Contents - Faperta

Genetic Transformation of Crops for Resistance to Insect Pests 231
TABLE 7.4
Insect-Resistant Transgenic Crops Expressing a-Amylase Inhibitors
Crop Inserted Gene Useful Trait References
Pea a-amylase inhibitors from
Phaseolus vulgaris
Tobacco a-amylase inhibitors from
wheat (WAAI)
a-amylase inhibitors from
bean (BAAI)
Resistant to bruchids. Shade et al. (1994)
Increased the mortality of
Carbonero et al. (1993)
lepidopteran larvae by 30 to 40%.
Resistant to Callosobruchus sp. Shade et al. (1994);
Schroeder et al. (1995)
Adzuki beans a-amylase Enhanced levels of resistance to
bruchids.
Pea a-amylase inhibitors (alpha
Al-1, and alpha Al-2)
alpha Al-1 inhibits pea bruchid
a-amylase by 80%.
Ishimoto et al. (1996)
Morton et al. (2000)
Enzymes
Several enzymes expressed in transgenic plants have shown resistance to lepidopteran
insects (Purcell et al., 1993; Smigocki et al., 1993; Corbin et al., 1994; X. Ding et al., 1998).
Cholesterol oxidase from Streptomyces is highly toxic to cotton boll weevil, Anthonomus
grandis (Boh.) (Cho et al., 1995), while polyphenol oxidases and peroxidases increase the
inhibitory effect of 5CQA (5-caffeoyl quinic acid) and cholorogenic acid by oxidizing the
dihydroxy groups to ubiquinones that covalently bind to nucleophilic (–SH2 and –NH2)
groups of proteins, peptides, and amino acids. Behle et al. (2002) produced transgenic
plants of tomato, L. esculentum, and South American tobacco, Nicotiana sylvestris Speg. &
Comes. and N. tabacum expressing 5 to 400 times higher peroxidase activity than corresponding
tissues of wild-type plants. The larvae of H. zea consumed 1.5 times less food on
leaf discs from transgenic plants compared with the leaf discs from the corresponding
nontransgenic plants. Lipoxigenase from soybean has also been shown to exhibit toxic
effects towards insects (Shukle and Murdock, 1983), and has been expressed in transgenic
plants, but resistance to insects has not been demonstrated.
The insect moulting enzyme chitinase, which degrades chitin to low-molecular-weight
soluble and insoluble oligosaccharides, is a metabolic target of selective pest control (Chit
Kramer and Muthukrishnan, 1997). The cDNA and genomic clones for the chitinase from the
hornworm, M. sexta have been isolated and characterized. Transgenic plants that express
hornworm chitinase constitutively exhibit resistance to insects. Transgenic tobacco plants
expressing the chitinase gene have shown resistance to several lepidopteran insects (X. Ding
et al., 1998). Accumulation of bean chitinase (BCH) increased as the potato plant developed,
with maximum levels recorded in mature plants (Down et al., 2001). A transformed entomopathogenic
virus that produces the enzyme chitinase displayed enhanced insecticidal activity.
Chitinase also potentiates the effi cacy of the toxin from B. thuringiensis. Field studies
involving alfalfa, Medicago sativa L., plants (parental, transgenic alpha-amylase-producing and
transgenic lignin peroxidase-producing plants) indicated that the lignin peroxidase transgenic
plants had signifi cantly lower shoot weight, and higher nitrogen and phosphorus content,
than the parental or transgenic amylase plants (Donegan et al., 1999). Signifi cantly
higher population levels of culturable, aerobic spore forming, and cellulose-utilizing bacteria,
lower activity of the soil enzymes dehydrogenase and alkaline phosphatase, and higher
soil pH levels were also associated with the lignin peroxidase transgenic plants.