Increased growth in transgenic tobacco plants over-expressing the mtHSP70 homologue, PHSP1: Towards an understanding of the underlying mechanism

Matrix-located mitochondrial heat-shock proteins (mtHSP70s) have been identified in all eukaryotic systems studied to date and it is becoming clear that these chaperones have diverse functions. The yeast mtHSP70 is essential for the import and subsequent folding of newly synthesised proteins from the cytosol into the mitochondrial matrix. In addition to its role in mitochondrial protein import, it has been suggested that the plant mtHSP70 may also be involved in the phosphorylation of enzyme complexes, whilst a further role for the yeast protein is thought to be in the modulation of mitochondrial endonuclease activity. PHSP1 is a mtHSP70 homologue from pea leaf. It has been previously shown by our laboratory that overexpression of this protein in tobacco results in increased growth, relative to wild type, during seedling development. Levels of metabolites and maximum extractable activities of enzymes involved in carbon and nitrogen metabolism are presented here, together with respiratory and morphological analysis of leaf tissue from these plants. Data are discussed with respect to how these transgenic plants may aid our understanding of the metabolic roles that mitochondria play during plant development, with particular emphasis on carbon and nitrogen metabolis