Exploring the genetic basis of wound nectar secretion in Solanum dulcamara

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Nectar is a common plant trait to attract beneficial animals like pollinators. In general, nectar is a sugary solution, but supplements often enhance its attractiveness. Besides floral nectaries, many plants also bear nectaries on vegetative parts. Their so called extrafloral nectar (EFN) attracts predacious animals, commonly ants, which defend the plant against herbivores. Nectaries show a huge structural diversity and have evolved numerous times independently all across diverse plant taxa, so that their evolutionary origin is still an unsolved matter of debate.In Solanum dulcamara, we recently discovered a novel form of EFN that is not secreted from nectaries but directly at herbivore-inflicted wounds. This wound nectar (WN) also attracts ants for plant defence. As there is evidence that also other plants release ant-attracting wound saps, the hypothesis arose that wound nectar secretion might represent an early step in nectar evolution. Nectaries could have evolved as secondary structures dedicating the valuable reward specifically to beneficial animals by shaping location, timing and composition of nectar secretion. Such a scenario could elegantly explain the frequent gains and losses of nectaries throughout the plant kingdom and thus calls for further examination. This hypothesis is based on the assumption that nectar secretion arises from fundamental and evolutionary ancient mechanisms that can be easily co-opted to release nectar. However, it remains speculative until the mechanisms of WN release are identified and can be compared to those of EFN release from nectaries.To set the foundation for mechanistic comparisons of nectar release from wounds and nectaries, this project will address the three major goals to:1) discover genes that are activated in association with S. dulcamara’s WN secretion.2) unravel the key elements of molecular mechanisms behind S. dulcamara’s WN secretion by testing whether these genes are functionally involved in WN secretion.3) characterize the chemical properties and the ecological functionality of the WN secreted by S. dulcamara beyond the attractive function of its main constituent sucrose.To pursue these goals, we will I) screen for candidate genes that are transcriptionally correlated with WN secretion. In parallel we will II) establish a reverse genetics approach based on CRISPR-Cas9 mediated gene editing. Then will III) examine the involvement of the most likely candidate genes in WN secretion and ant attraction. Moreover, we will IV) survey whether S. dulcamara tailors the chemical composition of its WN to increase the benefit of the invested assimilates, as it is known for EFN secreting plants with structured nectaries.Besides providing comprehensive data on the completely unknown genetic basis of EFN release, this project will further broaden our knowledge into the chemistry and ecology of the newly discovered WN.