Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland.
Curr Biol. 2011 May 10;21(9):730-9. doi: 10.1016/j.cub.2011.03.059. Epub 2011 Apr 14.
Differences in floral traits, such as petal color, scent, morphology, or nectar quality and quantity, can lead to specific interactions with pollinators and may thereby cause reproductive isolation. Petunia provides an attractive model system to study the role of floral characters in reproductive isolation and speciation. The night-active hawkmoth pollinator Manduca sexta relies on olfactory cues provided by Petunia axillaris. In contrast, Petunia exserta, which displays a typical hummingbird pollination syndrome, is devoid of scent. The two species can easily be crossed in the laboratory, which makes it possible to study the genetic basis of the evolution of scent production and the importance of scent for pollinator behavior.
In an F2 population derived from an interspecific cross between P. axillaris and P. exserta, we identified two quantitative trait loci (QTL) that define the difference between the two species' ability to produce benzenoid volatiles. One of these loci was identified as the MYB transcription factor ODORANT1. Reciprocal introgressions of scent QTL were used for choice experiments under controlled conditions. These experiments demonstrated that the hawkmoth M. sexta prefers scented plants and that scent determines choice at a short distance. When exposed to conflicting cues of color versus scent, the insects display no preference, indicating that color and scent are equivalent cues.
Our results show that scent is an important flower trait that defines plant-pollinator interactions at the level of individual plants. The genetic basis underlying such a major phenotypic difference appears to be relatively simple and may enable rapid loss or gain of scent through hybridization.
花部特征（如花瓣颜色、气味、形态或花蜜质量和数量）的差异会导致与传粉者的特定相互作用，并可能由此导致生殖隔离。矮牵牛为研究花部特征在生殖隔离和物种形成中的作用提供了一个有吸引力的模式系统。夜行性天蛾传粉者烟夜蛾 Manduca sexta 依赖于 Petunia axillaris 提供的嗅觉线索。相比之下，表现出典型蜂鸟传粉综合征的 Petunia exserta 则没有气味。这两个物种在实验室中很容易杂交，这使得研究气味产生的遗传基础以及气味对传粉者行为的重要性成为可能。
在 P. axillaris 和 P. exserta 种间杂交产生的 F2 群体中，我们鉴定出两个决定两种物种产生苯类挥发物能力差异的数量性状位点（QTL）。其中一个位点被鉴定为 MYB 转录因子 ODORANT1。利用有气味的 QTL 相互导入进行了受控条件下的选择实验。这些实验表明，天蛾 M. sexta 更喜欢有气味的植物，并且气味在短距离内决定了选择。当暴露于颜色与气味的冲突线索时，昆虫没有表现出偏好，表明颜色和气味是等效的线索。
我们的结果表明，气味是一个重要的花部特征，它决定了个体植物层面的植物-传粉者相互作用。这种主要表型差异的遗传基础似乎相对简单，并且可能通过杂交迅速失去或获得气味。
