Different plant species as platform for molecular farming

The range of plant species amenable to transformation is growing at a phenomenal rate and it is unclear at present which species are optimal for molecular farming. Many factors need to be taken into consideration (Schillberg et al., 2003). The factors that are taken into consideration are the total biomass yield, the storage and distribution of the product. Various production platforms have been developed for molecular farming in plants which includes leafy crops (alfalfa, lettuce, Arabidopsis, spinach, tobacco), cereals and legumes (barley, maize, pea,pigeon pea, rice, wheat), fruits and vegetables (banana, carrot, potato, tomato, carrots), oil yielding plants (false flax, flax, rape, safflower, soybean, white clover, white mustard) and sugar crops (sugar beet and sugarcane) (Twyman et al., 2003 and 2005).

· Tobacco

Tobacco have well developed technology for gene transfer and expression, the high biomass yield, the potential for rapid scale-up owing to prolific seed production and the availability of large-scale infrastructure for processing. The demerits of this system include degradation of protein through proteolysis, the presence of toxic alkaloids, and interference of transgene with normal plant metabolism.

· Cereals and legumes

Cereals lack the phenolic substances, thereby increasing the efficiency of downstream processing (Ma et al., 2003). Legumes, such as alfalfa and soybean, and cereal crops, such as corn and rice, have been considered as ideal candidates for protein production because theprotein can be targeted to accumulate in the seed and the seed can be harvested and stored for an extended amount of time. Alfalfa and soybean produce lower amounts of leaf biomass than tobacco but have the advantage of using atmospheric nitrogen through nitrogen fixation, thereby reducing the need for chemical inputs.

· Fruits and vegetables

The main benefit of fruits, vegetables and leafy salad crops is that they can be consumed raw or partially processed, which makes them particularly suitable for the production of recombinant subunit vaccines, food additives and antibodies (Ma et al., 2003).

· Perennial grass

Perennial grasses like sugarcane provide a ‘secure’ platform for production of recombinant proteins. Sucrose, the food commodity derived from sugarcane, is sold as a refined crystal that is essentially free of protein, rather than a whole fruit or vegetable. Hence sugarcane producing a pharmaceutical protein was not mixed into the food supply; the food product (refined sucrose) would remain unaffected.

The high yield of recombinant proteins in plant always depends on the properties of protein to be targeted, expressing of these proteins in suitable plant species and targeting these proteins to the right cellular compartment for getting more yields as well as for easy downstream processing. Sugar yielding plants are known for their high biomass production and if proteins can be targeted to the storage tissues there could be a possibility of easy downstream processing as sugarcane juice obtained from sugarcane stem has negligible amount of proteins. This makes sugarcane a better platform for production of commercially important recombinant proteins.