Investigation of a Mitochondrial Twin Arginine Transport Pathway in Arabidopsis thaliana

Most proteins found in organelles such as chloroplasts or mitochondria are synthesized at a location different to their site of function. Cells therefore, must have efficient protein routing processes to allow proteins to go from their site of synthesis to their site of function, which may involve crossing multiple membrane systems. One such vital protein transport pathway is the Tat (Twin Arginine Translocation) pathway. The Tat pathway has been found in bacteria, archaea and eukaryotic organelles such as the chloroplast. The chloroplast Tat pathway (or analogous Tat pathways in bacteria) is capable of transporting fully folded proteins across membranes using only a proton motive force instead of ATP as an energy source. It is composed of three protein components, namely cpTatC, Tha4 and Hcf106 that work together to allow the transport of precursor proteins containing an obligate twin arginine motif in the targeting sequence. However, recent experiments using Nicotiana tabacum cells showed an up‐regulation of a mitochondrial gene coding for a putative mtTatC protein when the cells were subjected to salicylic acid treatment, which mimics a defense response in the plant to attack by pests. We have confirmed a similar upregulation under salicylic acid stress of the putative mitochondrial tatC gene in Arabidopsis thaliana . The presence and upregulation under stress of the mttatC gene suggests the possible presence of a mitochondrial Tat pathway. However, single nuclear genes encode the other cpTat components, which suggests either of the other components would likely dual localize to both organelles when the mtTat pathway was functional. To test for this, we have transformed Arabidopsis thaliana with Tha4‐GFP constructs and looked for its localization in the presence or absence of various biotic or abiotic stresses. Furthermore we are investigating mtTatC and Tha4 protein expression levels at different concentrations of salicylic acid in whole leaf tissue extract and in isolated mitochondria. Evaluating the presence of a mitochondrial Tat pathway will shed light on a unique protein sorting and transport mechanism in plant mitochondria, a facility previously thought to be lost during the mitochondrial evolutionary process. Support or Funding Information Dr. Dabney‐Smith Group, Center for Bioinformatics and Functional Genomics (CBFG, Center for Advanced Microscopy and Imaging (CAMI), DOE Office of Science Early Career Research Program (DE‐FG02‐10ER16138)