Abstract
The rice blast fungus Magnaporthe oryzae grows inside living host cells. Cytological analyses by live-cell imaging have revealed characteristics of the biotrophic invasion, particularly the extrainvasive hyphal membrane (EIHM) originating from the host plasma membrane and a host membrane-rich structure, biotrophic interfacial complex (BIC). Here, we observed rice subcellular changes associated with invasive hyphal growth using various transformants expressing specifically localized fluorescent proteins. The invasive hyphae did not penetrate across but were surrounded by the host vacuolar membrane together with EIHM even after branching. High-resolution imaging of BICs revealed that the host cytosol was accumulated at BIC with aggregated EIHM and a symplastic effector, Pwl2, in a punctate form. The vacuolar membrane did not aggregate in but closely surrounded the BIC. A good correlation was observed between the early collapse of vacuoles and damage of invasive hyphae in the first-invaded cell. Furthermore, a newly developed, long-term imaging method has revealed that the central vacuole gradually shrank until collapse, which was caused by the hyphal invasion occurring earlier in the neighboring cells than in the first-invaded cells. These data suggest that M. oryzae may suppress host vacuole collapse during early infection stages for successful infection.
Highlights
Rice blast caused by the ascomycete fungus, Magnaporthe oryzae, is the most destructive disease affecting cultivated rice (Oryza sativa L.)
Invasive hyphae grow inside the rice cell surrounded by the vacuolar membrane We first investigated the dynamics of rice cytosol in leaf sheath epidermal cells during the biotrophic invasion by M. oryzae
During the early stage when biotrophic interfacial complex (BIC) was predicted to be located at the primary hyphal tip (Fig. 1A), Cyto-G FP signals were accumulated near the fungal penetration site beneath the appressorium and at the primary hyphal tip in addition to the host nucleus
Summary
Rice blast caused by the ascomycete fungus, Magnaporthe oryzae, is the most destructive disease affecting cultivated rice (Oryza sativa L.). The penetration peg subsequently differentiates into infectious hyphae, which are primarily thin, become bulbous, and branch (20–36 hpi). At this stage, the invaded cells of the susceptible host plasmolyze in a hypertonic solution, indicating that they remain alive, whereas in the resistant host, the invaded cells lose the ability for plasmolysis and exhibit strong autofluorescence, indicating hypersensitive cell death (Koga 1994). The bulbous invasive hyphae usually grow to fill the first-invaded cell and colonize neighboring cells (36–48 hpi) At this stage, the first-invaded cells lose the ability for plasmolysis, whereas the second-invaded cells keep the ability. Lesions become visible (ca. 72 hpi), and sporulation occurs under humid conditions
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