Fast Diploidization in Close Mesopolyploid Relatives ofArabidopsis   

Abstract

Mesopolyploid whole-genome duplication (WGD) was revealed in the ancestry of Australian Brassicaceae species with diploid-like chromosome numbers (n = 4 to 6). Multicolor comparative chromosome painting was used to reconstruct complete cytogenetic maps of the cryptic ancient polyploids. Cytogenetic analysis showed that the karyotype of the Australian Camelineae species descended from the eight ancestral chromosomes (n = 8) through allopolyploid WGD followed by the extensive reduction of chromosome number. Nuclear and maternal gene phylogenies corroborated the hybrid origin of the mesotetraploid ancestor and suggest that the hybridization event occurred ;6 to 9 million years ago.The four, five, and six fusion chromosome pairs of the analyzed close relatives of Arabidopsis thaliana represent complex mosaics of duplicated ancestral genomic blocks reshuffled by numerous chromosome rearrangements. Unequal reciprocal translocations with or without preceeding pericentric inversions and purported end-to-end chromosome fusions accompanied by inactivation and/or loss of centromeres are hypothesized to be the main pathways for the observed chromosome number reduction. Our results underline the significance of multiple rounds of WGD in the angiosperm genome evolution and demonstrate that chromosome number per se is not a reliable indicator of ploidy level.

Molecular phylogeny and systematics of the tribe Chorisporeae (Brassicaceae)

“…However, considerable progress has recently been made both in phylogeny and systematics at the generic and tribal levels Bailey et al 2006;Beilstein et al 2006Beilstein et al , 2008Al-Shehbaz and Warwick 2007;Koch et al 2007;Warwick et al 2007;German and Al-Shehbaz 2008a;Mandáková and Lysak 2008;Koch and Al-Shehbaz 2009;Franzke et al 2009;German et al 2009; Electronic supplementary material The online version of this article (doi:10.1007/s00606-011-0452-0) contains supplementary material, which is available to authorized users. Khosravi et al 2009;Mandáková et al 2010;Couvreur et al 2010). As a result, a robust, phylogenetically supported classification system of 44 tribes encompassing ca.…”

Polyploid Evolution of the Brassicaceae during the Cenozoic Era

“…Postpolyploidy gene retention and subsequent genome evolution are also influenced by an interplay of both relative and absolute gene dosage constraints (Birchler and Veitia, 2007;Freeling, 2009;Bekaert et al, 2011;Hudson et al, 2011). Based on the age of WGDs, polyploid species are classified as neo-, meso-, or paleopolyploids (Mandáková et al, 2010b). Neopolyploids are the most recently formed polyploids (for example, Brassica napus), which are characterized by increased genome size, higher chromosome number, redundant gene content, and extant diploid ancestors (Ramsey and Schemske, 2002;Mandáková et al, 2010b).…”

“…Based on the age of WGDs, polyploid species are classified as neo-, meso-, or paleopolyploids (Mandáková et al, 2010b). Neopolyploids are the most recently formed polyploids (for example, Brassica napus), which are characterized by increased genome size, higher chromosome number, redundant gene content, and extant diploid ancestors (Ramsey and Schemske, 2002;Mandáková et al, 2010b). With the passage of time, neopolyploids evolve into mesopolyploids and subsequently into paleopolyploids by undergoing diploidization through gene loss (fractionation) and extensive rearrangement of genetic material (Song et al, 1995;Lynch and Conery, 2000;Wolfe, 2001).…”

The effect of different genome and cytoplasm on meiotic pairing in maize newly synthetic polyploids

“…Maize, Z. perennis and their hybrids is a good model system for allopolyploid study Allopolyploid, which plays a crucial role in plant speciation, probably undergoes genome change after formed (Mandakova et al 2010). Interestingly, in the newly synthesized allopolyploid, corresponds to a nature one, genome will change rapidly, if there is no corresponding nature allopolyploid, whereas genome will change slowly (Comai 2000).…”

“…In some neoallopolyploids, comparing with the parents, genome, which is not a simple accumulation, can change fast or in a long time (Mandakova et al 2010;Schnable et al 2012). The increased genes and genome dosages in neoallopolyploids can result in genome instability, such as chromosome imbalance, meiosis chaos, sequence loss and gene mutation (Wendel 2000;Levy and Feldman 2002;Liu and Wendel 2002;Chen 2007;Jackson and Chen 2010).…”