Microcolinearity between the grain protein content QTL region in wheat chromosome arm

The conservation of the linear order (colinearity) of genetic markers along large chromosome segments in wheat and rice is well established, but less is known at the molecular level (microcolinearity). Previous comparative maps between these two species revealed conserved linkage between rice chromosome 2 and wheat chromosome 6. As part of our efforts to identify a locus affecting Grain Protein Content (GPC) using a positional cloning approach, we established the microcolinearity between a region on wheat chromosome 6BS, including the GPC locus, and 20.4 cM on rice chromosome 2. Blast analysis of the rice BAC sequences covering the colinear GPC region against the Triticeae EST database revealed several sequences that were used as markers in the wheat genetic map. Using this approach we mapped eleven colinear genes between wheat and rice in this region. The closest markers flanking the GPC locus were mapped 0.9 cM apart in wheat and 100-kb apart in rice. Further work is underway to complete the mapping of additional wheat ESTs identified within the 100-kb rice sequence and to construct a physical map using a tetraploid wheat BAC library that contains a T. dicoccoides 6BS chromosome segment carrying the high GPC locus (http://agronomy.ucdavis.edu/ Dubcovsky/BAC-library/BAC_Langdon.htm). These results demonstrated a high level of microcolinearity between rice and wheat in the GPC region.