Why a Chloroplast Needs Its Own Genome Tethered to the Thylakoid Membrane—Co-Location for Redox Regulation

Abstract

A chloroplast is a subcellular organelle of photosynthesis in plant and algal cells. A chloroplast's genome encodes proteins of the photosynthetic electron transport chain along with proteins required to express them. Chloroplast-encoded photosynthetic proteins function in close contact with proteins whose precursors are encoded in the cell nucleus for cytosolic synthesis, import into the chloroplast, and subsequent processing. Protein complexes of photosynthetic electron transport thus contain polypeptides with one of two quite different sites of synthesis. Most chloroplast proteins are products of nuclear genes. Why not all? One proposal is that photosynthetic electron transport governs expression of genes for its own components: co-location of chloroplast genes with their gene products allows redox regulation of gene expression in individual organelles. Recent advances indicate that redox regulation impacts all stages of chloroplast gene expression. Here I propose that components of this regulation physically tether chloroplast DNA to the thylakoid membrane.