Plant Genome Comparison - Essay Example

ecause of its relevance to biosecurity as its seeds contain high levels of highly toxic ricin protein which acts as a ribosome inactivator (Chan et al. 1). For the purpose of the genomic comparison, three studies (The Arabidopsis Genome Initiative, Ming et al. and Chan et al.) exploring the genome content of these plants have been used in the succeeding sections. The Carica papaya genome is three times larger than the Arabidopsis thaliana genome but has fewer genes. In fact, Carica papaya has lesser genes than any angiosperm so far sequenced.

Its genome size is 372 Mbp while that of Arabidopsis thaliana is 125 Mbp. The genome of Ricinus communis is also fairly larger compared to Arabidopsis thaliana but smaller than Carica papaya, having a size of 350 Mbp. Compared to the Arabidopsis thaliana genome, Carica papaya genome has lesser disease resistance gene analogues. It also has minimal angiosperm gene set and lacks a recent genome duplication, which is unusual for other angiosperm genomes so far sequenced. The genome of Carica papaya is largely euchromatic but also has highly condensed heterochromatin knobs that represent 30–35% of its genomic DNA.

In Arabidopsis thaliana genome too, there are euchromatic and heterochromatic regions. Most protein coding genes in Arabidopsis thaliana reside in the euchromatic regions while heterochromatin regions around the centromere have transposons and other repetitive sequences. In fact, in Arabidopsis thaliana account for around 10% of the genome, almost one-fifth of the intergenic DNA. The genome assembly of Ricinus communis is fairly fragmented with several megabase-sized scaffolds. Fifty percent of the Ricinus communis genome is found to be repetitive DNA, one-third of which is retrotranposons and less than 2% DNA transposons.

BLASTZ alignment studies of chromosomal segments of Carica papaya with syntenic regions in Arabidopsis thaliana have shown that 34.8% of Arabidopsis thaliana genes in any one segment correspond