We use Nicotiana benthamiana. This Australian plant is a close relative of the tobacco plant (Nicotiana tabacum). It is a research model plant used by numerous scientists all over the world for experiments which is why many standard protocols and methods are well established for Nicotiana benthamiana. It is particularly easy to infiltrate with Agrobacterium, although it is not the only plant that can be infiltrated. We at Leaf Expression Systems value it because it is easy to grow and it reliably produces a large amount of biomass in a short period of time.
Plant expression is considered to be more cost effective (20-30%) due to the lower cost of upstream production (plant growth) when compared with other eukaryotic systems. Protein expression is achieved after about 1 week following infiltration for plant transient expression, which is much quicker than culture based systems which require weeks or months of expansion of cell cultures. Plant expression can be scaled simply by growing more plants. Scaling in other systems has limitations and issues are often encountered during this process.
Our growth chambers have a computer controlled system that ensures absolutely constant growing conditions. Light level, temperature and humidity are optimized to levels that ensure ideal growth conditions and maximal biomass and protein production.
Plants, like all living organisms, produce a great variety of different proteins. What set of proteins a plant can produce is determined by which genes it has available.
We at Leaf Expression Systems temporarily add a new gene, for the protein we want to express, to this set. To do this we use Agrobacterium to infiltrate Nicotiana benthamiana plant leaves. The Agrobacterium simply helps to carry the new gene into the cells of the leaves where protein production of the new gene starts just hours after infiltration. Only those leaf cells that have been delivered a gene will be expressing the new protein. After a couple of days, the leaves get harvested, the remaining plant parts are discarded and the protein of interest can be extracted from the harvested leaf tissue.
This process is called transient (lasting only for a short time, temporary, impermanent) gene expression, because in the life-cycle of the plant (6 weeks from sowing to protein harvest) the expression of a new/ foreign gene is only temporary (about 5-6 days) and only occurs in the infiltrated plant parts. With discarding of the plant material this temporary/ transient transformation event is lost and ceases to exist. Even if one would wait for the plant to produce seeds the offspring would not carry the added new gene.
In contrast, stable (permanent) gene expression can only be achieved in plants in which the new/ foreign gene is permanently integrated into every single cell of the plant, thus effectively creating a new plant with an altered genome. This can only be achieved by a far more complicated process that can take from 6 months up to 2 years making transient expression the by far quicker and cheaper option (without the risks and controversy involved with stable transformation.)
Plants and mammals produce different glycan forms, and while there are many similarities there are some important residues that are found only in plants or only in mammals, such as silylations that are found only in mammalian systems.
While these differences exist, plant platforms can be modified to allow humanised glycosylation of proteins.