Rampant Gene Loss in the Underground Orchid Rhizanthella gardneri Highlights Evolutionary Constraints on Plastid Genomes

Since the endosymbiotic origin of chloroplasts from cyanobacteria 2 billion years ago, the evolution of plastids has been characterized by massive loss of genes. Most plants and algae depend on photosynthesis for energy and have retained ∼110 genes in their chloroplast genome that encode components...

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Bibliographic Details
Published in:Molecular biology and evolution 2011-07, Vol.28 (7), p.2077-2086
Main Authors: Delannoy, Etienne, Fujii, Sota, Colas des Francs-Small, Catherine, Brundrett, Mark, Small, Ian
Format: Article
Language:English
Subjects:
Algae
Bayes Theorem
Chloroplasts - genetics
Cluster Analysis
Cyanobacteria
Environmental Sciences
Evolution
Evolution, Molecular
Flowers & plants
Gene Deletion
Genes, Plant
Genome, Plant
Genomes
Genomics
Orchidaceae
Orchidaceae - genetics
Orchidaceae - physiology
Parasitic plants
Photosynthesis
Photosynthesis - genetics
Phylogeny
Plants - genetics
Plastids
Protein Biosynthesis - genetics
Ribonucleic acid
RNA
RNA, Transfer - genetics
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Summary:Since the endosymbiotic origin of chloroplasts from cyanobacteria 2 billion years ago, the evolution of plastids has been characterized by massive loss of genes. Most plants and algae depend on photosynthesis for energy and have retained ∼110 genes in their chloroplast genome that encode components of the gene expression machinery and subunits of the photosystems. However, nonphotosynthetic parasitic plants have retained a reduced plastid genome, showing that plastids have other essential functions besides photosynthesis. We sequenced the complete plastid genome of the underground orchid, Rhizanthella gardneri. This remarkable parasitic subterranean orchid possesses the smallest organelle genome yet described in land plants. With only 20 proteins, 4 rRNAs, and 9 tRNAs encoded in 59,190 bp, it is the least gene-rich plastid genome known to date apart from the fragmented plastid genome of some dinoflagellates. Despite numerous differences, striking similarities with plastid genomes from unrelated parasitic plants identify a minimal set of protein-encoding and tRNA genes required to reside in plant plastids. This prime example of convergent evolution implies shared selective constraints on gene loss or transfer.
ISSN:0737-4038
1537-1719
DOI:10.1093/molbev/msr028