Missing gene means squash and aubergines don't know when to stop growing
Disabling one gene turns tomatoes pear-shaped, researchers have found. Squash, aubergines - and pears - probably owe their shape to the same effect.
Without the gene, called OVATE, the top of a fruit grows more than the bottom, giving it a long neck and a bulbous base, plant biologist Steven Tanksley and his colleagues at Cornell University, Ithaca, New York, have found1.
The gene probably stops growth in normal fruit by making a protein that controls other genes, says Tanksley. The model plant Arabidopsis has its own version, but nobody knew what it did.
Plant breeders developed strains of pear-shaped tomatoes in the early twentieth century. "But at some point in the intervening 50 years the material was lost," says Tanksley. His team reinvented the trait from an existing variety.
Most wild fruit - including the ancestors of cultivated crops - are small and round. An animal biting into them anywhere has a good chance of a mouthful of seeds. A long, seedless neck is a waste of a plant's resources.
But humans seem to like pear-shaped fruit. We eat the elongated varieties of many species. We might have bred for this trait for aesthetic reasons, suggests plant biologist John Doebley of the University of Wisconsin in Madison.
"Humans like novelty," says Doebley. "Rather than something practical, gardeners might just have enjoyed the curiosity value."
The genetics of fruit shape mirror other crop traits, where large differences between wild and domestic varieties come down to a few genetic discrepancies. One gene controls whether some cereals shed their seeds or keep them, for example. Tanksley's team have previously found a gene that controls tomato size.
Liu, J. Van Eck, J. Cong, B. Tanksley, S.D. A new class of regulatory genes underlying the cause of pear-shaped fruit. Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.162485999 (2002).