Reorganization of the endoplasmic reticulum in pea leaf epidermal cells infected by the powdery mildew fungus Erysiphe pisi

Abstract

S I' M M A R YDuring the formation of haustoria by biotrophic pathogens the synthesis of extra host plasma membrane (PM) is required to accommodate the invagination of the PM and its transition to the extrahaustorial membrane. This implicates alterations in host exocytosis, membrane trafficking and targeting. Probes for endoplasmic reticulum (ER) and whole-cell imaging by confocal laser scanning microscopy (CLSM) have been used to examine the organization of tbe endoplasmic reticulum (ER) in compatible interactions between pea leaf cells and Erysiphe pisi DC ex Saint-Amans. In uninfected epidermal cells, the dicarbocyanine dye DiOC|,(3) and tbe ER-specific anti-HDEL antibody sbowed cortical ER was an open network of tubules interspersed with lamellar cisternae, immediately beneath tbe cuticle. Endoplasmic reticulum in infected cells could not be stained with DiOCe(3) but anti-HDEL labelling re\ealed that tbe ER was no longer evenly distributed throughout the cortical cytoplasm but was concentrated in a tight netw ork in the viciniti,-of the baustorium particularly at early stages of infection. In some infected ctlls there was intense ER staining very close to the extrahaustorial membrane. Endoplasmic reticulum was also observed as large cisternae adjacent to the haustorial complex (HC), contrasting with tubular ER structures distal to tbe HC. In Western blots, anti-HDEL labelled one major band at 70 icDa (probably the BiP homologue) in extracts from uninfected and infected epidermis, mycelia and haustoria. .Additional proteins at 55 and 80 kDa were recognized in the fungal extracts. A minor protein at 50 kDa in uninfected pea is possibly upregulated in infected leaves. Overall, the results show tbat in a compatible pea powdery mildew interaction, the host cortical ER reorganizes around tbe developing HC from early to late stages of the infection process. This reorganization is likely to be involved in the exocytosis of new membrane and matrix materials whicb contribute to tbe expanding HC.

Accommodation of powdery mildew fungi in intact plant cells

“…Several host plasma membrane-resident proteins cannot be found in the EHM, suggesting either that this specific membrane sector is subject to profound modifications or that the EHM is newly synthesized during haustorium development . Both possibilities are supported by the observation that the plant's secretory machinery (in the form of endoplasmic reticulum and Golgi apparatus) is always present in close proximity to the haustorial complex (Leckie et al, 1995;Koh et al, 2005; R.E. and R.H., unpublished results; Fig.…”

Use of Molecular Cytology to Study the Structure and Biology of Phytopathogenic and Mycorrhizal Fungi

“…Polarization of the secretory apparatus within the cytoplasmic aggregate around the infection site would thus be expected to increase the efficiency of secretion in the defense reaction. Immunolabeling and ultrastructural studies have demonstrated a concentration of ER around haustoria in compatible interactions of Erysiphe and Uromyces (Leckie et al, 1995;Skalamera and Heath, 1995), but no changes in ER or Golgi bodies have yet been reported to occur in an incompatible interaction (see Perumalla and Heath, 1991;Skalamera and Heath, 1995). An increase in the number of Golgi bodies has, however, been documented in response to infection by arbuscular mycorrhizal fungi (Bonfante and Perotto, 1995).…”

Tête à tête inside a plant cell: establishing compatibility between plants and biotrophic fungi and oomycetes

“…A key aspect of this process must be the precisely regulated expansion and differentiation of the plant plasma membrane to form a new extrahaustorial membrane. This presumably involves a pathogen‐induced redirection of the plant secretory pathway, and indeed both plant ER and Golgi stacks are frequently reported to proliferate around the haustoria of obligate biotrophs (Leckie et al ., 1995; Heath & Skalamera, 1997; Takemoto et al ., 2003; Koh et al ., 2005). Similarly, GFP tagging shows that the plant cortical ER (but not Golgi) accumulates around intracellular hyphae of C. higginsianum and undergoes a local reorganization from a loose tubular arrangement to a compact cisternal format (R. O’Connell, unpublished), which may reflect increased synthesis of host proteins and lipids (Ridge et al ., 1999).…”