Suetsugu Kenji, Okada Hidehito
Department of Biology, Graduate School of Science, Kobe University, Kobe, Hyogo, 657-8501, Japan.
Institute for Advanced Research, Kobe University, 1-1 Rokkodai, Nada-Ku, Kobe, Hyogo, 657-8501, Japan.
Mycorrhiza. 2025 Apr 10;35(2):29. doi: 10.1007/s00572-025-01202-x.
Mycoheterotrophic plants, which depend entirely on mycorrhizal fungi for carbon acquisition, often exhibit high specificity toward their fungal partners. Members of Thismiaceae are generally recognized for their extreme mycorrhizal specialization and rarity. In this study, we examined the mycorrhizal associations of Relictithismia, a recently discovered monotypic genus within Thismiaceae, and Thismia abei, a Thismia species with a similar distribution in southern Japan, by employing high-throughput DNA sequencing of the 18S rRNA gene. Our analyses revealed that both R. kimotsukiensis and T. abei are predominantly associated with two specific virtual taxa (VTX00295 and VTX00106) of the genus Rhizophagus (Glomeraceae). These shared associations may reflect either phylogenetic niche conservatism, in which the common ancestor of R. kimotsukiensis and T. abei retained the same AM fungal partners, or convergent evolution, in which the AM fungal phylotypes were independently recruited due to their potential benefits for these mycoheterotrophic plants. Furthermore, BLAST searches demonstrated that VTX00295 and VTX00106 are widely distributed globally, suggesting that highly specialized mycorrhizal interactions are unlikely to be the primary drivers of the limited distribution and rarity of R. kimotsukiensis and T. abei. Overall, our findings enhance our understanding of high mycorrhizal specificity in Thismiaceae. However, broader investigations, combining extensive sampling of Thismiaceae species with ancestral state reconstruction, are needed to determine whether the shared associations detected here reflect phylogenetic niche conservatism or convergent evolution.
完全依赖菌根真菌获取碳源的菌根异养植物，通常对其真菌伙伴表现出高度特异性。水玉簪科植物成员通常因其极端的菌根专一性和稀有性而闻名。在本研究中，我们通过对18S rRNA基因进行高通量DNA测序，研究了水玉簪科内最近发现的单型属——残遗水玉簪属，以及在日本南部具有相似分布的水玉簪属物种阿部水玉簪的菌根关联。我们的分析表明，木津水玉簪和阿部水玉簪都主要与根内球囊霉属（球囊霉科）的两个特定虚拟分类单元（VTX00295和VTX00106）相关联。这些共同的关联可能反映了系统发育生态位保守性，即木津水玉簪和阿部水玉簪的共同祖先保留了相同的丛枝菌根真菌伙伴，或者是趋同进化，即由于这些菌根异养植物的潜在益处，丛枝菌根真菌的系统发育型被独立招募。此外，BLAST搜索表明VTX00295和VTX00106在全球广泛分布，这表明高度特化的菌根相互作用不太可能是木津水玉簪和阿部水玉簪分布有限和稀有的主要驱动因素。总体而言，我们的研究结果增进了我们对水玉簪科高度菌根特异性的理解。然而，需要更广泛的调查，将水玉簪科物种的广泛采样与祖先状态重建相结合，以确定这里检测到的共同关联是反映了系统发育生态位保守性还是趋同进化。
