In planta expression of highly thermostable enzymes

In planta enzyme expression uses plants instead of microbial bioreactors as a “factory” to produce industrial hydrolytic enzymes for biofuel production. The enzymes that are active at typical and ambient plant growth temperatures will hurt plant normal growth/phenotypes and produce shriveled seeds as reported in the research paper.


However, in planta expression of thermophilic enzymes have been suggested as a method to reduce the detrimental effects on plants as these enzymes have higher temperature optima than encountered during plant growth. As a result, the plant stover can be pretreated at a relatively high temperature to induce their activation during processing.


Since a typical enzyme cocktail will require a combination of different class of enzymes to work together to destroy the cell wall for hydrolysis, is it possible to find all the key enzymes with thermophilibility and express them into a single plant without impacting plant growth?

The advantages of in planta cell wall degrading enzyme expression

1. Can  produce biomass and hydrolytic enzymes in plant sisimultaneously
2. Since the enzymes are already embedded into cell wall, the resistance of mass transfer for exogenous enzymes for diffusion is removed and non-selective binding of enzymes on lignin is avoided
3. Allow consolidated low temperature pretreatment and enzymatic hydrolysis
4. Similar or more sugar production in plant by overexpression of hydrolyitc enzymes

As a result, low cost sugar production is possible.

In planta expression of biomass cell-degrading enzymes: the solution to cheap sugar for biorefinery

One of the approaches to utilize lignocellulosic biomass as feedstocks for biorefibery is through biological conversion. Currently, an efficient, rapid, and complete enzymatic hydrolysis of biomass using low enzyme loadings is still one of the major technical and economical bottlenecks in this process because of the lack of low cost pretreatment technology as well as high cost of enzymes. Since lignocellulosic biomass is composed of a matrix with multiple intertwined biopolymers (cellulose, hemicelluloses, lignin and extractives), it requires several different classes of enzymes in large quantities to efficiently release fermentable sugars. As a result, it is necessary to produce different classes of enzymes individually in a large scale and then make cocktails for biomass hydrolysis. Because of the high cost and limited capacity for producing these enzymes through fermentation, today, it is still a big challenge to develop an efficient enzyme production system for rapid and less expensive biomass depolymerization.

However, all these enzymes required for biomass enzymatic hydrolysis are produced naturally by a range of microbial species including bacteria and fungi. Many cell wall-degrading enzymes have been isolated and characterized and more are still not uncovered. Availability of genome sequences of Trichoderma reesei and other organisms have increased inventory of enzymes for biomass utilization.

Plants have already been used as a “factory” in industry to produce enzymes and other proteins, carbohydrates, lipids, industrial polymers and pharmaceuticals. Successful technology is available for plant genetic transformation, farming of transgenic crops and harvesting, transporting and processing the plant matter. Therefore, expression of all different classes of cell wall-degrading enzymes  into plants provides great opportunity for developing biomass-specific enzyme cocktails, which will create a low sugar platform for biorefinery.

Two new papers on genetic modification of biofuel feedstocks

1. Genetic modification of lignin biosynthesis for improved biofuel production

2. Genetic improvement of C4 grasses as cellulosic biofuel feedstocks

Plant genetic engineering for biofuel production- a problem solver from the root

"Genetically engineering plants to produce cellulases and hemicellulases, and to reduce the need for pretreatment processes through lignin modification, are promising paths to solving this problem, together with other strategies, such as increasing plant polysaccharide content and overall biomass." A review paper published in Nature summarized the research progress in these aspects.

Two science research progress on biofuel plants

These two progress means more than the research itself. It will significantly impact the lignocellulosic biomass biofuel production process, equipment, and cost.

1. Modified Plants May Yield More Biofuel.

2. Modified Lignin Has Potential Benefits For Ethanol, Paper And Feed.