Plastid DNA
Plastid DNA (ptDNA), also known as chloroplast DNA (cpDNA or ctDNA) in photosynthetic organisms, is the DNA located in chloroplasts and other plastids. The discovery that chloroplasts contain ribosomes and perform protein synthesis revealed them to be genetically semi-autonomous.
- copies_per_old_chloroplast
- 15–20
Lore & Background
Most chloroplasts have their entire genome in a single ring, though dinophyte algae have their genome broken into about forty small plasmids. Over 95% of chloroplast DNA in corn has been observed in branched linear form rather than individual circles.
Reader's Guide
Plastid DNA is significant because it provides evidence for the endosymbiotic origin of chloroplasts from cyanobacteria. Comparison of gene sequences between cyanobacteria and chloroplast genomes confirmed this origin and revealed extensive gene transfer from the cyanobacterial ancestor to the nuclear genome. In land plants, 11–14% of nuclear DNA can be traced back to the chloroplast. The chloroplast genome encodes core photosynthetic machinery and factors for its expression, while about 95% of chloroplast proteins are encoded by nuclear genes. RNA editing within chloroplasts corrects mutations caused by the highly oxidative environment.
Did You Know?
- Over 95% of chloroplast DNA in corn has been observed in branched linear form rather than individual circles.
- In land plants, 11–14% of nuclear DNA can be traced back to the chloroplast, up to 18% in Arabidopsis.
- The parasitic Pilostyles has lost its plastid genes for tRNA.
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