SolRgene
SolRgene
Rx allele mining study
A survey of 1000 accessions across 200 species from the genus Solanum resulted in the identification of four novel functional orthologues of the disease resistance gene Rx1 in the wild potato species S. lepthophyes/sparsipilum, S. albicans, S. stenotonum and S. hondelmannii, Rx3, Rx4, Rx5 and Rx6, respectively, conferring extreme resistance to potato virus X (PVX). Functional analysis of the genes resulted in a specific hypersensitive response in an agroinfiltration assay on leaves of N. benthamiana in the presence of the elicitor of Rx1-mediated resistance. And an extreme resistance response was observed in a gene-for-gene-specific manner upon PVX infection of the corresponding genotypes. Our findings of Rx3, Rx4, Rx5 and Rx6, together with Rx1 from S. tuberosum ssp. andigena and Rx2 from S. acaule, represents the first example of functional orthologues from the class of NBS-LRR resistance genes, in six different plant species. Comparison within a dataset of 77 Rx1/Gpa2 homologues derived from 12 Solanum species with a nucleotide sequence similarity of 69 to 98% showed remarkable high similarity (>97%) of the LRR domain between the functional Rx orthologues and suggests that strong evolutionary constraints affect this part of the protein in order to maintain the Rx recognition specificity. Analysis for positive selection revealed very significant positive selection on codon sites within the LRR domain, but also within the CC- and NBS- domain. The occurrence of similar sequence exchange tracks in homologues isolated from different Solanum species indicates that interallelic exchanges took place before speciation. A line-up of species taxonomy with the structure and function of Rx shows that the Rx orthologues are of ancient origin derived from one ancestral gene and that Rx mediated PVX recognition arose before the groups of Tuberosa (Peru), Tuberosa (Bolivia, Argentina, Chile) and Acaule/Demissum diverged.