COMPARATIVE MAPPING OF THE 2 WHEAT LEAF RUST RESISTANCE LOCI LR1 AND LR10 IN RICE AND BARLEY

The wheat genome is large, hexaploid, and contains a high amount of re petitive sequences. In order to isolate agronomically important genes from wheat by map-based cloning, a simpler model of the genome must be used for identifying candidate genes. The objective of this study was to comparatively map the genomic regions of two wheat leaf rust disea se resistance loci, Lr1 and Lr10, in the putative model genomes of ric e and barley. Two probes cosegregating with the Lr1 gene on chromosome 5DL of wheat were studied. The rice sequences corresponding to the tw o probes were isolated and mapped. The two probes mapped to two differ ent rice chromosomes, indicating that the organization of the region o rthologous to Lr1 is different in rice and wheat. In contrast, synteny was conserved between wheat and barley in this chromosomal region. Th e Lrk10 gene cosegregated with Lr10 on chromosome 1AS in wheat. The ri ce gene corresponding to Lrk10 was mapped on rice chromosome 1, where it occurred in many copies. This region on rice chromosome 1 correspon ds to the distal part of the group 3S chromosomes in Triticeae. The sy nteny is conserved between rice chromosome 1 and the Triticeae group 3 S chromosomes up to the telomere of the chromosomes. On group 3S chrom osomes, we found a gene that is partially homologous to Lrk10. We conc lude that in the genomic regions studied, there is limited and only pa rtially useful synteny between wheat and rice. Therefore, barley shoul d also be considered as a model genome for isolating the Lr1 and Lr10 genes from wheat.