Widespread variation inNSP1, a gene involved in rhizobium nodulation, across species ofAcmispon(Fabaceae) from diverse habitats

Abstract

GRAS proteins comprise a large family of genes that play important roles in regulating gene expression throughout all stages of plant development. The physiological and phylogenetic breadth of GRAS proteins known among model species suggests that they may be useful as molecular genetic markers in non-model species. For example, GRAS genes involved in regulating legume–rhizobium symbioses may reveal ecological and evolutionary variation in these relationships. In this study, we collected sequences from Nodulation Signaling Protein 1 (NSP1), a gene involved in the development of an infection thread through which rhizobia enter roots, in five species of Acmispon Raf. to quantify genetic variation within and between closely related species and to compare sequence divergence in NSP1 from Acmispon with other legumes. We found a high degree of similarity of NSP1 from Acmispon with homologues in other angiosperms. Thirty-two unique alleles were identified within Acmispon, and much of this variation reflects spatial and geographic variation of sampled populations. There was no evidence of selection at the molecular level. Given the strong genetic structure found among Acmispon species, especially in a microsatellite region of the N-terminus, and the existence of homologues, NSP1 could be a useful phylogenetic marker across angiosperms.