How tearless onion gene editing could stop kitchen crying for good

The chemistry of kitchen tears

Slice into an onion, and your eyes sting within seconds. This kitchen misery happens because crushing the plant cells sets off a rapid chemical chain reaction. One specific enzyme, called lachrymatory factor synthase (LFS), grabs sulfur intermediates and turns them into a gas that irritates your eyes.

You can picture this process as a factory conveyor belt heading toward a chemical fork in the road. Normally, the LFS enzyme acts as a switchman, diverting ingredients down a side track that churns out tear-inducing gas. If you break that switch, the ingredients must stay on the main line instead. There, they form thiosulfinates—healthy compounds that inhibit cyclooxygenase-1 (COX-1) and boost the onion's nutritional value.

Snipping the switch

Researchers turned to tearless onion gene editing using CRISPR/Cas9 molecular scissors to disable this LFS switch. Onions are famously recalcitrant, meaning they strongly resist genetic lab work. To deliver the editing machinery, the team used the bacterium Agrobacterium tumefaciens, aiming multiple guide RNAs at once with a multiplex vector.

The scissors found their mark in tiny clumps of unorganised plant cells called callus. Out of 483 glowing callus lines, 101 carried mutations in the LFS gene. The team regenerated 71 whole plants and tested 30 of them. Nineteen carried confirmed mutations, with five lines exceeding a 50% mutation frequency. In the altered leaves, LFS enzyme activity dropped below 40% of normal, plunging as low as 21.5% in one line.

Petri-dish setbacks

There was a major catch. To keep the cells alive and edit them, the scientists had to maintain the callus tissue in dishes for up to three years. This prolonged isolation caused somaclonal variation, meaning spontaneous genetic defects piled up in the cells over time.

Think of it like repeatedly photocopying a photocopy: the underlying instructions blur. While our switchman analogy explains the tidy chemical bypass inside the plant, it breaks down here. In real life, cells do not simply lose one clean switch; they accumulate collateral wear and tear across their entire system. When moved into soil, the edited plants grew poorly, developed tiny roots, and died. Lab-grown bulbs measured a measly 20 to 30 millimetres across, compared to standard 100-millimetre bulbs grown from seeds. During vernalization—the cold treatment required to trigger flowering—the miniature bulbs rotted away, failing to produce any viable seeds.

What we still do not know

The team proved that gene editing can switch off the tear-producing enzyme, but big questions remain. It is still unclear whether the severe stunting came solely from the years spent in dish culture, or if Cas9 snipped off-target DNA sites elsewhere. Loss of the LFS enzyme itself might also play an unexpected role in plant health.

Researchers also do not know how full-sized bulbs grown in real field soil would actually taste. For now, testing direct methods on shoot tips might bypass the tissue dish phase entirely, bringing cooks one step closer to genuinely tearless cooking.