Map-based gene isolation in cereal genomes

Map-based cloning is a good strategy for gene isolation, if insertion mutagenesis-based forward and reversed genetic tools are not available for the genome of interest. Despite its universal potential, MBC is challenging in species with large genomes (e.g. wheat, maize, barley), and in context of cereal species can presently be considered routine only in the smallgenome crop and model-plant species, rice. In recent years, MBC has been successfully achieved in almost all cereals for one or more genes, due to the recent availability of whole genome sequences particularly in rice, and other genomic resources in all cereals. Still, even in an optimal progression of chromosome walking in Triticeae species the procedure remains laborious. However, resources have improved dramatically over the past five years and reached a level that any attempt of MBC is facilitated significantly. Especially for synteny-based gene isolation or for marker saturation, the completion of the rice genomic sequence provides a very important milestone of improved resources. Furthermore, the public availability of cereal genome research data via numerous databases has made essential information easly accessible. Progress in structural and functional genomics will facilitate further the map-based cloning of important genes in all cereals, although the isolation of QTLs may stay challenging. The importance of map-based cloning is increasing especially for sorghum and maize with the availability of dense physical maps and the genomic sequences (maize), so that several genes are likely to be isolated from these crops by positional cloning in the present decade.