DRR in chloroplast and mitochondria
According to the endosymbiotic theory of organelle evolution, plastids and mitochondria are descendants of a prokaryotic photosynthetic organism that established a symbiotic relationship with an early eukaryotic host [33]. Both organelles maintain a separate genome. Organelle genomes have not retained all genes of its ancestor because part of genes may have been lost, some of them functionally replaced by genes in the nucleus, while others have been transmitted to the nucleus [34]. Coordination of gene expression among nucleus, plastids and mitochondria is critical for plant development and survival. Although DRR in animal organelles has been studied up to some extent [35] but the role of organelle DRR in the survival and evolution of plants is less explored. However very recently few researchers have successfully demonstrated the presence of DRR processes in mitochondria and chloroplast [36,37]. Therefore, in the present study we have further predicted the cellular localization of all putative DRR genes in higher plants to gain the insight into organelles DRR. TargetP [38] prediction suggested that 17% and 10% of all DRR genes studied here in Arabidopsis were of chloroplast and mitochondrial origin respectively while 19% and 17% of rice genes were chloroplast and mitochondrial origin respectively (Figure 6). These significant similarities in number of organelle's gene probably indicated towards their strong conservation during evolution and needs further detail studies. 24 and 21 genes among Arabidopsis and rice DRR genes were prokaryotic specific. Four and eight genes among prokaryotic specific genes were predicted to be non-organeller gene. The presence of prokaryotic specific genes in nuclear genome may be due to the transfer of these genes from organelle's genome to nuclear genome during course of evolution because the migration of genetic information between mitochondria, chloroplasts and nuclei have been fundamental part of evolution and has a ongoing impact on the biology of cells.
Figure 6  Sub-cellular distributions of DRR genes. Distribution of rice and Arabidopsis DRR genes in different sub-cellular compartments.