Abstract:Microbial pathogens deliver effectors into plant cells to suppress plant immune responses and modulate host metabolism in order to support infection processes. We sought to determine if the Acidovorax avenae rice-virulent K1 strain can suppress pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) induced by flagellin isolated from the rice-avirulent N1141 strain. The flagellin-triggered PTI, including H2O2 generation, callose deposition, and expression of several immune-related genes were stro… Show more
“…Moreover, sequence analysis of regions flanking the transposons revealed that they were inserted into 68 different genes. In addition, multiple proteins were secreted by strains N1141 and K1 using their T3SS (Kondo et al, 2017;Kawaguchi et al, 2021). The presence of multiple effectors in A. avenae strains N1141 and K1 raises the question of whether NRHIF and KRHIF are the only ETI-inducible effectors for rice and finger millet, respectively.…”
Section: Discussionmentioning
confidence: 99%
“…When rice plants were inoculated with AKSF1-disruption mutants, disease symptom severity was reduced and bacterial growth was suppressed. These results indicate that AKSF1 is a novel effector that can suppress PTI in host rice plants (Kawaguchi et al, 2021). Interestingly, whole-genome sequencing of strain N1141 revealed that it lacks AKSF1.…”
Section: Introductionmentioning
confidence: 86%
“…We reported that inoculation of rice with the rice-avirulent strain N1141 of A. avenae caused ETI responses, including HR cell death, accompanied by loss of plasma membrane permeability, nuclear DNA fragmentation, and upregulation of ETI-related genes, including OsNAC4, which positively regulates HR cell death (Che et al, 1999;Kaneda et al, 2009). In contrast, the rice-virulent strain K1 can suppress PAMP-triggered immunity (PTI) caused by N1141 flagellin but cannot induce ETI responses in rice (Kawaguchi et al, 2021). Interestingly, a T3SS-deleted N1141 mutant (NΔT3SS) did not cause ETI responses, while the T3SS-deleted K1 mutant (KΔT3SS) was defective in PTI suppression (Kondo et al, 2012;Kawaguchi et al, 2021).…”
Section: Introductionmentioning
confidence: 99%
“…In contrast, the rice-virulent strain K1 can suppress PAMP-triggered immunity (PTI) caused by N1141 flagellin but cannot induce ETI responses in rice (Kawaguchi et al, 2021). Interestingly, a T3SS-deleted N1141 mutant (NΔT3SS) did not cause ETI responses, while the T3SS-deleted K1 mutant (KΔT3SS) was defective in PTI suppression (Kondo et al, 2012;Kawaguchi et al, 2021). These results indicate that strains N1141 and K1 have multiple effectors with different functions in rice.…”
Plant pathogenic bacteria inject effectors into plant cells using type III secretion systems (T3SS) to evade plant immune systems and facilitate infection. In contrast, plants have evolved defense systems called effector-triggered immunity (ETI) that can detect such effectors during co-evolution with pathogens. The rice-avirulent strain N1141 of the bacterial pathogen Acidovorax avenae causes rice ETI, including hypersensitive response (HR) cell death in a T3SS-dependent manner, suggesting that strain N1141 expresses an ETI-inducing effector. By screening 6,200 transposon-tagged N1141 mutants based on their ability to induce HR cell death, we identified 17 mutants lacking this ability. Sequence analysis and T3SS-mediated intracellular transport showed that a protein called rice HR cell death inducing factor (RHIF) is a candidate effector protein that causes HR cell death in rice. RHIF-disrupted N1141 lacks the ability to induce HR cell death, whereas RHIF expression in this mutant complemented this ability. In contrast, RHIF from rice-virulent strain K1 functions as an ETI inducer in the non-host plant finger millet. Furthermore, inoculation of rice and finger millet with either RHIF-deficient N1141 or K1 strains showed that a deficiency of RHIF genes in both strains results in decreased infectivity toward each the host plants. Collectively, novel effector RHIFs identified from A. avenae strains N1141 and K1 function in establishing infection in host plants and in ETI induction in non-host plants.
“…Moreover, sequence analysis of regions flanking the transposons revealed that they were inserted into 68 different genes. In addition, multiple proteins were secreted by strains N1141 and K1 using their T3SS (Kondo et al, 2017;Kawaguchi et al, 2021). The presence of multiple effectors in A. avenae strains N1141 and K1 raises the question of whether NRHIF and KRHIF are the only ETI-inducible effectors for rice and finger millet, respectively.…”
Section: Discussionmentioning
confidence: 99%
“…When rice plants were inoculated with AKSF1-disruption mutants, disease symptom severity was reduced and bacterial growth was suppressed. These results indicate that AKSF1 is a novel effector that can suppress PTI in host rice plants (Kawaguchi et al, 2021). Interestingly, whole-genome sequencing of strain N1141 revealed that it lacks AKSF1.…”
Section: Introductionmentioning
confidence: 86%
“…We reported that inoculation of rice with the rice-avirulent strain N1141 of A. avenae caused ETI responses, including HR cell death, accompanied by loss of plasma membrane permeability, nuclear DNA fragmentation, and upregulation of ETI-related genes, including OsNAC4, which positively regulates HR cell death (Che et al, 1999;Kaneda et al, 2009). In contrast, the rice-virulent strain K1 can suppress PAMP-triggered immunity (PTI) caused by N1141 flagellin but cannot induce ETI responses in rice (Kawaguchi et al, 2021). Interestingly, a T3SS-deleted N1141 mutant (NΔT3SS) did not cause ETI responses, while the T3SS-deleted K1 mutant (KΔT3SS) was defective in PTI suppression (Kondo et al, 2012;Kawaguchi et al, 2021).…”
Section: Introductionmentioning
confidence: 99%
“…In contrast, the rice-virulent strain K1 can suppress PAMP-triggered immunity (PTI) caused by N1141 flagellin but cannot induce ETI responses in rice (Kawaguchi et al, 2021). Interestingly, a T3SS-deleted N1141 mutant (NΔT3SS) did not cause ETI responses, while the T3SS-deleted K1 mutant (KΔT3SS) was defective in PTI suppression (Kondo et al, 2012;Kawaguchi et al, 2021). These results indicate that strains N1141 and K1 have multiple effectors with different functions in rice.…”
Plant pathogenic bacteria inject effectors into plant cells using type III secretion systems (T3SS) to evade plant immune systems and facilitate infection. In contrast, plants have evolved defense systems called effector-triggered immunity (ETI) that can detect such effectors during co-evolution with pathogens. The rice-avirulent strain N1141 of the bacterial pathogen Acidovorax avenae causes rice ETI, including hypersensitive response (HR) cell death in a T3SS-dependent manner, suggesting that strain N1141 expresses an ETI-inducing effector. By screening 6,200 transposon-tagged N1141 mutants based on their ability to induce HR cell death, we identified 17 mutants lacking this ability. Sequence analysis and T3SS-mediated intracellular transport showed that a protein called rice HR cell death inducing factor (RHIF) is a candidate effector protein that causes HR cell death in rice. RHIF-disrupted N1141 lacks the ability to induce HR cell death, whereas RHIF expression in this mutant complemented this ability. In contrast, RHIF from rice-virulent strain K1 functions as an ETI inducer in the non-host plant finger millet. Furthermore, inoculation of rice and finger millet with either RHIF-deficient N1141 or K1 strains showed that a deficiency of RHIF genes in both strains results in decreased infectivity toward each the host plants. Collectively, novel effector RHIFs identified from A. avenae strains N1141 and K1 function in establishing infection in host plants and in ETI induction in non-host plants.
“…Effectors from T3SS1 are generally detected earlier in the infection process and it has been suggested that they are more involved with the earlier stages of the vacuole maturation while effectors from T3SS2 are more involved with later stages [ 87 ]. Finally, experiments using mutants of Acidovorax avenae identified an effector protein ( A. avenae K1 suppression factor 1) that was associated with supressing the cellular response following recognition of flagellin associated molecular patterns [ 88 ].…”
Gram-negative bacteria are known to subvert eukaryotic cell physiological mechanisms using a wide array of virulence factors, among which the type three-secretion system (T3SS) is often one of the most important. The T3SS constitutes a needle-like apparatus that the bacterium uses to inject a diverse set of effector proteins directly into the cytoplasm of the host cells where they can hamper the host cellular machinery for a variety of purposes. While the structure of the T3SS is somewhat conserved and well described, effector proteins are much more diverse and specific for each pathogen. The T3SS can remodel the cytoskeleton integrity to promote intracellular invasion, as well as silence specific eukaryotic cell signals, notably to hinder or elude the immune response and cause apoptosis. This is also the case in aquatic bacterial pathogens where the T3SS can often play a central role in the establishment of disease, although it remains understudied in several species of important fish pathogens, notably in Yersinia ruckeri. In the present review, we summarise what is known of the T3SS, with a special focus on aquatic pathogens and suggest some possible avenues for research including the potential to target the T3SS for the development of new anti-virulence drugs.
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