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 Cry1Ab. For Coleoptera resistance, the maize expresses B. thuringiensis mCry3A and eCry3.1Ab. 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.

pZO1502; pZM26; pSYN12274; pDPG434

DNA insert from Bt11 vector pZO1502
Transcription of the Bacillus thuringiensis cry1Ab gene is under control of the Cauliflower Mosaic Virus (CaMV) 35S promoter and the Agrobacterium tumefaciens nopaline synthase (nos) terminator. The transcript initially contains Zea mays alcohol dehydrogenase 1 intron 6, which enhance gene expression.

Transcription of the Streptomyces viridochromogenes phosphinothricin N-acetyltransferase (pat) is under control of the CaMV 35S promoter and nos terminator. The transcript initially contains Zea mays alcohol dehydrogenase 1 intron 2 to enhance gene expression.

Note:
- The CaMV promoter associated with cry1Ab, was isolated from the CM1841 strain of CaMV using DdeI restriction digestion. However, the DdeI sites were converted into SacI sites.
- The CaMV promoter associated with pat was isolated from the Cabb-S strain of CaMV (AluI to DdeI fragment) and subsequently modified.
- The cry1Ab coding sequence encodes a truncated version corresponding to the N-terminal 615 amino acids of the full length Cry1Ab gene.
- The cloning of pat did not result in any amino acid sequence changes in the parental line.
- The nos terminator corresponds to the 423 to 678 basepairs of the nopaline synthase gene in A. tumefaciens.

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 5307 vector pSYN12274
The DNA insert contains two gene cassettes for an engineered chimeric protein eCry3.1Ab and an Escherichia coli phosphomannose isomerase (pmi).

Transcription of eCry3.1Ab is under control of a Cestrum Yellow Leaf Curling Virus promoter and an Agrobacterium tumefaciens nopaline synthase (nos) terminator. Transcription of pmi is under control of a Zea mays ubiquitin gene promoter and a nos terminator. The promoter contains the first intron of the ubiquitin gene, which will be initially included in the mRNA before splicing and for enhancing expression of pmi. Transcription is expected to be constitutive under both promoters and result in elevated levels of transgene expression.

Note:
- eCry3.1Ab is a result of a fusion of the 5′ end (Domain I, Domain II and 15 amino acids of Domain III) of a modified Cry3A gene (mcry3A) and the 3′ end (Domain III and Variable Region 6) of a synthetic Cry1Ab gene. The sequences were sourced from Bacillus thuringiesis.
- Southern blot analysis indicated that the parental line contains a single insertion of the vector and there was no integration of the vector backbone.
- Sequencing analysis indicated that the right and left T-DNA borders were truncated.

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.