2 Structure and Organization of the Arabidopsis thaliana Nuclear Genome

Abstract

The nuclear genome of Arabidopsis thaliana is unusually small for a flowering plant and has remarkably little dispersed repetitive DNA. These properties facilitate a series of different types of experiments in molecular genetics and have allowed facile cloning of many Arabidopsis genes by methods that would be difficult or impossible if the genome were larger or more typical in its content of repetitive sequences. Despite the unusual size and structure of the Arabidopsis nuclear genome, the structure of individual genes, the structure of chromosomes, the genetic properties, and the overall complement of genes in the genome are typical of those of other flowering plants.

GENOME SIZE
That A. thaliana is among the higher plants with the smallest genomes has been known for several decades: Sparrow and Miksche (1961) showed that radiation sensitivity and DNA content are related in plants. They then found that Arabidopsis is highly resistant to ionizing radiation, showing half-inhibition of vegetative growth only when exposed to 4,000 r/day of ionizing radiation. This is many-fold higher than the dose required for similar inhibition of the other plants tested. Sparrow et al. (1972) later showed a correlation of nuclear volume and genome size in plants and found A. thaliana to have the smallest nuclear volume among the angiosperms examined.

Subsequent measurements are more readily converted to quantitative estimates of nuclear genome size. Microspectrophotometry of Arabidopsis nuclei specifically stained for DNA with the Feulgen reaction indicates a haploid nuclear genome size of around 0.2 pg (~200 Mb) (Bennett and Smith...