The 1960s 'green revolution' in rice production in Asia selected for variants of a single gene that boosted yields across the continent. A new study finds that prehistoric farmers harnessed that same gene when they first domesticated rice as early as 10,000 years ago.
     The history of rice farming is very complex, but the basic facts are well established. All of today's domesticated rice belongs to the species Oryza sativa, which descends from the wild ancestor Oryza rufipogon. Oryza sativa has two major subspecies, japonica (short-grain rice grown mostly in Japan) and indica (long-grain rice grown mostly in India, Southeast Asia, and southern China).
     During the 1960s, yields were increased by selecting for mutations in a gene which shortens the plant's stem. Dwarf plants require less energy and nutrients - raising the number of grains that can be harvested - and are less vulnerable to storms.
     A team led by Makoto Matsuoka, of Nagoya University in Japan, examined the evolutionary history of mutations in this gene, identifying the ancient mutation called SD1-EQ which is closely associated with shorter stem length. While this mutation was found in japonica and to a lesser extent in indica varieties, it did not appear in the wild ancestor.
     Matsuoka and his colleagues conclude that the stem-shortening mutation arose during prehistoric times in japonica, when the plant was first being domesticated. They suggest that japonica and indica evolved from wild rice long before rice domestication began, and were independently domesticated in different regions. Later, the mutation found its way into indica plants, perhaps through crossbreeding.
     The findings fit well with the archaeological record of early rice production - particularly in northern China, where the earliest rice farmers cultivated at the shallow margins of wetlands, consciously or unconsciously selecting for shorter plants.

Edited from Science Magazine (7 June 2011)