Splinters of plastid and mitochondrial DNA in nuclear genomes of higher plants
Our previous studies revealed that nuclear genome of Arabidopsis and rice contains multiple plastid and/or mitochondrial DNA (ptDNA and mtDNA, respectively) splinters with intact copies of many organellar genes ( Shahmuradov et al, 2003 ). Recently, using the current annotations of nuclear genomes of these species, we show that nuclear copies of twelve known mitochondrial genes and five known plastid genes from Arabidopsis and rice, respectively, have known cDNA that supports occurrence of their transcription in nucleus. We also found that nuclear copies of eleven mitochondrial ORFs, annotated as hypothetical nuclear genes in Arabidopsis , are covered by long transcripts. So, nuclear copies of many organelle genes seem to be expressed in both genomes. Our findings suggest that, at least, some of these mitochondrial and plastid genes represent candidates to be evolutionary transferred to nucleus and present an intermediate stage of organelle-to-nucleus gene transfer process that continues at present time.