The CoRR hypothesis for genes in organelles

Abstract

Chloroplasts and mitochondria perform energy transduction in photosynthesis and respiration. These processes can be described in physico-chemical terms with no obvious requirement for co-located genetic systems, separat from those of the rest of the cell. Accordingly, biochemists once tended to regard endosymbiosis as untestable evolutionary speculation. Lynn Sagan's seminal 1967 paper "On the Origin of Mitosing Cells" outlined the evolution of eukaryotic cells by endosymbiosis of prokaryotes. The endosymbiont hypothesis is consistent with presence of DNA in chloroplasts and mitochondria, but does not assign it a function. Biochemistry and molecular biology now show that Sagan's proposal has an explanatory reach far beyond that originally envisaged. Prokaryotic origins of photosynthetic and respiratory mechanisms are apparent in protein structural insights into energy coupling. Genome sequencing confirms the underlying, prokaryotic architecture of chloroplasts and mitochondria and illustrates the profound influence of the original mergers of their ancestors' genes and proteins with those of their host cells. Peter Mitchell's 1961 chemiosmotic hypothesis applied the concept of vectorial catalysis that underlies biological energy transduction and cell structure, function, and origins. Continuity of electrical charge separation and membrane sidedness requires compartments within compartments, together with intricate mechanisms for transport within and between them. I suggest that the reason for the persistence of distinct genetic systems within bioenergetic organelles is the selective advantage of subcellular co-location of specific genes with their gene products. Co-location for Redox Regulation - CoRR - provides for a dialogue between chemical reduction-oxidation and the action of genes encoding its protein catalysts. These genes and their protein products are in intimate contact, and cannot be isolated from each other without loss of an essential mechanism of adaptation of electron transport to change in the external environment.

Keywords: Chemiosmotic hypothesis; Chloroplasts; Endosymbiont hypothesis; Mitochondria; Oxidative and photosynthetic phosphorylation; Photosynthesis; Redox signalling; Transcription.