Contents - Faperta

228 Biotechnological Approaches for Pest Management and Ecological Sustainability
in feeding and larval weight (De Leo et al., 1998). However, larvae fed on leaves from
plants expressing MTI-2 at low expression levels did not show increased mortality, but a
net gain in weight and faster development compared with the control larvae. These observations
were correlated with the differential expression of digestive proteases in the larval
gut, overexpression of existing proteases on low MTI-2 expression level plants, and induction
of new proteases on high MTI-2 expression level plants. The results emphasized the
need for development of a proteinase inhibitor-based defense strategy for plants with optimum
level of proteinase inhibitor activity relative to the pest’s sensitivity threshold to the
proteinase inhibitor being expressed. The cDNA for bovine spleen trypsin inhibitor (SI), a
homologue of bovine pancreatic trypsin inhibitor (BPTI), including the natural mammalian
presequence, has also been expressed in tobacco (Christeller et al., 2002). Stability of
SI was shown by the presence of protein at high levels in completely senescent leaves.
Modifi cations to the cDNA (3¢ and 5¢ changes and minor codon changes) resulted in a
20-fold variation in expression. Expression of modifi ed SI in transgenic tobacco leaves at
0.5% total soluble protein reduced both survival and growth of H. armigera larvae feeding
on leaves from the late fi rst instar. In larvae surviving for eight days, midgut trypsin activity
was reduced in SI tobacco-fed larvae, chymotrypsin activity increased, while the activities
of leucine aminopeptidase (cytosol aminopeptidase) and elastase-like chymotrypsin
remained unaltered (Christeller et al., 2002). Manduca sexta encoded protease inhibitors
expressed in N. tabacum also provide protection against insects (Thomas et al., 1995a).
Potato
Transgenic potato expressing the cysteine proteinase inhibitor, oryzacystatin (OCI) gene
resulted in up to 53% mortality of L. decemlineata (Lecardonnel et al., 1999). Feeding young
females of L. decemlineata on foliage from “Kennebec” potato (K 52) transformed with OCI
did not affect survival, incidence of diapause, relative growth rate, and reproductive fi tness
(Cloutier et al., 2000). However, effi ciency of conversion of ingested foliage during postemergence,
growth, and adaptation of the digestive proteolytic system to the inhibitory effect
of OCI were reduced. Three soybean protease inhibitor genes (KTi3, C-II, and PI-IV), when
transferred into potato, showed variable expression among different plants (Archetti et al.,
2000). The level of resistance to S. littoralis was particularly high in tobacco, where many
plants caused complete mortality of the larvae, while in potato, the larval mortality was
much less frequently achieved, but resulted in a reduction of larval weight gain by 50%.
A highly signifi cant correlation was observed between inhibitor content and larval weight.
Larval weight gain has been found to be dependent on the mid-gut proteolytic activity.
Cotton
Transgenic cotton lines expressing CpTi are resistant to H. armigera (Li et al., 1998). Protein ase
inhibitors of M. sexta have also been expressed in transgenic cotton to provide protection
against insects (Thomas et al., 1995b). Protease inhibitors accumulated to approximately
0.1% of total protein, depending on the tissue analyzed. Fecundity of cotton white fl y,
Bemisia tabaci (Genn.), was reduced signifi cantly compared to that on the controls.
Maize
The cysteine protease inhibitor oryzacystatin is effective for controlling the Southern
maize rootworm, D. undecimpunctata (Edmonds et al., 1996).