Stress-responsive enhanced expression of mitochondrial processing peptidase gene after UV exposure in mulberry

UV-induced gene expression was examined in mulberry plants using differenti al display method. A cDNA representing an enhanced mRNA expression in UV-st ressed leaves was sequenced and identified as the alpha -subunit of mitocho ndrial processing peptidase (alpha -MPP). Up-regulation of this gene varied in different tissues. Manganese superoxide dismutase, a protein encoded by a nuclear gene and transported to mitochondria, was found to be induced du ring UV stress condition. This induction was also accompanied by an increas ed cytochrome oxidase activity, reflecting an increase in the mitochondrial respiration following UV exposure. These results suggest that there is an increased protein import in the mitochondria under UV stress and the up-reg ulation of MPP gene exhibit an adaptive requirement in stressed plants to p rocess the proteins imported into the mitochondria. (C) 2001 Elsevier Scien ce Ireland Ltd. All rights reserved.