A research team led by the Indian Institute of Technology Gandhinagar has mapped and tested the genes behind the natural self-rejection system in two of India's most widely grown oilseed varieties, Brassica rapa toria and yellow sarson. Published in Frontiers in Plant Science with the Indian Council of Agricultural Research's Directorate of Rapeseed-Mustard Research at Bharatpur, the work matters for a country that imported about 56% of its edible oil in 2023–24 and wants high-yielding hybrid mustard.

Many flowering plants carry self-incompatibility: a molecular lock-and-key on the stigma lets a flower reject its own pollen and accept another plant's, forcing cross-breeding, avoiding inbreeding and producing hardier, more productive offspring. For breeders it is a gift — a mother plant that refuses its own pollen spares them from removing anthers from thousands of flowers by hand when they make hybrid seed. Toria rejects its own pollen; yellow sarson accepts it.

Self-incompatibility has been studied in Brassica napus (canola) but its molecular basis in India's commercial Brassica rapa was poorly known, said corresponding author Dr Subramanian Sankaranarayanan, assistant professor of biological sciences and engineering at IITGN. With co-first authors Hemal Bhalla and Kumari Ankita and colleagues Aman Ahlawat and Surabhi S. Rode, the team first confirmed the compatibility relationships by pollination experiments — in self-pollinated toria almost no pollen tubes grew, while the crosses filled with them.

They then cloned and sequenced four major genes — SRK, FER1, MLPK and ARC1, which act as the sensors, processors and executors of the rejection response — compared them with related species to confirm they were genuine, and modelled the proteins' three-dimensional shapes with AlphaFold3. To test function they dripped short synthetic antisense DNA strands onto the stigma to silence each gene temporarily, leaving no permanent change in the plant.

Muting SRK, FER1 or ARC1 collapsed toria's self-rejection and the flower began accepting its own pollen, confirmed by fluorescence microscopy of pollen-tube growth. MLPK, considered vital in related mustards, only partly weakened the response when silenced — a secondary or redundant role in this variety, said Bhalla. The team also measured a second defence: within minutes of an incompatible grain landing, the stigma deploys a burst of reactive oxygen species that halts pollen germination.

The findings give mustard breeders a defined genetic switch for controlling pollination in the varieties India actually grows — a foundation, the authors say, for commercial hybrid seed in a crop where self-reliance in cooking oil is a national goal, and of direct interest across the mustard-growing plains of South Asia.

Source: AgroPages