Defence-triggering molecules of the parasitic plant Cuscuta and the recognition by cell surface receptors

菟丝子属植物是一种既能侵染双子叶植物又能侵染单子叶植物的全寄生植物。这些寄生虫以吸器为特异性侵染器官，穿透寄主植物与脉管系统建立联系，并排出水分、溶质和糖。一个值得注意的例外是栽培番茄（Solanum lycopersicum），其显示出防御反应并且对Cuscuta reflexa具有抗性。我们发现番茄对C.在识别微生物相关分子模式（MAMP）后，免疫反应通常被激活。我们确定了富含亮氨酸的重复序列受体样蛋白（LRR-RLP）菟丝子受体1（CuRe 1），它检测寄生虫相关的分子模式，命名为菟丝子因子，并赋予对这种未知分子的反应性。CuRe 1还能提高对寄生线虫的抗性。当在其他易感植物中异源表达时，通过与其他LRR-RLP相比，CuRe 1具有一些突出的特性;它具有第二个预测的跨膜结构域（TM），这似乎是功能所必需的，并且CuRe 1不需要与体细胞胚胎发生受体激酶（SERKs）的共受体的配体依赖性缔合来激活防御信号。关于菟丝子因子，我们知道它存在于许多菟丝子属物种中;它是细胞壁衍生的小肽（分子量为2-3 kDa）的异质混合物，这些小肽都具有生物活性所必需的二级修饰（糖基化）。我们成功地扩大了菟丝子因子纯化方案，并在肽骨架的测序部分中迈出了第一步。然而，完整的aa序列以及Cuscuta因子的二次修饰仍然有待解决。在拟议的项目中，我们计划分两个主要部分对CuRe 1和Cuscuta因子进行研究;在A部分）“Cuscuta因子”中，我们的目标是确定Cuscuta因子的序列、结构和二次修饰。此外，我们还想破译受体激活的机制及其对寄生虫的天然功能。在部分B）“CuRe 1激活和相关下游信号传导”中，我们的目标是研究LRR-RLP CuRe 1、其特性以及其非凡的相互作用伙伴和相关启动的下游信号传导。

Cuscuta species are holoparasitic plants which infect both dicotyledonous and monocotyledonous hosts. With haustoria as specific infection organs, those parasites penetrate host plants to establish a connection to the vasculature and exhaust water, solutes and sugars. One notable exception is the cultivated tomato (Solanum lycopersicum) which shows defence responses and is resistant to Cuscuta reflexa. We discovered that tomato reacts to extracts of C. reflexa with immune responses normally activated after the recognition of microbe-associated molecular patterns (MAMPs). We identified the leucine-rich repeat receptor-like protein (LRR-RLP) Cuscuta Receptor 1 (CuRe1) which detects the parasite-associated molecular pattern, named Cuscuta factor, and confers responsiveness to this yet unknown molecule. CuRe1 also increased resistance to parasitic C. reflexa when heterologously expressed in otherwise susceptible plants. By comparison with other LRR-RLPs, CuRe1 has a few outstanding peculiarities; it has a second predicted transmembrane domain (TM) which seems essential for functionality, and CuRe1 does not require a ligand-dependent association with a co-receptor of the somatic embryogenesis receptor kinases (SERKs) to activate defence signalling. Concerning the Cuscuta factor, we know that it is present in many Cuscuta species; it is a cell-wall-derived, heterogeneous mix of small peptides (mw of 2-3 kDa) which all have a secondary modification (glycosylation) that is essential for the bio-activity. We successfully scaled up the Cuscuta factor purification protocol and made first steps in sequencing part of the peptide backbone. However, the full aa-sequence together with the secondary modification of the Cuscuta factor remains to be solved.In the proposed project we plan to work on both, CuRe1 and the Cuscuta factor in two mayor parts; in part A) "the Cuscuta factor", we aim to identify the sequence, structure and secondary modification of the Cuscuta factor. Furthermore we want to decipher the mechanism of receptor activation and its natural function for the parasite. In part B) "CuRe1 activation and related downstream signalling", we aim to work on the LRR-RLP CuRe1, its peculiarities as well as its extraordinary interaction partners and related initiated downstream signalling.