Investigation of a putative mitochondrial Twin Arginine Translocation pathway in Arabidopsis thaliana

The unique Twin Arginine Translocation (Tat) pathway which is composed of TatA, TatB and TatC, transports fully folded proteins without the use of ATP energy. It was thought to be lost from the mitochondrion, the powerhouse of the cell during post-endosymbiotic evolution. This study investigates the stress induced expression of a minimal, mitochondrial Tat pathway in Arabidopsis thaliana. We treated plants with salicylic acid (SA) stress which mimics the hypersensitive response and studied the putative mitoTat components over a 24-hour time period. qRT-PCR analysis indicated the upregulation of the mitochondrial gene mtTATC. Furthermore, immunoblot detection confirmed that the mtTATC protein is expressed at high SA concentrations. However, a minimal Tat system capable of translocation requires TatC as well as TatA (Tha4). Confocal microscopy data established the dual localization of nuclear encoded, chloroplast Tha4-GFP to the mitochondria. Together, our data illustrate the existence of a putative minimal mitoTat pathway at 4 hours post-treatment with high SA concentrations. Finally, we discuss the physiological significance of a SA-induced minimal mitoTat pathway in plant pathology.