Dr. Annkatrin Rose

Functional Analysis of Chloroplast Coiled-coil Proteins

Annkatrin Rose
Appalachian State University, Boone, NC 28608, USA

The chloroplasts of land plants exhibit unique features such as vesicle transport and formation of grana stacks that are not found in cyanobacteria and the chloroplasts of algae. Along with these features, chloroplasts also contain long coiled-coil proteins, which consist of two or more alpha-helices winding around each other. In eukaryotic cells, long coiled-coil domains are often involved in processes such as membrane stacking and vesicle transport, e.g. at the Golgi, while they are rare and typically absent in bacteria. This suggests that during the evolution of chloroplasts these proteins were imported from the eukaryotic host cell into the plastids following endosymbiosis, thus resulting in a unique blend of eukaryotic and prokaryotic characteristics not found in other organelles. Two examples for chloroplast-targeted coiled-coil proteins that appear to have been introduced during the evolution of plastids in land plants are MFP1 (Matrix attachment region-binding Filament-like Protein 1) and FLIP4 (Filament-Like Protein 4) in Arabidopsis thaliana. Their predicted structure suggests that they may be involved in protein complex formation and/or membrane trafficking, stacking or fusion events. We are studying the function of these proteins using a combination of reverse genetics, microscopy, physiology, molecular and biochemical methods. MFP1 is an integral thylakoid membrane protein, but in contrast to our initial hypothesis does not appear to be essential for thylakoid membrane stacking or survival of the plant. Instead, it may be involved in complex formation at the thylakoids and fine-tuning of photosynthesis processes under stress conditions. FLIP4 is encoded by a small family of two genes (AtFLIP4-1 and AtFLIP4-2) in Arabidopsis and appears to be located at the chloroplast envelope similar to a known vesicle transport protein. We have been unable to recover mutants lacking FLIP4 protein, suggesting that it is essential for seed formation or survival. Interestingly, preliminary results suggest that differential gene expression and protein targeting may have contributed to the preservation of both members of the FLIP4 gene family after gene duplication in Arabidopsis, yet they appear able to compensate for each other if the plant is lacking the function of only one gene. We are currently investigating the expression patterns of these genes in wildtype and mutant plants to better understand the mechanism of this phenomenon. Chloroplasts play an essential role in plant development, metabolism and crop yield. In order to improve plant productivity, it is crucial that we understand how chloroplasts function and adjust to changing environmental conditions. A better understanding of the mechanisms that helped land plants to fine-tune their photosynthetic apparatus and identification of some of the players involved could ultimately lead to the development of new strategies to enhance agronomic performance.

Talk at the Science in the Mountains Meeting, Boone, NC, April 11-12, 2013.