Nature Genet. http://doi.org/9z3 (2015)

Crop species undergo profound shifts in agronomic traits, such as architecture and fruit size, during domestication. Niels Müller of the Max Planck Institute for Plant Breeding Research, Cologne, and colleagues find that for tomatoes, the circadian clock also slowed down during domestication, probably allowing cultivation at higher latitudes.

The researchers observed that the circadian movements of leaves ran to a slower clock in cultivated tomatoes than in their wild ancestors. These had both a longer period and a delayed phase (time to maximum displacement). Similar deceleration was also seen in diurnal patterns of transcription.

A gene, EID1, was identified by map-based cloning, whose ‘wild’ allele significantly advanced the phase when introduced into cultivated tomato. Moreover, a selective sweep was observed around EID1, indicating the cultivated allele is adaptive and has been selected for by humanity. Plants bearing the cultivated allele have higher chlorophyll content than those carrying the wild allele under long photoperiods, suggesting the slowed clock might prevent fitness loss under the long summer days encountered by domesticated tomatoes far from their equatorial origins.

Whether changes in the circadian clock are common during crop domestication is unknown; however, adaptation of a plant's daily rhythms may prove to be a fertile field of exploration.