Overexpressed Arabidopsis Annexin4 accumulates in inclusion bodylike structures

Large protein complexes form in the cytosol of prokaryotes and eukaryotes as assemblies of functional enzymes or aggregates of misfolded proteins. Their roles in the cell range from critical components of metabolism to disease-causing agents. We have observed a novel structure in the cells of transgenic Arabidopsis thaliana that appears to be a form of inclusion body. These long, spindle-shaped structures form when Arabidopsis are transformed to express high levels of the protein Annexin4 fused to a fluorescent protein. These structures, previously named darts, are visible in all cells of the plant throughout development. Darts take on a variety of morphologies including rings and figure-eights. These structures are not associated with the endomembrane system and are not membrane bounded. Darts appear to be insoluble aggregates of protein analogous to bacterial inclusion bodies and eukaryotic aggresomes. Similar structures have not been observed in untransformed plants, suggesting darts are artifacts of transgenic overexpression.