Generation of a YAC contig encompassing the extra glume gene, eg, in rice

We have used DNA markers from a high density molecular map of rice (Oryza sativa) to tag a single gene expressed as a flower morphogenesis mutation, extra glume (eg). Using an F2 population segregating for eg, obtained from a cross between IR24 and F136 (eg/eg), we constructed a partial molecular map and located eg relative to restriction fragment length polymorphism markers. The region between two markers appears to span the eg locus on rice chromosome 1 and extends to a genetic length of 3.8 cM. The yeast artificial chromosome (YAC) library obtained from rice variety 'Nipponbare', which carries the wild-type allele of eg, was screened to completely cover the locus by overlapping YAC clones. The eg allele should be contained in two overlapping YACs. YAC size determination by pulsed-field gel electrophoresis indicated that this region has a physical length of approximately 400 kb. We anticipate that the tagging of eg in a relatively short stretch of DNA will allow a molecular characterization of this gene through map-based cloning. Key words : rice, gene tagging, YAC contig, flower morphogenesis, extra glume.