Flagellin from an Incompatible Strain of Acidovorax avenae Mediates H₂O₂ Generation Accompanying Hypersensitive Cell Death and Expression of PAL, Cht-1, and PBZ1, but Not of LOX in Rice

Abstract

Acidovorax avenae causes a brown stripe disease in monocot plants. We recently reported that a rice-incompatible strain of A. avenae caused hypersensitive cell death in rice and that the flagellin of the incompatible strain was involved in this response. The incompatible strain induced the rapid generation of H2O2 accompanying hypersensitive cell death and the expression of defense genes such as PAL, Cht-1, PBZ1, and LOX, whereas the compatible strain did not. The purified incompatible flagellin also induced the expression of PAL, Cht-1, and PBZ1, but LOX expression was not induced by the incompatible flagellin. PAL and LOX enzymatic activities were increased by inoculation with the incompatible strain, whereas only PAL activity was increased by the incompatible flagellin. Interestingly, the flagellin-deficient incompatible strain lost the ability to generate H2O2 and induce hypersensitive cell death, but PAL, Cht-1, and PBZ1 expression still were induced by inoculation with the deficient strain, suggesting that induction of these genes is regulated not only by flagellin but also by some other signal. Thus, the incompatible flagellin of A. avenae is a specific elicitor in rice, but it is not the only factor capable of inducing the rice defense system.

Increased rectal microbial richness is associated with the presence of colorectal adenomas in humans

“…Although, not much is known about its clinical epidemiology and pathogenicity in humans, it has been reported to also degrade nitro-aromatic compounds (Malkan et al, 2009). A potential mechanism for the Acidovoraxadenoma association could relate to the induction of local inflammation by increased flagellar proteins resulting from the higher abundance of Acidovorax (Tanaka et al, 2003;Takakura et al, 2008). Another potential mechanism could be related to changes in the local gut environment that favors increased abundance of specific taxa.…”

Glycosylation Regulates Specific Induction of Rice Immune Responses by Acidovorax avenae Flagellin

“…tin, and is expressed following N1141 flagellin infection (20). When cultured rice cells were treated with the S178A and S183A K1 flagellins and S178A/S183A K1 double substituted K1 flagellin, Cht-1 mRNA expression was induced 6 h after treatment.…”

“…We have reported that expression of PAL, which encodes phenylalanine ammonia-lyase and catalyzes the first step in the biosynthesis of lignin monomers and certain classes of phytoalexins, was increased upon the addition of purified N1141 flagellin but not purified K1 flagellin (20). To clarify whether the N1141 flagellin-specific induction of the PAL gene depends on the amino acid residues that are different between the N1141 and K1 flagellins, quantitative real time RT-PCR was performed using the purified and recombinant flagellins.…”

“…For example, strains isolated from rice, such as K1 and H8301, can infect only rice plants (virulent), whereas the N1141 strain isolated from finger millet cannot infect rice even after it is inoculated into rice tissues (avirulent). We reported that a rice avirulent N1141 strain of A. avenae induces several immune responses, such as hypersensitive response cell death, H 2 O 2 generation, and up-regulation of defense genes, whereas the rice virulent K1 and H8301 strains of A. avenae do not induce these immune responses (17)(18)(19)(20). To identify the specific recognition molecules that are related to the induction of these immune responses in cultured rice cells, a strain-specific antibody was raised against the avirulent strain and then * This work was supported in part by Grant-in-aid …”

Function of the rice gp91phox homologs OsrbohA and OsrbohE genes in ROS-dependent plant immune responses

“…We recently reported that several immune responses, such as H 2 O 2 generation, hypersensitive cell death accompanied by clear 180-bp nucleosomal DNA laddering, and immune-related genes were induced when cultured rice cells were inoculated with a riceincompatible strain of A. avenae. These responses were completely abolished when a rice-compatible strain of A. avenae was used as the inoculating pathogen (Che et al 1999;Tanaka et al 2001;Iwano et al 2002;Tanaka et al 2003;Fujiwara et al 2004). To identify the specific elicitor related to the induction of these immune responses in cultured rice cells, a strain-specific antibody was raised against the incompatible strain (N1141) and then absorbed by the compatible strain (H8301).…”