Scientists have identified a genetic mutation that acts as a major contributor to the extreme fruit size associated with the modern tomato, according to a study published online this week in Nature Genetics.
Modern cultivated tomatoes produce fruit as much as 1,000 times larger than their wild progenitors. One clear reason for the increase in tomato size during its domestication is the increased number of carpels ? organs ? which determines the final number of compartments in the fruit.
Steven Tanksley and colleagues crossed lines of tomatoes with either high or low compartment number, and carried out genetic mapping studies to identify the gene or genes responsible for the variation in carpel number. They identified an insertion of 6?8 kilobases in a gene they call fas only in the tomatoes with high compartment number. Expression of the gene is reduced in the developing flower buds in tomatoes carrying the insertion. A survey of 30 different lines of cerasiforme, the wild form of tomato thought to be related to the smaller progenitors, showed that none carried the insertion.
As the insertion is found exclusively in modern cultivated tomatoes, the authors suggest that the mutation occurred recently in tomato domestication, and then spread rapidly as a result of selection for larger fruit.