Transgenic Maize Locus Excision for Stable Vip3Aa Expression
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Solution Overview
Problem
Transgenes integrated non-specifically in plant genomes can exhibit varying expression levels and undesirable rearrangements, often containing selectable marker genes that are no longer needed, complicating the selection and transmission of desired traits.
Innovation Solution
Development of transgenic maize cells with a specific genetic configuration lacking a second ZmUbiInt promoter and operably linked phosphomannose isomerase coding region, utilizing site-specific recombinase systems to excise unwanted DNA elements and introduce new genes, resulting in maize plants resistant to insect infestations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If non-site specific integration methods are used to introduce transgenes, then the process is simpler and more flexible, but the transgenes exhibit varying expression levels and undesirable rearrangements occur
Solution Approach 1:
The transgene construct is divided into separate functional modules: a first expression cassette with promoter and coding region, and a second expression cassette with selectable marker and terminator. This segmentation allows independent optimization of each module's function and expression characteristics, resolving the contradiction between integration simplicity and expression consistency.
Solution Approach 2:
A first terminator element is introduced as an intermediary between the first and second expression cassettes. This terminator acts as a boundary element that prevents read-through transcription and ensures proper termination of the first coding region, thereby controlling expression levels and preventing rearrangements while maintaining the benefits of non-site specific integration.
2Ease of operation
If selectable marker genes are included in transgene insertion sites, then selection of desired traits is facilitated, but the markers are no longer needed after selection and complicate transmission
Solution Approach 1:
The selectable marker gene is placed in a separate second expression cassette that can be independently controlled. After selection, the marker can be removed or silenced without affecting the first expression cassette containing the desired transgene, thereby simplifying the overall structure while maintaining selection capability during the breeding process.
Solution Approach 2:
The transgene construct is segmented into distinct cassettes with the selectable marker isolated in the second cassette. This segmentation allows the marker to perform its selection function temporarily, then be removed or deactivated, leaving only the essential first expression cassette for trait transmission, thus reducing structural complexity over time.
3Reliability
If multiple promoters and coding regions are present in transgene insertion sites, then expression levels can be optimized, but undesirable rearrangements and genetic instability occur
Solution Approach 1:
The first terminator element serves as a stabilizing intermediary between the two expression cassettes. It provides a clear boundary that prevents interaction between the first and second coding regions, thereby maintaining genomic stability and preventing rearrangements while still allowing the first promoter to reliably drive expression of the desired transgene.
Solution Approach 2:
The first coding region is extracted and separated from the second expression cassette containing the selectable marker. This extraction prevents potential rearrangements between the two cassettes and maintains the stability of the transgene insertion site, while the first promoter continues to reliably drive expression of the isolated first coding region.
Data Source
AI summary
Transgenic INIR12 maize plants comprising a vip3Aa19 or vip3Aa20 expression cassette linked to a secondary nopaline synthase terminator element which lack a selectable marker gene and/or which comprise modifications that provide for facile excision of the INIR12 transgenic locus from the maize plant genome are provided. Genomic DNA of INIR12 transgenic plants, detection of INIR12 plants and products thereof, methods of making INIR12 plants, and use of INIR12 plants to facilitate breeding are disclosed.