Abstract
BackgroundPachycladon cheesemanii is a close relative of Arabidopsis thaliana and is an allotetraploid perennial herb which is widespread in the South Island of New Zealand. It grows at altitudes of up to 1000 m where it is subject to relatively high levels of ultraviolet (UV)-B radiation. To gain first insights into how Pachycladon copes with UV-B stress, we sequenced its genome and compared the UV-B tolerance of two Pachycladon accessions with those of two A. thaliana accessions from different altitudes.ResultsA high-quality draft genome of P. cheesemanii was assembled with a high percentage of conserved single-copy plant orthologs. Synteny analysis with genomes from other species of the Brassicaceae family found a close phylogenetic relationship of P. cheesemanii with Boechera stricta from Brassicaceae lineage I. While UV-B radiation caused a greater growth reduction in the A. thaliana accessions than in the P. cheesemanii accessions, growth was not reduced in one P. cheesemanii accession. The homologues of A. thaliana UV-B radiation response genes were duplicated in P. cheesemanii, and an expression analysis of those genes indicated that the tolerance mechanism in P. cheesemanii appears to differ from that in A. thaliana.ConclusionAlthough the P. cheesemanii genome shows close similarity with that of A. thaliana, it appears to have evolved novel strategies allowing the plant to tolerate relatively high UV-B radiation.
Highlights
Pachycladon cheesemanii is a close relative of Arabidopsis thaliana and is an allotetraploid perennial herb which is widespread in the South Island of New Zealand
Phylogenetic analysis of Pachycladon species based on five single-copy nuclear genes indicated that one of the genome copies was derived from the Arabidopsis lineage, while another was similar to both Arabidopsis and Brassica lineages [5]
Distinct expression of UV-B radiation-inducible genes in Pachycladon cheesemanii and Arabidopsis thaliana To further examine the UV-B radiation responses in P. cheesemanii and A. thaliana, we identified the P. cheesemanii homologues of 11 A. thaliana genes that function in the UVB-resistance 8 (UVR8)-dependent pathway and three homologues that play a role in the UVR8-independent pathway
Summary
Pachycladon cheesemanii is a close relative of Arabidopsis thaliana and is an allotetraploid perennial herb which is widespread in the South Island of New Zealand. Pachycladon is an allopolyploid genus of the Brassicaceae family with eight perennial species endemic to the South Island of New Zealand and one species to Tasmania (Australia). These Pachycladon species are believed to have originated around 1–3.5 million years ago in New Zealand and are primarily distributed across the alpine regions of the South Island [1, 2]. Pachycladon cheesemanii is the most widespread of the Pachycladon species with a Pachycladon’s allopolyploid genome (2n = 20) consists of two subgenomes which resulted from intra- or interspecific crossing [3].
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