Indian scientists have achieved a pioneering breakthrough by developing the country’s first low-pungent mustard which displays remarkable resistance to disease and pests. Notably, this scientific achievement leverages CRISPR/Cas9 gene editing technology while ensuring that the mustard remains non-GM and transgene-free.
The Challenges and Significance of Gene Editing in Mustard Breeding
Typically, Indian mustard seeds, Brassica juncea, carry around 120-130 parts per million (ppm) of glucosinolates. These sulphur and nitrogen-containing compounds are responsible for the distinctive pungency of mustard oil and meal. Besides, glucosinolates function as natural defenders equipping the plant to resist diseases and pests.
On a comparative scale, canola seeds have considerably lower glucosinolate levels, approximately 30 ppm. This lower concentration endows canola oil and meal with a specific pleasant taste. While the oil obtained from oilseeds is used for cooking, their remaining protein-rich meal is utilized as animal feed. However, the high glucosinolate content in rapeseed meal necessitates it to be mixed with grass and water before feeding to livestock to prevent conditions like goiter and internal organ abnormalities.
Given these considerations, scientists strived to create mustard seeds with lower glucosinolate content comparable to canola seeds. Still, such a reduction in glucosinolates risks making the plant more susceptible to pests and diseases.
How Gene Editing Is Revolutionizing Mustard Breeding
Employing CRISPR/Cas9, a precise gene-editing tool, scientists modified specific Glucosinolate Transporter (GTR) genes that influence the accumulation of glucosinolates in mustard seeds. The researchers targeted 10 out of the 12 GTR genes in a particular mustard variety, ‘Varuna’. The resultant genetic modifications deactivated the proteins generated by these genes, thereby significantly reducing glucosinolate levels within the seeds.
Impacts of Gene Editing on Plant Defense and Pest Resistance
The gene-edited mustard plants exhibited lower glucosinolate levels below the 30 ppm threshold applicable for canola-quality seeds. However, the leaves and pods surrounding the seeds manifested higher glucosinolate levels due to disrupted compound transport. This increased glucosinolate concentration bolsters the plant’s defense against pests, leading to enhanced resistance against both insect and fungal pests.
Distinguishing Genome Editing from Genetic Modification
The low-glucosinolate mustard lines result from genome editing (GE), standing apart from genetically modified (GM) crops where foreign genes are introduced. Instead, GE modifies existing genes without integrating new genetic material. In this context, the gene-edited mustard is completely transgene-free and lacks any foreign genes. Importantly, the CRISPR/Cas9 enzyme employed for gene editing doesn’t persist in the final genome-edited plants, further differentiating them from transgenic GM crops where introduced genes may remain.
Regulations and Future Outlook for Genetically-Modified Mustard
In India, genetically modified organisms undergo rigorous regulation requiring approval from the Genetic Engineering Appraisal Committee (GEAC). However, an official memorandum exempts genome-edited plants that don’t incorporate foreign DNA from mandatory GEAC approval for open field trials. Following clearance from the Institutional Biosafety Committee (IBSC), the newly-developed genome-edited mustard lines are set to undergo open field trials.
As India incurs substantial costs annually due to significant import volumes of edible oils, these breakthroughs promise to improve domestic oilseed production by enhancing crop yields, pest resistance, and product quality. This could significantly reduce India’s dependence on imported vegetable oils.
Status of Mustard Cultivation in India
Mustard is the most extensively cultivated oilseed crop in India, grown annually across a 9 million hectares area during the Rabi season. With its high average oil extractable content (38%), mustard serves as an excellent “oilseed” crop, providing both fat for humans and protein for animals. Areas like Rajasthan, Haryana, Madhya Pradesh, and Uttar Pradesh earn significant revenue from mustard cultivation.
Understanding CRISPR Cas9 Technology
CRISPR-Cas9 is a revolutionary gene-editing technology that enables geneticists to alter specific parts of the genome by accurately removing, adding, or modifying DNA segments. Two key components facilitate this process: a ‘molecular scissors’ enzyme called Cas9, which can cut the two strands of DNA at a precise location in the genome, and a guide RNA (gRNA) that directs Cas9 to the exact spot where it should make the cut, ensuring accurate and precise gene editing.
