Plant Organelles-to-Nucleus Retrograde Signaling

Plant cells contain two types of energy producing organelles: chloroplasts, which convert solar into chemical energy, and mitochondria, which convert stored energy into ATP. Cell organelles comprise thousands of various proteins; most of them are encoded by nuclear genes; only few genes, which encode mainly the components of the system of gene expression per se and of the respiratory (in mitochondria) or photosynthetic (in chloroplasts) chains, are localized in the genomes of organelles. Thus, the maintenance of cell organelle functional activity during cell growth and development depends predominantly on the nuclear genome encoding most organelle proteins and their own genomes encoding the limited but substantial number of proteins. In this connection, organelle ribosomes, photosystems, complexes of mitochondrial respiratory chain are mosaic in their origin; they are multiprotein complexes comprising subunits encoded by the nucleus and organelles. Therefore, special mechanisms are required for coordination of gene expression in various cell compartments. Since the nuclear genome plays a key role in the biogenesis and functioning of cell organelles, the main recent attention was paid to the analysis of so called anterograde regulation, which controls the flow of information from the nucleus and cytoplasm to organelles. Along with anterograde regulation, retrograde signaling occurs in the cells, when signals emitted by organelles control gene expression in the nucleus (Pesaresi et al. 2007; Yurina & Odintsova, 2007). In this review, we summarize the recent understanding of chloroplast-to-nuclear and mitochondria-to-nuclear retrograde regulation in plant, which involves multiple potential signaling pathways in relation to abiotic stress.