Abstract/Details

Rates of nucleotide substitution in higher plants and mammals

Wolfe, K.H.   Trinity College Dublin (University of Dublin) (Ireland) ProQuest Dissertations Publishing,  1990. U022583.

Abstract (summary)

The molecular evolution of genes in higher plants (angiosperms) and mammals has been investigated by comparison of nucleotide sequences. Nuclear genes in the two kingdoms have approximately equal mean absolute rates of synonymous nucleotide substitution. Silena substitutions accumulate in genes of plant mitochondrial, chloroplast and nuclear genomes in the approximate ratio 1:3:12. Since the mitochondrial genome of mammals is known to evolve 5 - 10 times faster than nuclear DNA, the rate in plant mitochondrial DNA (mtDNA) is perhaps 100 times slower than that in mammalian mtDNA. This contrasts with the rapid rate of structural rearrangement seen in plant (but not mammalian) mtDNA. Within the chloroplast genome, genes located in the inverted repeat (IR) region have an approximately fourfold lower rate of nucleotide substitution (both at silent sites in codons, and in noncoding DNA) than genes in single-copy regions of the genome. This suggests that there may be differences between the DNA repair mechanisms of single-copy and IR chloroplast DNA. Rates of nonsynonymous nucleotide substitution in chloroplast genes vary considerably among different plant lineages, as does the substitution rate in a chloroplast-encoded ribosomal RNA gene. Application of the molecular clock principle to sequences of chloroplast genes and of nuclear ribosomal RNA genes suggests that monocot and dicot plants last shared a common ancestor about 200 million years ago. This considerably predates the first appearance of angiosperms in the fossil record, and supports the controversial hypothesis that the early evolution of angiosperms occurred in habitats refractory to fossilisation. Dates are also estimated for the divergences between angiosperms and cycads, and between Chlamydomonas and the green algal lineage that gave rise to land plants. Nuclear genes vary considerably in synonymous substitution rate and base composition (G+ C content), both in mammals, and in plants of the grass family. In mammals, substitution rates in pseudogenes and at silent sites in functional genes are approximately equal, which suggests that silent sites are effectively neutral and that the differences among genes are due to variation in the rate and pattern of mutation rather than to selective constraints on codon usage. A theoretical model of DNA replication is developed which shows that parallel variation in mutation rate and base composition can arise if the concentrations of deoxyribonucleotides in the nucleus change during S-phase (the part of the cell cycle in which DNA replication occurs). Data on the silent substitution rate and base composition in 153 genes compared between mouse and rat shows that the real situation is more complicated than that predicted by the model. However, genes located close together on the chromosome tend to show similar substitution rates and base compositions, which supports the contention that the variation in these quantities reflects local variation in mutation processes. This phenomenon may underlie the `isochore' structure of mammalian and grass plant genomes.

Indexing (details)


Subject
Genetics
Classification
0369: Genetics
Identifier / keyword
(UMI)AAIU022583; Biological sciences
Title
Rates of nucleotide substitution in higher plants and mammals
Author
Wolfe, K.H.
Number of pages
1
Degree date
1990
School code
0770
Source
DAI-C 70/05, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
University/institution
Trinity College Dublin (University of Dublin) (Ireland)
University location
Ireland
Degree
Ph.D.
Source type
Dissertation or Thesis
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
U022583
ProQuest document ID
301416258
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
https://www.proquest.com/docview/301416258/