Abstract
Abiotic stress can influence the interactions between a pathogen and its host. In this paper, we analyzed the effects of salicylic acid (SA) and pH on the morphological development and pathogenicity of Magnaporthe oryzae, the pathogen that causes rice (Oryza sativa) blast. A strain of rice blast that overexpresses biotrophy-associated secreted protein 1 (BAS1) and a wild-type (WT) strain were pretreated with different levels of pH and different concentrations of SA to analyze M. oryzae colony growth, sporulation, spore germination, dry weight of hypha, and appressorium formation. Disease incidence and the expression of defense-related genes in infected rice were analyzed after pretreatment with pH 5.00 or pH 8.00 and 200 μM SA. The results showed that both SA and pH had some influence on morphological development, including sporulation and appressorium formation of the BAS1-overexpression strain. In the 200 μM SA pretreatment, there was a lower incidence of disease and higher expression levels of the rice defense-related genes PR1a, PAL, HSP90, and PR5 on leaves inoculated with the BAS1-overexpession strain compared with the WT strain, whereas, LOX2 appeared to be downregulated in the BAS1-overexpession strain compared with the WT. In both pH treatments, disease incidence and expression of HSP90 were higher and the expression of PR1a and PR10a and LOX2 and PAL was lower in leaves inoculated with the BAS1-overexpression strain compared with leaves inoculated with the WT strain. We conclude that SA and pH affect morphological development of the BAS1-overexpression blast strain, but that these factors have little influence on the pathogenicity of the strain, indicating that BAS1-overexpression may have enhanced the tolerance of this rice blast strain to abiotic stressors. This work suggests new molecular mechanisms that exogenous SA and pH affect the interactions between M. oryzae and rice.
Highlights
The effector proteins secreted by plant pathogens play a key role in the interaction between the pathogens and the host plant as well as in the progression of the disease
This paper studied the effects of an exogenous hormone (SA) and pH on the sporulation, spore germination, appressorium formation, and mycelial growth, pathogenicity of a strain of M. oryzae that overexpresses biotrophy-associated secreted protein 1 (BAS1)
The results showed that there was no significant difference between the different concentrations of salicylic acid (SA) on the colony growth of the BAS1-overexpressing strain or the WT strain, compared with the control plants of each strain that were pretreated with only dimethyl sulfoxide (DMSO) (Fig. 1)
Summary
The effector proteins secreted by plant pathogens play a key role in the interaction between the pathogens and the host plant as well as in the progression of the disease. Once effector proteins enter the host, they can both work in the extracellular matrix and change the host’s cellular environment to facilitate infection and colonization (Kamoun 2006; Ridout et al 2006; Hogenhout et al 2009; Białas et al 2017). Environmental conditions may play a role; many studies have reported that temperature and pH can influence the secretion of effector proteins by pathogens. Some real virulence factors can successfully suppress a host’s defense response, they still need to function in coordination with specific extracellular secreted proteins (Li et al 2012). We can conclude that pH is a major environmental factor that affects the fungus secreting effector proteins and promotes its colonization in the host’s tissues. Other studies have shown that the C. lunatus isolates with higher melanin levels are more virulent than those with lower melanin levels; melanin and related secondary metabolite are considered to be virulence factors of C. lunatus (Xu et al 2007; Gao et al 2012)
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