Interaction between the moss Physcomitrella patens and Phytophthora: a novel pathosystem for live‐cell imaging of subcellular defence

• Published in: Journal of microscopy (Oxford) 2016-08, Vol.263 (2), p.171-180
• Main Authors: OVERDIJK, ELYSA J. R., DE KEIJZER, JEROEN, DE GROOT, DEBORAH, SCHOINA, CHARIKLEIA, BOUWMEESTER, KLAAS, KETELAAR, TIJS, GOVERS, FRANCINE
• Format: Article
• Language: English
• Subjects: Actins - metabolism; Bryopsida - cytology; Bryopsida - parasitology; Cell Nucleus - metabolism; Cell Survival; Cell Wall - metabolism; Cytoplasm - metabolism; Defense; Infections; Intracellular Space; Live-cell imaging; Microscopy; Microscopy - methods; Pathogens; Physcomitrella patens; Phytophthora - pathogenicity; Phytophthora - physiology; Phytophthora capsici; Phytophthora infestans; Plant Diseases - parasitology; Plant-pathogen interaction; Subcellular defence
• ISSN: 0022-2720; 1365-2818
• DOI: 10.1111/jmi.12395

Summary Live‐cell imaging of plant–pathogen interactions is often hampered by the tissue complexity and multicell layered nature of the host. Here, we established a novel pathosystem with the moss Physcomitrella patens as host for Phytophthora. The tip‐growing protonema cells of this moss are ideal for visualizing interactions with the pathogen over time using high‐resolution microscopy. We tested four Phytophthora species for their ability to infect P. patens and showed that P. sojae and P. palmivora were only rarely capable to infect P. patens. In contrast, P. infestans and P. capsici frequently and successfully penetrated moss protonemal cells, showed intracellular hyphal growth and formed sporangia. Next to these successful invasions, many penetration attempts failed. Here the pathogen was blocked by a barrier of cell wall material deposited in papilla‐like structures, a defence response that is common in higher plants. Another common response is the upregulation of defence‐related genes upon infection and also in moss we observed this upregulation in tissues infected with Phytophthora. For more advanced analyses of the novel pathosystem we developed a special set‐up that allowed live‐cell imaging of subcellular defence processes by high‐resolution microscopy. With this set‐up, we revealed that Phytophthora infection of moss induces repositioning of the nucleus, accumulation of cytoplasm and rearrangement of the actin cytoskeleton, but not of microtubules. Lay description Plant diseases caused by pathogens, like fungi and bacteria, cause enormous losses in in agriculture worldwide. Host and pathogen use molecular weapons to battle for control of individual host cells. To visualize the battle and examine the weaponry of plant and pathogen we need advanced microscopy techniques. Leaves of higher plants have a complex structure and consist of multiple cell layers. This complexity and thickness is a major disadvantage for microscopy studies and therefore, we searched for a system that is more suitable for microscopic analyses of the battle between plant and pathogen. The moss Physcomitrella patens has tissues that are only one‐cell thick and therefore ideal for visualizing interactions with a pathogen over time using high‐resolution microscopy. We then tested four Phytophthora species for their ability to infect this moss. Phytophthora is a water mold, a filamentous microorganism that reproduces via spores and a major plant destroyer. We found two species,