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PLANT PEST RISK ASSESSMENT FOR MON 87460 CORN 

Monsanto Company has submitted a petition to APHIS seeking a determination that genetically 

engineered (GE) corn (Zea mays) event MON 87460 (APHIS number 09-055-01p-a1) is unlikely 

to pose a plant pest risk and, therefore, is no longer a regulated article under regulations at 7 CFR 

part 340. This plant pest risk assessment was conducted to determine whether MON 87460 corn 

is unlikely to pose a plant pest risk. If APHIS determines that MON 87460 corn is unlikely to 

pose a plant pest risk, APHIS then has no regulatory authority over that organism under its 

regulations at 7 CFR part 340. 

History of Development of MON 87460 Drought-Tolerant Corn 

Corn is the second major food and feed crop in world. Recently corn is also considered as a 

major biofuel crop in the U.S.; therefore, it is expected that U.S. corn cultivation may continue to 

increase in the coming years (USDA 2007). Conventional breeding methods have made 

enormous progress in corn crop improvement (Sprague and Dudley 1988). Despite those 

improvements the demand for corn far exceeds the current production level, leading to a 

worldwide grain shortage. 

As with many high yielding modern crop plants, drought is one of the major limiting factors in 

corn that prevents realization of optimum grain yield (Heisey and Edmeades 1999), and that 

problem may become a frequent feature across U.S. farmlands and elsewhere in the future. 

Abiotic stress is the primary cause of crop loss worldwide, reducing average yields for most 

major crop plants by more than 50% (Boyer 1982; Bray et al. 2000). In North America alone, it 

is estimated that 40% of annual crop losses are due to sub-optimal water availability (Boyer 

1982). Although some of the recent corn cultivars are bred to exhibit some degree of drought 

tolerance (Byrne et al. 1995; Tollenaar and Wu 1999; Bängiger et al. 2006), the current corn 

gene pool and conventional breeding techniques may not be able to bring a significant 

improvement for drought tolerance in future corn cultivars. In this regard, new biotechniques 

combined with conventional breeding methods offer potential new tools and avenues to harness 

drought tolerant gene from different sources to increase corn yield stability under water-limited 

conditions (Bänziger and Araus 2007). 

Drought conditions vary in nature, severity, and impact (Jacobsen and Shaw 1989; Close et al. 

1993; Campos et al. 2006). While extreme drought conditions prevent normal growth and 

development of plants leading to complete crop failure, suboptimal soil water at key plant 

growth stages can also substantially reduce crop yield. Drought tolerant crops are designed to 

escape water limitation through both genetic and agronomic manipulations. The strength of 

drought tolerance is a relative quantification measured over existing cultivars, which varies 

greatly among crop plants. Under no circumstances, however, it is likely that crop improvement 

alone can mitigate all economic losses under water-limited conditions; rather it has the potential 

to play a key role in minimizing crop loss in drought-prone areas (Heisey and Morris 2006). 

Monsanto has developed MON 87460 corn event (hereafter referred to as MON 87460) that is 

expected to reduce yield loss under water-limited conditions compared to conventional corn. 

The ability to withstand the water limitation in MON 87460 comes from an introduced gene 

called cold shock protein B (CSPB) derived from the bacterium Bacillus subtilis. The CSPB is a 
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RNA chaperone. RNA chaperones are ubiquitous and abundant proteins found in all living 

organisms and viruses. RNA tends to be kinetically trapped in misfolded forms, and RNA 

binding proteins, acting as chaperones, can resolve these structures, ensuring accessibility for its 

biological function. In bacteria, RNA chaperones are believed to play a general role in sustaining 

growth by favoring active transcription, translation, and/or ribosome assembly (Castiglioni et al. 

2008). In bacteria, the CSPB protein helps preserve normal cellular functions during certain 

stresses by binding cellular RNA and unfolding nontranslatable secondary structures affecting 

RNA stability and translation. As in bacteria, the CSPB protein in MON 87460 binds RNA and 

appears to help maintain plant cellular functions. 

Data submitted by Monsanto suggest that MON 87460 reduces yield loss, primarily through 

increased kernel number per ear, under water-limited conditions by minimizing the effect of 

water limitation on photosynthesis, stomatal conductance, and carbon fixation. On a plant level, 

corn yield losses associated with drought stress occur as a result of reduced synchrony between 

anthesis and silking, embryo loss, and/or reduced grain filling in viable kernels (Claassen and 

Shaw 1970; Boyer and Westgate 2004; Campos et al. 2006). Studies on conventional germplasm 

with enhanced drought tolerance show that yield improvements are attained through 

improvements in all of these endpoints (Bolanos et al. 1993: Bolanos and Edmeads 1996: Barker 

et al. 2005). Therefore, the enhanced yield stability of MON 87460 under water-limited 

conditions, conferred by the expressed CSPB protein, appears to be the result of improvements in 

the natural stress response mechanisms over conventional corn. 

 

MON 87460 corn has been field tested under APHIS regulations since 2002 and Monsanto 

provided data in the petition for field trials completed prior to the petition submission. Because 

MON 87460 reduces yield loss under water-limited conditions, Monsanto designed field studies 

to collect relevant data across a broad range of soil moisture (well watered and water-limited 

conditions) and environmental conditions relevant to where commercial production would be 

expected. Data submitted by Monsanto shows that under well-watered conditions, grain yield 

for MON 87460 is not significantly different from conventional corn, yet MON87460 

experienced reduced yield loss when water stress was around 20% less than normal. However, 

like conventional corn, MON 87460 is still subject to yield loss under severe water-limited 

conditions, particularly during flowering and grainfill periods when corn yield potential is most 

sensitive to water stress. In the following paragraphs APHIS BRS summarizes its plant pest 

risks assessment of MON 87460 because of inserted genetic elements and/or their products. 

Description of the Inserted Genetic Material

MON 87460 was developed through a plant pathogenic bacterium Agrobacterium tumefaciens 

mediated transformation of corn line LH59 embryos (Armstrong and Phillips 1988). However, 

the A. tumefaciens strain, ABI, that was used to develop MON 87460, was made non pathogenic 

by removing the pathogenic sequences present in Ti (tumor inducing) plasmid originally present 

in A. tumefaciens (Koncz and Schell 1986). The disarmed A. tumefaciens harbors a binary 

plasmid vector PV-ZMAP595 (Petition Figure III-1, p. 97). This vector was approximately 9.4 

kb and contained a single T-DNA delineated by left and right border regions with in which there 

were two expression cassettes: a cspB gene expression cassette, which contained coding 

sequence for CSPB protein, and a neomycin phosphotransferase II (nptII) expression cassette, 

which contained coding sequence for the NPTII protein. 
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The cspB expression cassette consisted of the following genetic elements (Petition Table IV-1, p. 

100): 

 Promoter, leader, and intron from the rice (Oryza sativa) actin gene, Ract1 (McElroy et 

al. 1990). 

 Full length coding sequences of Cold Shock Protein B (cspB) gene from the bacterium, 

Bacillus subtilis (Willimsky et al. 1992). 

 3' nontranslated terminator sequence of the transcript 7 gene from Agrobacterium 

tumefaciens that directs polyadenylation (Dhaese et al. 1983). 

The nptII expression cassette consisted of the following genetic elements (Petition Table IV-1, p. 

100): 

 loxP sequence from Bacteriophage P1 for the recombination site recognized by Cre 

recombinase (Russell et al. 1992). Cre-Lox recombination provides a way to knockout 

genes. 

 P-35S promoter for the 35S RNA of the Cauliflower mosaic virus (Odell et al. 1985). 

 CS-nptII coding sequence from Tn5 (Beck et al. 1982) in Escherichia coli encoding 

neomycin and kanamycin resistance (Fraley et al. 1983) that was used as a selectable 

marker during transformation selection. 

 T-nos 3' nontranslated sequence of the nopaline synthase (NOS) gene from A. 

tumefaciens. This sequence terminates gene expression by a polyadenylation site 

(Depicker et al. 1982). 

 loxP sequence from Bacteriophage P1 for the recombination site recognized by Cre 

recombinase (Russell et al. 1992). The loxP sites were inserted to facilitate the potential 

excision of the nptII cassette using CRE recombinase. 

In addition to the above-mentioned genetic elements, the insert also contained noncoding 

intervening sequences of 1-73 base pair length and right and left border sequences that were used 

during DNA cloning. 

Monsanto provided evidence demonstrating that: 

 the final product does not contain any of the backbone sequences outside of the T-DNA 

borders from the transformation vector, PV-ZMAp595 (Figure V-5, p. 117; Figure V15, p. 134), 

 the DNA inserted into the corn genome is present at a single locus and contains one 

functional copy of cspB and nptII genes (Figure V-4, p. 116; Figure V-14, p. 133), 
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 the sequence and organization of inserted genes in MON 87460 are identical to their 

original sequences and arrangements in the donor plasmid PV-ZMAp595 (based on 

DNA sequence analysis), 

 no novel open reading frames were created that spanned either the 5′ or 3′ junctions 

between the T-DNA and corn genomic sequences, and 

 the stability of introduced genes was demonstrated by the presence of introduced genes 

via Southern blot fingerprint of MON 87460 (Figures V-14 and V-15, p. 133-134) for 

seven generations tested (Figure V-13, p. 132) in the breeding history. The stability was 

further confirmed by the Mendelian inheritance of the T-DNA in MON 87460 (Petition 

Table V-3, p. 136). 

Two minor changes occurred during the MON 87460 transformation event; one in the inserted 

genetic element and one to the adjacent corn genomic DNA.. A part (733 base pairs) of the 

promoter, rice actin gene (Ract1), did not get incorporated into the transformed plant. According 

to Monsanto, this rearrangement probably resulted from double-strand break repair mechanisms 

in the plant during the Agrobacterium-mediated transformation process (Salomon and Puchta 

1998). Furthermore, analysis of the T-DNA insertion site indicated that a 22 base pair length of 

genomic DNA got deleted at the insert-to-plant DNA junction in MON 87460. Despite these 

minor genetic sequence modifications in MON 87460, neither the stability analysis of the 

inserted genetic elements over seven generations (Petition Figures V-14 and V-15, p. 133-134; 

Petition Table V-3, p. 136), nor the forage and grain compositional assessment (p. 151-174 in 

Petition) showed any biologically meaningful differences between MON 87460 and conventional 

corn control except for the drought tolerance traits. 

PLANT PEST RISK ASSESSMENT 

MON 87460 corn was produced by transformation of corn tissue using A. tumefaciens to 

introduce two genes: a gene (cspB) that confers drought tolerance and a gene (nptII) that 

facilitates selection of transformed plants. Because A. tumefaciens is a plant pest and some of 

the regulatory sequences (35S Promoter sequence from Cauliflower mosaic virus and nopaline 

synthase terminator sequence from A. tumefaciens) used to facilitate expression of these genes in 

corn were derived from plant pests, the engineered corn has been considered a regulated article 

under APHIS regulations at 7 CFR part 340. Part 340 regulates, among other things, the 

introduction of organisms and products altered or produced through genetic engineering which 

are plant pests or which there is reason to believe plant pests. APHIS regulations under 7 CFR 

part 340.1 defines a plant pest as "Any living stage (including active and dormant forms) of 

insects, mites, nematodes, slugs, snails, protozoa, or other invertebrate animals, bacteria, fungi, 

other parasitic plants or reproductive parts thereof; viruses; or any organisms similar to or allied 

with any of the foregoing; or any infectious agents or substances, which can directly or indirectly 

injure or cause disease or damage in or to any plants or parts thereof, or any processed, 

manufactured, or other products of plants." 

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

87460 com and its progeny in the absence of confinement. Of the information requested by 

APHIS for submission of a petition for nonregulated status (§ 340.6(c)(4)), APHIS examined 

information submitted by the applicant related to plant pest risk characteristics, expression of the 
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gene product, changes to plant metabolism, disease and pest susceptibilities, impacts on the 

weediness of any other plant with which it can interbreed, weediness of the regulated article, and 

impacts on nontarget organisms. Issues related to agricultural or cultivation practices are 

discussed in the Environmental Assessment for MON 87460 corn.

Potential Impacts of Genetic Modifications on Altered Disease and Pest Susceptibilities 

USDA-APHIS assessed whether MON 87460 corn is likely to have significantly increased 

disease and pest susceptibility. This assessment encompasses a thorough consideration of 

introduced traits, their impact on agronomic traits and plant composition, and interactions with 

pests and diseases. 

Introduced Traits 

MON 87460 contains drought tolerance traits from the introduced gene product CSPB protein 

and a selectable marker gene product NPTII protein. The CSPB protein in MON 87460 belongs 

to the cold-shock protein (CSP) family and is identical in amino acid sequence to the native 

CSPB protein produced in B. subtilis (Willimsky et al., 1992) with the exception of one amino 

acid change in the second position from leucine to valine. This amino acid change was 

implemented by Monsanto to facilitate the assembly of the plasmid vector PV-ZMAP595 for 

plant transformation. The structure of CSPB is well characterized (Schindelin et al. 1993; 

Schindelin et al. 1994) and in bacteria CSPs are composed of 67-73 amino acids (Graumann et 

al. 1997). The CSPB protein in MON 87460 consists of 66 amino acids (Petition Figure IV-1, p. 

102). Although Figure IV-1 shows 67 amino acids for the CSPB protein in MON 87460, which 

were predicted based on cspB coding sequence, following translation, however, the N-terminal 

methionine is cleaved by methionine aminopeptidase leaving 66 amino acids in the final CSPB 

protein in MON 87460 (Petition Appendix B, p. 283-284). CSPs are a group of small proteins 

that contain a highly conserved RNA-binding sequence identified as a cold shock domain (CSD). 

Under environmental stress, bacterial CSD-containing proteins have been shown to bind many 

types of RNA (Cristofari and Darlix, 2002), leading to sustainable translation, maintenance of 

mRNA levels, and improved cellular function. Similar to bacteria, CSD-containing proteins in 

plants also bind RNA, unfold RNA secondary structures caused by environmental stress, and 

help maintain cellular functions under stress. These plant CSD proteins share a high level of 

similarity to the bacterial CSPs and have been shown to share in vitro and in vivo functions with 

bacterial CSPs (Karlson and Imai 2003; Kim et al. 2007; Nakaminami et al. 2005 and 2006; 

Chaikam and Karlson 2008; Fusaro et al. 2007). As with bacterial and other plant CSDcontaining proteins, the CSPB protein from B.subtilis, which is expressed in MON 87460, binds 

RNA, unfolds RNA secondary structures, and accumulates in actively growing tissues (Figures I7 – I-9). CSPB accumulation is highest in rapidly growing areas of the leaf and seedling and 

tends to decline as the tissue matures. CSPB concentrations tend to increase over time in 

developing ears and decline over time in silks. Likewise, CSPB concentrations increase over 

time in immature tassels and either remain the same or decline in pollen. Taken together, the 

data on RNA binding, CSPB accumulation and CSPB localization in MON 87460 are consistent 

with the pattern of RNA binding, accumulation, localization, and functions described for plant 

CSD-containing proteins (Fusaro et al. 2007; Sasaki et al. 2007; Chaikam and Karlson 2008). 

Monsanto did not observe any abnormal or altered mechanisms of plant response to drought 

stress in transgenic CSPB-containing corn plants. Greenhouse experiments were conducted with 
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CSPB events that are genetically and phenotypically similar to MON 87460 to evaluate if these 

characteristics had been altered when compared with controls. The plants containing CSPB 

protein show broadly the same relative water content (Table I-4), leaf water potential (Figure I22), and leaf osmotic potential (Figure I-23) as the control plants. CSPB-containing plants 

accumulate similar levels of abscisic acid (ABA) (Figure I-24) and osmotically active solutes 

(sucrose, fructose, glucose, choline, proline, glycine betaine) as observed in controls (Figures I25 - 28). Results from these experiments suggest that common mechanisms of plant response to 

drought stress are not altered in transgenic CSPB-containing corn plants. Thus, like endogenous 

CSD proteins found in plants, the CSPB protein in MON 87460 interacts with RNA, 

accumulates, and localizes to rapidly growing tissues and in developing reproductive organs, 

thereby helping to maintain normal cellular function in those tissues critical to yield under waterlimited conditions. Monsanto observed that the major component contributing to the improved 

yield of MON 87460 under water-limited conditions was the increased number of kernels per 

plant (Petition Tables I-1 & I-2, p. 46-47), which is consistent with the current understanding of 

the effect of drought stress on corn yield potential (barker et al. 2005). 

NPTII protein is well characterized (Fuchs et al. 1993), and in MON 87460 NPTII protein 

consists of 264 amino acids (Petition Figure IV-2, p. 102). The NPTII protein in MON 87460 

confers resistance to kanamycin, so as to facilitate the selection of transformed plants (Bevan et 

al. 1983). The effect of NPTII protein on plant growth and development has been extensively 

evaluated through several lines of experimental evidence, and several products containing NPTII 

have been approved by regulatory agencies on a global basis(e.g. so far NPTII was used as a 

selectable marker in 28 petitions deregulated by APHIS BRS; 

http://www.isb.vt.edu/cfdocs/biopetitions1.cfm). NPTII is the most commonly used antibiotic 

resistance marker in several commercially grown biotechnology-derived crops including 

YieldGard® Rootworm corn (MON 863), Bollgard® cotton (MON 531), Bollgard®II cotton 

(MON 15985), and Roundup Ready cotton (MON 1445). NPTII protein was never found to 

facilitate plant pest characteristics to plants. Based on the known functions and mechanisms of 

these proteins (summarized in the petition), neither of these proteins are expected to directly alter 

susceptibility to plant pathogens. 

Compositional Analysis 

Compositional comparisons between MON 87460 and a conventional control were 

performed using the principles and analytes outlined in the OECD consensus documents 

for corn composition (OECD 2002 and 2006). The control substance was a conventional corn 

hybrid with genetic background similar to MON 87460. The investigation also included 15 other 

conventional commercial corn hybrids (Petition Appendix Tables E-1 and E-2, p. 311). The 

commercial reference hybrids selected by Monsanto for each study were adapted to the 

geographic region in which they were grown with selections based on agronomic characteristics 

such as relative maturity and drought tolerance ratings. The rationale for the use of commercial 

references in various experiments was to provide data for the development of a 99% tolerance 

interval for each variable analyzed. This interval is expected to contain, with 95% confidence, 

99% of the values obtained from the population of commercial corn highlighting the existing 

natural variability in the commercial corn under cultivation. The knowledge of existing natural 

variability was used to draw biological meanings into those statistically significant differences 

between MON 87460 and controls. This comparative evaluation also considered natural ranges 
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in corn component levels published in the literature or in the International Life Sciences Institute 

Crop Composition Database ((ILSI 2006). 

Monsanto’s compositional analyses of MON 87460 were based on forage and grain harvested 

from two different growing seasons, the first during 2006 in the U.S. conducted under typical 

agronomic practices and water conditions, and the second during 2006/2007 in Chile under wellwatered and water-limited conditions. Components evaluated in samples harvested from both 

studies included (1) moisture, protein, carbohydrates by calculation, fat, fiber, and ash in a 

proximate analysis, (2) essential macro- and micro-nutrients in a nutritional analysis, and (3) 

known endogenous toxicants and anti-nutrients. A supplementary analysis of secondary 

metabolites associated with stress tolerance was also conducted by Monsanto for samples from 

Chile in 2006 and 2007 (see Appendix E for details). In total, there were 434 comparisons made 

for compositional analyses (7 sets of comparisons x 53 components from grain) + (7 sets of 

comparisons x 9 components from forage). 

Overall, a comprehensive evaluation of MON 87460 and the control showed no biologically 

meaningful differences for grain and forage compositions either for major nutrients (Petition 

Table VII-2, p. 157-158; Table VII-3, p. 164; Table VII-5, p. 168) or for secondary metabolites 

(Petition Table VII-6, p. 171; Petition Table VII-7, p. 173). The few detected differences were 

either exceedingly small in magnitude or the mean component values of MON 87460 and the 

control were within the 99% tolerance interval. Therefore, based on the data presented by 

Monsanto on forage and grain, it is reasonable to assume that the foods and feeds derived from 

MON 87460 can be considered compositionally equivalent to those derived from conventional 

corn. 

Agronomic Properties 

Monsanto evaluated phenotypic and agronomic characteristics of MON 87460 in a 

comparative manner to assess plant pest potential (OECD, 1993). These assessments 

included 14 plant growth and development characteristics, five seed germination 

parameters, two pollen characteristics, several observations on plant-insect and plant-disease 

interactions, and plant responses to abiotic stressors (Petition Table VIII-1, p. 178). Monsanto 

provided phenotypic and agronomic data (see Section VIII. Phenotypic, Agronomic, and 

Environmental Interactions Assessment, p. 176-231) supporting their claims that MON 87460 is 

similar to unmodified control corn cultivar except for the intended drought tolerant trait and that 

MON 87460 does not possess characteristics that would confer a plant pest risk compared to 

conventional corn. Detailed agronomic and phenotypic characteristics are discussed further in 

relevant sections of this document, while the observed disease and pest susceptibility of MON 

87460 is discussed in the following paragraph. 

Monsanto used well-established qualitative or quantitative techniques to measure field trials for 

damage due to diseases (Anthracnose, Ear rot, Kernel rot, Eyespot, Fusarium, Gray leaf spot, 

Gray mold, Leaf blight, Maize dwarf mosaic virus, Northern leaf spot, Pythium, Rust, Seedling 

blight, Smut, Southern leaf blight, Stalk rot, Stewarts wilt, and Yellow leaf blight), insect pests 

(Aphids, Leafhoppers, Armyworms, Corn earworms, European corn borers, Southwestern corn 

borers, Grasshoppers, Corn rootworms, Flea beetles, Japanese beetles, Grape colaspis, 

Wireworms, White grubs, Spider mites, Seedcorn maggots) for two years conducted across 
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different agroecological conditions. The data submitted by Monsanto indicated no meaningful 

differences between MON 87460 corn and the non-transgenic counterparts for diseases (Petition 

Table H-2, p. 432), or insect pests (Petition Tables H-3 to H-7, p. 433-441; Table H-4, p. 434: 

Tables H-5 to H-6, p. p. 435-438). Thus MON 87460 corn is expected to be susceptible to the 

same plant pathogens and insect pests as conventional corn. 

Monsanto’s aforementioned data (description of the inserted genetic elements, expression of the 

gene product, compositional analysis, and agronomic and phenotypic observations) indicates that 

MON 87460 corn is not biologically different from conventional corn (with the exception of the 

CSPB3 and NPTII proteins), and MON87460 is no more susceptible to pests and diseases 

compared to conventional corn cultivars. 

Potential Impacts from Outcrossing (Gene Flow) to Sexually-compatible Wild Relatives 

Gene flow is a natural biological process with significant evolutionary importance. A number of 

angiosperm taxa are believed to be derived from hybridization or introgression between closely 

related taxa (Grant 1981; Soltis and Soltis 1993; Rieseberg 1997; Hegde et al. 2006), and even in 

the existing floras, the occurrence of hybridization or introgression is reported to be widespread 

(Stace 1987; Rieseberg and Wendel 1993; Peterson et al. 2002). It has been a common practice 

by plant breeders to artificially introgress traits from wild relatives into crop plants to develop 

new cultivars. However, gene flow from crops to wild relatives is also thought of as having a 

potential to enhance the weediness of wild relatives, as observed in rice, sorghum, sunflower and 

few other crops (see Table 1 in Ellstrand et al. 1999). 

Corn is a monoecious species with separate male and female inflorescences that enable cross 

pollination. Corn is predominantly a wind pollinated outcrosser with occasional bee visitation 

for pollen. Bees rarely visit female inflorescences (silk). Researchers recognize that: (i) the 

percent gene flow will vary by population, hybrid or inbred, (ii) the level of gene flow decreases 

with greater distance between the source and recipient plants; (iii) environmental factors affect 

the level of gene flow, (iv) corn pollen is viable for a relatively short period of time under field 

conditions, (v) corn produces ample pollen over an extended period of time, and (vi) corn is not 

pollinated by insects (pollinating insects, especially bees, are occasional visitors to the tassels but 

rarely visit silks of corn) (Jemison and Vayda, 2000; Luna et al., 2001). 

APHIS evaluated the potential for gene introgression to occur from MON 87460 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 

several members of the genus Zea, and to a much lesser degree with members of the genus 

Tripsacum (OECD 2003; Petition Table II-1, p. 82). 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 (Wilkes 1967; Matsuoke et al. 2002; Fukunaga et 

al. 2005). Corn and annual teosinte (Zea mays subsp. mexicana) are genetically compatible, 

wind-pollinated, and may hybridize when in close proximity to each other, e.g., in areas of 

Mexico and Guatemala. While some teosinte may be considered weeds in certain instances, they 

are also used by some farmers for breeding improved maize (Sánchez and Ruiz 1997 and 

references therein). Teosinte is described as being susceptible to many of the same pests and 

diseases that attack cultivated corn (Sánchez and Corral 1997). In the wild, introgressive 
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hybridization from corn to teosinte is currently limited, in part, by several factors including 

geographic isolation, differing degrees of genetic incompatibility, differences in flowering time 

in some cases, developmental morphology and timing of the reproductive structures, 

dissemination, and dormancy (Doebley 1990a and 1990b; Galinat 1988; Ellstrand 2007). 

Genetically based cross-incompatibility mechanisms are known to reduce hybrids between corn 

and teosinte when corn is the pollen source (Baltazar et al. 2005; Kermicle and Evans 2005), 

which thus acts as a significant constraint to introgression. 

Teosinte is not present in the U.S. other than as an occasional botanical garden specimen and a 

few small feral populations of Zea mexicana in Florida, Alabama, and Maryland and Zea 

perennis in South Carolina (http://plants.usda.gov). Introgression of genes from corn into 

teosinte or Tripsacum species has not been described to occur in nature in the U.S. Furthermore, 

MON 87460 is unlikely to outcross with sexually compatible species in the U.S. as differences in 

factors such as flowering time, geographical separation, and development factors make natural 

crosses in the U.S. highly unlikely. 

Corn is also distantly related to the species in the genus Tripsacum, which contains up to 16 

recognized species (Petition Table II-1, p. 82), most of which are native to Mexico, Central and 

South America, but three (T. dactyloides, T. floridatum, and T. lanceolatum) exist as wild and/or 

cultivated species in the continental U.S (OECD 2003); and two taxa (T. fasciculatum and T. 

latifolium) also occur in Puerto Rico (http://plants.usda.gov). In contrast with corn and teosinte 

which easily hybridize under certain conditions, special techniques are required to hybridize corn 

and Tripsacum and the offspring of the cross show varying levels of sterility (Galinat 1988; 

Mangelsdorf 1974; Russell and Hallauer 1980). Furthermore, none of the sexually compatible 

relatives of corn in the U.S. are considered to be weeds in the U.S. (Holm et. al. 1979). 

Therefore, even in those instances of accidental gene flow between MON 87460 corn and wild 

relatives, the transgenes of MON 87460 corn are unlikely to transform corn wild relatives into 

more weedy species. Based on the data presented in the petition, MON 87460 corn does not 

exhibit characteristics that cause it to be any weedier than other cultivated corn (see the section 

“Potential Impacts Based on the Relative Weediness of MON 87460 Corn” below). Moreover, 

its potential impact due to the extremely limited potential for gene introgression into teosinte is 

not expected to be any different than that of other cultivated corn varieties. Based on the above 

considerations, MON 87460 corn is unlikely to adversely impact sexually compatible wild 

relatives or their weediness characters. 

Potential Impacts Based on the Relative Weediness of MON 87460 Corn 

In the U.S., corn is not listed as a weed (Crockett 1977; Holm et al. 1979; Muenscher 1980), nor 

is it present on the Federal Noxious Weed List (7 CFR part 360; 

http://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/weedlist2006.pdf). 

Furthermore, corn is grown throughout the world without any report that it is a serious weed or 

that it forms persistent feral populations. Corn is poorly suited to survive without human 

assistance and is not capable of surviving as a weed (Baker 1965; Keeler 1989; Galinat 1988). 

Like many domesticated crops, corn seed from a previous year’s crop can overwinter and 

germinate the following year. For instance, the appearance of corn seedlings in soybean fields 

following a corn crop is a common occurrence. Manual or chemical measures are often applied 

to remove these volunteers, but the plants that are not removed do not typically result in feral 
10

populations in subsequent years. Corn does not possess suit of traits that are characteristics of 

successful weeds (Baker 1965; Keeler 1989). 

APHIS assessed whether MON 87460 corn is any more likely to become a weed than the 

isogenic nontransgenic corn line, or other corn varieties currently under cultivation. The 

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

of the unique characteristics of MON 87460 corn evaluated under field conditions, including 

potential weedines traits such as seed dormancy and germination, rate of growth and 

development, flowering, seed dispersal, seed yield, and persistence of free living populations 

outside cultivation. Monsanto collected phenotypic and agronomic field data from field trials 

conducted at 27 U.S. locations during the 2006 and 2007 growing seasons that included diverse 

agroecological regions representative of the major corn-growing areas of the upper mid-west in 

the U.S. Likewise, Monsanto also collected complimentary data from four field trials from Chile 

(Petition Table VIII-2, p. 189). In addition, data on abiotic stress tolerance from greenhouse and 

growth chamber assays were used to characterize the extent of stress tolerance imparted by the 

insertion of the cspB gene and determine whether any potential changes in tolerance enhanced 

weediness potential in MON 87460. 

For the majority of the traits assessed, there were no statistically significant differences between 

MON 87460 and nontransgenic control (Petition Tables VIII-4 to VIII-12, p. 192-204; Tables 

VIII-14 to VIII-16, p. 208-210). No biologically meaningful differences were detected in the 

germination and dormancy of seed from MON 87460. In particular, the absence of hard seed 

supports a conclusion of no increased weediness potential of MON 87460 compared to 

conventional corn for germination and dormancy characteristics (Petition Table VIII-14, p. 208). 

No differences were detected in pollen morphology or viability between MON 87460 and the 

control (Petition Table VIII-15 & VIII-16, p. 209-210). Results from the genotypeenvironmental interaction assessments also support the conclusion that MON 87460 has no 

increased susceptibility or tolerance to specific diseases, arthropods, or abiotic stressors, with the 

exception of drought. Development of deep root system is typically one of the agronomic traits 

that has potential to enhance weediness in the natural environment. However that may not be the 

case with corn, as inbred lines with poor early root development exhibited higher yields under 

drought stress than ones with accelerated early development of roots (Bruce et al. 2002). It has 

been reasoned that the improved performance of corn cultivars to drought stress probably comes 

from better water use efficiency (Messmer et al. 2009). Finally, MON 87460 was not altered in 

its ability to volunteer in cultivated fields or survive in areas not managed for agricultural 

production compared to conventional corn. 

Based on the agronomic field data and literature survey concerning corn’s weediness potential, 

MON 87460 corn is unlikely to persist as a troublesome weed or to impact on current weed 

management practices. Furthermore, extensive post-harvest monitoring of field trial plots 

planted with MON 87460 under USDA-APHIS notifications (Appendix N, p. 519-523) did not 

reveal any differences in survivability or persistence relative to other corn. These data suggest 

that MON 87460 is no more likely to become a weed than conventional corn. 
11

Potential Impacts on Nontarget Organisms, Including Beneficial Organisms 

Monsanto is in consultation with FDA about food and feed derived from corn event MON 87460 

and has submitted a comprehensive assessment of food and feed safety data on CSPB and NPTII 

proteins of MON 87460 to FDA. Monsanto considered the following factors to establish food 

and feed safety of introduced gene products. 

 The donor organism of the CSPB protein, B. subtilis, is not pathogenic, is often 

used as a food additive, is present in many fermented foods, and has a history of 

safe consumption. In 1999, FDA designated enzyme preparations from this 

organism as GRAS (generally recognized as safe, FDA, 1999). 

 The B. subtilis CSPB shares a high percent of identity with CSPs present in other 

bacterial species broadly used by the food industry and with CSD-containing 

proteins in plant species used as a food. Many foods prepared with the help of B. 

subtilis have been consumed for a long time with no documented history of any 

adverse effects to human health. CSPB protein present in MON 87460 shares amino acid 

identity to other naturally occurring CSD-containing proteins found in 

food and feed products. The amino acid identity of CSPB ranges from 35% to 98.5% 

across different plant and bacterial species. The CSPB protein is homologous to the CSP 

proteins found in the genera Lactobacillus, Lactococcus, Bifidobacterium, and E. coli, 

which are normally present in gastrointestinal flora and, therefore, considered to be safe. 

 A dietary safety assessment conducted to evaluate the risks to humans and 

animals from the CSPB and NPTII proteins present in the foods and feeds derived 

from MON 87460 did not cause any observed adverse effects even at the highest 

tested dose levels. 

 CSPB protein represents no more than 0.00007% of the total protein in the grain 

of MON 87460. Digestive fate experiments conducted with the CSPB protein 

demonstrated that the full-length protein is rapidly digested in simulated gastric fluid, a 

characteristic shared among many proteins with a history of safe consumption. Proteins 

that are rapidly digestible in mammalian gastrointestinal systems are unlikely to be 

allergens when consumed. 

 CSPB and NPTII proteins do not share any amino acid sequence similarities with 

known allergens, gliadins, glutenins, or protein toxins which have adverse effects 

to mammals. 

 The safety of the NPTII protein and its donor organism, E. coli, have been 

recognized by regulatory agencies and well documented. All existing data 

suggest that the NPTII protein represents a negligible hazard to human health and is safe 

for consumption. 

The introduced gene products of MON 87460 do not contain pesticidal activity and are not 

aimed at any target organisms as a control measure. As mentioned earlier, MON 87460 is found 

to be safe for human and animal consumption. Therefore, Monsanto assessed the nontarget 
12

impact of MON 87460 on all those exposed organisms (e.g. pests, diseases, and beneficial 

arthropods) in the corn agroecosystem. 

During the U.S. and Chile phenotypic field studies at 31 locations in 2006 and 

2007, each field site was rated at four time intervals during the season for specific insects 

(pest and non-pests), and diseases (Petition Section VIII.F.1, p. 211-212) to evaluate whether the 

plant-disease or plant-insect interactions of MON 87460 were altered compared to commercial 

corn. Out of nearly 388 pest and non-pest arthropod evaluations, only two differences were 

observed between MON 87460 and the control. Grasshopper damage was lower for MON 87460 

compared to the control and European corn borer damage was higher for MON 87460 compared 

to the control. These differences were within the range of the references observed for corn 

cultivars. Likewise, out of the more than 425 disease stressor observations, no differences were 

detected between MON 87460 and the control. These results support the conclusion that no 

biologically meaningful interactions were observed with the species exposed to MON 87460 and 

that MON 87460 is not different in its environmental interactions relative to other corn. 

Potential Impacts from Transferring Genetic Information from MON 87460 Corn to 

Organisms with which It cannot Interbreed 

APHIS examined the potential for the new genetic material inserted into MON 87460 corn to be 

horizontally transferred to other organisms without sexual reproduction and whether such an 

event could lead directly or indirectly to disease, damage, injury or harm to plants, including the 

creation of more virulent pathogens. The horizontal gene transfer between unrelated organisms 

is one of the most intensively studied fields since 1940, and the issue gained extra attention with 

the release of transgenic plants into the environment (Droge et al. 1998). Horizontal gene 

transfer has been implicated as a major contributor to the spread of antibiotic resistance amongst 

pathogenic bacteria and the emergence of increased virulence in bacteria, eukaryotes, and 

viruses; and has contributed to major transitions in evolution. 

Potential for Horizontal Gene Transfer to Bacteria, Fungi, OR Viruses 

The MON 87460 contains two genes and two noncoding regulatory sequences from bacteria. 

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

unlikely to occur based on the following observations. Although there are many opportunities 

for plants to directly interact with fungi and bacteria (e.g. as commensals, symbionts, parasites, 

pathogens, decomposers, or in the guts of herbivores), so far there are no reports of horizontal 

gene transfer to bacteria from eukaryotes or from plants to fungi (as reviewed in Keese 2008). 

The only genes likely to be transferred successfully from genetically engineered plants to 

bacteria are other bacterial genes. Horizontal transfer from and expression in bacteria of the 

foreign DNA inserted into the nuclear genome of MON 87460 corn 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; Kaneko et al. 2002; 

Wood et al. 2001). 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, 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 
13

humans or animals, or in the environment, is remote (http://vm.cfsan.fda.gov/~dms/opaarmg.html). APHIS also considered whether horizontal transfer of DNA from MON 87460 corn 

to plant viruses was likely to occur and would lead to the creation or selection of a more virulent 

plant pathogen through recombination with other plant viruses. This issue has been considered 

before by other science review panels and government regulatory bodies (for a general review of 

the issue see Keese 2008). There are two noncoding regulatory sequences (35S and LoxP) from 

virus present in MON 87460 corn. These two sequences have not been implicated in viral 

recombination raising safety concerns (Hull et al. 2000). 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 MON 87460 corn. Due to 

the lack of plant pest risk from the inserted genetic material, the lack of atypical responses to 

disease or plant pests in the field, the lack of weediness characteristics of MON 87460 corn, 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 MON 87460 corn is unlikely to pose a 

plant pest risk. 
14

References 

Armstrong, C.L., and Phillips, R. L.. 1988. Genetic and cytogenetic variation in plants 

regenerated from organogenic and friable, embryogenic tissue cultures of maize. 

Crop Science 28: 363-369. 

Baker, H. B. 1965. Characteristics and modes of origin of weeds. Pp. 147-169 in H. G. 

Baker and G. L. Stebbins (eds.), The genetics of colonizing species. Academic Press, London. 

Baltazar, B. M., Sánchez González, J. J., de la Cruz-Larios, L., and Schoper, J. B. 2005. 

Pollination between maize and teosinte: an important determinant of gene flow in Mexico. 

Theoretical and Applied Genetics 110: 519–526.

Bänziger, M., and Araus, J. 2007. Recent advances in breeding maize for drought and salinity 

stress tolerance. PP 587-601in M.A. Jenks and P.M. Hasegawa and S.M. Jain (eds.), Advances 

in Molecular Breeding Toward Drought and Salt Tolerant Crops. Springer, Dordretch, 

Netherlands. 

Bängiger, M., Setimela, P. S., Hodson, D., and Vivek, B. 2006. Breeding for improved drought 

tolerance in maize adapted to southern Africa. Agricultural Water Management 80: 212-224. 

Barker, T., Campos, H., Cooper, M. Dolan, D. Edmeades, G. O., Habben, J. Schussler, J. Wright, 

D., and Zinselmeoer, C. 2005. Improving drought tolerance in maize. Plant Breeding Review 

25: 173-253. 

Beck, E., Ludwig, G., Auerswald, E. A., Reiss, B. and Schaller, H. 1982. Nucleotide 

sequence and exact localization of the neomycin phosphotransferase gene from 

transposon Tn5. Gene 19: 327-336. 

Bevan, M.W, Flavell, R. B., and Chilton, M.D. 1983. A chimeric antibiotic resistance gene as a 

selectable marker for plant cell transformation. Nature 304: 184-187. 

Bolanos, J., and Edmeades, G. O. 1996. The importance of the anthesis-silking interval in 

breeding for drought tolerance in tropical maize. Field Crops Research 48: 65-80. 

Bolanos, J., Edmeades, G. O., and Martinez, L. 1993. Eight cycles of selection for drought 

tolerance in tropical maize. III. Responses in drought-adaptive physiological and morphological 

traits. Field Crops Research 31: 269-286. 

Boyer, J. S. 1982. Plant productivity and environment. Science 218: 443–448. 

Boyer, J. S., and Westgate, M. E. 2004. Grain yields with limited water. Journal of 

Experimental Botany 55: 2385-2394. 

Bray, E.A. Bailey-Serres, J., and Weretilnyk, E. 2000. Responses to abiotic stresses. Pp. 1158-

1249 in W. Gruissem, B. Buchannan and R. Jones (eds.) Biochemistry and Molecular Biology of 

Plants. American Society of Plant Physiologists, Rockville, MD. 
15

Brown, J. R. 2003. Ancient horizontal gene transfer. Genetics 4: 121-132. 

Bruce, W.B., Edmeades, G. O., and Barker, T. C. 2002. Molecular and physiological 

approaches to maize improvement for drought tolerance. Journal of Experimental 

Botany 53: 13-25. 

Byrne, P.F., Bolanos, J., Edmeades, G. O. and Eaton, D. L. 1995. Gains from selection 

under drought versus multilocus testing in related tropical maize populations. Crop Science 35: 

63-69. 

Campos, H., Cooper, M., Edmeades, G. O., Loffler, C., Schussler, J. R. and Ibanez. M. 2006. 

Changes in drought tolerance in maize associated with fifty years of breeding for yield in the 

U.S. Corn Belt. Maydica 51: 369-381. 

Castiglioni, P., Warner, D., Bensen, R. J., Anstrom, D. C., Harrison, J., Stoecker, M., Abad, M., 

Kumar, G., Salvador, S., Ordine, R. D., Navarro, S., Back, S., Fernandes, M., Targolli, J., 

Dasgupta, S., Bonin, C., Luethy, M. H., and Heard, J. E. 2008. Bacterial RNA chaperones 

confer abiotic stress tolerance in plants and improved grain yield in maize under water-limited 

conditions. Plant Physiology 147: 446-455. 

Chaikam, V., and Karlson, D. 2008. Functional characterization of two cold shock 

domain proteins from Oryza sativa. Plant Cell and Environment 31: 995-1006. 

Claassen, M. M., and Shaw, R. H. . 1970. Water deficit effects on corn. II. Grain 

components. Agronomy Journal 62: 652-655. 

Close, T. J., Fenton, R. D., Yang, A., Asghar, R., DeMason, D. A., Crone, D. E., Meyer, N. C., 

and Moonan, F. 1993. Dehydrin: the protein. Current Topics in Plant Physiology 10: 104-118. 

Cristofari, G., and Darlix, J. L. 2002. The ubiquitous nature of RNA chaperone proteins. 

Progress in Nucleic Acid Research and Molecular Biology 72: 223-268. 

Crockett, L. 1977. Wildly Successful Plants: North American Weeds. University of 

Hawaii Press, Hawaii. 

Depicker, A., Stachel, S., Dhaese, P., Zambryski, P., and Goodman, H. M. 1982. Nopaline 

synthase: transcript mapping and DNA sequence. Journal of Molecular and 

Applied Genetics 1: 561-573. 

Dhaese, P., De Greve, H., D., Gielen, J., Seurinck, L., Van Montague , M. and Schell, J. 1983. 

Identification of sequences involved in polyadenylation of higher plant nuclear 

transcripts using Agrobacterium T-DNA genes as models. EMBO Journal . 2: 419- 

426. 

Doebley, J. 1990a. Molecular evidence for gene flow among Zea species. BioScience 

40: 443- 448. 
16

Doebley, J. 1990b. Molecular systematics of Zea (Gramineae). Maydica 35:143-50. 

Dröge, M., Puhler, A., and Selbitschka, W. 1998. Horizontal gene transfer as a biosafety 

issue: A natural phenomenon of public concern. Journal of Biotechnology 64: 75-90. 

Ellstrand, N. C., Prentice, H. C., and Hancock, J. F. 1999. Gene flow and introgression 

from domesticated plants into their wild relatives. Annual Review of Ecology and Systematics 

30: 539-563. 

Ellstrand, N.C., Garner, L. C., Hegde, S., Guadagnuolo, R., and Blancas, L. 2007. 

Spontaneous hybridization between maize and teosinte. Journal of Heredity 

98: 183-187. 

FDA (Food and Drug Administration). 1999. Carbohydrase and protease enzyme preparations 

derived from Bacillus subtilis or Bacillus amyloliquefaciens; affirmation of GRAS status as 

direct food ingredients, Final Rule. Federal Register 64:19887-19895, U.S. Food and Drug 

Administration, Washington, D.C. 

Fraley, R.T., Rogers, S.. G., Horsch, R. B., Sanders, P. R., Flick, J. S., Adams, S. P., 

Bittner, M. L., Brand, L. A., Fink, C. L., Fry, J. S., Galluppi, G. R., Goldberg, S. B., 

Hoffmann, N. L., and Woo, S. C. 1983. Expression of bacterial genes in plant cells. 

Proceedings of the National Academy of Sciences (USA) 80: 4803-4807. 

Fuchs, R.L., R.A. Heeren, M.E. Gustafson, G.J. Rogan, D.E. Bartnicki, R.M. 

Leimgruber, R.F. Finn, A. Hershman, and S.A. Berberich. 1993. Purification and 

characterization of microbially expressed neomycin phosphotransferase II 

(NPTII) protein and its equivalence to the plant expressed protein. 

BioTechnology 11: 1537-1542. 

Fukunaga, K., Hill, J., Vigouroux, Y., Matsuoka, Y., Sanchez, J. S., Liu, K., Buckler, E. S., and 

Doebley, J. 2005. Genetics 169: 2241–2255. 

Fusaro, A.F., Bocca, S.N, Ramos, R.L.B., Barroca, R.M., Magioli, C., Jorge, V.C., 

Coutinho, T.C., Rangel-Lima, C.M., De Rycke, R., Inze, D., Engler, G., and 

Sachetto-Martins, G. 2007. AtGRP2, a Cold-induced Nucleo-cytoplasmic RNAbinding 

Protein, has a role in flower and seed development. Planta. 225: 1339-1351 

Galinat, W.C. 1988. The origin of corn. Pp.1-31 in Sprague, G.F. and J.W. Dudley (eds.) Corn 

and Corn Improvement. 3rd ed., American Society of Agronomy, Crop Science Society of 

America, and Soil Science Society of America, Madison, WI. 

Grant, V. 1981. Plant speciation. Columbia University Press, New York. 
17

Graumann, P., T.M. Wendrich, M.H.W. Weber, K. Schroder, and M.A. Marahiel. 1997. 

A family of cold shock proteins in Bacillus subtilis is essential for cellular growth 

and for efficient protein synthesis at optimal and low temperatures. Molecular Microbiology 25: 

741-756. 

Hegde, S.G., Nason, J. D., Clegg, J. M., and Ellstrand, N. C. 2006. The evolution of 

California’s wild radish has resulted in the extinction of its progenitors. Evolution 60:1187-

1197. 

Heisey, P. W., and Edmeades, G. O. 1999. Maize production in drought-stressed environments: 

Technical options and research resource allocation. Part I of CIMMYT 1997/1998 World Facts 

and Trends: Maize Production in Drought-Stressed Environments: Technical Options and 

Research resource Allocation. Mexico, D. F.: CIMMYT. 

Heisey, P.W., and Morris, M.L. 2006. Economic impact of water limited conditions on 

cereal grain production. Pp. 17-48 in J.M. Ribaut (ed.) Drought Adaptation in Cereals. Haworth 

Press Inc., Binghamton. 

Holm, L., Pancho, J. V., Herbarger, J. P., and Plucknett, D. L. 1979. A Geographical Atlas of 

World Weeds. John Wiley and Sons, New York. 

Hull, R., Covey, S. N., and Dale, P. 2000. Genetically modified plants and the 35S promoter: 

assessing the risks and enhancing the debate. Microbial Ecology in Health and Disease 12: 1-5. 

ILSI (International Life Sciences Institute). 2006. International Life Sciences Institute 

Crop Composition Database, version 3.0. http://www.cropcomposition.org/ (Last modified: 

10/1/2008) 

Jacobson, J. V., Shaw, D. C. 1989. Heat-stable protein and abscisic acid action in barley 

aleurone cells. Plant Physiology 91: 1520-1526. 

Jemison, J.M., and Vayda, M. 2000. Pollen transport from genetically modified corn. 

Page 145 in 2000 Agronomy Abstracts. American Society of Agronomy (ASA), 

Madison, Wisconsin. 

Kaneko, T., Nakamura, Y., Sato, S., Asamizu, E., Kato, T., Sasamoto, S., Watanabe, A., 

Idesawa, K., Ishikawa, A., Kawashima, K., Kimura, T., Kishida, Y., Kiyokawa, C., Kohara, M., 

Matsumoto, M., Matsuno, A., Mochizuki, Y., Nakayama, S., Nakazaki, N., Shimpo, S., 

Sugimoto, M., Takeuchi, C., Yamada, M., and Tabata, S. 2000. Complete genome structure of 

the nitrogen-fixing symbiotic bacterium Mesorhizobium loti. DNA Research 7: 331-338. 

Kaneko, T., Nakamura, Y., Sato, S., Minamisawa, K., Uchiumi, T., Sasamoto, S., 

Watanabe, A., Idesawa, K., Iriguchi, M., Kawashima, K., Kohara, M., Matsumoto, M., 

Shimpo, S., Tsuruoka, H., Wada, T., Yamada, M., and Tabata, S. 2002. Complete genomic 

sequence of nitrogen-fixing symbiotic bacterium Bradyrhizobium japonicum USDA110. DNA 

Research 9: 189-197. 
18

Karlson, D., and Imai, R. 2003. Conservation of the cold shock domain protein family in 

plants. Plant Physiology 131: 12-15 

Kermicle, J. L., and Evans, M. M. S. 2005. Pollen-pistil barriers to crossing in maize 

and teosinte result from incongruity rather than active rejection. Sexual Plant Reproduction 18: 

187–194. 

Keeler, K. 1989. Can genetically engineered crops become weeds? Bio/Technology 7: 1134- 

1139. 

Keese, P. 2008. Review Article: Risks from GMOs due to horizontal gene transfer. 

Environmental Biosafety Research 7: 123-149. 

Kim, J.Y., Park, S. J., Jang, B. S., Jung, C. H., Ahn, S. J., Goh, C. H., Cho, K., Han, O., and 

Kang, H. S. 2007. Functional characterization of a glycine-rich RNA-binding protein 2 

in Arabidopsis thaliana under abiotic stress conditions. Plant Journal 50: 439-451. 

Koncz, C., and Schell, J. 1986. The promoter of Tl-DNA gene 5 controls the tissue specific 

expression of chimeric genes carried by a novel type of Agrobacterium binary vector. Molecular 

and General Genetics 204: 383-396. 

Koonin, E. V., Makarova,K. S., and Aravind, L. 2001. Horizontal gene transfer in 

prokaryotes: quantification and classification. Annual Review of Microbiology 55: 709-742. 

Luna, S.V., Figueroa, J. M., Baltazar,B. M., Gomez, R. L., Townsend, R., and Schoper, J. B. 

2001. Maize pollen longevity and distance isolation requirement for effective 

pollen control. Crop Science 41: 1551-1557. 

Mangelsdorf, P.C. 1974. Corn: its Origin, Evolution, and Improvement. Harvard 

University Press, Cambridge, MA. 

Matsuoka, Y., Vigouroux, Y., Goodman, M. M., Sanchez, J., Buckler, E., and Doebley, J. 

2002. Proceedings of National Academy of Sciences (USA) 99: 6080–6084. 

McElroy, D., Zhang, W., Cao, J., and Wu, R. 1990. Isolation of an efficient actin promoter 

for use in rice transformation. Plant Cell 2: 163-171. 

Messmer, R., Fracheboud, Y., Banziger, M., Vargas, M., Stamp, P., and Ribaut, J-M. 2009. 

Drought stress and tropical maize: QTL-by-environment interactions and stability of QTLs 

across environments for yield components and secondary traits. Theoretical and Applied 

Genetics 119: 913–930. 

Muenscher, W. C. 1980. Weeds. 2nd Edition. Cornell University Press, New York. 
19

Nakaminami, K., Karlson, D.T., and Imai, R. 2006. Functional conservation of cold 

shock domains in bacteria and higher plants. Proceedings of the National 

Academy of Sciences (USA) 103: 10122-10127 

Nakaminami, K., Sasaki, K., Kajita, S., Takeda, H., Karlson, D., Ohgi, K., and Imai, R. 

2005. Heat stable ssDNA/RNA-binding activity of a wheat cold shock domain 

protein. FEBS Letters 579: 4887-4891. 

OECD (Organization for Economic Co-operation and Development). 1993. Safety 

considerations for biotechnology: Scale-up of crop plants. Organization for Economic Cooperation and Development, Paris, France. 

OECD (Organization for Economic Co-operation and Development). 2002. Consensus 

document on compositional considerations for new varieties of maize (Zea mays): key food and 

feed nutrients, antinutrients and secondary plant metabolites. Organisation for Economic Cooperation and Development. Paris, France. 

OECD (Organization for Economic Co-operation and Development). 2003a. Consensus 

document on the biology of Zea mays subsp. mays (maize). Series on Harmonisation of 

Regulatory Oversight in Biotechnology, No. 27, OECD, Paris. 

OECD (Organization for Economic Co-operation and Development). 2003b. Considerations for 

the safety assessment of animal feedstuffs derived from genetically modified plants. Series on 

the Safety of Novel Foods and Feeds. Paris, France 

OECD (Organization for Economic Co-operation and Development). 2006. An Introduction to 

the Food/Feed Safety Consensus Documents of the Task Force. Organisation for Economic Cooperation and Development, Paris, France. 

Odell, J.T., Nagy, F., and Chua, N-H. 1985. Identification of DNA sequences required for 

activity of the cauliflower mosaic virus 35S promoter. Nature 313: 810-812. 

Peterson, C.D., Pearman, D. A., and Dines, T. D. 2002. New Atlas of the British flora. 

Oxford University Press, London, U.K. 

Rieseberg, L. H. 1997. Hybrid origins of plant species. Annual Review of Ecology and 

Systematics 28: 359-389. 

Rieseberg, L.H., and Wendel, J. F. 1993. Introgression and its consequences in plants. Pp. 

70–109 in R.G. Harrison (ed.) Hybrid Zones and the Evolutionary Process. Oxford University 

Press, Oxford, U.K. 

Russell, W.A., and Hallauer, A. R. 1980. Corn. Pp. 299-312 in W. R. Fehr and H.H. Hadley 

(eds.) Hybridization of Crop Plants. American Society of Agronomy and Crop Science Society 

of America, Madison, Wisconsin. 
20

Russell, S.H., Hoopes, J. L., and Odell, J. T. 1992. Directed excision of a transgene from the 

plant genome. Molecular and General Genetics 234: 49-59. 

Sánchez, G. J. J. and Ruiz, C. J. A. 1997. Teosinte distribution in Mexico. Pp 

18-39 in J. A. Serratos, M. C. Willcox, and F. Castillo-Gonzalez (eds.) Gene Flow among Maize 

Landraces, Improved Maize Varieties, and Teosinte: Implications for Transgenic Maize. 

CIMMYT, Mexico, D.F. 

Sasaki, K., Kim, M. H., and Imai, R. 2007. Arabidopsis cold shock domain protein 2 

is a RNA chaperone that is regulated by cold and developmental signals. Biochemical and 

Biophysical Research Communications 364: 633-638. 

Schindelin, H., Marahiel, M. A., and Heinemann, U. 1993. Universal nucleic acid-binding 

domain revealed by crystal structure of the B. subtilis major cold-shock protein. 

Nature. 364:164-168. 

Schindelin, H., Jiang, W., Inouye, M. and Heinemann, U. 1994. Crystal structure of CspA, 

the major cold shock protein of Escherichia coli. Proceedings of the National Academy of 

Sciences (USA) 91: 5119-5123. 

Salomon, S. and Puchta, H. 1998. Capture of genomic and T-DNA sequences during 

double-strand break repair in somatic plant cells. EMBO Journal 17: 6086-6095. 

Sprague, G. F. and Dudley, J. F. (editors). 1988. Corn and Corn Improvement, 3rd Edition. 

ASA-CSSA-SSSA, Madison, WI. 

Soltis, D.E., and Soltis, P. S. 1993. Molecular data and the dynamic nature of polyploidy. 

Critical Reviews in Plant Sciences 12: 243–273. 

Stace, C.A. 1987. Hybridization and the plant species. Pp. 115–127 in K.M. Urbanska 

(ed.) Differentiation Patterns in Higher Plants. Academic Press, New York. 

Tollenaar, M., and Wu, J. 1999. Yield improvement in tropical maize is attributable to greater 

stress tolerance. Crop Science 39: 1597-1604.USDA-APHIS. 2000. 

USDA (U.S. Department of Agriculture). 2007. USDA Agricultural Projections to 2016 

Office of the Chief Economist, Washington, DC. 

Wilkes, H. G. 1967. Teosinte: The closest relative of maize. The Bussey Institute, Harvard 

University, Cambridge, MA. 

Willimsky, G., H. Bang, G. Fischer and M.A. Marahiel. 1992. Characterization of cspB, a 

Bacillus subtilis inducible cold shock gene affecting cell viability at low temperatures. Journal 

of Bacteriology 174: 6326-6335. 
21

Wood, D. W., Setubal, J. C., Kaul, K., Monks, D. E., Kitajima, J. P., Okura, V. K., Zhou, Y., 

Chen, L., Wood, G. E., Almeida Jr., N. F., Woo, L., Chen, Y., Paulsen, I. T., J. Eisen, J. A., 

Karp, P. D., Bovee Sr., D., Chapman, P., Clendenning, J., Deatherage, G., Gillet, W., Grant, C., 

Kutyavin, T., Levy, R., Li, M.-J., McClelland, E., Palmieri, A., Raymond, C., Rouse, G., 

Saenphimmachak, C., Wu, Z., Romero, P., Gordon, D., Zhang, S., Yoo, H., Tao, Y., Biddle, P., 

Jung, M., Krespan, W., Perry, M., Gordon-Kamm, B., Liao, L., Kim, S., Hendrick, C., Zhao, ZY., Dolan, M., Chumley, F., Tingey, S. V., Tomb, J-F., Gordon, M. P., Olson, M. V., and Nester, 

E. W. 2001. The genome of the natural genetic engineer Agrobacterium tumefaciens C58. 

Science 294: 2317-2323.