It is a common complaint in the produce aisle: tomatoes today might be big, but they are tasteless. Now researchers say they can remedy the problem by tweaking genes that affect sugar levels in the fruit.
While their wild relatives produce small, sweet fruit, domesticated tomatoes grown industrially have been bred for high yields, resulting in varieties that are 10-100 times bigger.
Now scientists in China say they have identified two genes that put a brake on sugar production in tomatoes during ripening, and created gene-edited versions of domesticated varieties to result in fruit that is large but also sweet.
Prof Sanwen Huang, the director general of the agricultural genomics institute at the Chinese Academy of Agricultural Science, Shenzhen, said it was necessary to balance the needs of consumers with those of producers and farmers.
“As farmers want larger tomatoes and higher yield, the consumers want sweeter tomatoes,” he said. “Our discovery of the sugar brake genes leads to [breeding of a] sweeter tomato without sacrificing fruit size and yield, breaking the negative relationship between yield and quality.”
Writing in the journal Nature, the researchers describe how they first explored the genomes of wild and cultivated tomato plants, identifying two similar genes associated with the sugar content of the fruit. They say the versions of these genes associated with high sweetness are prevalent in wild tomato plants, but have largely been lost in modern varieties.
Further work revealed the versions of the genes found in domesticated tomato plants enabled the production of an enzyme that labelled another sugar-making enzyme for destruction within cells. By contrast, the versions of these genes found in wild plants limited the production of this enzyme, resulting in sweeter tomatoes.
When the team used the gene-editing tool Crispr-Cas9 to make precise changes to the DNA of domesticated tomato plants, preventing these genes from working properly, they found the resulting fruit had up to 30% higher sugar content than those of unmodified plants. Unexpectedly, however, there was no significant difference in fruit weight or yield. While the gene-edited tomatoes had fewer, lighter seeds, they germinated as normal.
The researchers say their work suggests the two genes work as sugar brakes during fruit ripening, probably to ensure there is enough energy for the development of seeds.
Huang said the new tomatoes could end up in supermarkets within three to five years; the team noted other gene-edited tomatoes were already available in Japan.
However, it might be a while before others can taste the fruits of such science: while new laws support growing of gene-edited crops in England and Wales, secondary legalisation needed to implement the law has not yet been passed.
