Poster: Plant-pathogen interactions

Abs # 508: The receptor for the fungal effector Ethylene-Inducing Xylanase is a member of a novel resistance-like gene family in the tomato

Presenter:	Ron, Mily , milyr@post.tau.ac.il
Authors	Ron, Mily  (A)   Avni, Adi  (A)
Affiliations:	(A): Tel-Aviv University, Department of Plant Sciences

An ethylene–inducing xylanase (EIX) is a potent effector of plant defense responses in specific cultivars of tobacco and tomato. The tomato LeEix locus was characterized by map-based cloning, which led to the identification of a novel gene cluster from which three members (LeEix1, LeEix2 and LeEix3) were isolated. LeEix1 and LeEix2 are functional genes while LeEix3 is likely to be a pseudogene. Similarly to the Ve resistance genes in tomato, the deduced amino acid sequences encoded by LeEix1 and LeEix2 contain a leucine zipper, an extracellular leucine-rich repeat (LRR) domain, a trans-membrane domain and a C-terminal domain with the YXXΦ endocytosis signal (Φ represents an amino acid with a hydrophobic side chain). Silencing the LeEix gene expression prevented the binding of FITC- labeled EIX to cells of an EIX-responsive plant and the hypersensitive response was inhibited. Over-expression of LeEix1 and LeEix2 genes in EIX non-responsive plants enabled the binding of EIX, although only LeEix2 could transmit the signal that induced the hypersensitive response (HR). Binding studies with FITC-labeled EIX were performed with LeEix2-producing COS7 cells. The results showed direct binding of EIX to LeEix2. Structural analysis of the LeEix genes suggests they belong to a class of cell-surface glycoproteins with a receptor–mediated endocytosis signal. A mutation in the endocytosis signal of LeEix2 (Y993A) abolished its ability to induce the HR, suggesting endocytosis plays a key role in the signal transduction pathway.