Resource readings:

• Products on the market
• Global acreage data

B. thuringiensis protoxin expression in plants

• Challenge is that they are not well-expressed in plants
• Methods to increase levels of expression have been attempted

Table 18.1 (p. 446) - effects of protein truncation and codon bias

Plant(s)	Gene	%Expression	Insecticidal
Tobacco	cryIA(b), full	0.0001-0.0005	No
Tobacco	cryIA(b), truncated	0.003-0.012	Yes
Tobacco	cryIA(a), full	Not detected	No
Tobacco	cryIA(a), truncated	0.00125	Yes
Tobacco	cryIA(c), truncated	<0.014	Yes
Tobacco	cryIA(b), truncated	0.0001	Yes
Cotton	cryIA(b), truncated, WT	<0.002	No
Cotton	cryIA(b), truncated, PM	0.05-0.1	Yes
Tomato, tobacco	cryIA(b), truncated, WT	0.002	Yes
Tomato, tobacco	cryIA(b), truncated, PM	0.002-0.2	Yes
Tomato, tobacco	cryIA(b), truncated, FM	0.3	Yes

Details of codon usage on p. 448

Table 18.2 Susceptibility of tomato plants to insect damage

	% of plants or fruits damaged
	Wild-type tomato plants		Transgenic tomato plants
Insect	No insecticide	Insecticide	No insecticide	Insecticide
Tobacco hornworm	47.5	3.75	1.25	0.00
Tomato fruitworm	20.1	ND	6.4	ND
Tomato pinworm	99.7	95.1	94.2	80.4

Readings on B.t. corn and the monarch butterfly:

• Losey JE, Rayor LS, Carter ME. Transgenic pollen harms monarch larvae. Nature. 1999 May 20;399(6733):214.
• Stanley-Horne, et al. Assessing the impact of Cry1Ab-expressing corn pollen on monarch butterfly larvae in field studies. Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 21, 11931-11936, October 9, 2001

Enzyme inhibitors

Fig 18.2 Cowpea trypsin inhibitor gene-based vector (vs. Tobacco Budworm)

Fig 18.3 Potato proteinase inhibitor II gene-based vector (vs. Pink Stem Borer in rice)

• 70-100% of wild-type rice severely damaged by pink stem borer
• 15-20% of transgenic rice severely damaged

PROTEINASE INHIBITOR PROTECTS RICE AGAINST INSECTS When attacked by insects, some plants produce insecticidal proteins as part of their natural defense response. Wounding caused by insect damage can induce plants to synthesize lectins, -amylase inhibitors, proteinase inhibitors, or other compounds intended to help ward off the attack. With a little help from plant scientists, the strategy soon may be adopted by a wider variety of important crop species. For example, Ray Wu and colleagues from Cornell University and Zhejiang Agricultural University in Hangzhou, China have engineered rice plants with a potato proteinase inhibitor gene, and shown that the plants are resistant to pink stem borer (Nature Biotechnology, April 1996). Proteinase inhibitors are a class of defense proteins that work by inhibiting enzymes in the predator's digestive system, so that feeding slows or stops and further development is delayed or arrested. Their utility as protective transgenes was established in earlier experiments with tobacco. Rice plants were engineered to express the potato proteinase inhibitor II gene (pin2) under the control of its own promoter teamed up with the first intron of the rice actin 1 gene. This promoter-intron combination has been shown to drive high-level, wound-inducible expression of foreign genes in transgenic rice plants. The transformation plasmid also carried the herbicide resistance bar gene linked to the CaMV 35S promoter, allowing transformants to be selected on the basis of resistance to phosphinothricin. Fifth generation plants of two primary transgenic lines and two transformation-derived nontransgenic lines were assayed for pink stem borer resistance. Rice stem borer damage is visible as seedless dead panicles, called whitehead. In the bioassay, four second instar larvae were weighed and placed on plants at early heading stage. Five weeks later, tillers showing whitehead symptom were counted and the larvae were weighed again. Over both lines, at least 70% of the tillers on nontransgenic control plants showed the whitehead symptom; larvae had increased their weight 3-4 fold and developed to the fourth or fifth instar stage. Less than 18% of the tillers on plants expressing the pin2 gene showed whitehead; larvae showed little weight gain and were still in the second-third instar stage. Transgenic rice expressing a proteinase inhibitor gene joins other rice lines successfully engineered for insect and disease resistance. Breeders now have available lines expressing a Bt -endotoxin gene or a viral coat protein gene conferring resistance to rice stripe virus. Pat Traynor http://gophisb.biochem.vt.edu/news/1996/news96.may.html

Herbicide-resistant plants (e.g. "Roundup Ready" from Monsanto)

Overview: Horticulture 250 lecture from Purdue University

Nutritional supplementation

Golden rice - commentary from the World Bank

Golden rice - commentary from the Council for Biotechnology Information

"Monsanto Co. has agreed to provide royalty-free licenses to speed up work on a genetically modified rice that could alleviate vitamin A deficiency around the world." Science 2000 Aug 11;289(5481):843-5

Other views:

• "[The golden rice] is being promoted in order to salvage a morally as well as financially bankrupt agricultural biotech industry. ... The scientific/social rationalization for the project exposes a reductionist self-serving scientific paradigm that fails to see the world beyond its own narrow confines. The ëgolden riceí is a useless application."

• "Where is the golden rice? A lifesaving grain is being held hostage by anti-science activists "