Positive selection in the leucine-rich repeat domain of Gro1 genes in Solanum species

In pathogen resistant plants, solvent-exposed residues in the leucine-rich repeat (LRR) proteins are thought to mediate resis- tance by recognizing plant pathogen elicitors. In potato, the gene Gro1-4 confers resistance to Globodera rostochiensis. The investigation of variablity in different copies of this gene represents a good model for the verification of positive selection mechanisms. Two datasets of Gro1 LRR sequences were constructed, one derived from the Gro1-4 gene, belonging to dif- ferent cultivated and wild Solanum species, and the other belonging to paralogues of a resistant genotype. Analysis of non- synonymous to synonymous substitution rates (Ka/Ks) highlighted 14 and six amino acids with Ka/Ks >1 in orthologue and paralogue datasets, respectively. Selection analysis revealed that the leucine-rich regions accumulate variability in a very specific way, and we found that some combinations of amino acids in these sites might be involved in pathogen recognition. The results confirm previous studies on positive selection in the LRR domain of R protein in Arabidopsis and other model plants and extend these to wild Solanum species. Moreover, positively selected sites in the Gro1 LRR domain show that coevolution mainly occurred in two regions on the internal surface of the three-dimensional horseshoe structure of the domain, albeit with different evolutionary forces between paralogues and orthologues.