The International Consortium on Agricultural Biotechnology Research (ICABR)
Value of Engineered Virus Resistance in Crop Plants and Technology Cooperation with Developing Countries
V. M. Aquino, University of the at Los Banos
R. Hautea, ISAAA-SEAsia Center
W. K. Kaniewski, Monsanto
N. D. Lam, Institute of Biotechnology
C. A. Ong, V. Pillai, Malaysian Agricultural Research and Development Institute
K. Romyanon, Kasetsart University
Transformation of plants with viral genes was proven to produce resistance to the virus from which the genes were derived. The technology was successfully used to produce resistance in agriculturally important crops such as potato, tomato, squash, wheat, and others. The benefits of transgenic virus resistance include increased yield, reduced pesticide use to control vectors of viruses, and improved crop quality. The coat protein (CP) gene was most often used to confer resistance. In some cases the expression of CP correlated with resistance, and strong evidence for prevention of uncoating was shown. For potyviruses there may be CP and RNA mechanisms, which can confer resistance in transgenic plants. High levels of resistance can be produced in plants transformed with viral replicase genes which include the full-length gene, and various deletions or sequence modifications. The mechanism of resistance in replicase-expressing plants is complex and may involve expression of a protein that blocks virus replication and/or movement, as well as postranscriptional gene silencing. In general, it has been demonstrated that plants resistant to mechanical inoculation are also resistant to vector transmission. Prior to commercialization extensive field testing and regulatory approvals are required to address agronomic performance, preservation of cultivar characteristics, and food/environmental safety.
The development of transformation techniques broadens the possibility of use of engineered virus resistance in plant breeding. There are many destructive virus diseases of crop plants worldwide, and biotechnology may be the fastest and most efficient way to produce resistant cultivars. One example could be papaya production affected by potyvirus, papaya ringspot virus (PRSV). Field resistance of papaya to PRSV was demonstrated in Hawaii, however resistance did not hold for Asian isolates of PRSV. The Papaya Biotechnology Network was formed and is sponsored by five Asian countries (Malaysia, Thailand, Philippines, Vietnam and Indonesia) and by ISAAA and Monsanto. A large effort is currently being undertaken to improve Agrobacterium transformation of papaya. The CP and replicase genes from the most common isolates from five participating countries were cloned and sequenced. The sequences revealed possible patterns of virus spread in South East Asia, as well as the probability of recombination events during the evolution of PRSV. Several binary vectors for Agrobacterium-mediated transformation were constructed, using both CP and replicase genes and their modifications. Transgenic plants are being produced and will be tested for resistance. If successful, the technology would improve the yield and quality of papaya fruit.