Diversification of Lrk/Tak kinase gene clusters is associated with subfunctionalization and cultivar-specific transcript accumulation in barley.

Lrk (Lr10 receptor-like kinase) and Tak (Triticum aestivum kinase) belong to the receptor-like kinase (RLK) supergene family in higher plants. Three Lrk/Tak gene regions spanning greater than 600 kb were identified via a genome-wide survey of barley gene-rich BAC clones. Two Lrk/Tak gene clusters are positioned on barley chromosome 3 (3H) and another is localized on chromosome 5 (1H), with each Lrk and Tak open reading frame physically positioned in a back-to-back orientation. Thirteen new Lrk/Tak-like fragments were cloned from the two clusters on 3H and the single cluster on 1H, respectively, and compared phylogenetically with other grass Lrk/Tak-like genes, including a 280-kb Lrk/Tak cluster on rice chromosome 1S. Physically clustered Lrk/Tak-like genes always form monophyletic groups; this suggests that the primary mechanism of expansion of the Lrk/Tak RLK super family was by tandem duplication, of which most members were duplicated after speciation of the Poaceae. Cultivar-dependent transcript accumulation of some Lrk/Tak family members on 3H, as revealed via Barley1 GeneChip microarray analysis, is consistent with the hypothesis of subfunctionalization of Lrk/Tak members following tandem duplication.