Like men's private parts, the female parts of flowers tend to dangle either to the right or left. But what determines that preference? A study published in the 13 June issue of Nature shows that the trait is determined by just a single gene, inherited in classic Mendelian fashion.
In many unrelated plant species, the female sex organ known as the style can either hang to the left or right side of the flower, a phenomenon called enantiostyly. Left-dangling and right-dangling flowers are mirror-images, like left and right hands. In the past, botanists assumed that enantiostyly was just a curiosity; most figured that a flower's "handedness" was a matter of chance that meant nothing to the plant's fitness.
Challenging that common wisdom, Linley Jesson and Spencer Barrett of the University of Toronto, Canada, decided to breed different specimens of a plant called Heteranthera multiflora, which sports yellow flowers with left- or right-dangling styles. Just like Mendel did with pea plants in the 19th century, they carefully mated different types of flowers and kept statistics on the traits of their offspring. They found that a single gene with two alleles determines the style's left or right dangle; right turned out to be dominant. Although the researchers know the gene's location, they have yet to find out what protein it produces.
The division helps prevent inbreeding, the researchers say. When they let bees visit left-dangling flowers, the team discovered that they became dusted with pollen on their right flanks; when they next buzzed across to another left-dangling flower, pollination was unlikely; but when they visited a right-dangling flower, the pollen was well placed to rub off on the waiting style. Thus, enantiostyly appears to lower the frequency of mating between closely related plants.
The finding not only solves an old riddle, but it might have practical use as well, says biologist Hugh Dickinson of the University of Oxford, United Kingdom. "There is great interest in the genes which determine plant architecture," Dickinson says, because those genes might shed light on a range of plant diseases.