Herbicide tolerant, insect resistant maize

The modified maize event was a result of cross-breeding modified parental lines and demonstrates herbicide tolerance and insect resistance. For Lepidoptera resistance, the maize expresses Bacillus thuringiensis Vegetative insecticidal protein 3Aa20 and Cry1F. For Coleoptera resistance, the maize expresses B. thuringiensis mCry3A. In addition to the insecticidal proteins, the maize also expresses Streptomyces viridochromogenes phosphinothricin N-acetyltransferase for glufosinate tolerance and a modified native Zea mays 5-enolpyruvylshikimate-3-phosphate synthase for tolerance to glyphosate. A selectable marker, Escherichia coli phosphomannose isomerase, is also present and was used during the transformation of the parental line using mannose selection.

pNOV1300; pZM26; PHI8999A; pDPG434

DNA insert from MIR162 vector pNOV1300
In the parental MIR162 maize, a variant of the native B. thuringiensis vegetative insecticidal protein 3Aa (vip3Aa), termed vip3Aa20, was inserted into the transformation cassette. Transcription of vip3Aa20 commences at the Z. mays ubiquitin gene promoter and then transcribes vip3Aa20 followed by intron 9 of Z. mays phosphoenolpyruvate carboxylase, before terminating at the CaMV 35S terminator. The intron enhances expression of the transgene.

A second expression cassette, containing E. coli phosphomannose isomerase (pmi), was also inserted into the parental genome. The gene is under the control of another ubiquitin promoter and transcription terminates at the Agrobacterium tumefaciens nopaline synthase (nos) terminator.

Note:
- Southern blot analyses demonstrated that the T-DNA insert contains: (i) single copies of vip3Aa20 and pmi gene; (ii) two copies of the maize ubiquitin promoter; (iii) one copy of the nos terminator; and iv) no backbone sequences from transformation plasmid pNOV1300.
- Vip3Aa20 is a variant of the native Vip3Aa, which has codon changes that result in M129I (methionine to isoleucine at position 129) and K284Q (lysine to glutamine at position 284) amino acid substitutions.

DNA insert from MIR604 vector pZM26
The parental plant contains two expression cassettes: (i) modified Cry3a (mCry3a) originally from Bacillus thuringiensis and (ii) phosphomannose isomerase (pmi) from Escherichia coli.

Expression mCry3a is under control of a Zea mays metallothionein-like gene promoter and an Agrobacterium tumefaciens nopaline synthase (nos) terminator. Transcription of pmi is under the control of Z. mays ubiquitin gene promoter and an A. tumefaciens nos terminator. The transcript initially also contains an intron from Z. mays ubiquitin-1 to enhance gene expression.

Note:
- mCry3a was originally obtained from the native cry3a gene, but was modified to enhance gene expression in maize. The synthetic version of the protein (mCry3a) contains the same amino acid sequences of the native version, except for the modified serine-protease recognition site.
- The following changes in the pmi occurred: the valine at position 61 has been substituted by alanine (V61A) and glutamine at position 210 has been substituted by histidine (Q210H). Please note no apparent change of function occurred.
- Southern blot and qPCR analysis indicated that a single insertion of both expression cassettes occurred and there was no integration of the vector backbone.

DNA insert from TC1507 vector PHI8999A
DNA fragment PHI8999A contains two adjacent plant gene expression cassettes for Bacillus thuringiensis cry1F and Streptomyces viridochromogenes pat.

Transcription of cry1F is directed by the promoter and first exon and intron of the maize (Zea mays) ubiquitin gene and terminates at the Agrobacterium tumefaciens ORF25 terminator.

Transcription of the pat gene commences from the Cauliflower Mosaic Virus (CaMV) 35S promoter and ends at the CaMV 35S terminator.

Note:
- The coding sequence of both genes has been optimized to achieve a high level of expression in maize.
- The sequences of the complete cry1F and pat are identical to those in the original plasmid.
- The Cry1F protein includes the F604K (phenylalanine to lysine at position 604) amino acid substitution, which was introduced to create a specific restriction site for cloning purposes.

DNA insert from GA21 vector pDPG434
Transcription of Zea mays modified 5-enolpyruvylshikimate-3-phosphate synthase (mepsps) commences from the Oryza sativa (rice) actin 1 promoter and terminates at the Agrobacterium tumefaciens nopaline synthase terminator. The transcribed elements (from 5' to 3') are expected to be as follows: first intron of rice actin 1, a synthetic transit peptide and mepsps. Transcription of mepsps is expected to occur constitutively due to the rice actin promoter. Gene expression is additionally enhanced by the rice actin intron. Post-translation, the optimized transit peptide targets mEPSPS to the chloroplasts.

Note:
- The coding sequence of mepsps was obtained through site-directed mutagenesis to create a modified version of the native enzyme to confer glyphosate tolerance with similar enzymatic function.
- The Rice Actin 1 promoter contains a portion of the first intron of the Actin 1 and thus corresponds to the 5' end of the gene.
- The optimized transit peptide was derived from maize and sunflower (Helianthus sp.) ribulose 1,5 -bisphosphate carboxylase oxygenase sequences.
- Southern blot analysis indicated that an insert containing three complete tandem copies of the insert and one incomplete copy were inserted into the parental genome. The incomplete copy contains rice actin promoter, the optimized transit peptide and a truncated mepsps sequence without the nos 3' untranslated region (as uncovered by sequence analysis).
- Sequencing analysis indicated a truncated rice actin promoter in the 5' end of the insertion event, only containing 148 bp of the promoter region.
- The modified maize expresses only the full-length mEPSPS protein.