Icelandic accession of Arabidopsis thaliana confirmed with cytogenetic markers and its origin inferred from whole-genome sequencing

In this paper, we report the first discovery of Arabidopsis thaliana in Iceland. In May 2015, the plants were located growing on warm geothermal soil around the hot spring Deildartunguhver in Reykholt, West Iceland. Flower buds and leaves were collected and used for subsequent cytogenetic analyses and DNA sequencing. Whole plant specimens were deposited at the Icelandic AMNH herbarium and were assigned accession number VA21379. The accession was found to be diploid with 2n=2x=10, as expected for this species. At meiosis I (diakinesis) it formed five normal bivalents. Ribosomal FISH mapping revealed two pairs of 5S rDNA loci and two pairs of NORs. Fine-scale chromosome painting using BAC clones specific for chromosomes At1 and At4 confirmed the standard structure of these chromosomes. Furthermore, the painting revealed an absence of the 1.17-Mb paracentric inversion on the At4 short arm in the Icelandic accession, in contrast to the inversion-bearing A. thaliana accessions more prevalent in North America. The sequencing of multiplexed whole-genome libraries identified the Swedish accession Ham-1 as the closest relative of the Icelandic accession, with, however, a markedly low SNPmatch score. We conclude that although the Icelandic accession appears to be more genetically related to populations from Scandinavia than to other European accessions, it did not originate from any of the populations represented in the global collection of the 1001 Genomes accessions of A. thaliana.