One of the most remarkable aspects of recombinant DNA
technology is when a protein belonging to the exclusive
realm of animals can be successfully used in plants to help
them fight against pathogens that are difficult to control.
The expression of viral- or nematode-specific antibodies in
planta and hence, the term plantibody, (Gibbs 1997,
Smith 1996) is a promising new avenue for controlling plant
pathogens (Schots et al. 1992). This
unconventional method of pathogen control relies on cloning
the variable parts of the light (VL) and the (VH) heavy
chains of an antibody molecule linked to a carrier peptide;
the expression of the plantibodies in the transgenic plant
can lead to their accumulation in the plant cell cytosol.
These plantibodies will specifically interact with the
intended target inactivating its biological function (Zhang
and Wu 1998). So far, two clever strategies have been
devised against two important plant pathogens: Tomato
Spotted Wilt Virus (TSWV) (Franconi et al. 1999) and
root-knot nematodes Meloidogyne spp. (Baum et al.
1996). (http://www.gcw.nl/nieuws/art/a99_1/a99_1_5.htm)
In the case of TSWV, the production of secretory
monoclonal antibodies from the corresponding cloned
mammalian gene will allow the engineered plant to inactivate
the N, G1/G2 and NSm proteins of the virus. TSWV is a
destructive pathogen of tomato crops and no reliable method
of control is available. In the case of root-knot nematodes
a cellulase from M. incognita, and other Meloidogyne
species, in addition to other stylet secreted proteins (Figure
5.1), have been selected as targets for this strategy (Baum
et al. 1996). The plant parasitic nematode’s
cellulases are important in the initial steps of
pathogenesis. The rationale of selecting cellulases as the
target of plantibodies is that upon contact between the
anti-cellulase plantibody and the nematode cellulase, the
migration of the nematode inside the plant will be stopped
or diminished. If successful, this strategy will allow
farmers to avoid using highly toxic nematicides, soil
sterilants or fumigants. Other useful targets under analysis
are the proteins involved in the initiation of the cell
cycle that leads to the generation of giant cells that
support the feeding nematodes in infected roots (Vrain
1999).
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Figure
5.1 Stained stylet proteins generated by an
infective juvenile (J2) of the potato cyst nematode Globodera
rostochiensis. Photo courtesy Wageningen Laboratory
of Nematology. The web address for this image is http://www.spg.wau.nl/nema/r_epw-1.htm. |
These two examples of plantibodies are under study and
development, but practical applications are still far from
reaching the field until a more complete picture of the
molecular interactions involved in these pathosystems
emerges.
References
Baum, T.J., Hiatt, A, Parrott,
W.A., Pratt, L.H., Hussey R.S. 1996. Expression in tobacco of a
functional monoclonal antibody specific to stylet secretions
of the root-knot nematode. Mol. Plant Microbe. In.,
9:382-387.
Franconi, A., Roggero, P.,
Pirazzi, P., Arias, F.J., Desiderio, A., Bitti, O., Pashkoulov,
D.,
Mattei, B., Bracci, L., Masenga, V., Milne, R.G., Benvenuto,
E. 1999.
Functional expression in bacteria and plants of an scFv
antibody fragment against tospoviruses. Immunotechnology,
4:189-201.
Gibbs, W.W. 1997.
Biotechnology – Plantibodies. Sci. Am., 277: 44.
Schots, A., deBoer, J.,
Schouten, A., Roosien, J., Zilverentant, J.F., Pomp, H., Bouwmansmits,
L., Overmars, H., Gommers, F.J., Visser, B., Stiekema, W.J., Bakker, J.
1992. Plantibodies- a flexible approach to design resistance
against pathogens. Neth. J. Plant Pathol., 9:39-46.
Smith, M.D. 1996. Antibody
production in plants. Biotechnol Adv., 14:267-281.
Vrain, T.C. 1999. Engineering
natural and synthetic resistance for nematode management. J.
Nematol. 31:424-436.
Zhang, Z.H., Wu, L.P. 1998.
Research and development of expressing antibodies in plants.
Prog. Biochem. Biophys., 25:136-139.
