Nitrate Reductase M527I Mutation Lowers Plant Nitrate
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Solution Overview
Problem
There is a need to reduce nitrate levels in plants, particularly in tobacco, to minimize the formation of carcinogenic compounds like tobacco-specific nitrosamines (TSNAs), as high nitrate levels are associated with various cancers and current genetic modification approaches face challenges in commercialization, especially in non-transgenic and non-genetically modified organisms (non-GMO) methods.
Innovation Solution
A non-transgenic approach involving mutation of the Nicotiana tabacum nitrate reductase enzyme by substituting methionine at position 527 with isoleucine (M527I) reduces nitrate levels in plants, achieving lower nitrate accumulation without impacting biomass, nicotine, or other alkaloid content, thereby modulating nitrate reductase activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If genetic modification approaches are used to reduce nitrate levels, then nitrate accumulation is reduced, but commercialization difficulty increases
Solution Approach 1:
The invention changes the amino acid sequence parameter of nitrate reductase by introducing specific mutations (such as S523D substitution) to alter enzyme activity. This modifies the biochemical parameter of nitrate reduction efficiency, enabling reduced nitrate accumulation without requiring transgenic approaches, thus resolving the contradiction between reducing nitrate levels and maintaining commercialization ease.
2Quantity of substance
If nitrate reductase activity is increased to reduce nitrate levels, then nitrate accumulation decreases, but TSNA formation risk increases
Solution Approach 1:
The invention modifies the kinetic parameters of nitrate reductase through amino acid substitutions that change the enzyme's catalytic efficiency and substrate affinity. By optimizing these parameters, the enzyme converts nitrate to nitrite more efficiently during curing, reducing the nitrate pool available for TSNA formation while controlling nitrite accumulation through regulated enzyme activity.
Solution Approach 2:
The invention implements preliminary action by enhancing nitrate reduction capacity before the curing process begins. The modified nitrate reductase is already present in the plant tissue, ready to rapidly convert nitrate to nitrite when curing conditions are applied, thereby preventing nitrate accumulation that would otherwise lead to TSNA formation during subsequent curing.
3Ease of manufacture
If conventional breeding methods are used, then non-GMO status is maintained, but nitrate level reduction efficiency is insufficient
Solution Approach 1:
The invention introduces specific amino acid substitutions in nitrate reductase that fundamentally change the enzyme's catalytic parameters, including turnover number and substrate affinity. These parameter changes result in dramatically improved nitrate reduction efficiency compared to conventional breeding, achieving up to 90% nitrate reduction while maintaining non-GMO status through mutation breeding rather than transgenic modification.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The M527I mutation in Nicotiana tabacum nitrate reductase enzyme results in a 37% reduction in nitrate levels in cured leaves, improving the commercial viability of the plants and products while maintaining comparable biomass and alkaloid content.
Implementation Method 1
the expression or activity of a nitrate reductase enzyme is deregulated. The deregulated nitrate reductase enzyme has an amino acid substitution at a position corresponding to position 523 of the polypeptide encoding nitrate reductase
Data Source
AI summary
A plant cell comprising: (a) a polynucleotide sequence encoding a nitrate reductase polypeptide comprising a contiguous polypeptide sequence of SEQ ID NO: 5 or SEQ ID NO: 7, wherein methionine is substituted for an amino acid that reduces nitrate reductase activity in the plant cell as compared to a control plant cell; (b) a polypeptide sequence encoded by the polynucleotide sequence set forth in (a); or (c) a construct, vector or expression vector comprising the polynucleotide sequence set forth in (b).