Genome Evolution and the Origin of Australian Crucifers

We showed previously that three endemic Australian crucifer species (Brassicaceae) have undergone a whole-genome duplication (WGD) followed by extensive and species/lineage-specific diploidization (Mandáková et al. 2010, The Plant Cell 22: 2277-2290). Some of the lowest chromosome numbers (n = 4-7) known for crucifers can be found among the Australian endemics.

The present study aimed to analyze the genome structure in species from different Australian crucifer genera by comparative chromosome painting (CCP). Ancestral Crucifer Karyotype (ACK) with eight chromosomes served as a reference genome for CCP analyses. The structure of two ACK chromosomes was investigated in 12 species belonging to nine genera (Arabidella, Ballantinia, Blennodia, Cuphonotus, Geococcus, Harmsiodoxa, Microlepidium, Phlegmatospermum, and Stenopetalum) with variable chromosome numbers (n = 4, 5, 6, and 7). As all the inspected genomic blocks were found duplicated and rearranged within the analyzed genomes, we conclude that all the genera experienced presumably the same mesopolyploid WGD event, followed by massive karyotype reshuffling toward diploid-like genomes. Mechanisms of genome diploidization will be discussed.

The phylogeny of Australian Brassicaceae species was inferred using three nuclear (chalconsynthase, phytochrome A and Luminidependens) and two plastid (ndhF and trnL-trnF) single-copy genes. Two paralogous copies of nuclear genes identified in Australian mesopolyploids support the theory of their allopolyploid origin. The results of our phylogenetic study showed that putative ancestors of Australian crucifers were presumably closely related to tribes Crucihimalayeae and Smelowskieae.

This work was supported by the European Social Fund (CZ.1.07/2.3.00/20.0189, CZ.1.07/2.3.00/30.0037).