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Plant Pest Risk Assessment for Event 3272 Corn

This plant pest risk assessment is to determine whether Event 3272 corn is unlikely to 

pose a plant pest risk. If APHIS determines that a genetically engineered (GE) organism 

is not a plant pest, then the GE organism is not subject to the regulatory requirements of 7 

CFR part 340.

APHIS’ authority to regulate genetically engineered organisms under the Plant Protection 

Act (PPA) (7 U.S.C. Sec 7701 et seq.) is limited to those GE organisms that are plant

pests as defined under Section 403(14) of the PPA (7 U.SC. 7702(14)). 

“Plant Pest - The term “plant pest” means any living stage of any of the following 

that can directly or indirectly injure, cause damage to, or cause disease in any 

plant or plant product:

(A) A protozoan.

(B) A nonhuman animal.

(C) A parasitic plant.

(D) A bacterium.

(E) A fungus.

(F) A virus or viroid.

(G) An infectious agent or other pathogen

(H) Any article similar to or allied with any of the articles specified in the 

preceding subparagraphs.”

APHIS will use the information submitted by the applicant in its petition for nonregulated 

status, per § 340.6(c)(4), to determine the plant pest risk associated with the regulated 

article. Specifically, APHIS uses the information related to plant pest risk characteristics, 

disease and pest susceptibilities, expression of the gene product, new enzymes, or 

changes to plant metabolism, weediness of the regulated article, any impacts on the 

weediness of any other plant with which it can interbreed, and the transfer of genetic 

information to organisms with which it cannot interbreed to analyze the potential plant 

pest risk, if any, associated with Event 3272 corn. Issues related to agricultural or 

cultivation practices will be considered in the Environmental Assessment for Event 3272 

corn. Event 3272 corn is not genetically engineered to produce a toxin or pesticide, thus 

Event 3272 corn is not targeted for use against pests in corn agriculture. Thus, APHIS 

did not examine the effects of the regulated article on nontarget organisms. However, 

APHIS does examine the effects of Event 3272 corn on animals, plants, and threatened 

and/or endangered species (TES) species in the Environmental Assessment. APHIS has 

not identified any issues related to indirect plant pest effects on agricultural production 

caused by Event 3272 corn.

Potential impacts to be addressed in this risk assessment are those that pertain to the use 

of Event 3272 corn and its progeny in the absence of confinement. The genetically 

engineered construct inserted in Event 3272 corn was evaluated to determine if the 

introduced genetic sequences cause plant disease. Morphological characteristics of Event 

3272 corn were analyzed to determine if this corn variety would become weedy or 
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invasive. The potential for gene flow to, and introgression of the genetically engineered 

constructs into, other corn varieties or wild relatives of corn were also evaluated to 

determine the potential of increased weedy or invasive characteristics in other plant 

species. APHIS also analyzed the propensity of Event 3272 corn to become a greater 

reservoir of plant pests (insects or pathogens) compared to conventional corn and 

potential for horizontal gene transfer.

Development of Alpha-Amylase Event 3272 Corn

Microbially-produced alpha-amylases are commonly used commercially in the starchprocessing step during corn dry grind and wet milling processing. Syngenta has 

developed a thermostable alpha-amylase enzyme (AMY797E) expressed in Event 3272 

corn grain for use in the dry grind fuel ethanol process in the U.S. The product concept 

of Event 3272 corn is that Event 3272 grain will serve as the source of alpha-amylase 

enzyme in the dry-grind ethanol process, replacing the addition of microbially-produced 

enzyme. Event 3272 corn will be grown using current agronomic practices, and grain 

expressing AMY797E alpha-amylase enzyme will be processed at the ethanol processing 

plant.

1. Description of inserted genetic material and potential of the material to 

cause plant disease.

Event 3272 corn has been genetically engineered to contain two transgenes: (1) the 

amy797E gene encoding the theromostable AMY797E alpha-amylase enzyme and (2) the 

pmi (manA) gene from Escherichia coli, which encodes the enzyme phosphomannose 

isomerase, used as a selectable marker. The AMY797E alpha-amylase enzyme is a 

chimeric, thermostable enzyme derived from three alpha-amylase genes originating from 

three hyperthermophilic microorganisms of the archaeal order Thermococcales. This 

enzyme was selected by Syngenta due to its increased thermostability and activity during 

dry grind ethanol production from corn. AMY797E is functionally similar to those 

thermostable, genetically engineered alpha-amylases (e.g. Bacillus species) currently 

used, and have a history of safe use in food and feed processing (Janeček et al. 1999, 

Lévêque et al. 2000, Pariza and Johnson 2001, Olempska-Beer et al. 2006). The 

expression of amy797E is driven by the promoter from a corn seed storage (gamma-zein) 

gene, which directs the accumulation of alpha-amylase in the corn kernel. The pmi gene 

is from one of the main species of bacteria living in mammal intestines, E. coli, and is 

driven by the polyubiquitin promoter from corn. 

This genetic insert also contains the terminator sequences from two plant pests, 

cauliflower mosaic virus and Agrobacterium tumefaciens. Both of these sequences are 

well-characterized, and are non-coding regulatory regions only. These sequences will not 

cause Event 3272 to promote plant disease.

DNA was introduced into corn cells from a proprietary corn line using disarmed (nonplant pest causing) Agrobacterium tumefaciens-mediated transformation methodology 

with the transformation vector designated pNOV7013. Plant cells containing the 

introduced DNA were then selected by culturing in the presence of mannose. After the 
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initial incubation with Agrobacterium, the broad-spectrum antibiotic cefotaxime was 

included in the culture medium to kill any remaining Agrobacterium. Therefore, no part 

of the plant pest A. tumefaciens is remaining in Event 3272 corn due to the transformation 

method. 

Data from Southern analyses demonstrate that Event 3272 plants: (1) contain a single 

copy of both amy797E (Figure 3-4, page 35 of petition) and pmi (Figure 3-6, page 36 of 

petition) genes, (2) contain a single copy of both the gamma-zein (Figure 3-8, page 37 of 

petition) and ubiquitin promoters (Figure 3-10, page 38 of petition), and (3) do not 

contain sequences from the transformation plasmid (pNOV7013) (Figure 3-12, page 40 

of petition) that were not intended to be transferred to Event 3272 (i.e.‘backbone 

sequences’). DNA sequences of Event 3272 corn confirmed that the overall integrity of 

the intended insert and the contiguousness of the functional elements have been 

maintained (page 30, Figure 3-15, and page 42 of petition). Statistical analyses over 

multiple generations confirm that the amy797E gene is stably integrated and is inherited 

over generations in the expected fashion (Table 3-2, page 31 of petition). Therefore, only 

the expected genetic material was stably inserted into Event 3272 corn, and there is no 

expectation that plant disease will result due to the genetic construct in Event 3272 corn.

2. Potential impacts based on the relative weediness and/or invasiveness 

of Event 3272 corn

APHIS assessed whether Event 3272 corn is any more likely to become a weed than the 

nontransgenic recipient corn line, or other corn currently cultivated. The assessment 

encompasses a thorough consideration of the basic biology of corn and an evaluation of 

unique characteristics of Event 3272 corn.

In the U.S., corn is not listed as a weed in the major weed references (Muenscher 1980, 

Holm et al. 1991, Holm et al. 1997) nor is it listed as a noxious weed species by the U.S. 

Federal Government (7 CFR part 360). Furthermore corn has been grown throughout the 

world without any report that it is a serious weed. Cultivated corn is unlikely to become 

a weed because it is not generally persistent in undisturbed environments without human 

intervention. Although corn volunteers are not uncommon, they are easily controlled by 

herbicides or mechanical means and rarely reappear in a second season. Corn also 

possesses few of the characteristics of plants that are notably successful weeds (Baker 

1965, Keeler 1989).

Syngenta conducted agronomic field trials of Event 3272 corn at a total of 25 locations in 

the U.S. corn belt during the 2003 and 2004 growing seasons. Field trial data (Tables 5-

3, 5-4, 5-5, 5-6, 5-7, 5-8, Appendix 4 of petition) indicated that Event 3272 corn does not 

exhibit characteristics that would cause it to be weedier than the parental corn line. 

Growth habitat was not remarkably different between Event 3272 corn and the control 

hybrid (Table 5-3 of petition). Two measures of late season integrity of the corn plant, 

late season intactness and push test scores, were slightly depressed in Event 3272 plants;

however a third integrity measure, percent broken stalks, was elevated in Event 3272 

plants compared to the non-transgenic control hybrids. Thus, overall, growth habitat 

characteristics did not differ in Event 3272 corn compared to the hybrid controls. 
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Vegetative vigor assessments (Table 5-4 of petition) conducted by Syngenta indicate that 

early emergence vigor, early growth rating and ear height characteristics were all similar 

between Event 3272 corn and the control hybrids. Plant height was found to be 

significantly shorter in Event 3272 corn compared to the hybrid control plants. However, 

plant height reduction is unlikely to be associated with a trend toward increasing 

weediness. 

Syngenta also evaluated the reproductive characteristics (Table 5-5 of petition) of Event 

3272 corn. The percentage of barren plants was slightly elevated in Event 3272 corn 

compared to the nontransgenic hybrid controls, and this was the only reproductive 

variable that differed between the two plant types. In terms of weediness, an increase in 

barren plants in Event 3272 corn would not increase the risk of weediness because it does 

not indicate a potential increase in reproductive output.

There was no increase in weediness potential as measured by differences in primary 

dormancy (germination potential) or secondary dormancy (overwintering ability) (Table 

5-8 of petition). There was a slight decrease in the ability of Event 3272 seeds to survive 

the ‘winter conditions’ test (5oC) compared to the nontransgenic control plants. 

However, a decrease in seed survival would not correspond to an increase in secondary 

dormancy and increased weediness. In addition, there were no changes to abiotic stress 

tolerance (as measured by early root lodging, late root lodging, and percent snapped 

plants) (Table 5-3 of petition). 

The introduced traits, increased alpha-amylase accumulation in the grain and expression 

of PMI, are not expected to cause Event 3272 corn to become a weed or improve the 

ability of this corn variety to survive without human intervention. Nor is there any 

foreseeable reason to conclude that these two genes would affect this variety’s survival in 

the wild. None of the characteristics of weeds described by Baker (Baker 1965) involves

increased alpha-amylase or PMI levels, and there is no reason to expect that these traits 

would result in increased weediness. Event 3272 corn is unchanged in its susceptibility to 

injury by commercially available herbicides, and thus could be chemically-controlled. 

Therefore, there is no selective advantage to corn containing AMY797E or PMI 

compared to conventional corn, and there is no increased potential for weediness or 

invasiveness from Event 3272 corn.

3. Potential impacts from gene flow and gene introgression from Event 

3272 corn into its sexually-compatible relatives.

Zea mays L. subsp. mays is a member of the Maydeae tribe of the grass family, Poaceae. 

It is a monoecious annual plant that requires human intervention for its seed dispersal and 

propagation. The species is open-pollinated through wind movement of pollen. 

Additional information on the biology of maize can be found within the Organisation for 

Economic Co-Operation and Development (OECD) consensus document (OECD 2003).
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In assessing the risk of gene introgression from Event 3272 corn into its sexually 

compatible relatives, APHIS considered two primary issues: 1) the potential for gene 

flow and introgression, and 2) the potential impact of introgression.

APHIS evaluated the potential for gene introgression to occur from Event 3272 corn to 

sexually compatible wild relatives and considered whether such introgression would 

result in increased weediness. Cultivated corn, or maize, Zea mays L. subsp. mays, is 

sexually compatible with other members of the genus Zea, and to a much lesser degree 

with members of the genus Tripsacum.

In general, gene flow from cultivated agricultural crops to domesticated, wild or weedy 

relatives has most likely occurred ever since the domestication of a particular crop, 

assuming sexually compatible species are present (Stewart Jr. et al. 2003). Based upon 

currently available data, there have been a relatively low number of confirmed cases of 

introgression (Stewart Jr. et al. 2003).

Wild diploid and tetraploid members of Zea, collectively referred to as teosinte, are 

normally confined to the tropical and subtropical regions of Mexico, Guatemala, and 

Nicaragua. A few isolated populations of annual (Zea mexicana) and perennial (Zea

perennis) teosinte have been reported to exist in the past in Alabama, Florida, South 

Carolina, and Maryland (USDA-NRCS 2007), but are likely no longer in existence (USEPA 2000), or are small isolated occurrences. None of these teosinte species has been

shown to be an aggressive weed in its native or introduced habitats. The Mexican and 

Central America teosinte populations primarily exist within and around cultivated corn

fields; they are partially dependent on agricultural niches or open habitats, and in some 

cases are grazed upon or fed to cattle which distribute the seed. While some teosinte may 

be considered to be weeds in certain instances, they are also used by some farmers for 

breeding improved maize (Sánchez and Ruiz 1997). Teosinte is described to be 

susceptible to many of the same pests and diseases which attack cultivated corn (Sánchez 

and Ruiz 1997)

All teosinte members can be crossed with cultivated corn to produce fertile F1 hybrids 

(Wilkes 1967, Doebley 1990a). In areas of Mexico and Guatemala where teosinte and 

corn coexist, they have been reported to produce hybrids. Of the annual teosintes, Z. 

mays subsp. mexicana forms frequent hybrids with maize, Z. luxurians hybridizes only 

rarely with maize, whereas populations of Z. mays subsp. parviglumis are variable in this 

regard (Wilkes 1977, Doebley 1990a). Research on sympatric populations of maize and 

teosinte suggests introgression has occurred in the past, in particular from maize to Z. 

mays subsp. luxurians and Z. mays subsp. diploperennis and from annual Mexican 

plateau teosinte (Z. mays subsp. mexicana) to maize (Kato Y. 1997) and references 

therein). 

Nevertheless, in the wild, introgressive hybridization from maize to teosinte is currently 

limited, in part, by several factors including distribution, differing degrees of genetic 

incompatibility, temporal separation in flowering time, differences in developmental 

morphology, variation in dissemination methods, and disparities in dormancy (Galinat 
6

1988, Doebley 1990a, 1990b). First-generation hybrids are generally less fit for survival 

and dissemination in the wild, and show substantially reduced reproductive capacity 

which acts as a significant constraint on introgression. 

Teosinte has coexisted and co-evolved in close proximity to corn in the Americas over 

thousands of years, but corn and teosinte maintain distinct genetic constitutions despite 

sporadic introgression (Doebley 1990a). The potential for gene introgression from Event 

3272 corn into teosinte would increase if varieties are developed and approved for 

cultivation in locations where these teosintes are located. However, hybridization in 

nature is extremely unlikely because the distributions of teosinte and Z. mays do not 

overlap (http://www.maizegenetics.net/index.php?page=domestication/taxonomydistribution.html), and 

because of differences in developmental morphology and reproductive timing between 

the two species. Additionally first-generation corn-teosinte hybrids are generally less fit 

for survival and dissemination, and they show substantially reduced reproductive 

capacity. Therefore, it is very unlikely that gene introgression into a wild corn relative 

will occur. Moreover, since Event 3272 corn does not exhibit characteristics to cause it to 

be any weedier than other cultivated corn, its potential impact due to the limited potential 

for gene introgression into teosinte is not expected to be any different from that of other 

cultivated corn varieties. 

The genus Tripsacum contains up to 16 recognized species, most of which are native to 

Mexico, Central and South America, but three exist or have existed as wild and/or 

cultivated species in the U.S. (Hitchcock 1971, USDA-NRCS 2007). Though many of 

these species occur where corn might be cultivated, gene introgression from Event 3272

corn under natural conditions is highly unlikely or impossible. Hybrids of Tripsacum

species with Zea are difficult to obtain outside of a laboratory and are often sterile or 

have greatly reduced fertility, and none is able to withstand even the mildest winters 

(Beadle 1980, Galinat 1988). Furthermore, none of the sexually compatible relatives of 

corn in the U.S. is considered to be a weed in the U.S. (Holm et al. 1997). AMY797E 

and PMI do not confer a selective advantage to plants that contain these genes. Thus, the 

likelihood of introgression is extremely low. In the highly unlikely event that 

introgression to a wild relative would occur, acquisition of the amy797E or pmi gene 

would not be expected to transform the wild relative into a weed. 

4. Potential of Event 3272 corn to harbor plant pests (insects and disease)

The data submitted by Syngenta indicated no significant differences between Event 3272 

corn and the non-transgenic counterparts for disease (as measured by northern corn leaf 

blight and southern corn leaf blight observations, and gray leaf spot rating) and pest 

susceptibility (as measured by European corn borer damage) (Table 5-7 of petition). The 

data presented in the petition indicated no difference in compositional and nutritional 

quality of Event 3272 corn compared to conventional corn, apart from the presence of 

AMY797E and PMI. Although some of the variables measured by the applicant showed 

statistically significant differences between Event 3272 corn and the nontransgenic 

hybrid controls (Tables 6-1 to 6-6, pages 70-76), none of the values for the forage and 

grain composition characteristics was outside the range of natural variability of 

conventional corn as found in the International Life Sciences Institute Crop Composition 
7

Database (Ridley et al. 2004, ILSI 2006) or in the OECD consensus document on corn 

composition (OECD 2003). Therefore, the composition of Event 3272 is not biologically 

different than conventional corn, and is thus susceptible to the same pest population as 

conventional corn. Additionally, Event 3272 corn is similarly affected by typical plant 

diseases found in corn, and does not harbor an altered pest or pathogen community 

compared to other corn varieties. 

5. Transfer of genetic information to organisms with which it cannot 

interbreed

Horizontal gene transfer and expression of DNA from a plant species to bacteria is 

unlikely to occur. First, many genomes (or parts thereof) have been sequenced from 

bacteria that are closely associated with plants, including Agrobacterium and Rhizobium 

(Kaneko et al. 2000, Wood et al. 2001, Kaneko et al. 2002). There is no evidence that 

these organisms contain genes derived from plants. Second, in cases where review of 

sequence data implied that horizontal gene transfer occurred, these events are inferred to 

occur on an evolutionary time scale on the order of millions of years (Koonin et al. 2001, 

Brown 2003). Third, transgene DNA promoters and coding sequences are optimized for 

plant expression, not prokaryotic bacterial expression. Thus even if horizontal gene 

transfer occurred, proteins corresponding to the transgenes are not likely to be produced. 

Fourth, the FDA has evaluated horizontal gene transfer from the use of antibiotic 

resistance marker genes, and concluded that the likelihood of transfer of antibiotic 

resistance genes from plant genomes to microorganisms in the gastrointestinal tract of 

humans or animals, or in the environment, is remote (http://vm.cfsan.fda.gov/~dms/opaarmg.html). Therefore APHIS concludes that horizontal gene transfer is unlikely to occur 

and thus poses no significant environmental or plant pest risk. 

Conclusion

APHIS has reviewed and conducted a plant pest risk assessment on Event 3272 corn.

Due to the lack of plant pest risk from the inserted genetic material, the lack of weediness 

characteristics of Event 3272 corn, the lack of atypical responses to disease or plant pests 

in the field, the lack of deleterious effects on non-targets or beneficial organisms in the 

agro-ecosystem, and the lack of horizontal gene transfer, APHIS concludes that Event 

3272 corn is unlikely to pose a plant pest risk.

Moreover, APHIS has also concluded that the existence of the alpha-amylase enzyme, by 

itself, does not constitute a plant pest in Event 3272 corn. The alpha-amylase enzyme 

engineered into Event 3272 corn is not one of the organisms listed in the statutory 

definition of a plant pest. Enzymes such as alpha-amylase are proteins that catalyze 

chemical reactions. Enzymes are not “living.” Thus, enzymes cannot be plant pests 

because they are not living and cannot be a “living stage” of any of the organisms 

(“articles”) listed in the PPA’s definition of a plant pest in subparagraphs (A) through (G) 

of 7 U.S.C. 7702(14). Likewise, the Event 3272 corn alpha-amylase enzyme also cannot 

be a living stage of any article similar to or allied with any of the articles specified in 

subparagraphs (A) through (G), and thus does not fall within the statutory definition of a 

plant pest as listed in subparagraph (H) of the PPA’s plant pest definition (i.e., “Any 

article similar to or allied with any of the articles specified in the preceding 
8

subparagraphs”). APHIS has determined that the alpha-amylase enzyme engineered into 

Event 3272 corn is not a plant pest because the alpha-amylase enzyme in Event 3272 

corn is not living and thus cannot itself be a living stage of any organism listed in the

PPA’s plant pest definition. 

APHIS has determined that neither Event 3272 corn, nor the alpha-amylase enzyme in 

Event 3272 corn, is a “living stage” of any of the organisms (articles) listed in 

subsections A-H of the PPA’s plant pest definition, Moreover, neither Event 3272 corn 

nor the alpha-amylase enzyme in Event 3272 corn is an article that harbors plant pests. 

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