(Inside Science) — 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.

The oldest known reference to citruses dates back to roughly 2200 B.C., when tributes of mandarins and pomelos wrapped in ornamental silks were presented to the imperial court of Yu the Great in China. More citruses are now grown than an