US Agency Announces Assessment of MON 87429 Herbicide-Resistant Corn

The genetic event MON 87429 manifests resistance to the herbicides dicamba, glufosinate, quizalofop, 2,4-dichlorophenoxyacetic acid and glyphosate

30.03.2024 | 08:18 (UTC -3)
SchubertPeter

The United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) announced the availability of a draft environmental impact statement (EIS) and pest risk assessment (PPRA) for corn with the genetic event MON 87429. This corn, which shows resistance to the herbicides dicamba, glufosinate, quizalofop, 2,4-dichlorophenoxyacetic acid and glyphosate, promises to facilitate the production of hybrid corn seeds, according to official notes.

The document prepared by APHIS assesses the potential environmental impacts and pest risks that could arise from approving a request for this corn to be considered unregulated. The agency has opened the draft for public review and comment, with a deadline for receiving input of May 6, 2024.

Regulatory context and Bayer petition

Under the authority of the plant pest provisions of the Plant Protection Act, the regulations at 7 CFR part 340 regulate, among other things, the importation, interstate movement, or release into the environment of genetically engineered or modified organisms that are plant pests. or present a plausible risk of plant pest.

The petition for unregulated status, assessed under the version of regulations in effect at the time it was received, was submitted by Bayer. This request seeks determination of unregulated status for corn MON 87429, arguing that it is unlikely to pose a plant pest risk and therefore should not be regulated under the APHIS regulations at 7 CFR part 340.

Public consultation and environmental impact assessment

Upon receipt of Bayer's petition and a preliminary review, APHIS decided that an EIS, rather than an environmental assessment, was the appropriate analysis under the National Environmental Policy Act (NEPA) for Bayer's petition. According to official information, this is due, in part, to data on potential problems with dicamba drift and volatilization and the associated economic impacts, as well as the Environmental Protection Agency's (EPA) decision to cancel the registration of three products containing dicamba.

APHIS published a notice of intent in April 2021, announcing plans to prepare an EIS to consider the potential impacts on the human environment of determining unregulated status for MON 87429 corn. The initial public consultation process resulted in 3.069 comments, with concerns ranging from the potential for herbicide drift to harm non-resistant crops and wild plants to economic impacts, weed resistance to herbicides, effects on soil microbiota, pollinators, biodiversity and endangered species.

Taking public comments into account, the draft EIS focuses on primary themes related to weed management and herbicide resistance, herbicide use with MON 87429 corn, potential effects of exposure to introduced genes and gene products on human health and wildlife, gene flow and potential invasiveness of MON 87429 corn, in addition to potential socioeconomic impacts.

APHIS has now opened a deadline for review and comments on the EIS and PPRA.

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UPDATE ON 01/04/2024

Corn containing MON 87429 was released for sale in Brazil in 2022. Below, part of the technical opinion from the National Technical Biosafety Commission (CTNBio) that supported the decision:

"This is a commercial application for corn MON 87429 tolerant to the herbicides dicamba, glufosinate, herbicides from the aryloxyphenoxypropionate group and 2,4-dichlorophenoxyacetic acid (2,4-D). Additionally, MON 87429 corn has specific tissue tolerance to the herbicide glyphosate to facilitate hybrid corn seed production. MON 87429 corn has the gene demethylase (dmo) Stenotrophomonas maltophilia which expresses the dicamba mono-oxygenase (DMO) protein that confers tolerance to the herbicide dicamba, the phosphinothricin-N-acetyltransferase (pat) gene of Streptomyces viridochromogenes which expresses the PAT protein which confers tolerance to the herbicide glufosinate and the ft_t gene, a modified version of the R-2,4-dichlorophenoxypropionate dioxygenase (Rdpa) gene from Sphingobium herbicidovorans, which expresses the FT_T protein (FOPs and 2,4-D dioxygenase) that confers tolerance to FOPs and 2,4-D herbicides. Corn MON 87429 also has the cp4 epsps gene that expresses the protein 5-enolpyruvylshikimate-3-phosphate synthase from Agrobacterium sp. strain CP4 (CP4 EPSPS) which confers specific tissue tolerance to glyphosate for use in the production of hybrid seeds.

Corn MON 87429 uses an endogenous corn regulatory element to target CP4 EPSPS mRNA for degradation of this protein in tassel tissues, resulting in reduced expression of CP4 EPSPS protein in the tassel, including pollen. Appropriate applications of the herbicide glyphosate produce a non-viable pollen phenotype and allow desirable cross-pollinations to occur in corn without the use of mechanical or manual detasseling methods to control self-pollination in female lines.

Maize MON 87429 contains a dmo expression cassette that expresses a single DMO precursor protein that is post-translationally processed during the chloroplast targeting process into two forms of the DMO protein; referred to as BMD+1 and BMD+0. The DMO+1 form is identical to the DMO+0 form, with the exception of containing an additional amino acid in the N-terminal region, a cysteine ​​residue, derived from alternative processing of the chloroplast transit peptide APG6. Given this degree of similarity, the term DMO protein will be used below to refer to both forms of the protein and distinctions will be made only where necessary. DMO proteins similar to those produced in MON 87429 corn are also present in MON 88701 cotton, MON 87708 soybeans and MON 87419 corn that were approved for commercial release by CTNBio in 2017 (cotton and soybeans) and 2018 (corn). The safety of the DMO protein has been favorably evaluated after extensive reviews by regulatory agencies in at least 12 different countries. Although there are minor differences in amino acid sequence, the DMO proteins expressed in maize MON 87429 are identical to previously reviewed DMO proteins in terms of catalytic site structure, function, immunoreactivity, and substrate specificity.

Corn MON 87429 was produced by Agrobacterium-mediated transformation methodology using the plasmid PV-ZMHT519224. This plasmid contains a unique transfer DNA (T-DNA), which is delineated by right and left end regions. T-DNA contains the dmo, pat, ft_t and cp4 epsps expression cassettes. After transformation, traditional breeding, segregation, selection and screening were used to identify plants that contained the dmo, pat, ft_t and cp4 epsps expression cassettes and did not contain any plasmid matrix sequences.

Characterization of the DNA insertion in corn MON 87429 was performed using a combination of sequencing, polymerase chain reaction (PCR), and bioinformatics. The results of this characterization demonstrated that maize MON 87429 has only one copy of the intended T-DNA containing the expression cassettes of the dmo, pat, ft_t and cp4 epsps genes that are inherited stably over several generations and segregated according to the principles of Mendel's Laws.

Protein expression levels in corn MON 87429 were used to assess exposure to proteins introduced through ingestion of food or feed and potential environmental exposure.

The results provide evidence that the differences in the mean values ​​of the components between MON 87429 corn and the conventional control do not imply a significant difference from the point of view of human and animal safety, especially since the differences are smaller than the natural variation. due to other sources (i.e. environmental and varietal influences). These results support the general conclusion that MON 87429 was not a major contributor to variation in the levels of these components in corn grain or forage and confirmed the compositional equivalence of MON 87429 corn to conventional control corn in the levels of these components.

The phenotypic observations and environmental interactions evaluated in this study demonstrate that MON 87429 corn does not consistently differ from conventional control corn, and that the significant differences found were punctual and do not represent characteristics that constitute potential environmental risks and potential increase in the persistence of the crop as a plant weed. Based on this information, it can be concluded that MON 87429 corn is as safe as the conventional control corn used in the study for the parameters evaluated."

Mosaic Biosciences March 2024