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High rates of nucleotide substitution in nuclear small-subunit (18S) rDNA from holoparasitic flowering plants.

Authors
  • Nickrent, D L
  • Starr, E M
Type
Published Article
Journal
Journal of molecular evolution
Publication Date
Jul 01, 1994
Volume
39
Issue
1
Pages
62–70
Identifiers
PMID: 8064875
Source
Medline
License
Unknown

Abstract

Relative rate tests, using Gnetum as a reference taxon, were conducted on nuclear 18S rRNA sequences from 10 angiosperms including autotrophic nonparasites (Arabidopsis, Asarum, Glycine, Malpighia, and Zea), a chlorophyllous hemiparasite (Arceuthobium--Viscaceae), and achlorophyllous holoparasites (Balanophora--Balanophoraceae, Prosopanche--Hydnoraceae, and Rafflesia and Rhizanthes--Rafflesiaceae). Compared with Glycine, the mean number of substitutions per site (K) for five autotrophic angiosperms is 0.036 whereas for the holoparasites K = 0.126, i.e., 3.5 times higher. Comparisons of autotrophic species with short and long generation times showed no differences in K; hence, divergent rRNA sequences in the holoparasites are likely attributable to other mechanisms. These might include genetic bottlenecks, effective population size, and/or molecular drive. High substitution rates appear to be associated only with those parasitic angiosperms that have developed a highly modified haustorial system and extreme nutritional dependence upon the host. At present, high substitution rates in these parasites confound attempts to determine their phylogenetic position relative to other angiosperms.

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