AFFINITY TAGS Short peptide sequences added to recombinant proteins, which bind strongly to particular affinity matrices and can be used to purify recombinant proteins.
AGROBACTERIUM-MEDIATED TRANSFORMATION Transformation that is achieved using the natural gene-transfer mechanism of Agrobacterium tumefaciens.
AGROINFILTRATED LEAVES Usually leaves of tobacco (although many other species can be used) that are transiently transformed with Agrobacterium tumefaciens, which results in the transient expression of recombinant proteins. This is a useful strategy for testing expression constructs and obtaining small amounts of protein for analysis before going to the expense of transgenics.
APOPLAST The extracellular space. In plants, this is a large and continuous network of cavities under the cell wall. Proteins that are secreted from the cell often remain trapped here.
BATCH, FED-BATCH, PERFUSION AND CONTINUOUS FERMENTATION Batch fermentation is a closed system in which all of the substrate is added at the beginning, whereas in the fed-batch process the substrate is added in increments as fermentation proceeds. Continuous fermentation is an open system in which substrate is added continuously at a steady rate. Perfusion fermentation is a continuous process that allows cells to be grown at high density, and so results in increased biomass and product yields.
DIABODY A recombinant antibody that comprises the heavy- and light-chain variable regions joined by a flexible peptide linker. The linker is long enough to allow separation of the domains so that two of the polypeptides can assemble into a dimer, making the antibody divalent.
DICOLYLEDONOUS PLANTS (Dicots). Broad-leaf flowering plants the seeds of which contain two cotyledons (embryonic seed leaves that either remain in the seed when the plant germinates or emerge and become green). Examples include potato, tomato, tobacco and all peas and beans.
ELECTROPORATION Transformation that is achieved by exposing cells or protoplasts to a brief pulse of electricity, which results in the formation of transient membrane pores through which DNA can be taken up into the cell.
ENTEROTOXIGENIC Producing toxins in the gut that specifically affect the intestinal mucosa.
EPITOPE A single antigenic determinant on a protein that is recognized by an antibody. A single protein can have many epitopes.
FRIABLE CALLUS TISSUE Callus tissue is undifferentiated plant tissue, which grows when seeds or explants are cultured on media that contains an appropriate balance of plant hormones. Friable callus tissue is easily broken into fragments.
HETEROLOGOUS In the context of this article, a gene or protein that is not derived from the species in which it is expressed.
HYBRIDOMA CELLS A hybrid cell line that is created by fusing a mortal antibody-producing B-lymphocyte with an immortalized myeloma line. The hybridoma line is immortal and produces a continuous supply of a particular monoclonal antibody.
LEAF GUTTATION FLUID Fluid that seeps from the apoplast onto the leaf surface. In plants with large leaves, such as tobacco, large amounts of guttation fluid can be produced each day.
LEYDIG CELLS Interstitial cells in the testis that are responsible for the production of male sex hormones, such as testosterone, and are important in male sexual differentiation.
MINIBODY A recombinant antibody in which the heavy- and light-chain variable regions are part of the same polypeptide chain, which also includes the heavy-chain hinge region and one heavy-chain constant domain.
MOLECULAR CHAPERONES Proteins the function of which is to ensure correct folding of other proteins during or after synthesis, or the refolding of denatured proteins.
MOLECULAR FARMING The large-scale production of recombinant proteins in living cells or organisms; frequently applied to the use of crop plants or domestic animals as expression hosts because of the allusion to agriculture.
MONOCOTYLEDONOUS PLANTS Narrow-leaf plants the seeds of which contain one cotyledon. Examples include cereals, grasses, orchids and lilies.
POSITION EFFECTS When transgenes integrate into genomic DNA, the expression level is often influenced by the surrounding chromatin. Local regulatory elements, such as enhancers, also influence transgene expression. Position effects lead to wide variations in transgene expression levels, even in plants that are transformed with identical constructs.
PROTOPLAST TRANSFORMATION Any technique for introducing DNA into unwalled plant cells (protoplasts), such as calcium phosphate transfection, PEG transfection or electroporation.
RHIZOSPHERE The soil zone that surrounds plant roots, which is rich in microorganisms and in which interactions occur between plants and microbes.
SIGNAL PEPTIDE A short sequence of mainly hydrophobic amino acids at the N-terminus of secreted proteins. This peptide is captured by a signal-recognition particle as it emerges from the ribosome, which allows the ribosome to be transported to the endoplasmic reticulum.
SINGLE-CHAIN FV FRAGMENTS (scFvs). Monoclonal antibody derivatives that comprise a single polypeptide in which the variable regions of the heavy and light immunoglobulin chains are joined together by a flexible linker. scFvs are advantageous because only one transgene is required, and the molecules themselves are small and lack the effector functions of normal antibodies; however, a disadvantage is that they are univalent, whereas serum antibodies are divalent.
SITE-DIRECTED MUTAGENESIS An in vitro mutagenesis procedure that is often carried out using the polymerase chain reaction in which specific mutations are introduced into a DNA molecule.
SOLANACEAE A family of flowering plants (order Solanales) that comprise 
100 genera and 2,500 species, many of which are economically important as food or medicinal crops. Examples include tobacco, potato and tomato.
T-DNA BORDER SEQUENCES Imperfect 25 bp direct repeat sequences that flank the piece of DNA that is transferred to the plant genome by Agrobacterium tumefaciens. These sequences are recognized by the bacterial VIRD1 and VIRD2 proteins, which form an endonuclease complex. Cleavage of the border sequences initiates T-DNA transfer.
TRANSPLASTOMIC A transgenic plant in which the transgene is found in the plastid genome rather than the nuclear genome.
WHISKER TRANSFORMATION Transformation that is achieved by mixing walled plant cells with silicon carbide fibres that penetrate the cell wall and membrane, which generate pores through which DNA can be taken up into the cell.
