Control of flowering time and spike development in cereals: the earliness per se Eps-1 region in wheat, rice, and Brachypodium

The earliness per se gene Eps-A (m) 1 from diploid wheat Triticum monococcum affects heading time, spike development, and spikelet number. In this study, the Eps1 orthologous regions from rice, Aegilops tauschii, and Brachypodium distachyon were compared as part of current efforts to clone this gene. A single Brachypodium BAC clone spanned the Eps-A (m) 1 region, but a gap was detected in the A. tauschii physical map. Sequencing of the Brachypodium and A. tauschii BAC clones revealed three genes shared by the three species, which showed higher identity between wheat and Brachypodium than between them and rice. However, most of the structural changes were detected in the wheat lineage. These included an inversion encompassing the wg241-VatpC region and the presence of six unique genes. In contrast, only one unique gene (and one pseudogene) was found in Brachypodium and none in rice. Three genes were present in both Brachypodium and wheat but were absent in rice. Two of these genes, Mot1 and FtsH4, were completely linked to the earliness per se phenotype in the T. monococcum high-density genetic map and are candidates for Eps-A (m) 1. Both genes were expressed in apices and developing spikes, as expected for Eps-A (m) 1 candidates. The predicted MOT1 protein showed amino acid differences between the parental T. monococcum lines, but its effect is difficult to predict. Future steps to clone the Eps-A (m) 1 gene include the generation of mot1 and ftsh4 mutants and the completion of the T. monococcum physical map to test for the presence of additional candidate genes.