We have identified genetic systems that can be used to expand the analysis of the roles of mitochondria in plants. It is particularly important to preserve the integrity of mitochondria under stress because the mitochondrial inter-membrane space is the repository for a set of proteins that initiate cell death processes when released to the cytosol. Our primary experimental models for testing how mitochondrial respiratory defects affect the expression of nuclear genes are maize respiratory-deficient NCS (non-chromosomal stripe) mutants that carry defined deletions in mitochondrial DNA. We first showed that a nucleus-coded mitochondrial protein, alternative oxidase (AOX), associated with environmental stress responses, is induced in maize mtDNA deletion mutants (Karpova et al. 2002). AOX may work synergistically with other antioxidant enzymes to preserve mitochondria, and hence cells, under adverse conditions. We further demonstrated that three distinct aox genes are transcriptionally activated in response to different lesions in mitochondrial DNA (Karpova et al. 2002).   More recently, we have shown that, in response to mitochondrial impairment, a number of "heat shock protein" (hsp) genes are activated (Kuzmin et al. 2004, in press). Surprisingly, the primary signal from the mitochondrion to activate nuclear genes does not involve either calcium or reactive-oxygen-dependent pathways, but appears to originate from a reduction in mitochondrial transmembrane potential. AOX is highly induced highly under conditions of pathogen attack; therefore understanding the aox genes, as well as the total mitochondrial-nuclear signaling and response pathways, could provide new tools to enhance internal plant defenses.

Some of the work is reviewed in:

Newton, K.J., S. Gabay-Laughnan and R. DePaepe. 2004. Mitochondrial mutations in plants. Advances in Photosynthesis and Respiration.  In press.

Recent publications acknowledging IMBA support:

Karpova, O.V., E.V. Kuzmin, T.E. Elthon and K.J. Newton  2002. Differential expression of alternative oxidase genes in maize mitochondrial mutants.  Plant Cell 14:  3271-3284.

Kuzmin, E., Karpova O., Elthon, T. and Newton K. Mitochondrial respiratory deficiencies signal up-regulation of genes for heat shock proteins. Journal of Biological Chemistry, in press.