CTNBio commissions issue opinion releasing short corn MON 94804

Scientists from the National Technical Biosafety Commission (CTNBio), in a meeting held this November, issued a technical opinion commercially releasing the short-stature genetically modified corn MON 94804. This is an event belonging to Monsanto (Bayer).

The variety may be used in human and animal food and in "any other activities related to this GMO and any progenies derived from it."

There is still no information on when varieties containing the technology will be on sale.

In the video below, recorded on March 1, 2023, at Bayer's experimental station in Santa Cruz das Palmeiras, agronomist Hallison Vertuan explains the development of this technology.

Understand the scientific aspect of MON 94804

The technical aspects involved in the issue were scientifically described in the following terms:

The development of short crops such as rice and wheat had a transformative impact on global agriculture through the Green Revolution. The identification of the genes responsible for these characteristics shows that they interfere with the action or production of the plant hormone GA. GAs are essential for many developmental processes in plants, including stem elongation, seed germination, and floral transition. The GA biosynthesis that has been characterized in many plant species is catalyzed by multiple enzymes. Among these enzymes, GA 20 oxidase (GA20ox) is a key enzyme in the synthesis of bioactive GAs in the later steps of the GA biosynthesis pathway.

In maize, five ZmGA20ox genes were initially identified. Four additional putative ZmGA20ox genes were also identified in the Maize Genetics and Genomics database. According to the publicly available atlas of global transcription profiles for maize genes, the ZmGA20ox3 and ZmGA20ox5 genes showed relatively higher expression levels in vegetative tissues and lower expression levels in reproductive tissues among the nine ZmGA20ox genes.

Furthermore, phylogenetic analysis of the ZmGA20ox gene family revealed that ZmGA20ox3 and ZmGA20ox5 shared high sequence homology with the rice semi-dwarf gene, OsGA20ox2 known as the Green Revolution gene, which was one of the most important genes deployed in modern rice breeding. rice. All three of these genes, ZmGA20ox3, ZmGA20ox5, and OsGA20ox2, are clustered in the same clade. With these considerations, the ZmGA20ox3 and ZmGA20ox5 genes were selected as target endogenous maize genes for suppression of gene expression in the development of MON 94804 maize.

To accurately and effectively suppress gene expression of the above-mentioned target maize endogenous genes, a microRNA (miRNA)-mediated suppression cassette was developed that works through an RNA interference (RNAi) process. The RNAi mechanism is a natural process in eukaryotic organisms for the regulation of endogenous gene expression. MiRNAs can trigger the RNAi mechanism like other small non-coding RNAs such as small interfering RNA (siRNA).

The MOA of MON 94804 has been studied and described in detail. The GA20ox_SUP suppression cassette is composed of the rice tungro bacilliform virus (RTBV) promoter, the HSP70 intron, the miRNA-coding sequence designated GA20ox_SUP and the GST43 terminator. The gene encoding the miRNA, GA20ox_SUP, was designed with rice sequences to provide the backbone of the initial transcript and maize sequences to provide an inverted repeat sequence derived from coding sequences of the maize ZmGA20ox3 and ZmGA20ox5 genes. The expressed inverted repeat transcript is recognized by the endogenous RNAi machinery, resulting in the downregulation of target endogenous GA biosynthetic genes ZmGA20ox3 and ZmGA20ox5. The expression levels of both target endogenous gene transcripts were reduced in most tissues, including the peduncle internode.

It is important to demonstrate the target gene specificity of the GA20ox_SUP suppression cassette to assess the potential for unintended off-target gene suppression. To demonstrate the specificity of the target gene, the expression levels of ZmGA20ox1, the gene most homologous to the two target genes in maize, were quantified. Unlike the target genes ZmGA20ox3 and ZmGA20ox5, no consistent trend of reduced expression level of ZmGA20ox1 was observed in the evaluated tissues. In some tissues, ZmGA20ox1 expression deviated from control, which is likely a result of the well-documented compensatory mechanism of a GA-dependent feedback loop that regulates the expression level of some GA20ox genes. The results demonstrate that the suppression of gene expression by the GA2ox_SUP miRNA20 produced from the GA20ox_SUP suppression cassette is specific for the ZmGA20ox3 and ZmGA20ox5 target genes.

The effect of suppressing the expression of the ZmGA20ox3 and ZmGA20ox5 genes on endogenous levels of bioactive GA was also evaluated. Bioactive GAs, GA1 and GA4 were significantly reduced without any significant reduction of GA levels being detected in reproductive tissues. Therefore, suppression of both target genes resulted in the reduction of bioactive GA levels most significantly in the stalk internode, leading to a reduction in stalk internode length, which consequently reduced overall plant height without affecting reproductive potential when compared to control corn.

Furthermore, GAs are known to play an important role in regulating seed germination. MON 94804 seeds showed normal germination, as demonstrated by the equivalent seedling count in the field. Furthermore, the reproductive phenology of MON 94804 corn suggested no changes in days to 50% anthesis, days to 50% earing, and normal ear development compared to control corn. Considering all these data, "the results support the conclusion that miRNA-mediated suppression of target GA biosynthetic gene expression led to intended changes (i.e., reduced peduncle internode length leading to reduced overall plant height) without unintended impacts observed on other metabolic, physiological, or developmental processes.”

CTNBio demonstration on short corn MON 94804

The extract from the technical opinion approving the commercial release of corn with event MON 94804 contains the following:

"CTNBio, after analyzing the request for commercial release of genetically modified short-stature corn MON 94804 (corn MON 94804), decided to DEFER in accordance with this technical opinion.

Considering that CTNBio standards are based on internationally accepted technical criteria, which the biosafety assessment of corn MON 94804 concludes about its similarity to conventional corn in terms of biosafety for the environment and human and animal health, CTNBio decided to DEFER.

Given the above and considering the internationally accepted criteria in the risk analysis process of genetically modified corn, it is possible to conclude that the MON 94804 event in the commercial release process is safe.

The data presented in the majority request for corn MON 94804 comply with current standards and legislation that aim to guarantee the biosafety of the environment, agriculture, human and animal health, and allow us to conclude that corn MON 94804 is substantially equivalent to conventional corn, being its safe consumption for human and animal health.

Regarding the environment, it can be concluded that genetically modified subcombinations are not potentially causing significant degradation of the environment, maintaining an identical relationship with the biota to conventional corn.

CTNBio did not identify a non-negligible risk, therefore the company is exempt from the post-commercial release monitoring plan, as determined in Article 18, first paragraph of CTNBio's RN32."

Other information about Bayer's short-stature corn can be read at:

• Bayer and Pairwise communicate agreement to advance in short-stature corn

• Bayer introduces Preceon 'smart corn' system in the US