Genome hybridization: A universal way for the origin and diversification of organelles as well as the origin and speciation of eukaryotes

Abstract

The origin of organelles (mitochondrion, chloroplast and nucleus) remains enigmatic. The endosymbiotic hypothesis that chloroplasts, mitochondria and nuclei descend from the endosymbiotic cyanobacterium, bacterium and archaebacterium respectively is dominant yet uncompelling, while our discovery of de novo organelle biogenesis in the cyanobacterium TDX16 that had acquired the genome of its green algal host Haematococcus pluvialis disproves this hypothesis. In light of organelle biogenesis in the cyanobacterium TDX16 in combination with the relevant cellular and molecular evidence, we propose genome hybridization hypothesis (GHH) that the origin of organelles and origin of eukaryotes as well as the diversification of organelles and speciation of eukaryotes are unified and achieved by genome hybridization: the endosymbiotic cyanobacteria/bacteria obtain the genomes of their archaebacterial or eukaryotic hosts and hybridize with their own ones resulting in expanded genomes containing a mixture of hybrid prokaryotic genes and eukaryotic genes, and thus have to compartmentalize to accommodate different genes for specialized function of photosynthesis (chloroplast), respiration (mitochondrion) and DNA preservation (nucleus), and consequently turn into photosynthetic/heterotrophic eukaryotes. Accordingly, eukaryotes and their organelles are of multiple origins, while the formation of cancer cells is the speciation of eukaryotes as cancer cells are new species of unicellular eukaryotes arising from bacteria. Therefore, GHH provides a theoretical framework unifying evolutionary biology, cancer biology and cell biology and directing the integrated multidisciplinary research.