Effects of turnip crinkle virus infection on the structure and function of mitochondria and expression of stress proteins in turnips

We have investigated the effect of turnip crinkle virus (TCV) infection on mitochondrial structure and function in turnips (Brassica rapa cultivar “Just Right”). TCV infection resulted in plants with small, mottled leaves with severely crinkled edges, and in a 46% reduction in storage root mass. TCV infection resulted in specific vesicularization of mitochondrial outer membranes where TCV replication is thought to occur, with no apparent affect on other cellular membrane systems. Immunoblot analysis of mitochondrial proteins from storage roots indicated that the TCV p28 protein, which is essential for viral replication, was associated with mitochondria and that mitochondrial heat shock protein 70 and cpn60 levels increased upon TCV infection. Isolation of mitochondrial outer membranes further showed TCV p28 protein enrichment in the outer membrane as compared with total mitochondrial proteins or total cellular proteins. Analysis of mitochondrial electron transport chain activities indicated that TCV infection resulted in a 54% decrease in exogenous NADH-dependent oxygen uptake and a 8% decrease in succinate-dependent oxygen uptake. Together these results indicate that TCV infection induces a stress response in mitochondria and a reduction in the ability of mitochondria to supply adenosine 5’-triphosphate to the cell. Abbreviations: ATP, adenosine 5’-triphosphate; HSP70, heat shock protein 70; I, infected turnips; IgG, immunoglobulin G; Mi, whole miochondia; NADH, nicotinamide adenine dinucleotide (reduced); OM, outer mitochondrial membranes; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TCV, turnip crinkle virus; TP, total cellular protein.