Business Potential for Agricultural Biotechnology - Asian Productivity ...

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Summary of Findings
field trials from 1996 to 1999, the transgenic papaya exhibited high degrees of protection against
PRSV in the Republic of China. Unfortunately, 18 months after planting in the fourth field trial,
unexpected symptoms of severe distortion on fully expanded leaves, stunning on apex, watersoaking
on petioles and stem, and yellow ringspot on fruit were noticed on PRSV CP-transgenic
papaya plants. The causal agent was distinguished from PRSV by host reactions and serological
properties and later identified as Papaya leaf distortion mosaic virus (PLDMV), a potyvirus
which originated from Okinawa, Japan, in 1954. All PRSV CP-transgenic papaya lines were susceptible
to PLDMV infection when evaluated under greenhouse conditions. Therefore, in the Republic
of China PLDMV will be considered a serious threat to papaya production once PRSV
CP-transgenic papaya is widely used for the control of PRSV.
In order to control two or more viruses, transgenic plants with multiple resistances have
been generated by combining the entire CP gene of more than one virus, with each gene driven
by a promoter and a terminator. Transgenic lines expressing these chimeric CP constructs were
resistant to the corresponding viruses and protected from mixed infection such as Cucumber
mosaic virus, Watermelon mosaic virus, and Zucchini yellow mosaic virus. Furthermore, transgenic
plants with resistance to a potyvirus and a tospovirus can be obtained through the PTGS
mechanism by fusing a segment of tospoviral N gene to a segment of potyviral CP gene. This
strategy was used to develop double resistance to both PRSV and PLDMV. An untranslatable
chimeric construct that contained the truncated PRSV CP and PLDMV CP genes was then transferred
to papaya. Through the PTGS mechanism, transgenic papaya plants carrying this chimeric
transgene indeed conferred resistance against both PRSV and PLDMV under greenhouse conditions.
These transgenic papaya plants with double resistance are considered to have great potential
for the control of PRSV and PLDMV in Taiwan. In four-year field trials, a super PRSV
strain 5-19 which infected transgenic papaya lines was found. The breakdown of the transgenic
resistance by a strong gene-silencing suppressor of a super strain has a strong impact on the application
of transgenic crops for virus control. A chimeric construct targeting at multiple viral
genes, including the gene determining viral virulence and gene silencing suppression, such as the
HC-Pro gene of a potyvirus, may minimize the chance of emergence of a super virus for overcoming
the transgenic resistance.
Commercial-scale Production of Valuable Plant Biomass and Secondary Metabolites Using
a Bioreactor System
Plants are a de facto biological factory that produces an immense array of fine chemical
compounds highly valued in pharmaceutical, food, and bioenergy industries. Thus it is of huge
business interest to grow plant cells, tissues, and even entire organisms at commercial scales.
Having proven its medicinal superiority in traditional medicine, Korean Mountain Ginseng
(KMG) has a high market value among Korean people that has stimulated much interest in
producing its biomass for commercialization. However, there have been only a few success
stories of plant cultures at the commercial scale. Recently, a group at VitroSys Inc. successfully
implemented an industrial-scale bioreactor system for the commercial production of Korean
Mountain Ginseng (Panax ginseng C. A. Meyer). The bioreactor system holds a promising
future for applications, such as the large-scale production of diverse secondary metabolites from
plant tissues.
Commercialization of Agricultural Crop Biotechnology Products
High-quality seed of crop cultivars with the desirable genetic background still form the
foundation for farming. Biotechnology offers the best opportunity to meet the challenge of improving
on the potential in seeds and also of providing the enabling knowledge to express that
potential. Crops developed through biotechnology are produced by the stable insertion of one or
a few well-defined genes into the genome of a plant. The gene(s) produce one or a few proteins
that confer the trait of interest (e.g., insect resistance). Of the thousands of individual plants that