New GM toxin looms over our food.

• Author: Cummins, Joe
• Position: Bacillus thuringiensis

The soil bacterium, Bacillus thuringiensis (Bt), has proven to be a rich source of toxins for killing insect pests. Most of the toxin genes now being used in genetically modified (GM) crops are produced in sporulating Bt, and belong to the Cry family: designated Cry1, Cry 2 etc. up to at least Cry 41. The Cry genes are further distinguished as Cry1A, Cry1B etc for substantial sequence variations, and labeled Cry1Aa, Cry1Ab etc. for very small differences in sequence. The Cry gene toxins target specific insect cell receptor proteins and create pores that lead to osmotic lysis of the insect gut cells. Only a few Cry genes have found favor in GM crops. Along with the Cry genes, Cyt genes have been characterized that are distinct from Cry genes and act by breaking open the insect's blood cells.

In recent years, vegetative insecticidal proteins (VIP) have been found to have potent, broad-spectrum activity against insects. VIP genes are not homologous to Cry and Cyt genes, and bind to cell membrane proteins different from the other toxins.

Syngenta Corporation, producers of chemical and biological pesticides, has patented the VIP genes for use in transgenic crop plants and microbes. Syngenta's United States patent 6,429,360 covers the use of Bt-VIP genes and their synthesis and alteration to improve performance in crop plants. Syngenta's patent provided evidence that VIP3A toxin produced apoptotic type of cell death, including the production of membrane-bound apoptotic bodies and activation of endonuclease enzymes that cleave chromatin into discrete fragments.

Apoptosis (meaning petals falling from a flower) is a form of programmed cell death common to all cells with discrete nuclei. It is a part of normal development, but the VIP3A toxin uses programmed cell death to destroy the cells of the insect gut. In order to function fully in the plant cells, the BtVIP3A gene is modified in its coding sequence; a strong promoter added, as well as an intron to facilitate transfer of the pre-messenger RNA from nucleus to cytoplasm; and the usual transcription terminator and polyA addition sequences.

The insect VIP3A receptor was identified and its characteristic "death" recognition sequence was characterized. Organisms whose cells have nuclei generally have receptors with death signals and the insect VIP3A receptor is a unique member of the class of sequences.

Syngenta has petitioned the US Environmental Protection Agency (EPA) for commercial release of...