Exploring the genetic basis of wound nectar secretion in Solanum dulcamara
Final Report Abstract
Nectar is a common plant trait to attract beneficial animals like pollinators. Extrafloral nectaries (EFN) attract predacious animals, commonly ants, which defend the plant against herbivores. Solanum dulcamara secretes a new form of EFN without nectaries, directly at herbivore-inflicted wounds. This wound nectar (WN) also attracts ants for plant defence. As also other plants release ant-attracting wound saps, WN secretion might represent an early step in nectar evolution - a hypothesis that would elegantly explain the frequent losses and gains of nectaries throughout the plant kingdom. This calls for an identification of the mechanisms of WN release comparing them to those of EFN release from nectaries. In this project, we developed approaches to discover and functionally test genes that may be associated with S. dulcamara’s WN secretion. We characterised the phenology of S. dulcamara’s WN secretion, which is enhanced under drought conditions and variable betweengeographically distinct accessions. We determined WN secretion as an inheritable trait that is segregating in a population of plants originating from America, which we can use to find the genes determining the trait. Using CRISPR-Cas9-mediated mutation, we investigated a Sweet gene of high homology to a sucrose transporter known to be involved in floral nectar secretion in other plants and found that it is not required for WN secretion. However, we discovered that loss of wound-induced JA-biosynthesis (due to LoxD mutation) results in higher WN production despite JA-signalling actives WN secretion. As JA-signalling is required for the majority of the plant’s wound response but not for WN production, the established LoxD mutants provide new opportunities to identify the genes involved in the molecular mechanisms underlying WN secretion. We established assays to sensitively measure for differences in ant attraction and ongoing analyses will further characterize the composition and ecological functionality of the WN secreted by S. dulcamara.
