Analysis of adaptive ribosomal gene diversity in wild plant populations from contrasting climatic environments

Plant populations may contain variation that reflects adaptation to local environmental conditions. Clues to adaptive evolution of plants may be found in the genomes of species growing in diverse environments or across steep environmental gradients, and under stress. We have examined populations of wild relatives of barley and rice across diverse environmental gradients. Greater diversity, in a nuclear biotic stress defense gene and in chloroplast genes, was found in the more stressed, hotter and dryer environments. This may reflect the greater heterogeneity of these environments. Adaptation of plants to different abiotic stresses (temperatures and levels of water availability) may also require significant adaptation to the different biotic (pest and disease) pressures in these environments. Plants growing across environmental gradients revealed greater diversity in a defense gene (Isa) in more stressed, hotter and dryer environments.2 Chloroplast genome diversity also exhibited a similar variation with environment.3 We now report analysis of nuclear ribosomal genes from the same wild population. Two contrasting environments did not show significant differences in the level of diversity. However the pattern of SNP distribution within the rDNA did vary with greater SNP density in the RNA coding sequences compared with the internal transcribed spacers.