Exploring the genetic basis of wound nectar secretion in Solanum dulcamara

花蜜是一种常见的植物特征，可以吸引传粉者等有益的动物。一般来说，花蜜是一种含糖的溶液，但补充剂往往会增强它的吸引力。除了花蜜腺，许多植物的营养部位也有蜜腺。它们所谓的花外花蜜(EFN)吸引了捕食性动物，通常是蚂蚁，它们保护植物免受食草动物的攻击。蜜腺显示出巨大的结构多样性，并在不同的植物分类群中独立进化了无数次，因此它们的进化起源仍然是一个悬而未决的问题。在茄子中，我们最近发现了一种新的形式的EFN，它不是从蜜腺中分泌出来的，而是直接在食草动物造成的伤口上分泌的。这种伤口花蜜(WN)也会吸引蚂蚁进行植物防御。由于有证据表明，其他植物也会释放吸引蚂蚁的伤口汁液，因此出现了一种假设，即伤口花蜜分泌可能代表着花蜜进化的早期步骤。蜜腺可能进化为二级结构，通过塑造蜜汁分泌的位置、时间和组成，将宝贵的奖励专门奉献给有益的动物。这种情况可以很好地解释整个植物界蜜腺的频繁得失，因此需要进行进一步的研究。这一假设是基于这样的假设，即花蜜分泌来自基本的和进化的古老机制，可以很容易地利用这些机制来释放花蜜。为了为伤口和蜜腺释放蜜汁的机制比较奠定基础，本项目将致力于以下三个主要目标：1)发现与杜氏链霉菌WN分泌相关的激活基因。2)通过测试这些基因是否参与WN分泌的功能，解开杜氏链霉菌分泌WN的分子机制的关键要素。3)表征杜氏链霉菌分泌的WN的化学性质和生态功能，超越其主要成分蔗糖的诱人功能。为了追求这些目标，我们将筛选与WN分泌相关的候选基因。同时，我们将建立一种基于CRISPR-Cas9介导的基因编辑的反向遗传学方法。然后将研究最有可能的候选基因与WN分泌和蚂蚁吸引的关系。此外，我们还将调查杜卡马拉是否会调整其WN的化学成分，以增加所投资同化物的效益，因为它是具有结构蜜汁的EFN分泌植物。除了提供关于EFN释放的完全未知的遗传基础的全面数据外，该项目还将进一步拓宽我们对新发现的WN的化学和生态学的认识。

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.