Signalling in plant mitochondria. Redox regulation of gene expression & characterisation of a pea nucleoside diphosphate kinase

This work contributes to our understanding of mitochondrial responses to changing environmental conditions in plants. The first part of this thesis is focused in the study of redox regulation of mitochondrial gene expression. By using inhibitors, the redox state of the components of the mitochondrial respiratory chain was selectively affected. Effects of the altered redox state of these components on mitochondrial translation were studied. This approach allowed the identification of the respiratory complex II as a key component of regulation of mitochondrial translation. Furthermore, results indicating that protein phosphorylation might be part of this regulatory system are also presented.

The other aspect investigated in this work is the characterisation of a recently isolated mitochondrial protein, the pea mitochondrial nucleoside diphosphate kinase (pea mtNDPK). Cloning, expression studies, organellar targeting and phylogenetic analysis of this protein are described. Functional characterisation of the pea mtNDPK revealed a role in stress response. It was found, that the pea mtNDPK interacts with a novel 86 kDa protein, of which synthesis is up-regulated upon heat stress in vivo. The pea mtNDPK seems to have various oligomeric states, suggesting its interaction with different types of substrates. The data presented here indicate that the pea mtNDPK most likely is part of the plant mitochondrial response to heat stress, possibly acting as a modulator of the heat up-regulated 86 kDa protein.