New Delhi: Scientists from the National Agri-Food and Biomanufacturing Institute have successfully performed genome editing in peas, overcoming a key technical hurdle that has complicated the crop’s genetic modification in the past.
In a paper published in the scientific journal Plant Cell Reports on 24 August, scientists genetically transformed pea cells to regenerate into plants. They also demonstrated how CRISPR-Cas9—a precise gene-editing tool—can be successfully delivered to edit a target gene, making future gene editing of important pea traits much easier.
The study highlighted that while genome editing has been a precise and rapid strategy for crop improvement, its application in pea was more challenging compared to other crops. This is was primarily because it is very hard to grow peas from cells in a lab (in-vitro), and the current editing methods only work on a few specific varieties of peas.
“The regeneration and Agrobacterium-mediated transformation systems were optimised, and the dicotyledonary node (DCN) was identified as the preferred explant for multiplex CRISPR/Cas9-based genome editing in pea,” the study reads.
In simpler terms, CRISPR-Cas9 can be used to make precise changes to a plant’s DNA. However, prior to that, scientists first need to get the CRISPR machinery inside the plant cells and then regenerate an entire plant from those modified cells.
This becomes difficult in peas because their tissues are recalcitrant to tissue culture, meaning that, unlike other crops, they do not readily grow back into complete plants after being manipulated in laboratories. Transformation efficiency also varies substantially between pea varieties.
The process
In this particular experiment, the paper states that scientists were not trying to develop a new commercial pea variety, but were trying to develop a process that makes genome editing in peas easier and more efficient.
Genome editing is a type of genetic engineering which relies on ‘editing’ plant genes rather than ‘modifying’ them. This process allows scientists to make specific changes to an organism’s DNA by adding, deleting, or altering their genetic material.
This process is considered safer, healthier and environmentally friendly, as no foreign genes are incorporated into the plant, and the crop’s naturally present genes are altered to promote mutations in their DNA sequence.
“CRISPR/Cas genome editing has emerged as the most effective tool for trait improvement in several crops. However, successful genome editing requires an efficient regeneration system and transformation pipelines for delivering CRISPR/Cas components, ideally applicable across diverse plant species and genotypes,” the study reads, adding that being able to efficiently grow genetically modified cells into whole plants was key for successful genome editing.
For the study, researchers compared three types of tissues or explants—embryonic axis, DCN and nodal segment. These are pieces of living tissue, taken from the plant to grow in a lab. Of the three explants, the DCN performed the best, showing 100 per cent shoot-bud induction and an average of 39.7 shoots per explant.
They also used optimised combinations of plant hormones to accentuate certain features. For instance, BAP and kinetin were used for shoot formation, while shoot elongation and rooting were improved using GA3, IAA, NAA and BAP—four major plant growth regulators (hormones) used in plant tissue culture, agriculture, and horticulture to control growth, rooting, and shoot multiplication.
The paper states that scientists used Agrobacterium tumefaciens—a bacterium commonly used to transfer DNA into plants. They then tested the plants by changing parameters such as Agrobacterium concentration, infection duration, vacuum infiltration and co-cultivation time.
Scientists found that across 10 cultivars, they obtained transient transformation efficiencies ranging from 23.33 per cent to 90 per cent in DCN explants and 6.66 per cent to 93.33 per cent in embryonic-axis explants. This was significant because the transformation can potentially behave very differently between varieties. Once the tissue had been transformed, they tested it with CRISPR-Cas9 editing of the PsPDS gene–phytoene desaturase, involved in carotenoid biosynthesis.
This breakthrough was significant because not enough research has happened around the genome editing of pea, when compared to other crops, including rice or wheat, a senior scientist of the Department of Science and Technology (DST) told ThePrint.
“This lag has been because of the difficulty in getting transformed cells to regenerate into healthy plants,” the scientist said.
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Other areas of genome editing
In May last year, the Union Agriculture Ministry released two varieties of genome-edited rice—DRR Rice 100 (Kamla) and Pusa DST Rice 1. Scientists bred improved GE mutants of Samba Mahsuri and Cottondora Sannalu varieties using CRISPR-Cas SDN-1 (site-directed Nucleases-1) technology to develop the new varieties.
This gained attention not just for being the world’s first such varieties, but also for being the first step toward the new-age, climate-resilient crops which India has been pushing for.
Scientists from the Indian Agricultural Research Institute (IARI), the apex institute that developed the GE rice, are also working on developing genetically edited mustard, which is likely to be released by 2027.
(Edited by Saptak Datta)