Parasitic molecular cues during plant-plant interaction - recognition and influence on host plants

菟丝子属植物以全寄生的形式存在，通过吸器穿透茎感染几乎所有双科植物。吸器与寄主的维管束相连，吸收水分、碳水化合物和营养物质。在最近的一项工作中，我们发现了抗性番茄的一个受体（Cuscuta receptor 1, CuRe1）作为识别Cuscuta糖肽的关键成分，定义为Cuscuta因子1 （CuF1）。在cuf1感知后，CuRe1启动防御反应，当在其他易感寄主植物中表达时，也会导致抗性增加。CuRe1将C. reflexa识别为异源，但番茄除外。通常，寄生物不被寄主识别，并主动操纵寄主向易感方向发展：维管束薄壁细胞开始分裂、分化，最终与木质部和韧皮部的寄主细胞连接。什么类型的分子线索启动和调节这些易感性机制？在自己的初步工作中，我们克隆了在菟丝子感染期间上调的寄主植物基因启动子。利用它们作为植物系统中的启动子：：报告基因（荧光素酶）构建体，这些构建体可以作为检测用逐步纯化的Cuscuta提取物处理后荧光素酶活性的工具，并最终有助于识别操纵寄主植物信号传导的新Cuscuta因子（CuFs）。初步结果表明存在不同的新cuf，这些cuf将被进一步表征和鉴定。令人惊讶的是，在一个启动子：：荧光素酶结构的情况下，CuF1也能够触发荧光素酶的表达，这表明CuF1除了在番茄中触发防御的独家作用外，还具有相关作用。这种cuf1诱导的替代信号也暗示了在易感宿主中存在一种不依赖于cuf1的感知机制。在一个补充项目中，我们的目标是确定寄主植物中寄生CuFs的检测机制，并希望获得有关易感性相关信号的知识。我们将使用拟南芥受体突变体，这些突变体在我们的实验室中可用。将种植突变植株，感染Cuscuta，并根据改变的易感性进一步分析。此外，我们手头有多种拟南芥的资料（1001基因组计划），我们将进行额外的检查。通过传统的基于图谱的克隆或全基因组关联研究（GWAS）来鉴定受干扰易感性表型的相关基因。cuf感知的新成分或相关信号成分将通过成熟的方法进一步分析，如受体-配体相互作用、定位、蛋白质-蛋白质相互作用等研究。此外，我们将通过测定菟丝子在突变体或转基因植物上生长后的生物量来证明其生物学相关性。这将有助于破译植物与植物相互作用所需的新成分的分子和生物学作用。

Plants of the genus Cuscuta live as holoparasites and infect nearly all dicot plants by penetrating stems with haustoria. Haustoria connect to the vascular bundles of their hosts and withdraw water, carbohydrates and nutrients. In a recent work, we identified a receptor (Cuscuta receptor 1, CuRe1) of resistant tomato as a critical component to recognize a Cuscuta glycopeptide, defined as Cuscuta factor 1 (CuF1). Upon CuF1-perception, CuRe1 initiates defense responses and also leads to increased resistance when expressed in otherwise susceptible host plants. The recognition of C. reflexa as alien by CuRe1 is an exception of tomato. Usually, the parasite stays unrecognized by its host and actively manipulates it towards susceptibility: Parenchymal cells of the vascular bundles start to divide, differentiate and finally connect to the parasitic cells of both Xylem and Phloem. What type of molecular cues initiate and regulate these mechanisms of susceptibility? In own preliminary work, we cloned promoters of host plant genes that are up-regulated during a Cuscuta infection. Using them as promoter::reporter-gene (luciferase) constructs in plant systems, these constructs serve as tools to detect luciferase activity upon treatment with stepwise purified Cuscuta extracts and will finally help to identify new Cuscuta factors (CuFs) that manipulate host plant signaling. First results indicate the presence of different new CuFs which will be further characterized and identified. Surprisingly, CuF1 was also able to trigger the luciferase expression in case of one promoter::luciferase construct indicating a relevant role of CuF1 besides its exclusive role of triggering defense in tomato. Such alternative CuF1-induced signaling also hints to a CuRe1-independent perception mechanism existing in susceptible hosts.In a complementary project we aim to identify the detection mechanisms for parasitic CuFs in host plants and want to gain knowledge about the susceptibility related signaling. We will use Arabidopsis receptor mutants which collections are available in our laboratory. Mutant plants will be grown, infected with Cuscuta and further analyzed according altered susceptibility. Subsidiary, we have diverse Aarabidopsis accessions at hand (1001 Genomes project) that we will check in addition. Relevant genes of obtained phenotypes with disturbed susceptibility will be identified either by classical map-based cloning or by using Genome-wide association studies (GWAS). Novel components of CuF-perception or related signaling components will be further analyzed with well-established methods such as studies on receptor-ligand interaction, localization, protein-protein interaction, etc. Furthermore, we will prove the biological relevance by determining the Cuscuta biomass after growth on mutants or transgenic plants. This will help to decipher the molecular and biological role of novel components required for a plant-plant interaction.