The scent of roses (Rosa x hybrida) is composed of hundreds of volatile molecules. Monoterpenes represent up to 70% percent of the scent content in some cultivars, such as the Papa Meilland rose. Monoterpene biosynthesis in plants relies on plastid-localized terpene synthases. Combining transcriptomic and genetic approaches, we show that the Nudix hydrolase RhNUDX1, localized in the cytoplasm, is part of a pathway for the biosynthesis of free monoterpene alcohols that contribute to fragrance in roses. The RhNUDX1 protein shows geranyl diphosphate diphosphohydrolase activity in vitro and supports geraniol biosynthesis in planta.

1. Plants evolved strategies to attract pollinators that are essential for reproduction. However, plant defence against herbivores may trade off with pollinator attraction. 2. Here, we investigated the role of inducible plant secondary metabolites in such a trade-off. Our objective was to reveal the mechanisms underlying the effects of induced plant responses to pollination and herbivory. We assessed how responses of plants to pollination and insect herbivory affect the behaviour of flower visitors. Subsequently, we investigated how the production of volatile and non-volatile compounds changes after pollination and herbivory. 3. Both herbivores and pollinators induced important phenotypic changes in flowers. Brassica nigra plants respond to pollination and herbivory with changes in the profile of volatiles and non-volatiles of their flowers. Our results show that butterflies use different cues when searching for an oviposition site or a nectar source. Pollination status influenced the behaviour of butterflies, but not that of syrphid flies. 4. We discuss the results in the context of the trade-off between defence and reproduction in plants and suggest that systemic responses to herbivores can interfere with local responses to pollination. Therefore, these responses must be addressed in an integrated way because, in nature, plants are simultaneously exposed to herbivores and pollinators.

In the field, biotic and abiotic stresses frequently co-occur. As a consequence, common molecular signalling pathways governing adaptive responses to individual stresses can interact, resulting in compromised phenotypes. How plant signalling pathways interact under combined stresses is poorly understood. To assess this, we studied the consequence of drought and soil flooding on resistance of Solanum dulcamara to Spodoptera exigua and their effects on hormonal and transcriptomic profiles. The results showed that S. exigua larvae performed less well on drought-stressed plants than on well-watered and flooded plants. Both drought and insect feeding increased abscisic acid and jasmonic acid (JA) levels, whereas flooding did not induce JA accumulation. RNA sequencing analyses corroborated this pattern: drought and herbivory induced many biological processes that were repressed by flooding. When applied in combination, drought and herbivory had an additive effect on specific processes involved in secondary metabolism and defence responses, including protease inhibitor activity. In conclusion, drought and flooding have distinct effects on herbivore-induced responses and resistance. Especially, the interaction between abscisic acid and JA signalling may be important to optimize plant responses to combined drought and insect herbivory, making drought-stressed plants more resistant to insects than well-watered and flooded plants.