Dynamic evolution of NBS-LRR genes in bread wheat and its progenitors

Extensive studies have focused on the largest class of disease resistance genes (nucleotide binding site-leucine-rich repeat, NBS-LRR) in various plants. However, no research on the dynamic evolution of these genes in domesticated species and their progenitors has been reported. Recently published genome sequences of bread wheat and its two ancestors provide a good opportunity for comparing NBS-encoding genes between ancestors and their progeny. Over 2000 NBS-encoding genes have been identified in bread wheat, which is the largest number having been reported so far. Compared with other grass species, its two progenitors also contained more NBS-encoding genes, indicating that there was an expansion of these genes in their common ancestor. Interestingly, the inherited relationships of NBS-LRR genes among the bread wheat and its two progenitors were ambiguous and only 3 % single-copy orthologues retained gene order in three-way genome comparisons of the three genomes. Lots of NBS-encoding genes present in the either ancestor could not be found in the bread wheat. These results indicated that NBS-LRR genes in bread wheat might have evolved rapidly through a rapid loss of ancestor genes.