If you never eat grapefruit because you find them far too bitter, CRISPR varieties may be more to your taste. It has been shown that disabling one gene via gene editing can greatly reduce the level of the chemicals that make grapefruit so bitter.
鈥淚t could expand the market,鈥� says at the Volcani Center in Rishon LeZion, Israel. 鈥淜ids don鈥檛 usually like grapefruit because it鈥檚 too bitter for them.鈥�
He thinks this approach could even help save the citrus industry. A bacterial disease called citrus greening, also known as , is having a devastating impact on these fruits. The insects that spread the bacteria can鈥檛 survive in areas with cold winters, says Carmi, but cold-hardy citrus varieties are so bitter that they are inedible.
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The gene-editing approach could allow the creation of edible cold-hardy varieties for the first time, meaning citrus farming could shift from subtropical regions such as Florida to temperate ones like northern Europe.
The sourness of citrus fruits is due to their acidity, with lemons having particular high levels. Their bitterness, however, comes from a range of other compounds. Previous studies have shown that the bitterness of grapefruit is mainly due to a chemical called naringin, with closely related molecules called neohesperidin and poncirin also contributing.
So Carmi鈥檚 team has used CRISPR gene editing in one grapefruit variety to deactivate the gene for the enzyme that produces these three chemicals. It takes several years for grapefruit trees to start fruiting, so the researchers haven鈥檛 yet been able to taste the fruit. But none of the three chemicals was detectable in the leaves of the CRISPR grapefruit trees, so they are confident they won鈥檛 be present in the fruit either.
The edited trees also contain an added 鈥渕arker gene鈥� that makes it easy for the team to identify which plants were successfully edited. Because of this marker gene, the trees are transgenic, which would make it difficult and expensive to get approval to sell any fruit they bear in most countries. In some nations, including the US and Japan, plants with simple gene edits aren鈥檛 regarded as genetically engineered, so getting approval there is cheap and easy.
The team now plans to make the same edit in grapefruit without adding a marker gene. It is achievable, but involves a lot of work, says team member , also at the Volcani Center. 鈥淚t鈥檚 very tedious.鈥�
Other teams around the world are pursuing similar projects, says Carmi, but he thinks his group鈥檚 is the most advanced.
The researchers also plan to disable the same enzyme in a cold-hardy citrus such as the trifoliate orange, the fruit of which is inedible due to its high levels of naringin, neohesperidin and poncirin. The trees will then be crossed with popular varieties of citrus fruits such as oranges to try to create delicious seedless fruits while retaining the cold tolerance of trifoliate oranges. This could take many years to achieve.
This kind of gene editing could significantly alter the palatability of fruits, says at the University of Ottowa in Canada, who has studied naringin.
Another reason why some people don鈥檛 eat grapefruit is that it can inhibit the liver enzymes that break down drugs such as statins, leading to dangerously high levels in the blood for those taking them. Naringin is one of the chemicals in grapefruit responsible for this effect, but it isn鈥檛 the only one, says Mulivihill. 鈥淢any genes would have to be removed to completely eliminate grapefruit-drug interactions.鈥�
The Plant Journal
