Patterns of genomic integration of nuclear chloroplast DNA fragments in plant species.

The transfer of organelle DNA fragments to the nuclear genome is frequently observed in eukaryotes. These transfers are thought to play an important role in gene and genome evolution of eukaryotes. In plants, such transfers occur from plastid to nuclear [nuclear plastid DNAs (NUPTs)] and mitochondrial to nuclear (nuclear mitochondrial DNAs) genomes. The amount and genomic organization of organelle DNA fragments have been studied in model plant species, such as Arabidopsis thaliana and rice. At present, publicly available genomic data can be used to conduct such studies in non-model plants. In this study, we analysed the amount and genomic organization of NUPTs in 17 plant species for which genome sequences are available. The amount and distribution of NUPTs varied among the species. We also estimated the distribution of NUPTs according to the time of integration (relative age) by conducting sequence similarity analysis between NUPTs and the plastid genome. The age distributions suggested that the present genomic constitutions of NUPTs could be explained by the combination of the rapidly eliminated deleterious parts and few but constantly existing less deleterious parts.