Figure: Lemons are known for their face-puckering sour taste. Now scientists have uncovered the mysterious genes behind this acidity, new findings that could help farmers breed sweeter oranges, lemons, limes, grapefruit and other citrus fruit. (Genetic Literacy Project)

Citrus fruits have always been known for their sour, zesty taste. With a little help from science, researches have finally identified what gives the lemon, orange, grapefruit, and other similar fruits their particular tangy flavor.

Scientists from the University of Amsterdam found out that the sour taste of citrus fruits is due to the acidity in the vacuoles of the citrus' fruit cells. Vacuoles are the compartments of the cell that are filled with fluid that the cell needs to survive. In the case of the citrus fruit, it was found that the citrus' vacuole fluid is extremely acidic due to  CitPH1 and CitPH5 genes. These genes are not only responsible for the acidity of the cell vacuoles, but for the determination of the flower color as well. Results showed that citrus plants express more CitPH1 and CitPH5 compared to other sweet fruit varieties. Thus, the citrus produces more sour-flavored fruit. These findings can support future studies that may be able to determine just how sweet or sour we want our fruits to be.

Read more in Nature Communications and Genetic Literacy Project.