Evolution of St R -gene cluster in monocots species. Chromosome location, duplication and ancestry of the St gene cluster in A. sorghum, B. millet, C. rice, D. maize, and E. Brachypodium. Events preceding, (light grey) and post speciation (dark grey) are shown. F. Proposed ancestral R-gene cluster composition using an ancestral tree of grass species adapted from Bowman et al. , and phylogenetic analysis of homologous genes in each species. Genes colored in relation to St genes as follows; St1 blue, St2 red, and St3 green. Gene information is listed in Additional file 2.