Perspectives on communicating risks of chemicals

The Agrochemicals Division symposium "Perfecting Communication of Chemical Risk", held at the 244th National Meeting and Exposition of the American Chemical Society in Philadelphia, PA, August 19-23, 2012, is summarized. The symposium, organized by James Seiber, Kevin Armbrust, John Johnston, Ivan Kennedy, Thomas Potter, and Keith Solomon, included discussion of better techniques for communicating risks, lessons from past experiences, and case studies, together with proposals to improve these techniques and their communication to the public as effective information. The case studies included risks of agricultural biotechnology, an organoarsenical (Roxarsone) in animal feed, petroleum spill-derived contamination of seafood, role of biomonitoring and other exposure assessment techniques, soil fumigants, implications of listing endosulfan as a persistant organic pollutant (POP), and diuron herbicide in runoff, including use of catchment basins to limit runoff to coastal ecozones and the Great Barrier Reef. The symposium attracted chemical risk managers including ecotoxicologists, environmental chemists, agrochemists, ecosystem managers, and regulators needing better techniques that could feed into better communication of chemical risks. Policy issues related to regulation of chemical safety as well as the role of international conventions were also presented. The symposium was broadcast via webinar to an audience outside the ACS Meeting venue.

Radically rethinking agriculture for the 21st century

Population growth, arable land and fresh water limits, and climate change have profound implications for the ability of agriculture to meet this century's demands for food, feed, fiber, and fuel while reducing the environmental impact of their production. Success depends on the acceptance and use of contemporary molecular techniques, as well as the increasing development of farming systems that use saline water and integrate nutrient flows.

Practical delivery of genes to the marketplace

Although new technologies in genomics are powerful tools for discovering genes and gaining insight into their function, discovery of a gene itself does not ensure its practical application. Commercialization of transgenic crop plants has now taken place for more than a decade. Plant biotechnology, which can be seen as an extension of traditional plant breeding for crop improvement, offers one way to boost food, feed, fiber, and fuel production and has provided significant environmental and economic benefits. Like plant breeding, biotechnology introduces new traits with specific benefits into plants, and does so in a selective, precise, and controlled manner. Several steps are necessary before commercializing a crop with a biotechnology trait, including not only gene discovery and product development but also regulatory clearance, stewardship evaluation, and stakeholder dialogue. Examples will be drawn from the work at Monsanto on the development and commercialization of glyphosate-tolerant soybeans, which is representative of the first wave of agronomic traits.

Modification of the coding sequence enhances plant expression of insect control protein genes

Increased expression of the insect control protein genes of Bacillus thuringiensis in plants has been critical to the development of genetically improved plants with agronomically acceptable levels of insect resistance. The expression of the cryIA(b) gene was compared to partially modified (3% nucleotide difference) and to fully modified (21% nucleotide difference) cryIA(b) and cryIA(c) genes in tobacco and tomato. The modified genes increased the frequency of plants that produced the proteins at quantities sufficient to control insects and dramatically increased the levels of these proteins. Among the most highly expressing transformed plants for each gene, the plants with the partially modified cryIA(b) gene had a 10-fold higher level of insect control protein and plants with the fully modified cryIA(b) had a 100-fold higher level of CryIA(b) protein compared with the wild-type gene. Similar results were obtained with the fully modified cryIA(c) gene in plants. Specific sequences of the partially modified cryIA(b) gene were analyzed for their ability to affect cryIA(b) gene expression in tobacco. The DNA sequence of a single region was identified as important to the improvement of plant expression of the cryIA(b) gene. The increased levels of cryIA(b) mRNA were not directly proportional to the increased levels of CryIA(b) protein in plants transformed with the modified cryIA(b) genes, indicating that the nucleotide sequence of these genes had an effect in improving their translational efficiency in plants.

Insect resistant cotton plants

We have expressed truncated forms of the insect control protein genes of Bacillus thuringiensis var. kurstaki HD-1(cryIA(b) and HD-73 (cryIA(c) in cotton plants at levels that provided effective control of agronomically important lepidopteran insect pests. Total protection from insect damage of leaf tissue from these plants was observed in laboratory assays when tested with two lepidopteran insects, an insect relatively sensitive to the B.t.k. insect control protein, Trichoplusia ni (cabbage looper) and an insect that is 100 fold less sensitive, Spodoptera exigua (beet armyworm). Whole plants, assayed under conditions of high insect pressure with Heliothis zea (cotton bollworm) showed effective square and boll protection. Immunological analysis of the cotton plants indicated that the insect control protein represented 0.05% to 0.1% of the total soluble protein. We view these results as a major step towards the agricultural use of genetically modified plants with insect resistance in this valuable, high acreage crop.

Specificity and efficacy of purified Bacillus thuringiensis proteins against agronomically important insects

The host range and relative efficacy of three purified Bacillus thuringiensis insect control proteins were determined against 17 different agronomically important insects representing five orders and one species of mite. The three B. thuringiensis proteins were single gene products from B. thuringiensis ssp. kurstaki HD-1 (CryIA(b)) and HD-73 (CryIA(c)), both lepidopteran-specific proteins, and B. thuringiensis ssp. tenebrionis (CryIIIA), a coleopteran-specific protein. Seven insects showed sensitivity to both B. thuringiensis ssp. kurstaki proteins, whereas only 1 of the 18 insects was sensitive to B. thuringiensis ssp. tenebrionis protein. The level of B. thuringiensis ssp. kurstaki protein required for 50% mortality (LC50) varied by 2000-fold for these 7 insects. A larval growth inhibition assay was developed to determine the amount of B. thuringiensis ssp. kurstaki protein required to inhibit larval growth by 50% (EC50). This extremely sensitive assay enabled detection of B. thuringiensis ssp. kurstaki HD-73 levels as low as 1 ng/ml.

The sup-7(st5) X gene of Caenorhabditis elegans encodes a tRNATrpUAG amber suppressor

In earlier studies, we identified in Caenorhabditis elegans two informational suppressors sup-5 III and sup-7 X and recently showed that these suppressors acted via an altered tRNA to suppress translational termination at amber (UAG) stop codons. We now show that the sup-7 (st5) suppressor is a tRNATrpUAG amber suppressor. These studies utilized a radiolabeled purified tRNA fraction to identify hybridizing genomic sequences in a phage genomic library. DNA sequence analysis of the hybridizing segment of one clone showed that the probe recognized a tRNATrpUGG sequence. The sup-7 gene was shown to be one of an 11 or 12 member tRNATrp family by Southern blot analysis, taking advantage of an Xba I restriction site induced in the anticodon sequence by the mutational event to suppressor. Sequence analysis of a recombinant lambda clone containing sup-7 gene proved that sup-7(st5) is a tRNATrpUAG. This conclusive proof of the nature of sup7(st5) will permit unambiguous interpretation in genetic applications, and the availability of the cloned sequences may allow the sup-7 gene to be used to select for the reintroduction of DNA into C. elegans.

The yeast cloning vector YEp13 contains a tRNALeu3 gene that can mutate to an amber suppressor

We have shown that the yeast-Escherichia coli shuttle vector YEp13 contains, as part of its yeast chromosomal segment, a tRNALeu3 gene. We have also isolated and characterized a variant of YEp13 , namely YEp13 -a, which is capable of suppressing a variety of yeast amber-suppressible alleles in vivo. YEp13 -a differs from YEp13 by a single point mutation, which changes the three-nucleotide, plus-strand sequence corresponding to the tRNALeu3 anticodon from the normal C-A-A to C-T-A. This nucleotide change creates a site for the restriction enzyme XbaI in the suppressor tRNALeu3 gene. We have taken advantage of the correlation between the suppressor mutation and the XbaI site formation, to show that the tRNALeu3 gene on YEp13 corresponds to the genetically characterized yeast chromosomal amber suppressor SUP53 . We have also shown that SUP53 is located just centromere-distal to LEU2 on chromosome III. Finally, comparison of the DNA sequence of SUP53 and its flanking regions with the sequences of other cloned yeast tRNALeu3 genes has revealed considerable sequence homology in the immediate 5'-flanking regions of these genes.