Graduate School of Bioresources, Mie University, 1577 Kurimamachiya, Tsu, Mie, 514-8507, Japan.
Natural History Museum and Institute, Aoba-cho, Chuo-ku, Chiba, 260-8682, Japan.
J Plant Res. 2020 Nov;133(6):841-853. doi: 10.1007/s10265-020-01233-9. Epub 2020 Oct 24.
Mixotrophic plants obtain carbon by their own photosynthetic activity and from their root-associated mycorrhizal fungi. Mixotrophy is deemed a pre-adaptation for evolution of mycoheterotrophic nutrition, where plants fully depend on fungi and lose their photosynthetic activity. The aim of this study was to clarify mycorrhizal dependency and heterotrophy level in various phenotypes of mixotrophic Pyrola japonica (Ericaceae), encompassing green individuals, rare achlorophyllous variants (albinos) and a form with minute leaves, P. japonica f. subaphylla. These three phenotypes were collected in two Japanese forests. Phylogenetic analysis of both plants and mycorrhizal fungi was conducted based on DNA barcoding. Enrichment in C among organs (leaves, stems and roots) of the phenotypes with reference plants and fungal fruitbodies were compared by measuring stable carbon isotopic ratio. All plants were placed in the same clade, with f. subaphylla as a separate subclade. Leaf C abundances of albinos were congruent with a fully mycoheterotrophic nutrition, suggesting that green P. japonica leaves are 36.8% heterotrophic, while rhizomes are 74.0% heterotrophic. There were no significant differences in δC values among organs in both albino P. japonica and P. japonica f. subaphylla, suggesting full and high mycoheterotrophic nutrition, respectively. Among 55 molecular operational taxonomic units (OTUs) detected as symbionts, the genus Russula was the most abundant in each phenotype and its dominance was significantly higher in albino P. japonica and P. japonica f. subaphylla. Russula spp. detected in P. japonica f. subaphylla showed higher dissimilarity with other phenotypes. These results suggest that P. japonica sensu lato is prone to evolve mycoheterotrophic variants, in a process that changes its mycorrhizal preferences, especially towards the genus Russula for which this species has a marked preference.
兼性植物通过自身的光合作用和与根系相关的菌根真菌获得碳。兼性营养被认为是真菌异养营养进化的一种预先适应，在这种营养中，植物完全依赖真菌并失去光合作用。本研究旨在阐明不同表型的兼性营养 Pyrola japonica（杜鹃花科）的菌根依赖性和异养程度，这些表型包括绿色个体、罕见的无叶绿素变体（白化体）和一种具有小叶片的形式，P. japonica f. subaphylla。这三种表型是在两个日本森林中收集的。基于 DNA 条形码对植物和菌根真菌进行了系统发育分析。通过测量稳定碳同位素比值，比较了具有参考植物和真菌果实的各表型器官（叶片、茎和根）中 C 的富集情况。所有植物都被放置在同一个分支中，f. subaphylla 是一个单独的亚分支。白化体的叶片 C 丰度与完全菌根异养营养一致，表明绿色 P. japonica 叶片有 36.8%的异养性，而根茎有 74.0%的异养性。在白化体 P. japonica 和 P. japonica f. subaphylla 中，各器官的 δC 值没有显著差异，表明它们分别具有完全和高菌根异养营养。在所检测到的 55 个作为共生体的分子操作分类单元（OTU）中，红菇属在每个表型中最为丰富，其在白化体 P. japonica 和 P. japonica f. subaphylla 中的优势明显更高。在 P. japonica f. subaphylla 中检测到的 Russula spp. 与其他表型的相似度较低。这些结果表明，广义的 P. japonica 容易进化出菌根异养变体，这一过程改变了其菌根偏好，特别是对红菇属，该物种对其有明显的偏好。
