Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan.
Plant Physiol. 2021 Mar 15;185(2):491-502. doi: 10.1093/plphys/kiaa010.
The genus Cuscuta comprises stem holoparasitic plant species with wide geographic distribution. Cuscuta spp. obtain water, nutrients, proteins, and mRNA from their host plants via a parasitic organ called the haustorium. As the haustorium penetrates into the host tissue, search hyphae elongate within the host tissue and finally connect with the host's vascular system. Invasion by Cuscuta spp. evokes various reactions within the host plant's tissues. Here, we show that, when Arabidopsis (Arabidopsis thaliana) is invaded by Cuscuta campestris, ethylene biosynthesis by the host plant promotes elongation of the parasite's search hyphae. The expression of genes encoding 1-aminocylclopropane-1-carboxylic acid (ACC) synthases, ACC SYNTHASE2 (AtACS2) and ACC SYNTHASE6 (AtACS6), was activated in the stem of Arabidopsis plants upon invasion by C. campestris. When the ethylene-deficient Arabidopsis acs octuple mutant was invaded by C. campestris, cell elongation and endoreduplication of the search hyphae were significantly reduced, and the inhibition of search hyphae growth was complemented by exogenous application of ACC. In contrast, in the C. campestris-infected Arabidopsis ethylene-insensitive mutant etr1-3, no growth inhibition of search hyphae was observed, indicating that ETHYLENE RESPONSE1-mediated ethylene signaling in the host plant is not essential for parasitism by C. campestris. Overall, our results suggest that C. campestris recognizes host-produced ethylene as a stimulatory signal for successful invasion.
菟丝子属包含广泛地理分布的茎全寄生植物物种。菟丝子属植物通过一种称为吸器的寄生器官从宿主植物中获取水分、养分、蛋白质和 mRNA。当吸器穿透宿主组织时，搜索菌丝在宿主组织内伸长，最终与宿主的血管系统相连。菟丝子属植物的入侵会引起宿主植物组织内的各种反应。在这里，我们表明，当拟南芥（Arabidopsis thaliana）被菟丝子属植物（Cuscuta campestris）入侵时，宿主植物的乙烯生物合成促进了寄生虫搜索菌丝的伸长。当拟南芥植物被 C. campestris 入侵时，编码 1-氨基环丙烷-1-羧酸（ACC）合酶的基因（AtACS2 和 AtACS6）的表达在茎中被激活。当缺乏乙烯的拟南芥 acs 八倍体突变体被 C. campestris 入侵时，搜索菌丝的细胞伸长和内重复明显减少，而外源应用 ACC 则可以补充搜索菌丝生长的抑制。相比之下，在 C. campestris 感染的拟南芥乙烯不敏感突变体 etr1-3 中，未观察到搜索菌丝生长的抑制，表明宿主植物中 ETHYLENE RESPONSE1 介导的乙烯信号对于 C. campestris 的寄生不是必需的。总的来说，我们的结果表明，C. campestris 将宿主产生的乙烯识别为成功入侵的刺激信号。
