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Transgenic plants and plant viruses have potential advantages over other production systems for therapeutic proteins. 1) Plants are not susceptible to human and animal pathogens, such as viruses that can contaminate mammalian and avian cell lines used for production of many vaccines. Recent experiences of “mad cow” disease and theories of the possible origin of HIV from monkey cell lines have highlighted the need for increased product safety. 2) There are established protocols for preparing naturally occurring pharmaceuticals from plants. 3) Unlike bacteria, plants recognize the same glycosylation signals as other eukaryotic expression systems such as mammalian, insect, or yeast cell cultures and can thus produce glycosylated proteins. Although there are differences between plants and other eukaryotes in the types of sugar residues added to glycosylated proteins, it has been demonstrated several times that plant-produced proteins have similar stability and bioequivalence of function and that antigenicity is similar. 4) Plants can produce high yields; a single transgenic plant could yield as much human glucocerebrosidase as 500 placentae. We expressed an epitope from HIV-1 on the surface of bean yellow mosaic potyvirus (BYMV) coat protein (CP); protein produced in transgenic plants is recognized by a human monoclonal antibody that neutralizes most HIV-1 isolates. Epitope-modified BYMV-CP can be recovered from transgenic plants by incorporation into BYMV virions following infection of the transgenic plants. Modified virions display the HIV-1 epitope in a semi-regular array that should stimulate the immune system to a greater degree than free subunits. HIV epitope-bearing BYMV has been used to immunize mice to assess the immune response.
Gene silencing is one of the ways in which gene expression is controlled. The authors have developed a model system to study anthocyanin gene silencing using a recessive mutation in Petunia Juss. (Star mutation) and the ability of certain viruses to reverse the gene silencing mutation. In healthy plants, the star pattern was enhanced (increase in level of gene silencing) under high temperature or light growing conditions. Virus infection did not significantly influence the star pattern when plants were grown under either low-light or low-temperature conditions. Under high-light and -temperature conditions, virus infection reverses silencing, leading to a change in the star pattern. These changes in the star pattern corresponded to changes in gene expression. Viral infection had a greater affect on regulatory gene (Wd40, Myc, and Myb) expression than on structural gene expression (Chs and Ans).
Pepino mosaic virus (PepMV) was first found in pepino (Solanum muricatum) growing in coastal Peru in 1974 and described in 1980; it reappeared in protected tomato (Lycopersiconesculentum) in the Netherlands in 1999. Since then, it has been reported to occur in tomato in several countries including Austria, Belgium, Canada, France, Germany, Italy, Peru, Spain and the Canary Islands, the United Kingdom, and in 11 states within the United States. Three strains of PepMV found in the United States have been cloned and sequenced. Full-length genomic sequences were obtained for two strains, PepMV-US1 and PepMV-US2, from co-infected tomato plant samples from Arizona. The 3'-end sequence of PepMV-US3 came from infected tomato fruits from Maryland. The genome organization, motifs and domains typical of the genus Potexvirus, and of other PepMV isolates, were found in full-length sequences of both US1 and US2 isolates. Direct comparison of US1 and US2 at the nucleotide level revealed an 86.3% identity; whereas, when individually compared to the French and Spanish isolates, which share ∼99% identity at the nucleotide level, US1 and US2 had 82% and 79% identities to each, respectively. Pair-wise gene-for-gene comparisons between United States and European isolates revealed a similar trend. While unique, US1 is more closely related to the previously reported European isolates than is US2. The CP of US3 is nearly identical to the European isolates at the amino acid level. None of 18 tomato germplasm accessions or 10 cultivars were resistant to mechanical inoculation with US3; in contrast, no infection was detected in nine pepper cultivars or four germplasm accessions. Plants grown from seeds of infected tomato fruits did not test positive for PepMV.
There is concern that modern cultivars and/or agronomic practices have resulted in reduced concentrations of mineral elements essential to human nutrition in edible crops. Increased yields are often associated with reduced concentrations of mineral elements in produce, and a number of recent studies have indicated that, when grown under identical conditions, the concentrations of several mineral elements are lower in genotypes yielding more grain or shoot biomass than in older, lower-yielding genotypes. Potato is a significant crop, grown worldwide, yet few studies have investigated whether increasing yields, through agronomy or breeding, affects the concentrations of mineral elements in tubers. This article examines the hypothesis that increasing yields, either by the application of mineral fertilizers and/or by growing higher-yielding varieties, leads to decreased concentrations of mineral elements in tubers. It reports that the application of fertilizers influences tuber elemental composition in a complex manner, presumably as a consequence of soil chemistry and interactions between mineral elements within the plant, that considerable variation exists between potato genotypes in the concentrations of mineral elements in their tubers, and that, like in other crops, higher-yielding genotypes occasionally have lower concentrations of some mineral elements in their edible tissues than lower-yielding genotypes.
After more than 10 years of research, Monsanto scientists have developed improved seed potatoes that are protected from serious pests, including insects and disease. The first commercial products resulting from this effort were NewLeaf ® potatoes derived from `Russet Burbank' and `Atlantic' parents. The NewLeaf® product was commercialized in 1995 and contains a gene from Bacillus thuringiensis (variety tenebrionis) (B.t.t.). for the production of the Cry3A protein. Potatoes expressing this gene are completely protected from the Colorado potato beetle (CPB) and need no additional chemical protection for this insect pest. The U.S. Food and Drug Administration (FDA), U.S. Dept. of Agriculture (USDA), and U.S. Environmental Protection Agency (EPA) have all determined that these potatoes are the same in safety and nutritional composition as any other `Russet Burbank' and `Atlantic' potatoes. These potatoes have also been approved by Health Canada, Agri-Food Canada and Agriculture Canada and by Japan and Mexico for food use. Commercial growers across North America have experienced outstanding performance while growing NewLeaf® potatoes 3 years in a row. This level of performance is the result of stable, nonsignificant differences in expression of the Cry3A gene. The stable performance, also, is a result of an effective insect resistance management program based on maintaining CPB refuges near NewLeaf ® fields, reducing CPB populations, and monitoring for CPB surviving exposure to NewLeaf® potatoes. In 1998 NewLeaf Y®), conferring resistance to both CPB and potato virus Y, and NewLeaf Plus®, conferring resistance to CPB and potato leafroll virus will be commercially released.