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Researchers at the Indian Institute of Technology Gandhinagar (IITGN) have mapped and functionally validated the genes that control a natural self-rejection mechanism in two widely cultivated Indian oilseed crops, the Brassica rapa varieties toria and yellow sarson. The work, conducted in collaboration with the Indian Council of Agricultural Research–Directorate of Rapeseed-Mustard Research in Bharatpur, was recently published in Frontiers in Plant Science.
The research arrives at a critical moment for India. The country imported more than half of its edible oil in 2023-24, with imports meeting roughly 56% of domestic demand. As the government pushes for self-reliance, the findings offer plant breeders and farmers a new molecular foundation for producing high-yielding hybrid mustard on a commercial scale.
Many flowering plants possess a built-in safeguard known as self-incompatibility (SI), a 'lock and key' molecular mechanism that allows a flower to reject its own pollen and accept pollen from unrelated plants. By forcing cross-breeding, SI mixes genes, avoids inbreeding, and produces hardier, more productive offspring. For breeders, this natural system is invaluable, eliminating the need to hand-emasculate thousands of flowers when producing commercial hybrid seed.
'To maximise crop yields through hybridisation, we need precise control over pollination, which is aided by self-rejection,' said Dr. Subramanian Sankaranarayanan, the study's corresponding author and Assistant Professor in IITGN's Department of Biological Sciences and Engineering. 'Although SI has been extensively studied in Brassica napus (canola), the molecular basis of this mechanism is poorly characterised in India's commercially grown Brassica rapa varieties, toria and yellow sarson.'
The team, led by Dr. Sankaranarayanan with co-first authors Hemal Bhalla and Kumari Ankita, alongside colleagues Aman Ahlawat and Surabhi S. Rode, focused on the contrasting pollination behaviour of the two varieties. Toria rejects its own pollen, demonstrating self-incompatibility, while yellow sarson accepts it, demonstrating self-compatibility.
The 'lock and key' mechanism is located on the surface of the stigma, the plant's female reproductive tissue. Through controlled pollination experiments, the researchers established compatibility relationships by analysing pollen attachment, pollen tube growth, and seed development. Self-pollinated toria produced almost no growth, while in cross-pollinations, flowers filled with growing pollen tubes.
The team then combined molecular biology with computational analysis to characterise four major genes: SRK, FER1, MLPK, and ARC1. These genes code for proteins acting as the cellular sensors, processors, and executors of the plant's self-rejection response. The team cloned and sequenced the genes, comparing their genetic codes with those of related plants to build evolutionary family trees, confirming that the genes are genuine, well-conserved versions of known self-rejection genes.
Because a protein's function depends on its three-dimensional shape, the researchers modelled these structures using AlphaFold3, an artificial-intelligence tool from Google DeepMind. The detailed structural blueprints enabled the team to confirm that every protein carries the working parts needed to perform its expected role.
To verify gene function, the team temporarily silenced each gene, one at a time, using short, custom-made strands of synthetic DNA that latch onto a gene's instructions and stop the cell from reading them. The silencing is temporary and leaves no permanent change in the plant. When SRK, FER, or ARC1 was muted, toria's self-rejection collapsed, and the flowers began accepting their own pollen. Fluorescence microscopy confirmed robust pollen tube growth, demonstrating that the self-incompatibility barrier had been breached.
The study also produced a surprising finding regarding MLPK. 'Traditionally, this gene is considered vital to the self-rejection pathway in related mustard species,' explained Hemal Bhalla, co-first author and a PhD Scholar at IITGN. 'But, in toria, switching off MLPK only partially weakened the rejection response, indicating it plays a secondary or redundant role in this specific variety.'
The researchers also mapped a second defence layer by monitoring biochemical changes on the stigma surface within minutes of pollination. When incompatible pollen lands, the plant deploys a localised chemical shield of Reactive Oxygen Species (ROS), which halt pollen germination. The team visualised this using Nitro Blue Tetrazolium, a dye that darkens wherever ROS gather. Silencing SRK, FER, or MLPK dulled ROS release, while silencing ARC1 did not, suggesting that the flower operates two separate defence systems simultaneously, with ARC1 likely employing an alternative cellular degradation pathway to neutralise unwanted pollen.
The researchers also demonstrated that these genes are highly conserved across Brassica species, indicating that the underlying mechanism has remained largely unchanged through evolution. Cross-tests confirmed that toria and yellow sarson still interbreed successfully, with the resulting seeds showing near-complete germination, an important signal that the system is usable in real breeding programmes.
As climate change accelerates, bringing erratic monsoons, unseasonal heatwaves, and shifting pest pressures to the Indian subcontinent, the ability to breed hardier oilseeds quickly carries significant economic weight. India's heavy reliance on imported edible oil leaves both farmers and households exposed to global price shocks. Developing climate-resilient hybrid oilseeds is therefore central to the targets of India's National Mission on Edible Oils – Oilseeds and the United Nations Sustainable Development Goals 2 and 12.
'Our findings provide a clear molecular blueprint of how pollination is governed in India's oilseed varieties,' noted Kumari Ankita, co-first author and PhD Scholar at IITGN. 'Foundational genetics like this creates an execution pipeline for developing hybrids that are stacked with favourable traits, including higher oil content, disease resistance, and resilience to erratic weather.'
The research was supported by fellowships and grants from IITGN and the Government of India, including the Ministry of Education Prime Minister Research Fellowship, the University Grants Commission, the Department of Biotechnology, the DBT Ramalingaswami Re-entry Fellowship, and the Science and Engineering Research Board Start-up Research Grant.
Source: businessnewsthisweek.com