<p style="text-align: justify;">The NewLeaf&reg; Plus potato (<i>Solanum tuberosum</i>) lines RBMT21-129, RBMT21-350 and RBMT22-082 were produced by bioengineering the potato cultivar Russet Burbank to be resistant to the Colorado potato beetle (CPB) (<i>Leptinotarsa decemlineata</i> Say.) and to resist infection by potato leafroll virus (PLRV). These transgenic lines produce a version of the insecticidal protein, Cry3A, derived from <i>Bacillus thuringiensis</i> subsp. Tenebrionis, and the DNA sequences corresponding to open reading frames 1 (ORF-1) and 2 (ORF-2) from PLRV. Delta-endotoxins, such as the Cry3A protein expressed in Russet Burbank NewLeaf&reg; Plus potatoes, act by selectively binding to specific receptors 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. The Cry3A protein expressed in these potato lines exhibits highly selective insecticidal activity against a narrow range of coleopteran insects such as CPB, elm leaf beetle and yellow mealworm.</p>

<p style="text-align: justify;">The 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. PLRV is a spherical RNA virus belonging to the luteovirus group and is transmitted primarily by the green peach aphid (<i>Myzus persicae</i>). This virus has a worldwide distribution and commonly infects potato, causing serious disease and economic loss. The introduced viral sequences do not result in the formation of any infectious particles, nor does their expression result in any disease pathology. These transgenic potato cultivars exhibit the trait of resistance to infection and subsequent disease caused by PLRV through an incompletely understood process that has been termed &quot;replicase-mediated resistance&quot;, which may involve silencing of viral gene translation. 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 lines RBMT21-129 and RBMT21-350. 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). Line RBMT22-082 contained a copy of the 5-enolypyruvylshikimate-3-phosphate synthase (EPSPS) encoding gene from <i>A. tumefaciens</i> strain CP4 as a selectable marker. This gene was used as an alternative to antibiotic resistance selection in order to identify transformed plants during tissue culture regeneration and multiplication.</p>
