Heterotrophic Nutrition Strategies of the Parasitic Plant Cuscuta

寄生植物菟丝子的异养营养策略

• 批准号: 523910401
• 负责人: Professor Dr. Markus Albert
• 金额: --
• 依托单位: Department Biologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/523910401?language=en
• 关键词: Heterotrophic; Nutrition; Strategies; Parasitic; Plant

Cuscuta spp. are holoparasitic plants without roots and leaves that infect almost all dicotyledonous plants. Cuscuta spp. enwind the shoots of their host plants and develop specialized penetrating organs, the haustoria, to gain access to water, nutrients and assimilates. These multicellular organs invade the host's tissues and attach to the host's vasculature within seven to nine days. When the connection is complete, Cuscuta cells are directly connected to the tracheae of the xylem as well as to the phloem cells of the hosts. In particular, the phloem-phloem junction between host and parasite cells is established by interspecific plasmodesmata (PDs). Since this process, including PD formation and phloem connection, takes at least seven days, it is unclear whether other e.g. apoplastic feeding strategies are required. Furthermore, it is unclear whether an additional apoplastic nutrition generally takes place in order to enable nutrient absorption as efficiently as possible. In our own preliminary work, we infected Arabidopsis thaliana with Cuscuta reflexa and observed that the transcript of the bidirectional sucrose transporter AtSWEET10 (SUCROSE WILL EVENTUALLY BE EXPORTED TRANSPORTER 10) in A. thaliana is increased in early infection stages. Furthermore, reporter gene assays in transgenic A. thaliana plants revealed that the AtSWEET10 promoter is induced by penetration of the C. reflexa haustorium and gene expression for another sucrose transporter, AtSUC2, is also upregulated. In C. reflexa we identified CrSUT1 (SUCROSE TRANSPORTER 1) as the first sucrose transporter of C. reflexa and demonstrated gene expression in prehaustorial cells by in situ hybridization. CrSUT1 appears to be responsible for uptake of apoplastic sucrose into the prehaustorium during the early stages of infection. Taken together, these preliminary data indicate that Cuscuta spp. use strategies to feed on apoplastic sugars at the early infection stages before the symplastic connections via PDs are established. The subsequent joining process including interspecific PD formation between phloem cells is also not yet understood, and we therefore aim to use the Cuscuta – host plant model to study the detailed molecular mechanisms of interspecific PD formation as well as the parasitic and heterotrophic feeding strategies of Cuscuta. In the proposed project we therefore pursue two main goals: A) to unravel the early feeding strategies of Cuscuta spp., which occur independently of PD-mediated cell-cell contact and are especially important during the first days of host penetration; and B) functional studies of nutrient flux across PDs and the relevant developmental steps of PD formation between host and parasite cells.

Cuscuta spp.是一种无根无叶的全寄生植物，几乎感染所有双子叶植物。菟丝子缠绕在寄主植物的枝条上，并发育出专门的穿透器官——吸器，以获取水分、营养物质和同化物。这些多细胞器官侵入宿主的组织，并在7到9天内附着在宿主的脉管系统上。当连接完成时，库库塔细胞直接连接到木质部的气管以及宿主的韧皮部细胞。特别是，宿主和寄生虫细胞之间的韧皮部-韧皮部连接是由种间连丝（plasmodesmata, pd）建立的。由于包括PD形成和韧皮部连接在内的这一过程至少需要7天，因此尚不清楚是否需要其他如外泌体摄食策略。此外，目前尚不清楚是否为了尽可能有效地吸收营养，通常会进行额外的外胞体营养。在我们自己的前期工作中，我们用Cuscuta reflexa感染拟南芥，观察到拟南芥双向蔗糖转运蛋白AtSWEET10（蔗糖最终会被出口转运蛋白10）的转录在感染早期阶段增加。此外，在转基因拟南芥植物中进行的报告基因分析显示，AtSWEET10启动子是由C. reflexa吸器渗透诱导的，另一种蔗糖转运蛋白AtSUC2的基因表达也上调。在C. reflexa中，我们鉴定出CrSUT1（蔗糖转运蛋白1）是C. reflexa的第一个蔗糖转运蛋白，并通过原位杂交证实了该基因在吸前细胞中的表达。在感染的早期阶段，CrSUT1似乎负责将外胞体蔗糖摄取到吸器前。综上所述，这些初步数据表明，在通过pd建立共塑连接之前，Cuscuta在感染早期阶段使用策略以外体糖为食。随后的连接过程，包括韧皮部细胞之间的种间PD形成尚不清楚，因此我们旨在利用菟丝子-寄主植物模型来研究菟丝子种间PD形成的详细分子机制以及寄生和异养取食策略。因此，在拟议的项目中，我们追求两个主要目标：A)揭示Cuscuta spp.的早期摄食策略，这一策略独立于pd介导的细胞-细胞接触而发生，并且在宿主渗透的最初几天尤为重要；B)宿主与寄生虫细胞间PD间营养通量的功能研究以及PD形成的相关发育步骤。