Organisation of the plant genome in chromosomes

Abstract

SUMMARYThe plant genome is organized into chromosomes that provide the structure for the genetic linkage groups and allow faithful replication, transcription and transmission of the hereditary information. Genome sizes in plants are remarkably diverse, with a 2350-fold range from 63 to 149 000 Mb, divided into n = 2 to n = approximately 600 chromosomes. Despite this huge range, structural features of chromosomes like centromeres, telomeres and chromatin packaging are well-conserved. The smallest genomes consist of mostly coding and regulatory DNA sequences present in low copy, along with highly repeated rDNA (rRNA genes and intergenic spacers), centromeric and telomeric repetitive DNA and some transposable elements. The larger genomes have similar numbers of genes, with abundant tandemly repeated sequence motifs, and transposable elements alone represent more than half the DNA present. Chromosomes evolve by fission, fusion, duplication and insertion events, allowing evolution of chromosome size and chromosome number. A combination of sequence analysis, genetic mapping and molecular cytogenetic methods with comparative analysis, all only becoming widely available in the 21st century, is elucidating the exact nature of the chromosome evolution events at all timescales, from the base of the plant kingdom, to intraspecific or hybridization events associated with recent plant breeding. As well as being of fundamental interest, understanding and exploiting evolutionary mechanisms in plant genomes is likely to be a key to crop development for food production.

The obscure events contributing to the evolution of an incipient sex chromosome in Populus: a retrospective working hypothesis

“…Only about 4 % of higher plants are dioecious (Ainsworth 2000;Ming et al 2007;Heslop-Harrison and Schwarzacher 2011). This reproductive habit in Populus, along with the ubiquitous vegetative reproduction via root suckering, air layering, and/or cladoptosis, evolved proximally to or simultaneously with the advent of this family 65 million years ago, as nearly all members of the Salicaceae family displays these habits (Karrenberg et al 2002;Eckenwalder 1996).…”

Nucleosomes and centromeric DNA packaging

“…Typically, there are tandemly repeated satellite DNA sequences at the centromeres of chromosomes of animals and plants (4)(5)(6). Detailed work on the budding yeast Schizosaccharomyces pombe and brewer's yeast Saccharomyces cerevisiae identified relatively short DNA sequences and binding protein counterparts that direct chromosome segregation (7,8).…”

Two reported cytotypes of the emergent orchid model species Erycina pusilla are two different species

“…Comparable chromosome polymorphisms have been described in different species of the orchid family, such as Cephalanthera (Moscone et al 2007) and Paphiopedilum (Lan and Albert 2011). This variability plays a critical role in species evolution and has been considered to be a consequence of chromosome rearrangement (Faria and Navarro 2010;Heslop-Harrison and Schwarzacher 2011). Such rearrangement may increase or decrease the chromosome number in the karyotype and is termed ascending or descending dysploidy (Schubert and Lysak 2011;Leitch et al 2013;De Storme and Mason 2014;Yang et al 2014).…”