COMPARTMENT-SPECIFIC ACCUMULATION OF RECOMBINANT IMMUNOGLOBULINS IN PLANT-CELLS - AN ESSENTIAL TOOL FOR ANTIBODY-PRODUCTION AND IMMUNOMODULATION OF PHYSIOLOGICAL FUNCTIONS AND PATHOGEN ACTIVITY

Expression and stability of immunoglobulins in transgenic plants have been investigated and optimized by accumulation in different cellular compartments as cytosol, apoplastic space and endoplasmic reticulum (E R) as will be discussed in this review. In several cases described the highest accumulation of complete active antibodies was achieved by ta rgeting into the apoplastic space. High-level expression of active rec ombinant single-chain Fv antibodies (scFv's) was obtained by retention of these proteins in the lumen of the endoplasmic reticulum. This has been shown for leaves and seeds of transgenic tobacco as well as for potato tubers. Transgenic tobacco seeds, potato tubers and tobacco lea ves can facilitate stable storage of scFv's accumulated in the ER over an extended (seeds, tubers) or a short (leaves) period of time. The e xpression of specific scFv's in different plant species, plant organs and cellular compartments offers the possibility of blocking regulator y factors or pathogens specifically. Examples are scFv's expressed in the cytosol and the apoplastic space of transgenic plant cells modulat ing the infection process of plant viruses and a cytosolically express ed scFv that influenced the activity of phytochrome A protein. The imm unomodulation approach has been shown to be also applicable for invest igating the action of the phyto-hormone abscisic acid (ABA). High-leve l accumulation of specific anti-ABA scFv's in the ER of all leaf cells has been used to block the influence of ABA on the stomatal functions . Seed-specific expression of high amounts of anti-ABA-scFv's at a def ined time of seed-development induced a developmental switch from seed ripening to vegetative growth. It has been demonstrated that ER reten tion is essential for the accumulation of sufficient scFv to bind high concentrations of ABA in the transgenic seeds.