Validation of CAPS marker WR003 for the leaf rust resistance gene Lr1 and the molecular evolution of Lr1 in wheat

The wheat leaf rust resistance gene Lr1 encodes a typical coiled-coil nucleotide-binding site leucine-rich repeat (CC-NBS-LRR) of resistance protein containing 1 344 amino acids. WR003, a cleaved amplified polymorphic sequence (CAPS) marker is derived from the LRR regions of Lr1. In this study, a worldwide collection of 120 Aegilops tauschii accessions and 282 hexaploid wheat varieties was screened for Lr1 alleles using WR003, and the specificity of WR003 for Lr1 was confirmed by pathogenicity tests and genotype analysis. The sequence alignment and phylogenetic tree analysis of 38 Lr1 haplotypes provided a further view of the molecular evolution of Lr1. The results showed that there were very few polymorphisms between the Lr1 alleles from Ae. tauschii and hexaploid wheat with the same resistance phenotype. The polymorphisms of the Lr1 haplotypes were mainly between the different resistance lines, rather than between the different ploidy levels. These results indicate that Lr1 originated from Ae. tauschii and differentiated into resistant and susceptible genotypes before its introgression into hexaploid wheat. Therefore, it is likely that wheat Lr1 has at least two major variants for disease resistance and susceptibility, and except for certain point mutations, few gene conversions and genetic re-combinations occurred during the hexaploid wheat domestication.