The discovery of a gene that packs corn and rice grains with sugars is reported in a study published online this week in Nature Genetics. The gene may be responsible for the large difference in observed seed sizes between wild and domesticated grains.
Early farmers selected for large seeds in grain crops, such as corn and rice, because of their increased nutritional value. Grain size is largely determined by a process called seed filling, in which sugars are incorporated into the seed. Defects in seed filling result in poor crop yield, and a better understanding of the process may lead to improvements in crop breeding.
Davide Sosso and colleagues show that a gene in corn called ZmSWEET4c is required for seed filling. They compared the gene sequences of cultivated corn to those of its wild ancestor and identified a mutation in ZmSWEET4c that was selected for during the domestication of corn. The authors show that ZmSWEET4c transports hexose sugars, which include glucose and fructose, across a specific cell barrier within the seed. They also find that a closely related gene in rice, OsSWEET4, was a target of selection during rice domestication. The authors suggest that the discovery of these transporters may ultimately help generate new high-yield corn and rice varieties.