April 24, 2017
Flowering plants depend on pollen vectors in order to reproduce. Yet a plant has a problem if a pollinator, which is attracted by the odors of sweet flowers, lays its eggs on the plant after pollination is complete, and from these eggs hatch voracious caterpillars ready to attack the tasty leaves with their enormous appetite.
Scientists from the Max Planck Institute for Chemical Ecology have discovered a gene in the wild tobacco species Nicotiana attenuata called NaTPS38, which regulates the production of an aromatic compound, the sesquiterpene (E)-α-bergamotene, in both flowers and leaves. “We observed that Nicotiana attenuata plants emit (E)-α-bergamotene in flowers at night to lure Manduca sexta moths as pollinators. The compound makes a moth keep its proboscis longer in a flower and pollination success is increased. The emission of the same compound in leaves attacked by Manduca sexta larvae during the day, however, attracts the predators of the larvae and acts as an indirect defense,” first author Wenwu Zhou summarizes. In this way, the tissue-specific emission of one compound helps the wild tobacco plants to interact most advantageously with Manduca sexta.
Although the gene NaTPS38 is very similar to a monoterpene synthase, it is nevertheless responsible for the production of the sesquiterpene (E)-α-bergamotene. Usually a gene from the sesquiterpene synthase family regulates the production of such a compound, but in this case, it appears that the gene NaTPS38 violated this general rule. Analyzing the function and evolutionary history of NaTPS38 revealed that this gene originated from a duplication of a monoterpene synthase which then evolved the ability to produce (E)-α-bergamotene, a sesquiterpene compound. This unique evolutionary process likely occurred before the divergence of different Solanaceae species, the plant family which includes tobacco.
The fact that a single gene in Nicotiana attenuata mediates both pollination and defense by producing tissue-specific (E)-α-bergamotene is an example of a phenomenon called ecological pleiotropy. “Accumulating evidence suggests that ecological pleiotropy may be quite common in plants. Our work demonstrates that interactions between different ecological factors, such as pollinators and herbivores, are important for plant evolution. However, we know little about the extent to which these interactions can affect the plant’s adaptation to its environment,” explains Shuqing Xu. The scientists are currently developing a new research program that aims to address this question systematically.