Mechanisms of chromosome rearrangements

Abstract

The striking diversity of land plants is associated with immense genetic variation manifested also by a wide range of genome sizes and chromosome numbers. Nuclear genome size across land plants varies more than 2,300-fold from ~64 Mb (Genlisea aurea; Greilhuber et al. 2006) to ~150,000 Mb (Paris japonica; Pellicer et al. 2010). Accordingly, chromosome numbers can vary from n = 2 in six angiosperm species (Vanzela et al. 1996; Cremonini 2,005) to n > 320 in the angiosperm Sedum suaveolens (Uhl 1978) and n = c. 720 in the fern Ophioglossum reticulatum (Khandelwal 1990). This extensive variation of chromosome numbers among land plants is driven by two main trends in opposite directions: chromosome numbers increase through polyploidy (whole-genome duplications, WGD) and decrease through structural chromosome rearrangements (descending dysploidy). Genomic and cytogenetic analyses indicate that probably all land plants have experienced at least one WGD event (Jaillon et al. 2009; Soltis et al. 2009; Van de Peer et al. 2009; see also Fawcett et al. 2012, this volume) followed by more or less extensive karyotype reshuffling towards diploid-like genomes (e.g. Wolfe 2001; Thomas et al. 2006; Cenci et al. 2010; Mandáková et al. 2010a). Karyotypic changes at a given ploidy level are mediated by chromosome rearrangements such as insertions, duplications, deletions, inversions and translocations altering the size and morphology of chromosomes. Centric fissions and different types of reciprocal translocations combined with meiotic (mis)segregation may lead to a reduction or increase of chromosome number (descending/ascending dysploidy).