Abstract
BackgroundAvr-Pita was the first effector identified in the blast fungus (Magnaporthe oryzae)–rice (Oryza sativa) pathosystem. However, the molecular mechanism underlying its effects on the host plant has remained a long-standing mystery.ResultsHere, we report that ectopically expressing Avr-Pita in rice enhances susceptibility to M. oryzae and suppresses pathogen-associated molecular pattern (PAMP)-triggered defense responses. Avr-Pita targets the host mitochondria and interacts with the cytochrome c oxidase (COX) assembly protein OsCOX11, a key regulator of mitochondrial reactive oxygen species (ROS) metabolism in rice. Overexpressing Avr-Pita or OsCOX11 increased COX activity and decreased ROS accumulation triggered by the fungal PAMP chitin. OsCOX11-overexpressing plants showed increased susceptibility to M. oryzae, whereas OsCOX11-knockdown plants showed resistance to M. oryzae.ConclusionsTaken together, these findings suggest that the fungal pathogen M. oryzae delivers the effector Avr-Pita to the host plant, where it enhances COX activity thus decreasing ROS accumulation. Therefore, this effector suppresses host innate immunity by perturbing ROS metabolism in the mitochondria.
Highlights
Plants have evolved sophisticated mechanisms to perceive and respond to pathogen attack, such as pathogenassociated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI) (Liu et al, 2014)
The PUbi::Avr-Pita plants had larger disease lesions and higher relative fungal biomass than wild-type (WT) plants at 12 days post inoculation (Fig. 1a–c). These results indicate that ectopic expression of AvrPita enhances rice susceptibility to M. oryzae
Avr-Pita was the first fungal effector protein identified from M. oryzae, the devastating fungal pathogen that causes rice blast disease, but its role in this plant–pathogen interaction is poorly understood
Summary
Plants have evolved sophisticated mechanisms to perceive and respond to pathogen attack, such as pathogenassociated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI) (Liu et al, 2014). AvrPiz-t interacts with the nucleoporin protein APIP12 to suppress host immunity (Tang et al, 2017). Another well-documented Avr protein, AvrPii, disrupts host immune systems by interacting with NADP-MALI C ENZYME 2 (OsNADP-ME2) to inhibit NADP-ME activity or by interacting with two exocytosis complex OsExo proteins (Fujisaki et al, 2015; Singh et al, 2016). These evidences indicate that Avr proteins may target to various host factors to manipulate host immunity. The molecular mechanism underlying its effects on the host plant has remained a longstanding mystery
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