Detailed comparison between the wheat chromosome group 7 short arms and the rice chromosome arms 6S and 8L with special reference to genes involved in starch biosynthesis.

Rice bacterial artificial chromosome (BAC) clones have been identified that contain sequences orthologous to each EST localized to wheat chromosome 7AS deletion stocks by Southern blot hybridization. This information has been used to relate the DNA sequence included in each wheat deletion stock to a complement of rice BACs. A virtual contig was used that covered 90 cM (21 Mb) of DNA sequence (with a gap for the 6S/8L junction). Comparison of the positions of orthologous genes on the rice virtual contig and on wheat chromosome 7AS showed that there was an unexpectedly low level of synteny (31.4%) and a high level of chromosome rearrangements (68.6%). The non-syntenous loci were of two classes: wheat and rice genes found at different locations in the genome (32.6%), and ESTs in wheat not present in rice (36.0%). Four starch synthetic genes, GBSSI, SSI, SSIIa and DBEI, were located at similar positions on wheat chromosome 7AS and the virtual rice contig covering wheat chromosome 7AS. A preliminary comparison between the short arms of chromosome 7A and 7D in wheat showed that both chromosomes had a similar level of sequence synteny with rice. Therefore, there appears to be considerable variation in gene order between wheat chromosome 7S and rice chromosome 6S and 8L.