Secreted effector that acts as an elicitor of hypersensitive response (HR) specifically on plants carrying defense protein R4, through its interaction with this protein. Oomycete Avh family proteins have a modular structure with an N-terminal signal peptide (SP), an RXLR-dEER domain and a C-terminus with a variable number of modules that consist of W, Y and L motifs after highly conserved residues. The C-ter of Avr4 contains 3 W motifs, 1 Y motif but no L motif. The RXLR-dEER motif functions as a host targeting signal (HTS). The region containing the W2 motif, in combination with either the W1 or W3 motif, triggers a necrotic response in host plants carrying the resistance gene R4. Belongs to the RxLR effector family.