By Shuvarghya ChakrabortyB.Sc. Agriculture (Hons.) Student (3rd Year)
Palli Siksha Bhavana (Institute of Agriculture), Visva Bharati
An “Out of the box” thinking: Where we stand and what can we achieve
Gene therapy pertains to replace the defective copy of a gene with a good copy of that gene particularly to correct some genetic defect. Gene therapy is mainly used in medical science particularly for advanced therapeutics to combat with some incurable diseases. But in plant science there is no such report of gene therapy. But technologies and scopes are there in this regard particularly when we think of smart crop development.
How gene therapy can be applied in plant science
Gene therapy in plants can be done with the help of genome editing (i.e. CRISPER Cas9, talen, zfn etc.) to modify a position in plant genome selectively and also insert the desirable so called good copy of that particular gene. As per the technology, at first, we have to first design a guide-RNA (gRNA) complementary to our desired position in the genome and then we have to develop a vector construct as per our experiment. This vector construct will contain mainly five (5) components.
- Guide-RNA (gRNA) construct
- Gene segment of our choice
- Cas9 gene segment
- Crisper gene segment
- Other accessory elements e.g. promoters, markers etc.
After that we have to introgress the vector construct via Agrobacterium mediated transformation protocol (AMTP) and Select for transgenic plants, regenerating the whole plant as per tissue culture protocol available for that species.
In transformed plant genome, the gRNA will be the edit complex to the target genomic region and Cas9 will cleave out the existing gene region. The replaced copy of that gene will be inserted at the same portion by a process called Homology Directed Repair (HDR). It is hypothesized that, in transgenic lines, the new gene will be expressed producing the desirable phenotype.
A model for plant gene therapy in rice
Here I will depict a model scheme for gene therapy in rice (Oryza sativa) particularly to combat biotic stress.
Bacterial leaf blight (BLB) of rice is a world wide problem to rice growing countries. The disease is caused by a gram negative bacteria called Xanthomonas oryzae p.v. oryzae. To combat with this particular disease, there is a huge quantum of research is going on particularly in classical breeding, molecular breeding, transgenic breeding, but no particular and sustainable solution is achieved till date. In this particular context scientist are very much optimistic about plant gene therapy to terminate this problem forever. Since the completion of rice genome sequencing project in 2005, a number of negative regulator for this disease have been identified in rice genome. A very much noted gene among them is spl11 gene. This gene increases the disease susceptibility of rice cultivars by negatively regulating the resistance genes against the disease (e.g. xa21, xa5, xa13 etc.) in rice plant.
Scientist use the genome editing technique to edit this negative regulator gene and replacing it with a good copy of gene which will be the positive regulator of resistance genes concerned for that disease. By this method of gene therapy a Novel Resistance Pathway (NPR) can be engineered in rice cultivars that will definitely boost up the status of rice production all over the world by permanently terminating BLB disease of rice.
Plant Gene therapy is a potential technology. But more research and development is needed in this field to make this technology cost effective, sustainable and vibrant enough so that it will be accepted by world wide research community not to just correct specific problems in crops but to use it as a next generation breeding tool for flourishing the whole scenario of world agriculture.
- Gene therapy in plants by Barbara Hohn & Holger Puchta, Proceedings of the National Academy of Sciences. Jul 1999, 96 (15) 8321-8323; DOI: 10.1073/pnas.96.15.8321
- Agrobacterium Mediated Plant Transformation: Biology and Applications by Hau-Hsuan Hwang, Manda Yu & Erh-Min Lai, The Arabidopsis Book, 2017(15). DOI: https://doi.org/10.1199/tab.0186