DNA polymorphism, haplotype structure and balancing selection in the leavenworthia PgiC locus

A study of DNA polymorphism and divergence was conducted for the cytosolic phosphoglucose isomerase (PGI:E.C.5.3.1.9) gene of five species of the must ard genes Leavenworthia: Leavenworthia stylosa, L. alabamica, L. crassa, L. uniflora, and L. torulosa. Sequences of all interval 2.3-kb PgiC gene regi on spanning exons 6-16 were obtained from 14 L. stylosa plants from two nat ural populations and from one to several plants for each of the other speci es. The level of nucleotide polymorphism in L. stylosa PgiC gene was quite high (pi = 0.051, theta = 0.052). Although recombination is estimated to be high ill this locus, extensive haplotype structure was observed for the en tire 2.3-kb region. The L. stylosa sequences fall into at least two groups, distinguished by the presence of several indels and nucleotide substitutio ns, and one of the three charge change nucleotide replacements within the r egion sequenced correlates with the haplotypes. The differences between the haplotypes are older than between the species, and the haplotypes ale stil l segregating in at least two of five species studied. There is no evidence of recent or ancient population subdivision that could maintain distinct h aplotypes. The age of the haplotypes and the results of Kelly's Z(nS) and W all's B and Q tests with recombination suggest that the haplotypes are main tained due to balancing selection at or near this locus.