Ancient diversity of splicing motifs and protein surfaces in the wild emmer wheat (Triticum dicoccoides) LR10 coiled coil (CC) and leucine-rich repeat (LRR) domains.

In this study, we explore the diversity and its distribution along the wheat leaf rust resistance protein LR10 three-dimensional structure. Lr10 is a leaf rust resistance gene encoding a coiled coil-nucleotide-binding site-leucine-rich repeat (CC-NBS-LRR) class of protein. Lr10 was cloned and sequenced from 58 accessions representing diverse habitats of wild emmer wheat in Israel. Nucleotide diversity was very high relative to other wild emmer wheat genes (π= 0.029). The CC domain was found to be the most diverse domain and subject to positive selection. Superimposition of the diversity on the CC three-dimensional structure showed that some of the variable and positively selected residues were solvent exposed and may interact with other proteins. The LRR domain was relatively conserved, but showed a hotspot of amino acid variation between two haplotypes in the ninth repeat. This repeat was longer than the other LRRs, and three-dimensional modelling suggested that an extensive α helix structure was formed in this region. The two haplotypes also differed in splicing regulation motifs. In genotypes with one haplotype, an intron was alternatively spliced in this region, whereas, in genotypes with the other haplotype, this intron did not splice at all. The two haplotypes are proposed to be ancient and maintained by balancing selection.