Plant Nuclear Genome Composition
JS (Pat) Heslop‐Harrison, University of Leicester, Leicester, UK
Thomas Schmidt, Technische Universität Dresden, Dresden, Germany
Published online: August 2012
DOI: 10.1002/9780470015902.a0002014.pub2
Abstract
The plant nuclear genome consists of deoxyribonucleic acid (DNA) divided among the chromosomes within the cell nucleus. Plant genomes contain coding and regulatory sequences for genes
and repetitive DNA. They are evolutionarily dynamic and analysis provides insights into the evolution of genes and genomes,
supporting studies of species phylogeny and plant breeding. The amount of DNA present in plant genomes, nearly constant within
one species, varies over some 2300 times between species; the majority of the difference is accounted for genome duplication,
or by various classes of repetitive DNA which may be dispersed widely along chromosomes or located in arrays at a small number
of loci. Bioinformatics and genome sequence analysis show conservation of many gene sequences across all plants. Repetitive
DNA motifs may be conserved over large taxonomic groupings or evolve rapidly. Repetitive DNA plays an important role as a
structural component of plant chromosomes (e.g. telomeres and centromeres) and affects gene regulation.
Key Concepts:
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Plant nuclear genome sizes, constant in a species, vary from 60 000 000 base pairs of DNA (written as 60 Mbp) to 150 000 Mbp,
a range of 2300 times.
-
The DNA of plant nuclear genomes is wrapped around the histone proteins to form nucleosomes, and the resulting chromatin is
organised into linear chromosomes with characteristic numbers, sizes and morphology in each species.
-
Genomes contain coding sequences, typically for 25 000–40 000 genes, and regulatory sequences, as shown by genome sequencing
and bioinformatics.
-
Size variation comes from polyploidisation, genome or chromosome duplication, and particularly amplification of DNA motifs
to give repetitive DNA.
-
Repetitive DNA consists of sequences that amplify via RNA intermediates (retrotransposons), through copying and reinsertion
of DNA (DNA transposable elements), or other mechanisms (satellite and microsatellite DNA).
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Some repetitive DNA encodes genes, in particular the 45S and the 5S ribosomal RNA genes (rDNA); other repetitive DNA has structural
roles at the telomeres or chromosomal ends and the centromeres where chromosomes attach to microtubules during segregation.
In most species, much of the repetitive DNA has no known function.
Keywords: tandemly repeated DNA; transposable elements; in situ hybridisation; chromosomes; genomes; nucleus; retrotransposons; repetitive DNA; satellite DNA; heterochromatin
References
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Further Reading
Feschotte C and
Pritham EJ
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A cornucopia of Helitrons shapes the maize genome.
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Many chapters in the ELS are relevant and up to date.
Our understanding of plant genomes continues to develop rapidly as DNA sequence information is gained. Recent papers presenting complete genome sequences often put into context and expand the general findings of all previous sequences published; see, e.g.
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Wang H,
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(2011)
The genome of the mesopolypoid crop species Brassica rapa.
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Web Links
As well as the sequences and functional annotation of proteins in the Genbank/EMBL/DDJB databases, many species have genomic databases where much of the current information about plant genomes is described. These include Arabidopsis: The Arabidopsis Information Resource, TAIR, www.arabidopsis.org (see particularly ‘education and outreach’) and The Institute for Genome Research, TIGR www.tigr.org (many genome projects).
The US National Science Foundation (the grant body funding major plant genome projects in the United States) has the ‘National Plant Genome Initiative’ and their website, www.nsf.gov, includes accessible, accurate and current information and reports.
Genome sizes of plants are given in the database at http://www.rbgkew.org.uk/cval/
