Fine structure mapping of a gene-rich region of wheat carrying Ph1, a suppressor of crossing over between homoeologous chromosomes

The wheat gene-rich region (GRR) 5L0.5 contains many important genes, including Phi, the principal regulator of chromosome pairing. Comparative marker analysis identified 32 genes for the GRR controlling important agronomic traits. Detailed characterization of this region was accomplished by first physically localizing 213 wheat group 51-specific markers, using group.5 nulli-tetrasomics, three Phi gene deletion/insertion mutants, and nine terminal deletion lines with their breakpoints around the 5L0.5 region. The Phi gene was localized to a much smaller region within the GRR (Phi gene region). Of the 61 markers that mapped in the four subregions of the GRR, 9 mapped in the Phi gene region. High stringency sequence comparison (e < 1 x 10(-25)) Of 157 group 5L-specific wheat ESTs identified orthologs for 80% sequences in rice and 71% in Arabidopsis. Rice orthologs were present on all rice chromosomes, although most (34%) were on rice chromosome 9 (119). No single collinear region was identified in Arabidopsis even for a smaller region, such as the Phi gene region. Seven of the nine Phi gene region markers mapped within a 450-kb region on R9 with the same gene order. Detailed domain/motif analysis of the 91 putative genes present in the 450-kb region identified 26 candidates for the Phi gene, including genes involved in chromatin reorganization, microtubule attachment, acetyltransferases, methyltransferases, DNA binding, and meiosis/anther specific proteins. Five of these genes shared common domains/motifs with the meiosis specific genes Zip1, Scp1, Cor1, RAD50, RAD51, and RAD57. Wheat and Arabidopsis homologs for these rice genes were identified.