromosome-5A Vrn-A1 region. This evidence proposes two possibilities, first the wheat Vrn-A1 is an orthologue of the rice CK2alpha, and second the wheat CK2alpha which has not yet been identified is located independently but tightly linked to Vrn-A1. To clarify whether the wheat CK2alpha gene is conserved in the Vrn-A1 region and to elucidate the above two possibilities, we attempted to isolate this gene from the wheat cDNA library and to map it on the chromosome-5A region that is syntenous to the rice Hd6 region. The isolated cDNA clone showed an extremely high homology with the Arabidopsis CK2alpha gene. Using this clone as a probe genomic Southern-blot analyses of the aneuploid lines available in Chinese Spring assigned the wheat homologue of CK2alpha to the long arm of chromosome 5A. Furthermore, a linkage analysis using an F(2) population having recombination in the Vrn-A1 region revealed that the wheat CK2alpha, designated as tck2a, is tightly linked to Vrn-A1 by 1.1 cM