Guayule Can Turn Thar Desert Green
By TA News Bureau:
India’s Thar Desert, the world’s ninth largest subtropical desert, can be turned green by commercial cultivation of guayule to produce industrial scale natural rubber as a supplementary to Hevea rubber. Dr Shashi Kumar, Leader, Metabolic Engineering Group at the Delhi-based International Centre for Genetic Engineering and Biotechnology (ICGEB) says this will not only enhance farmers’ incomes but also counter migration to cities in search of livelihood. The biotechnologist, who has several patents to his credit, has done considerable research in plant genetic transformation that can help produce more latex from guayule. In an interview to Tyre Asia he said the genetic approach his team has developed could substantially improve latex yields in rubber trees as well.
The international press chased Dr Shashi Kumar and headlined his biotechnology inventions when he developed through biosynthesis of tobacco artemisinin, considered the most effective treatment against malaria, the most infectious disease that kills every year two million people, mainly children. The method he developed was to orally administer whole plant cells generated from double transgenic plant lines.
His genetic knowledge and research skills have also been directed to improve the latex yield from guayule as he finds it supplementary to the rubber produced from Hevea brasiliensis. While the latter can grow only humid tropical zones, guayule is a semi-desert plant that can thrive well in the Thar desert.
“While Hevea brasiliensis can flourish in the dense tropical rainforest conditions, guayule can be home for the Thar desert of India,” he said an interview to Tyre Asia. “So the plantation is not competitive but supplementary to each other as well. Both species thrive in different regions and may be used for different applications.”
The guayule latex could be used for products for medical applications (heart valves etc.) and condoms, especially for those who suffer from the type-1 latex allergy. The Hevea latex is suitable for heavy duty commercial products, including tyres while guayule has the potential to become an important cash crop in Thar desert for medical usage since clinical studies have shown that Hevea brasiliensis latex antibodies does not react with guayule latex; thus, guayule provides an alternative source of rubber products for using those who has hypersensitivity with Hevea latex, he points out.
As a large part of the Thar is not suited for conventional crops, this lacuna can be filled by guayule cultivation so that farmers’ income would substantially increase. This new agriculture practice would also counter the migration crises to the cities.
“Therefore, the central and Rajasthan governments should initiate further research and development programme on guayule as that could open the door for the commercialisation of this important crop in the Thar desert,” he says.
Dr Kumar was able to substantially improve the latex yield by two to four folds through the genetic technique of over-expression of IPP (isoprenoid) pathway of yeast into the rubber tree or guayule. He has been granted a US patent for engineering rubber production in plants, among other things.
In his present job at ICGEB, he has developed many patented technologies that are ready for commercial transfer: Engineering rubber production in plants; Super genetically engineered marine algal strain; Carbon concentration mechanism in micro-algal species to increase production of lipids to obtain bio-fuel; Generation of double transgenic plant lines for anti-malarial drug artemisinin biosynthesis in tobacco for effective treatment by oral delivery of whole plant cells.
Elaborating on his current research on development of callus transformation system for guayule, Dr Kumar explained that callus is a mass or clump of single cells. Each cell has a totipotency (the ability of a single cell to divide and produce all of the differentiated cells in an organism) to convert itself in the form of plantlet under the influence of specific plant growth regulators, also called plant hormones.
“In our study, guayule callus was produced using plant hormones, which was used for the genetic transformation with the help of agrobacterium strain. The agrobacterium is capable of injecting their genes into the normal plant cells and causing uncontrolled cell growth. Scientists have customised these strains and are now using them as a vehicle to inject the useful genes. This process is known as plant genetic transformation,” he explains.
Once the genetic transformation is established in 2-3 days of incubation, bacterium growth needs to be ceased with the help of bacteriostatic agents (antibiotics). Dr Kumar’s team has used a selected regenerative type of callus instead of leaf explant (a technique to organo-typically culture cells from a piece of tissue from a plant)for the genetic transformation since most of the callus produced from the guayule is not regenerative into plantlets.
“When we do the genetic transformation of whole plant tissue like leaf discs etc. a different kind of callus is produced from infected leaf discs, which may be of regenerative or non-regenerative in nature. Therefore, to ensure 100% regeneration, we developed a method based on the regenerative callus,” he says.
Under this method the transformation efficiency of regeneration is found to be way higher than conventional reported methods. Moreover, guayule is a recalcitrant in-vitro regeneration meaning it is very poor in regeneration in the test tubes. “Therefore, callus based transformation system is important in case of guayule. Using this genetic approach more latex production is desirable.”
When asked whether agrobacterium infection can prevent regeneration of leafs, Dr Kumar explained that the leaf explants of guayule are rich in the phenolic compounds. When they are subjected to the incision or wound, they leach out a considerable amount of phenolic compounds. The wound site acts as an entry point for agrobacterium and it results in the release of phenolic substances, which is necessary for virulent (Vir) gene induction of agrobacterium.
The high phenolic compounds leaching out from the wound site lead to the browning effect in plant tissue due to the oxidation of phenolic compounds in the presence of light. It causes the death/ necrosis of plant tissues and plant tissues lose their regeneration potential.
The callus cell cultures of guayule have a negligible amount of phenolic compounds, which do not let resurgence of the agrobacterium growth during and after genetic transformation process. “Therefore, callus is a better tissue for the purpose of genetic transformation using agrobacterium for improving latex productivity in both Parthenium argentatum (guayule) and Hevea brasiliensis (rubber tree).”
Browning of localised tissues following oxidization of phenolic compounds from cut or wound site in leaf explants leads to loss of the transgenic tissues, which are important to produce the genetically modified plant. “To overcome this barrier, we have developed an alternative genetic transformation method, which is based on the 100% regenerative callus, free from any kind of browning problem that hinder the regeneration capacity of plant cells and transformation efficiency as well in the guayule, which is a recalcitrant crop,” he says.
Elaborating on his research on guayule germplasm and genetic engineering aimed at proliferating guayule and increase the output of latex, Dr Kumar said the growth of plant and latex productivity and refinement of germplasm are important aspects that can be done by plant breeding,
“DNA barcoding to differentiate Parthenium species and lines is possible. Using the genetic transformation approach, we are aiming at enhancing the Isopentenyl Pyrophosphate (IPP) in guayule, which is the direct precursor of rubber molecule biosynthesis,” he explains.
The IPP is produced in the plant by both the cytosolic mevalonate (MVA) and the plastidic methyl-erythritol phosphate (MEP) pathways. Using the model plant system, Dr Kumar’s team has shown that a higher IPP can be produced in a plant by genetic engineering of yeast mevalonate pathway into chloroplasts. The overexpression of IPP (isoprenoid) pathway of yeast into the rubber tree or guayule via genetic approach could substantially improve the latex yield (two to four fold higher).
Dr Kumar believes that if the government takes appropriate policy measures the Thar desert could be turned green by cultivating guayule which will improve the quality of life of the people, discourage them from urban migration and contribute to India’s rubber economy as a supplement to production from Heave trees.