Basic Biology Program, Graduate School of Integrated Sciences for Life, Hiroshima University, Hiroshima, Japan.
Department of Biological Science, Graduate School of Science, Hiroshima University, Hiroshima, Japan.
Appl Environ Microbiol. 2020 Aug 18;86(17). doi: 10.1128/AEM.00671-20.
A large number of strains in the species complex (biovar 1 ) have been known as causative pathogens for crown gall and hairy root diseases. Strains within this complex were also found as endophytes in many plant species with no symptoms. The aim of this study was to reveal the endophyte variation of this complex and how these endophytic strains differ from pathogenic strains. In this study, we devised a simple but effective screening method by exploiting the high resolution power of mass spectrometry. We screened endophyte isolates from young wheat and barley plants, which are resistant to the diseases, and identified seven isolates from wheat as members of the species complex. Through further analyses, we assigned five strains to the genomovar (genomic group) G1 and two strains to G7 in Notably, these two genomovar groups harbor many known pathogenic strains. In fact, the two G7 endophyte strains showed pathogenicity on tobacco, as well as the virulence prerequisites, including a 200-kbp Ri plasmid. All five G1 strains possessed a 500-kbp plasmid, which is present in well-known crown gall pathogens. These data strongly suggest that healthy wheat plants are reservoirs for pathogenic strains of Crown gall and hairy root diseases exhibit very wide host-plant ranges that cover gymnosperm and dicot plants. The species complex harbors causative agents of the two diseases. Recently, endophyte isolates from many plant species have been assigned to this species complex. We isolated seven endophyte strains belonging to the species complex from wheat plants and revealed their genomovar affiliations and plasmid profile. The significance of this study is the finding of the genomovar correlation between the endophytes and the known pathogens, the presence of a virulence ability in two of the seven endophyte strains, and the high ratio of the pathogenic strains in the endophyte strains. This study therefore provides convincing evidence that could unravel the mechanism that maintains pathogenic agents of this species and sporadically delivers them to susceptible plants.
大量的 种复合体（生物变种 1）菌株已被确认为冠瘿病和发根病的致病病原体。该复合体中的菌株也被发现为许多无症状植物物种的内生菌。本研究旨在揭示该复合体的内生菌变异，以及这些内生菌株与病原菌株的不同之处。在本研究中，我们通过利用质谱的高分辨率能力，设计了一种简单但有效的筛选方法。我们从对这些疾病具有抗性的年轻小麦和大麦植物中筛选内生菌分离物，并从小麦中鉴定出 7 个分离物为 种复合体成员。通过进一步分析，我们将 5 个菌株分配到基因组变种（基因组群）G1，2 个菌株分配到 G7，特别是这两个基因组变种群包含许多已知的致病菌株。事实上，这两个 G7 内生菌株对烟草表现出致病性，以及毒力先决条件，包括一个 200-kbp Ri 质粒。所有 5 个 G1 菌株都携带一个 500-kbp 质粒，该质粒存在于著名的冠瘿病病原体中。这些数据强烈表明，健康的小麦植物是 冠瘿病和发根病的致病菌株的储库。这两种疾病表现出非常广泛的宿主植物范围，涵盖了裸子植物和双子叶植物。 种复合体携带这两种疾病的病原体。最近，许多植物物种的内生菌分离物已被分配到该物种复合体。我们从小麦植物中分离出 7 种属于该物种复合体的内生菌株，并揭示了它们的基因组变种归属和质粒图谱。本研究的意义在于发现内生菌与已知病原体之间的基因组变种相关性，在 7 个内生菌菌株中的 2 个中存在毒力能力，以及内生菌菌株中致病性菌株的高比例。因此，本研究提供了令人信服的证据，可以揭示维持该物种病原体的机制，并偶尔将其传递给易感植物。
