Dear Klaus and Prakash,
We thought the people on your listserves might be interested, if they did
not already know, to learn what we found about the promoters used in the
different Bt corns used in the Losey and Wraight studies.
C. L. Wraight et al. used a corn variety that contains Monsanto event 810
to test for toxicity of the pollen to black swallowtails under field
conditions. This event was produced by microprojectile bombardment of
embryogenic tissue with a plasmid containing the cry1Ab gene under the
control of the enhanced cauliflower mosaic virus 35S promoter and the
hsp70 maize intron (http://www.biotechknowledge.com/showlib_us.php3?2378).
Losey et al. used a different variety of corn for their experiments,
containing Novartis event 176. This corn contains the cry1A(b) gene under
the control of the phosphoenolpyruvate (PEP) carboxylase promoter, which
is expressed in green tissues. It also contains the same cryIA(b) gene
under the control of a maize pollen-specific promoter (P. L. Fearing et
al., 1997. Quantitative analysis of CryIA(b) expression in Bt maize
plants, tissues and silage, and stability of expression over successive
generations, Molecular Breeding 3:169-176.) The resulting Bt concentration
in the pollen of this corn variety is many times higher than in the one
using the 35S promoter to drive B.t. expression.
Therefore this difference in promoters and their ability to support
expression of B.t. in pollen would explain the differences seen in the
lethality to butterfly larvae. You rarely see this mentioned in
discussions of these two different sets of experiments. We have tried to
inform reporters as they call to discuss these issues.
Petra Frey and Peggy Lemaux
Department of Plant Biology
University of California, Berkeley