DNA variation in the basic chitinase locus (ChiB) region of the wild plantArabidopsis thaliana

Nucleotide variation in a 2.2-kbp region of basic chitinase (ChiB) locus in 17 ecotypes of Arabidopsis thaliana Tvas compared with previously investig ated regions to investigate genetic mechanisms acting on DNA polymorphism. In the ChiB region, dimorphic DNA variation was detected, as in the Adh and ChiA regions. Nucleotide diversity (pi) of the entire region was 0.0091, w hich was similar to those of the two other regions. About half of polymorph ic sites (37/87) in the ChiB region were observed in only two ecotypes. Taj ima's D was negative but not significantly, while Fu and Li's D* was positi ve. Neither McDonald-Kreitman nor Hudson, Kreitman, Aguade tests showed a s ignificant result, indicating that these loci were under similar evolutiona ry mechanisms before and after speciation. Linkage disequilibria were obser ved within the three regions because of dimorphic polymorphisms. Interlocus linkage disequilibrium was not detected between the Adh and the two chitin ase regions, but was observed between the ChiA and ChiB regions. This could be due to epistatic interaction between the two chitinase loci, which are located on different chromosomes.