<p style="text-align: justify;">The Russet Burbank cultivar, RBMT15-101, and Shepody potato cultivars SEMT15-02 and SEMT15-15 (NewLeaf&reg; Y ) were bioengineered to be resistant to two important potato pests, the Colorado potato beetle (CPB, <i>Leptinotarsa decemlineata</i> Say.) and the ordinary (O) strain of potato potyvirus Y (PVY-O).</p>

<p style="text-align: justify;">Resistance to attack by CPB was accomplished by introducing the <i>cry3A</i> gene from <i>Bacillus thuringiensis</i> subsp. tenebrionis, which encodes an insecticidal crystalline Cry3A delta-endotoxin protein. Insecticidal activity is caused by the selective binding of Cry3A protein to specific sites localized on the brush border midgut epithelium of susceptible insect species. Following binding, cation-specific pores are formed that disrupt midgut ion flow and thereby cause gut paralysis, ultimately leading to bacterial sepsis and death. Delta-endotoxins, such as the Cry3A protein expressed in CPB resistant potato lines, exhibit highly selective insecticidal activity against a narrow range of coleopteran insects such as CPB, elm leaf beetle and yellow mealworm. Their specificity of action is directly attributable to the presence of specific receptors in the target insects. There are no receptors for delta-endotoxins of <i>B. thuringiensis</i> on the surface of mammalian intestinal cells, therefore, livestock animals and humans are not susceptible to these proteins.</p>

<p style="text-align: justify;">PVY is the type member of the potyvirus group and is an aphid-transmissible, rod-shaped, RNA virus that commonly infects potato, causing serious disease and economic loss. Pathogen-derived resistance to PVY was conferred by introducing the coat protein (CP) gene from the ordinary, or O-strain, of this virus. The coat protein forms a protective coat around the RNA genome of the virus and comprises 95% by mass of the virus particle. Although the exact mechanism is not fully understood, these transgenic potato lines exhibit resistance to infection and subsequent disease caused by PVY through a process that is related to viral cross-protection. The introduced viral sequences do not result in the formation of any infectious particles, nor does their expression result in any disease pathology.</p>

<p style="text-align: justify;">An antibiotic resistance marker gene (<i>neo</i>) encoding the enzyme neomycin phosphotransferase II (NPTII), which inactivates aminoglycoside antibiotics such as kanamycin and neomycin, was also introduced into the genome of these plants. This gene was derived from a bacterial transposon (Tn5 transposable element from <i>Escherichia coli</i>) and was included as a selectable marker to identify transformed plants during tissue culture regeneration and multiplication. The expression of the <i>neo</i> gene in these plants has no agronomic significance and the safety of the NPTII enzyme as a food additive was evaluated by the United States Food and Drug Administration in 1994 (US FDA, 1994).</p>
