The identification of a gene that controls whether petunia flowers attract pollination by hawkmoths at night or by hummingbirds during the day is reported in a paper published online this week in Nature Genetics. These results show one way that plants can evolve new pollinator partnerships.
Flowering plants often rely on animals-for example, bees or bats-for pollination. These partnerships require flowers to develop traits, such as color and scent, to attract the right pollinators. Over evolutionary time, plants may acquire changes in these traits that allow them to attract new pollinators. How these pollinator shifts occur is still not well understood.
Cris Kuhlemeier and colleagues studied the genetic basis of ultraviolet (UV) light absorbance, an important trait for attracting nocturnal pollinators, in three species of the South American Petunia to better understand how pollinator shifts happen. Petunia inflata, the most ancestral of the three petunia species, has small, purple flowers and is only pollinated by bees. Petunia axillaris has white flowers that attract nocturnal hawkmoths. Petunia exserta has bright red flowers that are pollinated by hummingbirds.
Of the three species, P. axillaris absorbs the highest levels of UV light, and hawkmoths are more attracted to P. axillaris flowers with higher levels of UV light absorbance than those with lower levels. The authors find that evolved differences in UV absorbance between the species could be explained by changes to a single gene, MYB-FL. The shift from bee to hawkmoth pollination in some Petunia species after their divergence from P. inflata was accompanied by a mutation in MYB-FL that greatly increased the levels of a major class of UV-absorbing compounds in the flower. A different mutation arose later that disabled MYB-FL in the shift from hawkmoth pollination in P. axillaris to hummingbird pollination in P. exserta.