Key Laboratory of Biology and Genetic Improvement of Oil Crops, Ministry of Agriculture and Rural Affairs, Oil Crops Research Institute, Chinese Academy of Agricultural Sciences, Wuhan, Hubei, 430062, China.
Department of Biology, University of Saskatchewan, Saskatoon, SK, S7N 5E2, Canada.
Phytopathology. 2020 Oct;110(10):1704-1712. doi: 10.1094/PHYTO-02-20-0029-R. Epub 2020 Aug 17.
As a soilborne protist pathogen, causes the devastating clubroot disease on Brassicaeae crops worldwide. Due to its intracellular obligate biotrophic nature, the life cycle of is still not fully understood. Here, we used fluorescent probe-based confocal microscopy and transmission electron microscopy (TEM) to investigate the infection process of on the susceptible host under controlled conditions. We found that can initiate the primary infection in both root hairs and epidermal cells, producing the uninucleate primary plasmodium at 1 day postinoculation (dpi). After that, the developed multinucleate primary plasmodium underwent condensing and cytoplasm cleavage into uninucleate zoosporangia from 1 to 4 dpi. This was subsequently followed by the formation of multinucleate zoosporangia and the production of secondary zoospores within zoosporangium. Importantly, the secondary zoospores performed a conjugation in the root epidermal cells after their release. TEM revealed extensive uninucleate secondary plasmodium in cortical cells at 8 dpi, indicating the establishment of the secondary infection. The subsequently developed into binucleate, quadrinucleate, and multinucleate secondary plasmodia from 10 to 15 dpi, during which the clubroot symptoms appeared. The uninucleate resting spores were first observed in the cortical cells at 24 dpi, marking the completion of a life cycle. We also provided evidence that the secondary infection of may represent the diploid sexual life stage. From these findings, we propose a refined life cycle of which will contribute to understanding of the complicated infection biology of .
作为一种土壤传播的原生动物病原体， 会在全世界的芸薹属作物上引发毁灭性的根肿病。由于其细胞内专性生物营养的性质， 的生命周期仍不完全清楚。在这里，我们使用基于荧光探针的共聚焦显微镜和透射电子显微镜（TEM）来研究 在易感宿主 下的受控感染过程。我们发现， 可以在根毛和表皮细胞中启动初级感染，在接种后 1 天（dpi）产生单核初级原生质体。之后，发育良好的多核初级原生质体在 1 到 4 dpi 期间经历浓缩和细胞质分裂，形成单核游动孢子囊。随后形成多核游动孢子囊，并在游动孢子囊中产生次生游动孢子。重要的是，次生游动孢子在释放后在根表皮细胞中进行配合。TEM 在 8 dpi 时在皮层细胞中显示出大量的单核次生原生质体，表明建立了次生感染。 随后在 10 到 15 dpi 期间发育成双核、四核和多核次生原生质体，在此期间出现根肿病症状。单核休眠孢子首先在皮层细胞中观察到，标志着生命周期的完成。我们还提供了证据表明 的次生感染可能代表了二倍体有性生命阶段。根据这些发现，我们提出了 的改良生命周期，这将有助于理解 的复杂感染生物学。
