The Podosphaera xanthii haustorium, the fungal Trojan horse of cucurbit-powdery mildew interactions

• Published in: Fungal genetics and biology 2014-10, Vol.71, p.21-31
• Main Authors: Martínez-Cruz, Jesús, Romero, Diego, Dávila, José C., Pérez-García, Alejandro
• Format: Article
• Language: English
• Subjects: Ascomycota - metabolism; Ascomycota - physiology; Ascomycota - ultrastructure; Callose; Cucurbita - cytology; Cucurbita - parasitology; Glucans - metabolism; Haustorial lobes; Haustorium purification; Hyphae - metabolism; Hyphae - physiology; Hyphae - ultrastructure; Microscopy; Obligate biotrophy; Plant Diseases - parasitology; Plant Leaves - cytology; Plant Leaves - parasitology; Podosphaera xanthii; Vesicles
• ISSN: 1087-1845; 1096-0937
• DOI: 10.1016/j.fgb.2014.08.006

[Display omitted] •The ultrastructure of Podosphaera xanthii haustoria was documented.•A positive correlation between callose deposition and haustorial development was found.•A method for isolation of P. xanthii haustoria was adapted.•Size and number of haustorial lobes can be taken as indicators of haustorial maturity.•Haustorial lobes are the primary pathogen structure associated with vesicle trafficking. The powdery mildew fungi are obligate biotrophic plant pathogens that develop a specialized structure for parasitism termed haustorium, which is responsible for nutrient uptake and factor exchange with the plant. In this work, we present a detailed microscopy analysis of the haustoria of the cucurbit powdery mildew fungus Podosphaera xanthii, a major limiting factor for cucurbit production worldwide. Despite being located inside plant epidermal cells, transmission electron microscopy (TEM) analysis showed the characteristic highly irregular outline of the extrahaustorial membrane that separates the extrahaustorial matrix of haustoria from the cytoplasm of the plant cell. TEM analysis also revealed the presence of some vesicles and electron-dense plaques of material surrounding the haustoria. In confocal microscopy analysis and aniline blue staining we found a positive correlation between haustorial development and deposition of callose, which is distributed as plaques around haustorial complex. In this study, a method for the isolation of P. xanthii haustoria was also adapted, which permitted the analysis of the formation of haustorial lobes and the visualization of vacuoles and the pool of vesicles inside the haustorial complex. Our findings suggested that the haustorial lobes were responsible for vesicular trafficking and most likely act as the main mediators of the fungus-plant dialogue. All of these findings were integrated into a model of the P. xanthii-host cellular interactions.