Limits...
The plasmodesmal protein PDLP1 localises to haustoria-associated membranes during downy mildew infection and regulates callose deposition.

Caillaud MC, Wirthmueller L, Sklenar J, Findlay K, Piquerez SJ, Jones AM, Robatzek S, Jones JD, Faulkner C - PLoS Pathog. (2014)

Bottom Line: We found that the pdlp1,2,3 triple mutant is more susceptible to Hpa while overexpression of PDLP1 enhances plant resistance, suggesting that PDLPs enhance basal immunity against Hpa.Haustorial encasements are depleted in callose in pdlp1,2,3 mutant plants whereas PDLP1 over-expression elevates callose deposition around haustoria and across the cell surface.These data indicate that PDLPs contribute to callose encasement of Hpa haustoria and suggests that the deposition of callose at haustoria may involve similar mechanisms to callose deposition at plasmodesmata.

View Article: PubMed Central - PubMed

Affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom.

ABSTRACT
The downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa) is a filamentous oomycete that invades plant cells via sophisticated but poorly understood structures called haustoria. Haustoria are separated from the host cell cytoplasm and surrounded by an extrahaustorial membrane (EHM) of unknown origin. In some interactions, including Hpa-Arabidopsis, haustoria are progressively encased by host-derived, callose-rich materials but the molecular mechanisms by which callose accumulates around haustoria remain unclear. Here, we report that PLASMODESMATA-LOCATED PROTEIN 1 (PDLP1) is expressed at high levels in Hpa infected cells. Unlike other plasma membrane proteins, which are often excluded from the EHM, PDLP1 is located at the EHM in Hpa-infected cells prior to encasement. The transmembrane domain and cytoplasmic tail of PDLP1 are sufficient to convey this localization. PDLP1 also associates with the developing encasement but this association is lost when encasements are fully mature. We found that the pdlp1,2,3 triple mutant is more susceptible to Hpa while overexpression of PDLP1 enhances plant resistance, suggesting that PDLPs enhance basal immunity against Hpa. Haustorial encasements are depleted in callose in pdlp1,2,3 mutant plants whereas PDLP1 over-expression elevates callose deposition around haustoria and across the cell surface. These data indicate that PDLPs contribute to callose encasement of Hpa haustoria and suggests that the deposition of callose at haustoria may involve similar mechanisms to callose deposition at plasmodesmata.

No MeSH data available.


Related in: MedlinePlus

PDLP1 promotes membrane tubule formation at the extra-haustorial interface.Transmission electron micrographs of Hpa Waco9 haustoria observed in Col-0 (A) and PDLP1 OE (B) plants harvested 6 DPI. Boxes represent regions from which high magnification images (C, D, E, F) were taken. High magnification images of the host-pathogen interface in Col-0 (C–E) and PDLP1 OE (F) show that the EHMx and EHM forms an electron dense structure that has membrane invaginations (arrows) at the host surface. In regions in which the haustorium is encased the EHM is not continuously defined and may comprise the EHM and inner membrane of the encasement, thus this membrane is differentially denoted EHMs to allow for the possibility of multiple membrane layers. (F) Membrane invaginations are longer and more abundant in PDLP1 OE plants. (G) An oblique section of the surface of an haustorium in a PDLP1 OE cell illustrates the density and length of these protrusions. Ha, haustorium; En, encasement; EHMxt, extrahaustorial matrix translucent; EHMxd, extrahaustorial matrix dense. Scale bars are 2 µm (A and B), 100 nm (C–F) and 500 nm (E).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4231120&req=5

ppat-1004496-g006: PDLP1 promotes membrane tubule formation at the extra-haustorial interface.Transmission electron micrographs of Hpa Waco9 haustoria observed in Col-0 (A) and PDLP1 OE (B) plants harvested 6 DPI. Boxes represent regions from which high magnification images (C, D, E, F) were taken. High magnification images of the host-pathogen interface in Col-0 (C–E) and PDLP1 OE (F) show that the EHMx and EHM forms an electron dense structure that has membrane invaginations (arrows) at the host surface. In regions in which the haustorium is encased the EHM is not continuously defined and may comprise the EHM and inner membrane of the encasement, thus this membrane is differentially denoted EHMs to allow for the possibility of multiple membrane layers. (F) Membrane invaginations are longer and more abundant in PDLP1 OE plants. (G) An oblique section of the surface of an haustorium in a PDLP1 OE cell illustrates the density and length of these protrusions. Ha, haustorium; En, encasement; EHMxt, extrahaustorial matrix translucent; EHMxd, extrahaustorial matrix dense. Scale bars are 2 µm (A and B), 100 nm (C–F) and 500 nm (E).

Mentions: To further examine structural differences in encased haustoria in wild-type and PDLP1 OE plants, we next observed haustoria by transmission electron microscopy. In both encased and unencased haustoria, the EHMx appeared to consist of two layers that differ in electron density: an electron dense layer adjacent to the EHM and an electron translucent layer adjacent to the haustorial membrane (Figure 6). The translucent layer of the EHMx did not appear different in thickness or quality between wild-type and PDLP1 OE cells (Figure 6A–F) and may correspond with the haustorial wall [12]. However, while in wild-type plants the electron dense layer of the EHMx stained similarly to the plant cell wall, and may represent the true EHMx [12], this layer was frequently more densely stained relative to the host cell wall in PDLP1 OE plants (Figure 6B). At higher magnification, this increased staining density in the EHMx correlates with the presence of membrane invaginations at the boundary between the electron dense layer of the EHMx and the host cell (arrows, Figure 6C–G). When the haustorium is fully or partially encased, the model for haustorium formation would suggest that an additional membrane layer would be present here. In our images, each time the haustorium was encased (Figure 6C, F, G) we did not see clear evidence of an additional membrane layer but this may be due to the increased membrane convolution in these regions, or alternately poor membrane preservation. In the PDLP1 OE line, membrane invaginations are uniform in diameter (approximately 25 nm) and in an oblique section could be measured to be greater than 450 nm long (Figure 6G). Invaginations, or convolution of the EHM, were also observed in wild-type cells but when compared with haustoria in PDLP1 OE plants were less frequent and shorter in length (Figure 6C–E, Table S2).


The plasmodesmal protein PDLP1 localises to haustoria-associated membranes during downy mildew infection and regulates callose deposition.

Caillaud MC, Wirthmueller L, Sklenar J, Findlay K, Piquerez SJ, Jones AM, Robatzek S, Jones JD, Faulkner C - PLoS Pathog. (2014)

PDLP1 promotes membrane tubule formation at the extra-haustorial interface.Transmission electron micrographs of Hpa Waco9 haustoria observed in Col-0 (A) and PDLP1 OE (B) plants harvested 6 DPI. Boxes represent regions from which high magnification images (C, D, E, F) were taken. High magnification images of the host-pathogen interface in Col-0 (C–E) and PDLP1 OE (F) show that the EHMx and EHM forms an electron dense structure that has membrane invaginations (arrows) at the host surface. In regions in which the haustorium is encased the EHM is not continuously defined and may comprise the EHM and inner membrane of the encasement, thus this membrane is differentially denoted EHMs to allow for the possibility of multiple membrane layers. (F) Membrane invaginations are longer and more abundant in PDLP1 OE plants. (G) An oblique section of the surface of an haustorium in a PDLP1 OE cell illustrates the density and length of these protrusions. Ha, haustorium; En, encasement; EHMxt, extrahaustorial matrix translucent; EHMxd, extrahaustorial matrix dense. Scale bars are 2 µm (A and B), 100 nm (C–F) and 500 nm (E).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4231120&req=5

ppat-1004496-g006: PDLP1 promotes membrane tubule formation at the extra-haustorial interface.Transmission electron micrographs of Hpa Waco9 haustoria observed in Col-0 (A) and PDLP1 OE (B) plants harvested 6 DPI. Boxes represent regions from which high magnification images (C, D, E, F) were taken. High magnification images of the host-pathogen interface in Col-0 (C–E) and PDLP1 OE (F) show that the EHMx and EHM forms an electron dense structure that has membrane invaginations (arrows) at the host surface. In regions in which the haustorium is encased the EHM is not continuously defined and may comprise the EHM and inner membrane of the encasement, thus this membrane is differentially denoted EHMs to allow for the possibility of multiple membrane layers. (F) Membrane invaginations are longer and more abundant in PDLP1 OE plants. (G) An oblique section of the surface of an haustorium in a PDLP1 OE cell illustrates the density and length of these protrusions. Ha, haustorium; En, encasement; EHMxt, extrahaustorial matrix translucent; EHMxd, extrahaustorial matrix dense. Scale bars are 2 µm (A and B), 100 nm (C–F) and 500 nm (E).
Mentions: To further examine structural differences in encased haustoria in wild-type and PDLP1 OE plants, we next observed haustoria by transmission electron microscopy. In both encased and unencased haustoria, the EHMx appeared to consist of two layers that differ in electron density: an electron dense layer adjacent to the EHM and an electron translucent layer adjacent to the haustorial membrane (Figure 6). The translucent layer of the EHMx did not appear different in thickness or quality between wild-type and PDLP1 OE cells (Figure 6A–F) and may correspond with the haustorial wall [12]. However, while in wild-type plants the electron dense layer of the EHMx stained similarly to the plant cell wall, and may represent the true EHMx [12], this layer was frequently more densely stained relative to the host cell wall in PDLP1 OE plants (Figure 6B). At higher magnification, this increased staining density in the EHMx correlates with the presence of membrane invaginations at the boundary between the electron dense layer of the EHMx and the host cell (arrows, Figure 6C–G). When the haustorium is fully or partially encased, the model for haustorium formation would suggest that an additional membrane layer would be present here. In our images, each time the haustorium was encased (Figure 6C, F, G) we did not see clear evidence of an additional membrane layer but this may be due to the increased membrane convolution in these regions, or alternately poor membrane preservation. In the PDLP1 OE line, membrane invaginations are uniform in diameter (approximately 25 nm) and in an oblique section could be measured to be greater than 450 nm long (Figure 6G). Invaginations, or convolution of the EHM, were also observed in wild-type cells but when compared with haustoria in PDLP1 OE plants were less frequent and shorter in length (Figure 6C–E, Table S2).

Bottom Line: We found that the pdlp1,2,3 triple mutant is more susceptible to Hpa while overexpression of PDLP1 enhances plant resistance, suggesting that PDLPs enhance basal immunity against Hpa.Haustorial encasements are depleted in callose in pdlp1,2,3 mutant plants whereas PDLP1 over-expression elevates callose deposition around haustoria and across the cell surface.These data indicate that PDLPs contribute to callose encasement of Hpa haustoria and suggests that the deposition of callose at haustoria may involve similar mechanisms to callose deposition at plasmodesmata.

View Article: PubMed Central - PubMed

Affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom.

ABSTRACT
The downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa) is a filamentous oomycete that invades plant cells via sophisticated but poorly understood structures called haustoria. Haustoria are separated from the host cell cytoplasm and surrounded by an extrahaustorial membrane (EHM) of unknown origin. In some interactions, including Hpa-Arabidopsis, haustoria are progressively encased by host-derived, callose-rich materials but the molecular mechanisms by which callose accumulates around haustoria remain unclear. Here, we report that PLASMODESMATA-LOCATED PROTEIN 1 (PDLP1) is expressed at high levels in Hpa infected cells. Unlike other plasma membrane proteins, which are often excluded from the EHM, PDLP1 is located at the EHM in Hpa-infected cells prior to encasement. The transmembrane domain and cytoplasmic tail of PDLP1 are sufficient to convey this localization. PDLP1 also associates with the developing encasement but this association is lost when encasements are fully mature. We found that the pdlp1,2,3 triple mutant is more susceptible to Hpa while overexpression of PDLP1 enhances plant resistance, suggesting that PDLPs enhance basal immunity against Hpa. Haustorial encasements are depleted in callose in pdlp1,2,3 mutant plants whereas PDLP1 over-expression elevates callose deposition around haustoria and across the cell surface. These data indicate that PDLPs contribute to callose encasement of Hpa haustoria and suggests that the deposition of callose at haustoria may involve similar mechanisms to callose deposition at plasmodesmata.

No MeSH data available.


Related in: MedlinePlus