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Why So Sour, Lemons?

Researchers have uncovered genes that may make citrus like lemons sour, Inside Science reports.

A team from the University of Amsterdam noted that, in petunias, alterations to the seven PH loci affect the acidity of its petal vacuoles and petal homogenates, leading its flowers to become blue. Based on that, they examined PH orthologs in lemons, oranges, and pummelos to determine whether they contribute to the buildup of acid in Citrus vacuoles.

As they report in Nature Communications, the researchers found PH1 and PH5 homologs — known as CitPH1 and CitPH5 — to be highly expressed in acidic fruit and downregulated in non-acidic fruit. In particular, they traced this downregulation to inactivating mutations in CitAN1 or regulatory mutations that affect the expression of CitAN1, CitPH3, or CitPH4.

Co-senior author Ronald Koes tells Inside Science that their findings could aid in faster breeding of new varieties of fruit, as growers wouldn't have to wait until the plant matured to get a sense of the acidity of its fruit.