Course Of Symbiogenetic Hereditary Ratchet In Plants

Evolution of life materialised the cellular world of prokaryotes somewhere3.5billion years ago. Its transition into the eukaryotic world took approximately two billion years. This transition had indeed been supported by hundreds of molecular innovations which radically transformed the populations of ancestral eukaryotes. One of the major evolutionary accomplishments of these ancestral eukaryotes is thought to be the materialisation of phagotrophy. It enabled symbiosis in the respective populations of ancestral eukaryotes. Symbioses had been producing some stable endosymbiotic consortia. More than two billion years ago, symbiogenesis appears on the evolutionary timescale and starts working on a stable consortium of an ancestral eukaryote and alpha-proteobacterium and accomplishes the transformation of endosymbiont into mitochondrium. Till that time, symbiogenetic processes selected further six confirmed endosymbiotic consortia and equipped the eukaryotic world with photosynthesis.The content of this dissertation resonates with the systematic efforts to accomplish following aims:i) to further expand the scientific understanding of symbiogenesis; ii) to highlight its role in transition of the prokaryotic world into the eukaryotic world; iii) to study the contribution of symbiogenesis in the preservation and evolution of one of the most important components of living world:membranes; iv) to track the foot-steps of symbiogenesis in the living world, and v) to produce an outlook focusing on the future impact of symbiogenetic hereditary ratchet in plants.Cellular heredity in its entirety includes organelle genomes, membranes, and ribosomes. This dissertation followed the foot-steps of symbiogenesis in two spheres of cellular heredity:(i) membrane inheritance and (ii) organelle genomes. It elaborates how symbiogenesis preserved and utilised all the important components and structures of prokaryotic membranes during the transition of prokaryotic to eukaryotic world. Foot-steps of symbiogenesis in the second sphere of cellular inheritance are elaborated with intensive computational analyses. From an extensive synthesis of literature and results of computational analyses, this dissertation learns that symbiogenetic processes show a clear tendency of emptying the endosymbiotic cellular organelles from genomes and transferring valuable hereditary information into the nucleus. This process has been working like a one way ratchet. For the plant kingdom, this dissertation names this process as "symbiogentic hereditary ratchet".In silico experiments were performed to track the course and current accomplishment of symbiogenetic hereditary ratchet in plants. To highlight the inter-compartmental DNA exchanges, homology between the plastid, mitochondrial, and nuclear genomes was studied within a species using NUCmer. Quantitative contribution of plastid (cyanobacterial) and mitochondrial (a-proteobacterial) genome in the nuclear genome was also evaluated by the statistical analysis of the results obtained from NUCmer.To see the shift in the hereditary information in the cell from a different angle, and to find the putative cyanobacterial proteins encoded by nuclear genomes of the selected plants, a computational experiment was carried out for selected8species with more than1,000cyanobacterial, other prokaryotic and fungal reference species. The results show that the organelle genes are still being ratcheted towards the nuclear genome in plants. The results for the putative cyanobacterial genes in the nuclear genome of selected species show some genes in the act of being transferred, with a nuclear as well as plastid copy.