Sequence and analysis of chromosome 2 of the plant Arabidopsis thaliana

Arabidopsis thaliana (Arabidopsis) is unique among plant model organisms in having a small genome (130-140 Mb), excellent physical and genetic maps, a nd little repetitive DNA. Here we report the sequence of chromosome 2 from the Columbia ecotype in two gap-free assemblies (contigs) of 3.6 and 16 meg abases (Mb). The latter represents the longest published stretch of uninter rupted DNA sequence assembled from any organism to date. Chromosome 2 repre sents 15% of the genome and encodes 4,037 genes, 49% of which have no predi cted function. Roughly 250 tandem gene duplications were found in addition to large-scale duplications of about 0.5 and 4.5 Mb between chromosomes 2 a nd 1 and between chromosomes 2 and 4, respectively. Sequencing of nearly 2 Mb within the genetically defined centromere revealed a low density of reco gnizable genes, and a high density and diverse range of vestigial and presu mably inactive mobile elements. More unexpected is what appears to be a rec ent insertion of a continuous stretch of 75% of the mitochondrial genome in to chromosome 2.