Energy transduction anchors genes in organelles

Abstract

The work of mitochondria and chloroplasts is energy transduction in respiration and photosynthesis. The physico-chemical mechanisms of bioenergetics do not directly involve genes and heredity, and furthermore, redox chemistry is intrinsically mutagenic. Thus the small, functional genomes of mitochondria and chloroplasts are an oddity. Although extensively sequenced and catalogued, cytoplasmic genomes are still not explained. Genomic lethargy is not the answer. Some genes linger from the bacterial ancestors of these organelles, true, but most have left, and new ones arrive. There is a mounting case for a massive and indiscriminate intracellular gene transfer between organelles and the cell nucleus, with the frequency of relocation being comparable to that of mutation. Nevertheless, a few organellar proteins, all working at the core of bioenergetics, always seem to keep the genes encoding them close at hand. Stability amid flux suggests the invisible hand of selection. Selection for what? There are clues, and the beginnings of experimental support, for the theory that expression of mitochondrial and chloroplast genes is regulated by the function of their gene products. For safe and efficient energy transduction, genes in organelles are in the right place at the right time.

Origin of mitochondria by intracellular enslavement of a photosynthetic purple bacterium

“…Contrary to widespread assumptions (Allen et al 2005), it is unnecessary to postulate special reasons besides difficulty of protein reimport, plus historical accident (Cavalier-Smith 2002b), why most mitochondrial lineages failed to transfer all vital proteins to the nucleus and similarly lose local genomes (de Grey 2005). My argument that presequencebased import of IM proteins preceded that of matrix proteins is consistent with the greater complexity of the latter, additionally requiring Pam16 (Frazier et al 2004), I suggest added last of all.…”

Why chloroplasts and mitochondria retain their own genomes and genetic systems: Colocation for redox regulation of gene expression

“…Nevertheless a range of circumstantial evidence is consistent with respiratory electron transport exerting redox control over mitochondrial gene expression and requiring mitochondrial DNA (55)(56)(57).…”

Differential Coloring Reveals That Plastids Do Not Form Networks for Exchanging Macromolecules

“…Plastids, notably chloroplasts, trap solar energy by transducing it through an electron transport chain and progressively channeling it into the production of an energy-rich carbon compound. The reverse happens in mitochondria, where energy is released during progression through an electron transport chain (Buchanan et al, 2000;Allen et al, 2005;Taiz and Zeiger, 2010). Interestingly, the internal thylakoid lumen in chloroplasts is proton rich and relatively acidic, whereas in mitochondria, it is the intermembrane space, external to the mitochondrial matrix, that becomes progressively acidic.…”

“…Plastids, especially chloroplasts, are responsible for the trapping of solar energy into carbon rich compounds, whereas mitochondria are involved in releasing energy from metabolites to drive active processes within the cell. The two organelles also transduce energy similarly through a chemiosmotic mechanism involving an electron transport chain (Mitchell, 1961;Allen et al, 2005). Sporadically, mitochondria and plastids extend tubules (Wildman et al, 1962;Menzel, 1994;Logan et al, 2004), named matrixules and stromules, respectively (Kö hler et al, 1997;Scott et al, 2007).…”