Yunnan Key Laboratory of Plant Reproductive Adaptation and Evolutionary Ecology, Institute of Biodiversity, School of Ecology and Environmental Science, Yunnan University, Kunming 650500, China.
Ministry of Education Key Laboratory for Transboundary Ecosecurity of Southwest China, State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming 650500, China.
Plant Physiol. 2023 Jul 3;192(3):2554-2568. doi: 10.1093/plphys/kiad198.
Mycorrhizae are ubiquitous symbioses established between fungi and plant roots. Orchids, in particular, require compatible mycorrhizal fungi for seed germination and protocorm development. Unlike arbuscular mycorrhizal fungi, which have wide host ranges, orchid mycorrhizal fungi are often highly specific to their host orchids. However, the molecular mechanism of orchid mycorrhizal symbiosis is largely unknown compared to that of arbuscular mycorrhizal and rhizobial symbiosis. Here, we report that an endophytic Sebacinales fungus, Serendipita indica, promotes seed germination and the development of protocorms into plantlets in several epiphytic Epidendroideae orchid species (6 species in 2 genera), including Dendrobium catenatum, a critically endangered orchid with high medicinal value. Although plant-pathogen interaction and high meristematic activity can induce the hypoxic response in plants, it has been unclear whether interactions with beneficial fungi, especially mycorrhizal ones, also involve the hypoxic response. By studying the symbiotic relationship between D. catenatum and S. indica, we determined that hypoxia-responsive genes, such as those encoding alcohol dehydrogenase (ADH), are highly induced in symbiotic D. catenatum protocorms. In situ hybridization assay indicated that the ADH gene is predominantly expressed in the basal mycorrhizal region of symbiotic protocorms. Additionally, the ADH inhibitors puerarin and 4-methylpyrazole both decreased S. indica colonization in D. catenatum protocorms. Thus, our study reveals that S. indica is widely compatible with orchids and that ADH and its related hypoxia-responsive pathway are involved in establishing successful symbiotic relationships in germinating orchids.
菌根是真菌与植物根系之间建立的普遍共生关系。特别是兰花，需要与相容的菌根真菌共生才能完成种子萌发和原球茎发育。与宿主范围广泛的丛枝菌根真菌不同，兰花菌根真菌通常对其宿主兰花具有高度特异性。然而，与丛枝菌根和根瘤菌共生相比，兰花菌根共生的分子机制在很大程度上仍不清楚。在这里，我们报告了一种内生Sebacinales 真菌，印度被毛孢（Serendipita indica），可以促进几种附生型 Epidendroideae 兰花物种（2 个属中的 6 个种）的种子萌发和原球茎发育为植物，包括具有高药用价值的濒危兰花物种金钗石斛（Dendrobium catenatum）。虽然植物-病原体相互作用和高分生组织活性可以诱导植物的缺氧反应，但尚不清楚与有益真菌（特别是菌根真菌）的相互作用是否也涉及缺氧反应。通过研究金钗石斛和印度被毛孢之间的共生关系，我们确定了缺氧反应基因，如编码醇脱氢酶（ADH）的基因，在共生的金钗石斛原球茎中高度诱导。原位杂交分析表明，ADH 基因主要在共生原球茎的基部菌根区表达。此外，ADH 抑制剂葛根素和 4-甲基吡唑均降低了印度被毛孢在金钗石斛原球茎中的定殖。因此，我们的研究表明，印度被毛孢与兰花广泛兼容，ADH 及其相关的缺氧反应途径参与了萌发兰花中成功共生关系的建立。
