Glycan moiety of flagellin in Acidovorax avenae K1 prevents the recognition by rice that causes the induction of immune responses

Recognition of pathogen-associated molecular patterns (PAMPs) such as flagellin, a main component of the bacterial flagellum, constitutes the first layer of plant immunity and is referred to as PAMP-triggered immunity (PTI). The rice avirulent N1141 strain of gram-negative phytopathogenic bacterium, Acidovorax avenae, induces PTI including H(2)O(2) generation, while flagellin from the rice virulent K1 strain of A. avenae does not induce these immune responses. Mass spectrometry analyses revealed that total 1,600-Da and 2,150-Da of glycan residues were present on the flagellins from N1141 and K1, respectively. A deglycosylated K1 flagellin induced immune responses in the same manner as N1141 flagellin, suggesting that the glycan in K1 flagellin prevent epitope recognition in rice. We identified three genes in K1 flagella operon, which regulate structural modification of glycan in K1 flagellin. The immature glycan-attached flagellin from three genes deletion mutant, KΔ3FG, induced H(2)O(2) generation in cultured rice cells, whereas the K1 mature-type flagellin did not cause a detectable increase in H(2)O(2). The data indicate that the immature glycan of flagellin from KΔ3FG cannot prevent the epitope recognition in rice.