Delivery of Phytophthora sojae effector Avr1b in planta requires PI3P-binding, but does not require N-terminal cleavage
B. TYLER (1), Q. Wang (1), F. Arredondo (1), Y. Fang (1), E. Perez (1) (1) Center for Genome Research and Biocomputing, Oregon State University, U.S.A.

A major class of effectors produced by oomycetes contains RxLR motifs that mediate entry of these effectors into plant cells. We previously showed that these effectors can bind to specific lipids including phosphatidylinositol-3-phosphate (PI3P). PI3P-binding requires the RxLR motif, plus in some cases, C-terminal regions of the protein. In order to validate that PI3P-binding mediates host cell entry in planta, we have shown that heterologous PI3P-binding proteins such as yeast VAM7p can functionally replace the RxLR domain of Phytophthora sojae effector Avr1b, and can deliver this effector into soybean cells during a natural P. sojae infection. The Avr1b and various derivative mutant proteins can be specifically detected in culture supernatants after de-glycosylation, indicating that Avr1b is post-translationally modified. Some RxLR effectors such as Avr1b also undergo N-terminal cleavage following secretion, but others such as Avr4/6 do not. Cleavage of Avr1b occurs upstream of the RxLR motif, and the RxLR motif is not required for cleavage. Mutants of Avr1b that are not cleaved are delivered normally. We conclude that N-terminal cleavage is not required for delivery in planta. We are now using CRISPR-mediated gene replacement to refine these experiments.

Abstract Number: C5-3, P9-333
Session Type: Concurrent