Plant Immunity

A Fungus Gets SNAREd

Science Signaling  19 Feb 2008:
Vol. 1, Issue 7, pp. ec64
DOI: 10.1126/stke.17ec64

The resistance of Arabidopsis to infection by the fungus Blumeria graminis is partly mediated by preinvasion responses involving the syntaxin protein PEN1, a SNARE [soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor] component, but the mechanism involved is unclear. t-SNAREs, such as PEN1, are target membrane proteins that associate with vesicle (v)-SNAREs such as vesicle-associated membrane proteins (VAMPs) to mediate intracellular membrane fusion. Kwon et al. noticed that, whereas pen1-1 null mutant Arabidopsis showed poor resistance to B. graminis, plants with the pen1-3 allele, which contains a mutation that decreases the stability of SNARE-SNARE interactions, exhibited partial resistance to infection. Western blotting analyses showed the presence of a PEN1-containing complex in wild-type, but not pen1-3, leaves. Inoculation with B. graminis increased the abundance of this complex. Coimmunoprecipitation assays demonstrated that PEN1 formed a pathogen-dependent complex with the t-SNARE SNAP33 and with either VAMP721 or VAMP722. Transgenic plants that were inducibly deficient in both vamp721 and vamp722 showed increased susceptibility to fungal infection. Confocal microscopic analysis of vamp721- and vamp722­-deficient plants that expressed a fusion of VAMP722 and green fluorescent protein showed pathogen-dependent directed movement to and focal accumulation of VAMP722-containing complexes at the sites of B. graminis entry of leaf epidermal cells. This process resembled the formation of the synapse between a mammalian cytotoxic T cell and its target. Accumulation of the PEN1-SNAP32-VAMP722 complexes to sites of infection was associated with increased resistance to infection and improved repair of the plant cell wall. This study demonstrates that VAMP721 and VAMP722, which the authors showed were critical for plant development and growth, were coopted to mount a secretory response to fungal infection.

C. Kwon, C. Neu, S. Pajonk, H. S. Yun, U. Lipka, M. Humphry, S. Bau, M. Straus, M. Kwaaitaal, H. Rampelt, F. El Kasmi, G. Jürgens, J. Parker, R. Panstruga, V. Lipka, P. Schulze-Lefert, Co-option of a default secretory pathway for plant immune responses. Nature 451, 835-840 (2008). [PubMed]