Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan.
Graduate School of Information Sciences, Tohoku University, 6-3-09 Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan.
Plant Cell Physiol. 2017 Nov 1;58(11):1868-1877. doi: 10.1093/pcp/pcx121.
Stem parasitic plants (Cuscuta spp.) develop a specialized organ called a haustorium to penetrate their hosts' stem tissues. To reach the vascular tissues of the host plant, the haustorium needs to overcome the physical barrier of the cell wall, and the parasite-host interaction via the cell wall is a critical process. However, the cell wall components responsible for the establishment of parasitic connections have not yet been identified. In this study, we investigated the spatial distribution patterns of cell wall components at a parasitic interface using parasite-host complexes of Cuscuta campestris-Arabidopsis thaliana and Cuscuta japonica-Glycine max. We focused on arabinogalactan proteins (AGPs), because AGPs accumulate in the cell walls of searching hyphae of both C. campestris and C. japonica. We found more AGPs in elongated haustoria than in pre haustoria, indicating that AGP accumulation is developmentally regulated. Using in situ hybridization, we identified five genes in C. campestris that encode hyphal-expressed AGPs that belong to the fasciclin-like AGP (FLA) family, which were named CcFLA genes. Three of the five CcFLA genes were expressed in the holdfast, which develops on the Cuscuta stem epidermis at the attachment site for the host's stem epidermis. Our results suggest that AGPs are involved in hyphal elongation and adhesion to host cells, and in the adhesion between the epidermal tissues of Cuscuta and its host.
茎寄生植物（菟丝子属）会发育出一种专门的器官，称为吸器，以穿透宿主的茎组织。为了到达宿主植物的维管束组织，吸器需要克服细胞壁的物理屏障，而通过细胞壁的寄生虫-宿主相互作用是一个关键过程。然而，负责建立寄生连接的细胞壁成分尚未确定。在这项研究中，我们使用菟丝子属-拟南芥和菟丝子属-大豆的寄生-宿主复合物，研究了寄生界面细胞壁成分的空间分布模式。我们专注于阿拉伯半乳聚糖蛋白（AGPs），因为 AGPs 在菟丝子属的搜寻菌丝的细胞壁中积累。我们发现伸长的吸器中 AGPs 比预吸器中更多，这表明 AGP 的积累受到发育调控。通过原位杂交，我们在菟丝子属中鉴定了五个编码菌丝表达 AGP 的基因，这些基因属于成束相关的 AGP（FLA）家族，被命名为 CcFLA 基因。这五个 CcFLA 基因中的三个在固着器中表达，固着器在菟丝子属茎表皮的附着部位发育，用于附着宿主的茎表皮。我们的结果表明，AGPs 参与了菌丝的伸长和与宿主细胞的黏附，以及菟丝子属和其宿主的表皮组织之间的黏附。
