LENGTH POLYMORPHISM AND ALLELE STRUCTURE OF TRINUCLEOTIDE MICROSATELLITES IN NATURAL ACCESSIONS OF ARABIDOPSIS-THALIANA

The objective of this work was to assess the degree of trinucleotide m icrosatellite length polymorphism in the selfing species Arabidopsis t haliana. PCR amplifications of 12 microsatellite loci among 49 natural populations revealed between one to eight length variants (alleles) f or each locus. The average number of alleles per locus was four and th e average genetic diversity index was 0.43. Divergence between length variants was investigated at the nucleotide level. Several observation s emerge from the sequence data: (1) for most loci, length polymorphis m results only from variations in the number of trinucleotide repeats; (2) for a few others, some variability was noted in the flanking sequ ences; (3) for compound and interrupted loci containing two arrays of trinucleotide repeats, length variations preferentially affect the lon gest one. Five of the Arabidopsis thaliana accessions were clearly com posed of two sublines. In 2 other accessions, some heterozygous indivi dual plants, probably resulting from recent outcrosses, were found. A phylogenetic tree constructed on the basis of trinucleotide microsatel lite allelic diversity shows that genetic relationships among the acce ssions are not correlated with their geographic origin.