Next-Gen Characterizations Of Wheat Radiation Hybrids Provide Functional Insights On The Speciation Of The Grasses

Radiation hybrid (RH) is a methodology that has been employed since the ‘70s to produce reliable molecular maps in many species, including mammals and plants. In wheat (Triticum species), recent efforts have focused on the molecular characterization of RH populations targeting the D-genome. Four hundred selected individuals were screened with a newly developed Roche NimbleGene platform to provide a detailed scaffold of the entire D-genome. Further, a RH population of ~1,500 individuals targeting chromosome 1D were phenotyped for the species cytoplasm specific (scs) gene, involved in the compatible interaction between nucleus and cytoplasm. The Illumina platform was coupled with bulk segregant analysis of RH lines carrying or missing the scs gene (BulkSeq RH). After investigating 1M sites, in silico and in planta analysis revealed a single gene cosegregating with the scs locus, which translates a rhomboid-like protein. Analysis of expression behavior for this gene proved consistent with what is expected for the scs locus, and the tridimensional structure of its protein has a functional mutation in an amino acid that affects its catalytic behavior. Interestingly, the scs gene is believed to have been a major player in the speciation of the Triticeae tribe. The WheatZapper synteny tool (http://wge.ndsu.nodak.edu/wheatzapper/) confirmed that the gene order surrounding the scs locus is well conserved throughout the grasses, occurring in an evolutionary stable region where two paleochromosomes and a small portion of the mitochondrial genome fused together. The colinearity conservation of this unique region, together with the knowledge that rhomboid genes originated early in the ancestral eukaryotes, suggests a phyletic evolution of the scs locus consistent with its involvement in the speciation of the whole grass family.