Saccharum TST2b Promoter for Stem-Targeted Fatty Acid Accumulation
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Solution Overview
Problem
Current metabolic engineering strategies for lipid accumulation in bioenergy feedstocks, such as sugarcane, are inadequate for enhancing fatty acid and oil production in mature stem parenchyma cells, as existing promoters fail to drive specific expression in these tissues, and the import of phosphoenolpyruvate (PEP) into chloroplasts is not sufficiently engineered to boost fatty acid biosynthesis.
Innovation Solution
The use of Saccharum Tonoplast Sugar Transporter (TST) promoters, specifically pTST2b, operably linked to nucleic acids encoding a plastidic phosphoenolpyruvate/phosphate translocator (PPT) protein and a tonoplast-localized hexose transporter (SWEET16), to redirect sugar flux towards fatty acid production in stem cells, thereby increasing fatty acid and oil accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If constitutive overexpression of PPT is used to increase PEP import into chloroplasts, then fatty acid biosynthesis capacity is improved, but expression occurs in all tissues including non-target tissues where it is not needed
Solution Approach 1:
The patent applies local quality by using the TST2b promoter to drive PPT expression specifically in stem parenchyma cells, creating tissue-specific expression patterns. This ensures that PEP import enhancement occurs only in the target tissue (stem parenchyma) where lipid accumulation is desired, rather than constitutively in all plant tissues, thereby resolving the contradiction between productivity improvement and unwanted widespread expression
2Productivity
If existing promoters are used to drive gene expression in stem tissue, then expression in stem tissue is achieved, but specificity for mature stem parenchyma cells is insufficient
Solution Approach 1:
The TST2b promoter provides local quality by restricting gene expression to mature stem parenchyma cells specifically. The promoter was identified through RNA-seq analysis showing highest expression in mature stem parenchyma, and this specificity is maintained when driving PPT and SWEET16 expression, achieving precise cell-type targeted expression that existing promoters failed to provide
Solution Approach 2:
The patent uses the naturally occurring TST2b gene's promoter region as a template for achieving specific expression. By copying the regulatory elements from the native TST2b gene (which is naturally expressed in stem parenchyma), the invention replicates the natural tissue-specific expression pattern to drive transgene expression in the same cell type with high precision
3Quantity of substance
If sugar flux is redirected towards fatty acid production, then fatty acid and oil accumulation is increased, but photosynthesis and plant growth may be affected
Solution Approach 1:
The patent applies local quality by redirecting sugar flux to fatty acid production specifically in stem parenchyma cells through TST2b-promoter-driven expression of PPT and SWEET16. This localized metabolic engineering approach enhances lipid accumulation in the stem without disrupting photosynthesis in leaves or overall plant growth, as the genetic modifications are restricted to non-photosynthetic storage tissue where sugar redistribution occurs
Data Source
AI summary
Compositions and methods for increasing fatty acid and/or oil accumulation in the stems of plants are provided. Constructs including stem cell-specific promoters operably linked to nucleic acids encoding a plastidic phosphoenolpyruvate/phosphate translocator protein and a tonoplast-localized hexose transporter protein are described.