SummaryWe have developed combined transgene/virus vector systems for the expression of

SummaryTo investigate the role of subunit assembly in the intracellular deposition of multimeric recombinant proteins, we expressed a partially humanized secretory immunoglobulin in rice endosperm cells and determined the subcellular locations of the assembled protein and its individual components. Transgenic rice plants expressing either individual subunits or all the subunits of the antibody were generated by particle bombardment, and protein localization was determined by immunoelectron microscopy. Assembly of the antibody was confirmed by immunoassay and coimmunoprecipitation. Immunolocalization experiments showed no evidence for secretion of the antibody or any of its components to the apoplast. Rather, the nonassembled light chain, heavy chain and secretory component accumulated predominantly within endoplasmic reticulum-derived protein bodies, while the assembled antibody, with antigen-binding function, accumulated specifically in protein storage vacuoles. These results show that the destination of a complex recombinant protein within the plant cell is influenced by its state of assembly.

SummaryIn animals, organic cation/carnitine transporters (OCTs) are involved in homeostasis and distribution of various small endogenous amines (e.g. carnitine, choline) and detoxification of xenobiotics such as nicotine. Here, we describe the characterization of AtOCT1, an Arabidopsis protein that shares most of the conserved features of mammalian plasma membrane OCTs. Transient expression of an AtOCT1::GFP fusion protein in onion epidermal cells and Arabidopsis protoplasts supported localization in the plasmalemma. AtOCT1 functionally complemented the Dcit2/Dagp2p yeast strain that is defective in plasma membrane carnitine transport. Disruption of AtOCT1 in an Arabidopsis oct1-1 knockout mutant affected both the expression of carnitine-related genes and the developmental defects induced by exogenous carnitine. RT-PCR and promoteruidA fusion analysis showed that AtOCT1 was expressed in vascular tissues of various organs and at sites of lateral root formation. Correlating with this expression pattern, oct1-1 seedlings grown in vitro exhibited a higher degree of root branching than the wild-type, showing that the disruption of AtOCT1 affected root development under certain conditions.