A study of the phylogeny of Brassica rapa, B. nigra, Raphanus sativus, and their related genera using noncoding regions of chloroplast DNA

Authors: Yang Y-W.¹; Tai P-Y.¹; Chen Y.¹; Li W-H.²

Source: Molecular Phylogenetics and Evolution, Volume 23, Number 2, May 2002 , pp. 268-275(8)

Publisher: Academic Press

Abstract:

There are two evolutionary lineages in the genusBrassica: the rapa/oleracea lineage and the nigralineage. Using nuclear DNA sequences such as the intergenic spacer between 5S rRNA genes and the internal transcribed spacer between 18S and 25S rRNA genes, we and others had previously demonstrated that Raphanus sativus is closely related to the nigra lineage. In the present study, we sequenced the chloroplast noncoding region between trnT andtrnF and that between trnD and trnT in seven species and showed that R. sativus is more closely related to therapa/oleracea lineage than to the nigra lineage. The conflicting results from nuclear DNA and chloroplast DNA support the hypothesis that Raphanus was derived from a hybridization between therapa/oleracea and the nigra lineages. We estimated the date of this hybridization event to be 60% of the divergence time between the two Brassica lineages. In addition, the pattern and rate of nucleotide substitution were studied. There were more transversions than transitions in these noncoding regions, which have a high AT content. Furthermore, the proportion of transversions among the substitutions at a site increases with increasing A + T content of its two adjacent nucleotides. An influence of immediate 5 pyrimidine on substitution pattern is also observed when both adjacent bases in the two DNA strands are A or T. The rate of nucleotide substitution in the trnL group I intron is only about one third of the rate in the nearby intergenic spacers in the trnT–trnF fragment. The rate of nucleotide substitution in the rapa/oleracea lineage is at least 1.5 times that in the nigra lineage.

© 2002 Elsevier Science (USA)

Language: English

Document Type: Research article

Affiliations: 1: Institute of Botany, Academia Sinica, Taipei 11529, Taiwan 2: Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637, USA

Publication date: 2002-05-01

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• In this Subject: Biology
• By this author: Yang Y-W. ;  Tai P-Y. ;  Chen Y. ;  Li W-H.

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