A CELL BIOLOGY STUDY REVEALS NEW INSIGHTS INTO THE TRANSPORT MECHANISMS OF OOMYCETE EFFECTORS

Oomycete pathogens use dedicated effector proteins (also known as virulence factors) that manipulate the host during infection to the benefit of the pathogen. Despite extensive efforts, the understanding of how oomycete effector proteins are transported and delivered to the host is limited. Here, we show that Phytophthora capsici infecting Nicotiana benthamiana secretes its effectors through secretory pockets, haustoria, and from hyphae. We provide evidence that Avr3, belonging to the class of RxLR effector proteins that can be secreted and translocated to the plant cell, is found to accumulate in a distinct ring-shaped zone around the neck region of haustoria. The association with the haustorial neck is determined by an RxLR-EER motif and mutating this motif redirects Avr3 to the extrahaustorial matrix enveloping the full haustoria body. Furthermore, mass spectrometry analysis of immunoprecipitated Avr3 indicates that the RXLR motif remains intact when Avr3 is secreted from the haustorium during plant infection. We thus propose that the RXLR-EER motif determines the entry in the host cell by guiding Avr3 to the haustorial neck region, which may be a structure analogous to the Biotrophic Interfacial Complex of the fungus Magnaporthe sp.