Résumé
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► Only one putatively orthologous copy of
SymRK was detected in
Lupinus. ►
SymRK provides new useful data for phylogenetic inference in
Lupinus. ►
SymRK clarifies the relationships between Old World lupines. ►
SymRK evolves under a strong purifying selection in
Lupinus. ► There is no evidence that
SymRK is involved in rhizobial specificity in
Lupinus.
SymRK is one of the key genes involved in initial steps of legume symbiotic association with fungi (mycorrhization) and nitrogen-fixing bacteria (nodulation). A large portion of the sequence encoding the extracellular domain of SYMRK was obtained for 38 lupine accessions and 2 outgroups in order to characterize this region, to evaluate its phylogenetic utility, and to examine whether its molecular evolutionary pattern is correlated with rhizobial diversity and specificity in
Lupinus. The data suggested that, in
Lupinus,
SymRK is a single copy gene that shows good phylogenetic potential. Accordingly,
SymRK provided additional support to previous molecular phylogenies, and shed additional light on relationships within the Old World group of
Lupinus, especially among the African species. Similar to results of other studies, analyses of
SymRK sequences were unable to resolve placement of the Florida unifoliolate lineage, whose relationship was weakly supported to either the Old or the New World lupines. Our data are consistent with strong purifying selection operating on
SymRK in
Lupinus, preserving rather than diversifying its function. Thus, although
SymRK was demonstrated to be a vital gene in the early stages of the root-bacterial symbiotic associations, no evidence from present analyses indicate that this gene is involved in changes in rhizobial specificity in
Lupinus.