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International Laboratory for Tropical Agricultural Biotechnology

C.M. Fauquet, R.N. Beachy, J.-P. Brizard,* M.-E. Aleman,* C. Bonneau,** C. Brugidou,*** A. Chatterjee,**** L. Chen,***** A. de Kochko,* H. Huet,*** P. Marmey,* V. Massona,+ J. Mendez-Lozano,++ M. Padidam, +++ J. Pita,+ C. Schöpke,* N. Taylor,* B. Verdaguer,++++ P. Viegas,+++++ S. Zhang*****

* ORSTOM, Paris, France
** Université de Montpellier II, Montpellier, France
*** Université de Paris 7, Paris, France
**** Indian Agricultural Research Institute, New Delhi, India
***** Academia Sinica, Beijing, China
+ University of Harare, Harare, Zimbabwe
++ CINVESTAV, Irapuato-Léon, Mexico
+++ Tata Energy Research Institute, New Delhi, India
++++ Université de Toulouse, Toulouse, France
+++++ Bhabba Atomic Research Center, Bombay, India

The International Laboratory for Tropical Agricultural Biotechnology (ILTAB) is a research and training unit established to develop biotechnological methods for the control of plant viruses and other diseases in tropical crops. Our approaches include techniques developed in model plants and adapted to tropical plants, including rice, cassava, and tomato. Much of the research activity is directed toward the development of transformation techniques and the application of pathogen-derived resistance for control of diseases caused by plant viruses. Other projects include studies of the molecular diversity of geminiviruses and potyviruses and of promoters that are potentially useful for genetic engineering. Because transfer of technologies is an important goal of ILTAB, a rice transformation training center was created in 1994 and will run until 1999.

In 1995, we reported the first transfer, by genetic engineering, of a resistance gene from a wild species of rice to a susceptible cultivated rice variety; the gene conferred resistance to the bacterium Xanthomonas oryzae. The next year, we transferred the gene into useful varieties of rice that are cultivated on more than 24 million hectares around the world. R3-generation seeds of resistant lines have been sent to China and the Philippines, where the first field trials will be done by the fall of 1998. These tests will be the first large-scale field experiments done with transgenic rice expressing a gene of agricultural interest. This work is expected to have a significant impact on the development of bacteria-resistant rice varieties worldwide. ILTAB is involved in other collaborations to transfer this gene to other important rice varieties throughout the world.

In other studies, we showed that it is possible to engineer plants with as many as 14 different genes at one time. This technology offers the possibility of engineering de novo biochemical pathways in plants and shows that transgene expression of multiple genes is feasible.

Genetic transformation of cassava, first demonstrated at ILTAB in 1996, has been greatly improved and is near routine for several cassava genotypes. Cassava plants that contain several genes of interest, including genes to control viruses, are now in production. The technology is being transferred to several less developed countries, including Zimbabwe and Thailand, and soon will be transferred to Ivory Coast and Brazil.

An important component of plant genetic engineering is the need for a strong constitutive promoter to express foreign genes in transgenic plants. ILTAB scientists isolated such a promoter from a cassava virus and showed that the promoter is strongly expressed in all plants tested thus far, including monocotyledonous plants. In addition, we characterized the promoter to understand its mode of action, and we identified several tissue-specific sequence elements, that is, root-, phloem-, and mesophyl-specific cis-activating elements. From this unique promoter, we have derived a family of promoters of various strengths that are constitutive or tissue specific. A kit of plasmids for plant gene expression with this promoter has been developed for use by academic scientists in developing countries.

ILTAB is also interested in viral biodiversity, especially of viruses of worldwide distribution, in particular, the geminiviruses and potyviruses. Geminiviruses are single-stranded DNA viruses that devastate food crops in tropical countries. We have been involved in elucidating the etiology of 3 important emerging diseases in the world: the cassava mosaic epidemic in Uganda, the tomato leaf curl disease in Trinidad, and the cotton leaf curl disease complex in Pakistan. In each case, the newly isolated viruses are recombinants of several different geminiviruses.

A complete survey of all geminivirus sequences available led us to conclude that genetic recombination is a major force for geminivirus biodiversity and may promote emergence of new diseases caused by this virus. We also concluded that emergence of diseases caused by geminivirus is due to human activities, such as introduction of new plant genotypes, transport of insect vectors, and importation of viruses around the world. Therefore, new viral diseases most likely will emerge more often as such exchanges increase, and because geminiviruses apparently have a high capacity to recombine.

PUBLICATIONS

Bonneau, C., Brugidou, C., Chen, L., Beachy, R.N., Fauquet, C.M. Expression of the rice yellow mottle virus P1 protein in vitro and in vivo and its involvement in virus spread. Virology 244:79, 1998.

Chen, L., Zhang, S., Beachy, R.N., Fauquet, C.M. An efficient protocol for consistent production of transgenic rice plants. Plant Cell Rep., in press.

de Kochko, A., Verdaguer, B., Beachy, R.N., Fauquet, C.M. Cassava vein mosaic virus (CsVMV), type species for a new genus of plant double-stranded DNA viruses? Arch. Virol. 143:945, 1998.

Gonzalez de Schöpke, A.E., Schöpke, C., Taylor, N., Beachy, R.N., Fauquet,C.M. Regeneration of transgenic cassava plants (Manihot esculenta Crantz) through Agrobacterium-mediated transformation of embryonic suspension cultures. Plant Cell Rep. 17:827, 1998.

Opalka, N., Brugidou, C., Bonneau, C., Nicole, M., Beachy, R.N., Yeager, M., Fauquet, C.M. Movement of rice yellow mottle virus between xylem cells through pit membranes. Proc. Natl. Acad. Sci. U.S.A. 95:3323, 1998.

Verdaguer, B., de Kochko, A., Fux, C., Beachy, R.N., Fauquet, C.M. Functional organization of the cassava vein mosaic virus (CsVMV) promoter. Plant Mol. Biol. 37:1055, 1998.


Classification and Nomenclature of Viruses: International Committee on Taxonomy of Viruses

C.M. Fauquet

The International Committee on Taxonomy of Viruses (ICTV) is an internationally recognized association of virologists who work on the taxonomy and nomenclature of viruses. It has been an official body of the International Union of Microbiological Societies since 1966. The goals of the ICTV are to establish a standardized nomenclature and to build a universal system for virus classification.

As secretary of the ICTV, I coordinate the efforts of 52 study groups comprising more than 500 virologists. Among other activities, I participated in editing the Sixth ICTV Report, which was published in May 1995. This publication presents a uniform body of information, including (1) particle photographs and diagrams and (2) schematic representations of genome organizations and viral replication of the type species of 75 families and genera of viruses that infect bacteria, algae, fungi, mycoplasma, plants, invertebrates, and vertebrates. I also established for the ICTV a Web page located at the National Center for Biotechnology Institute, Bethesda, Maryland. The page provides updated information on ICTV and all the viral taxonomic information. A poster, "The Virosphere," has been published and is available on request. The 27th meeting of the executive committee of the ICTV was held at TSRI in March 1998. ICTV is now working on the Seventh ICTV Report, which is due at the next Congress of Virology in 1999.

PUBLICATIONS

Padidam, M., Maxwell, D.P., Fauquet, C.M. A proposal for naming geminiviruses. Arch. Virol. 142:2553, 1997.

 

 







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