Patterns of genetic diversity and differentiation in resistance gene clusters of two hybridizing European Populus species
csal
Caseys, CelineUnit of Ecology and Evolution, Department of Biology, University of Fribourg, Chemin du Musée 10, 1700, Fribourg, Switzerland
Stölting, KaiUnit of Ecology and Evolution, Department of Biology, University of Fribourg, Chemin du Musée 10, 1700, Fribourg, Switzerland
Barbará, ThelmaUnit of Ecology and Evolution, Department of Biology, University of Fribourg, Chemin du Musée 10, 1700, Fribourg, Switzerland
González-Martínez, SantiagoDepartment of Forest Ecology and Genetics, INIA-Forest Research Centre, 28040, Madrid, Spain
Lexer, ChristianUnit of Ecology and Evolution, Department of Biology, University of Fribourg, Chemin du Musée 10, 1700, Fribourg, Switzerland
2015
Published in:
Tree Genetics & Genomes. - Springer Berlin Heidelberg. - 2015, vol. 11, no. 4, p. 1-12
English
Resistance genes (R-genes) are essential for long-lived organisms such as forest trees, which are exposed to diverse herbivores and pathogens. In short-lived model species, R-genes have been shown to be involved in species isolation. Here, we studied more than 400 trees from two natural hybrid zones of the European Populus species Populus alba and Populus tremula for microsatellite markers located in three R-gene clusters, including one cluster situated in the incipient sex chromosome region. The results indicate that all three R-gene clusters present extensive linkage disequilibrium (LD). Outlier tests suggest balancing selection as a potential driver of R-gene diversity, but divergent selection was also detected. Nucleotide-binding site leucine-rich repeat (NBS-LRR) type R-gene clusters exhibit low species differentiation and appear to be affected by shared selection pressures between species, recurrent interspecific gene flow, or both. Our results are consistent with a role for R-gene clusters in the evolution of chromosome XIX, recently put forward as an incipient sex chromosome in Populus.