By Ely Oliveira-Garcia, Nicholas J. Talbot and Barbara Valent
Background: To cause disease in plants, fungal pathogens deliver effector proteins directly into plant cells. Inside the host, effectors suppress the plant immune system and enable pathogens to rapidly invade and proliferate within plant tissue. How effector proteins enter plant cells, however, is not understood. During plant infection, the devastating rice blast fungus forms a specialized interfacial region known as the biotrophic interfacial complex (BIC), which is necessary for effector delivery into plant cells. We set out to explore how the BIC fulfils this role and how effectors enter plant cells.
Question: How does the blast fungus deliver effector proteins across the plasma membrane into living rice cells? Does the effector delivery system involve endocytosis by plant cells?
Findings: Live cell imaging of the blast fungus growing in rice cells, provides evidence that effector proteins are packaged in dynamic vesicle-like membranous effector compartments (MECs) at the BIC. These MECs are bounded by the rice plasma membrane and clathrin light chain-1. Inhibition of endocytosis by chemical treatment or silencing rice genes involved in clathrin-mediated endocytosis prevent MEC formation and pathogenicity. An effector, Bas83, appears to play a role in recruiting regions of the plant membrane for endocytosis to the BIC. Taken together, our results provide evidence that clathrin-mediated endocytosis is necessary for effector translocation into plant cells.
Next steps: We would like to know how clathrin-mediated endocytosis is induced by the blast fungus during plant infection. How does Bas83 recruit plant membrane to promote endocytosis, for example, and can we identify new effectors involved in co-opting host endocytosis to enable internalization of cytoplasmic effectors?
Ely Oliveira-Garcia, Tej Man Tamang, Jungeun Park, Melinda Dalby, Magdalena Martin-Urdiroz, Clara Rodriguez Herrero, An Hong Vu, Sunghun Park, Nicholas J. Talbot & Barbara Valent (2023) Clathrin-mediated endocytosis facilitates the internalization of Magnaporthe oryzae effectors into rice cells. Plant Cell. https://doi.org/10.1093/plcell/koad094