Xanthomonas oryzae pv. oryzae, the causal pathogen of bacterial blight of rice, depends on its type III secretion system and associated effector proteins to grow and colonize the vascular tissues of rice plants.

The type III effectors include a family of closely related transcription activator-like (TAL) effectors and the rest of diverse effectors, so-called non-TAL effectors. Our understanding of non-TAL effectors for pathogenesis in rice blight is still limited. Here we report a feasible method to rapidly detect the activation of mitogen-activated protein kinase pathway in rice mesophyll protoplasts by the Xoryzae pv. oryzae derived peptidoglycan and screen for virulent effectors that can suppress the pathogen-associated molecular pattern triggered immunity (PTI) response. Amongst 17 non-TAL effectors transiently expressed in ricecells, we found that three effectors (XopZ, XopN, and XopV) were able to suppress the peptidoglycan-triggered MAPK activation. The triple mutant of the X. oryzae pv. oryzae strain PXO99A lacking XopZXopN, and XopV showed additively reduced virulence. Adding back either of genes restored the virulence of the triple mutant. Our results demonstrate the collective and redundant ability of defense suppression by non-TAL effectors in causing bacterial blight of rice.

 

See: https://www.ncbi.nlm.nih.gov/pubmed/30631333.

 

 

FIGURE 1

Pathogen-associated molecular pattern (PAMPs) activate MAPK cascade in rice protoplasts. (A) Rice protoplasts do not respond to flg22 treatment. Rice protoplasts were treated with 1 μM flg22, MAPK activation (top) and loading control (bottom) are shown. (B) flg22 activates endogenous MAPK cascade in Arabidopsisprotoplasts. Arabidopsis protoplasts were treated with 1 μM flg22, MAPK activation (top) and loading control (bottom) are shown. (C) Endogenous MAPK activation is induced by PGN under the lights. Rice protoplasts were treated with or without 5 mg/ml PGN, MAPK activation (top) and loading control (bottom) are shown. (D) PGN has weak effect on endogenous MAPK activation in the dark. Rice protoplasts were treated with or without 5 mg/ml PGN, MAPK activation (top) and loading control (bottom) are shown. (E) Endogenous MAPK cascade is activated at different temperature under the lights. Rice protoplasts were treated with or without 5 mg/ml PGN under the lights for 10 min, MAPK activation (top) and loading control (bottom) are shown. (F) Chitin activates endogenous MAPK cascade in rice protoplasts. Rice protoplasts were treated with 10 μM chitin, MAPK activation (top) and loading control (bottom) are shown. The data shown here are one representative of three independent experiments.