ACTIVATION OF MITOCHONDRIAL RESPIRATION IN CHLOROPHYLL-DEFICIENT RICE MUTANT SEEDLINGS

Abstract

Previously we described a knock-out mutant of the rice oschlh gene, which encodes a Mg-chelatase H subunit and is involved in chlorophyll biosynthesis. This mutant exhibits ATP-dependent activities of plasma membrane outward - rectifying K+ channel currents that are supported by mitochondrial activation. Here, we have investigated mitochondrial activity in oschlh mutants. Growth rates were similar between the wild type and the mutant, and were enhanced by the addition of sucrose under darkness, indicating that the mutants have active mitochondrial respiration. Proteomic analyses led to the identification of 41 proteins (P < 0.05) involved in a range of functions that differed between the mutant and the wild type. Of these, 15 were up-regulated and 26 were down-regulated by more than 2-fold in the mutant. We hypothesize that loss of functioning in the chloroplasts, mainly ATP production, can be restored via beneficial interactions with other cellular compartments, especially the mitochondria, through the inter-organellar regulation of metabolites. Oxygen consumption is greater during mitochondrial respiration in chlorina mutants than in the wild type, so that those mutants produce large amounts of ATP in the presence of sucrose. These results imply that gene expression of photosynthetic organisms is strongly connected through energy-driven networks of transcriptional regulators that can control factors in other cellular compartments, thus indicating the re-programming of cellular functions.