Bitter-free CRISPR grapefruits are now in development

If you never eat grapefruit because you find it too bitter, CRISPR varieties may be more to your taste. It has been shown that disabling a single gene through gene editing can significantly reduce the levels of the chemicals that make grapefruit so bitter.

“It could expand the market,” he says Nir Carmi at the Volcani Center in Rishon LeZion, Israel. “Kids usually don’t like grapefruit because it’s too bitter for them.”

He thinks this approach could even help save the citrus industry. A bacterial disease called citrus greening, also known as huanglongbinghas a devastating effect on these fruits. The insects that spread the bacteria can’t survive in areas with cold winters, Carmi says, but hardy citrus varieties are so bitter they’re inedible.

A gene-editing approach could make it possible for the first time to create edible frost-hardy varieties, meaning citrus cultivation could move from subtropical regions such as Florida to temperate regions such as northern Europe.

The sourness of citrus fruits is due to their acidity, with lemons having particularly high levels. However, their bitterness comes from a number of other compounds. Previous studies have shown that grapefruit’s bitterness is mainly due to a chemical called naringin, with contributions from closely related molecules called neohesperidin and poncirin.

So Carmi’s team used CRISPR gene editing in one variety of grapefruit to disable the gene for the enzyme that produces the three chemicals. It takes several years for grapefruit trees to start bearing fruit, so scientists haven’t been able to taste the fruit yet. But none of the three chemicals were detectable in the leaves of the CRISPR grapefruit trees, so they’re confident they won’t be present in the fruit either.

The engineered trees also contain an added “marker gene” that makes it easier for the team to identify plants that have been successfully engineered. Because of this marker gene, the trees are transgenic, which would make it difficult and expensive in most countries to get permission to sell any fruit they bear. In some countries, including the US and Japan, plants with simple genetic modifications are not considered genetically modified, so obtaining a permit is cheap and easy.

The team now plans to make the same modification in grapefruit without adding the marker gene. It’s achievable, but it takes a lot of work, says a team member Elena Plesseralso at Volcani Center. “It’s very tiring.

Other teams around the world are working on similar projects, Carmi says, but he thinks his group is the most advanced.

The researchers also plan to deactivate the same enzyme in cold-hardy citrus such as the trifoliate orange, whose fruit is inedible due to its high content of naringin, neohesperidin and poncirin. The trees will then be crossed with popular citrus fruit varieties such as oranges to try to create delicious stoneless fruit while maintaining the cold hardiness of trifoliate oranges. This can take many years to achieve.

This kind of genetic modification could significantly change the taste of the fruit, he says Erin Mulvihill at the University of Ottawa in Canada, who studied naringin.

Another reason some people don’t eat grapefruit is that it can inhibit liver enzymes that break down drugs like statins, leading to dangerously high blood levels in those who take them. Naringin is one of the chemicals in grapefruit responsible for this effect, but it’s not the only one, Mulivihill says. “Many genes would have to be deleted to completely eliminate grapefruit-drug interactions.”

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