Rapid evolution of the plastid translational apparatus in a nonphotosynthetic plant: loss or accelerated sequence evolution of tRNA and ribosomal protein genes.
The vestigial plastid genome of Epifagus virginiana (beechdrops), a nonphotosynthetic parasitic flowering plant, is functional but lacks six ribosomal protein and 13 tRNA genes found in the chloroplast DNAs of photosynthetic flowering plants. Import of nuclear gene products is hypothesized to compensate for many of these losses. Codon usage and amino acid usage patterns in Epifagus plastic genes have not been affected by the tRNA gene losses, though a small shift in the base composition of the whole genome (toward A+T-richness) is apparent. The ribosomal protein and tRNA genes that remain have had a high rate of molecular evolution, perhaps due to relaxation of constraints on the translational apparatus. Despite the compactness and extensive gene loss, one translational gene (infA, encoding initiation factor 1) that is a pseudogene in tobacco has been maintained intact in Epifagus.
Wolfe
K H
KH
Department of Biology, Indiana University, Bloomington 47405.
Morden
C W
CW
Ems
S C
SC
Palmer
J D
JD
D000595:Amino Acid Sequence; D001483:Base Sequence; D005075:Biological Evolution; D002736:Chloroplasts; D003062:Codon / Q000235:genetics; D017343:Genes, Plant; D016678:Genome; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010940:Plant Proteins / Q000235:genetics*; D014176:Protein Biosynthesis / Q000235:genetics; D011544:Pseudogenes / Q000235:genetics; D012343:RNA, Transfer / Q000235:genetics*; D012269:Ribosomal Proteins / Q000235:genetics*
D003062:Codon; D010940:Plant Proteins; D012269:Ribosomal Proteins; D012343:RNA, Transfer