Abstract
Salicylic acid (SA) is a key natural component that mediates local and systemic resistance to pathogens in many dicotyledonous species. However, its function is controversial in disease resistance in rice plants. Here, we show that the SA signaling is involved in both pathogen-associated-molecular-patterns triggered immunity (PTI) and effector triggered immunity (ETI) to Xanthomonas oryzae pv. Oryzae (Xoo) mediated by the recessive gene xa5, in which OsNPR3.3 plays an important role through interacting with TGAL11. Rice plants containing homozygous xa5 gene respond positively to exogenous SA, and their endogenous SA levels are also especially induced upon infection by the Xoo strain, PXO86. Depletion of endogenous SA can significantly attenuate plant resistance to PXO86, even to 86∆HrpXG (mutant PXO86 with a damaged type III secretion system). These results indicated that SA plays an important role in disease resistance in rice plants, which can be clouded by high levels of endogenous SA and the use of particular rice varieties.
Highlights
Salicylic acid (SA) is a key natural component that mediates local and systemic resistance to pathogens in many dicotyledonous species
To ascertain whether the eight TGACG-sequence-specific binding domain (TGA) genes were copartners of OsNPR3.3 participating in the bacterial blight resistance mediated by the xa[5] gene, we examined their expression in IRBB5 and IR24 challenged with the Xanthomonas oryzae pv. Oryzae (Xoo) strain PXO86 at the tillering stage by Quantitative real time RT-PCR (qRT-PCR) analysis
Previous studies have shown that many plant species, such as Arabidopsis, tobacco and cucumber, contain low basal levels of salicylic acid, which acts as a key signaling molecule in the activation of local or systemic acquired resistance, while rice plants contain high levels of endogenous SA, and SA levels cannot be increased by bacterial or fungal pathogens, suggesting that SA may not play a signaling role in rice disease resistance[52] but functions as an antioxidant molecule to protect rice from oxidative stress through modulating the redox balance[31]
Summary
Salicylic acid (SA) is a key natural component that mediates local and systemic resistance to pathogens in many dicotyledonous species. The resistance mediated by xa[5] was shown to result from the restricted bacterial movement[17], which depended on the effectors of pathogens and correlated with the reduced expression of the cognate susceptible genes[18]. These contradictory reports indicate that the mechanisms of xa[5] and Xa5 in bacterial blight resistance are complex. Many studies have shown that rice shares most regulatory components in SA signaling pathways with dicots, most pathogen infections do not result in increases in the SA level in rice, and exogenously applied SA cannot induce PR gene expression and disease resistance in many rice cultivars[52]
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