Abstract
Xanthomonas oryzae pv. oryzae (Xoo) is a gram-negative pathogen which causes leaf blight disease. Known traditional bactericides are not much more effective in inhibiting this bacteria than before. Selecting the virulence factor of the bacteria as the target without affecting their growth has been considered as a novel method for developing new anti-microbial drugs. Type III secretion systems (T3SS) are one of the important and highly conserved virulence factors in most gram-negative pathogens, which has been considered as an effective target to develop new anti-microbial drugs. In order to discover potential anti-microbial drugs against Xoo pathogens, a series of ethyl 2-nitro-3-arylacrylates compounds were screened. Among them, the compounds I-9, I-12, and I-13 could highly inhibit the promoter activity of a harpin gene hpa1, which were used to further check for the influence on bacterial growth and on the hypersensitive response (HR) caused by Xoo bacteria on non-host plants. The results showed that above compounds could reduce HR without affecting bacterial growth and survival. Moreover, qRT-PCR analysis indicated that treatment with the three inhibitors (I-9, I-12, and I-13) could suppress the expression of the Xoo T3SS in different extent. The mRNA levels of representative genes in the hrp cluster, including the key regulatory genes hrpG and hrpX, were decreased. Last but not least, in vivo test ensured that the above compounds reduced the disease symptoms of Xoo on the rice and Xcc on the Chinese radish.
Highlights
Xanthomonas oryzae pv. oryzae (Xoo) is a gram-negative rodshaped bacterium which is an important source of bacterial disease on rice (Mansfield et al, 2012)
T3SS is highly conserved among most gram-negative pathogenic bacteria and not necessary for bacterial growth and survival (Buttner, 2012; Xiang et al, 2018)
In order to make sure that the compounds could affect the expression of T3SS in Xoo, a library of compounds were used to test their effects on the promoter activity of the hpa1 gene (Table 1), whose expression is induced in the hrp-inducing medium XOM2
Summary
Xanthomonas oryzae pv. oryzae (Xoo) is a gram-negative rodshaped bacterium which is an important source of bacterial disease on rice (Mansfield et al, 2012). Oryzae (Xoo) is a gram-negative rodshaped bacterium which is an important source of bacterial disease on rice (Mansfield et al, 2012). Resistance of Xoo against these bactericides has been observed recently (Shi et al, 2015; Yu et al, 2016), which generally affects the essential factors in the process of bacterial growth and survival (Rasko and Sperandio, 2010; Fan et al, 2017). There is a demand for the development of novel classes of agents to combat resistance of Xoo that target bacterial virulence factors rather than their key processes of growth and survival (Barczak and Hung, 2009; Rasko and Sperandio, 2010). It was proved that these inhibitors may directly affect the components of the T3SS apparatus (Bowlin et al, 2014; Jessen et al, 2014), or the function of regulating T3SS gene expression (Guo et al, 2005; Yang et al, 2014), or through several indirect interactions (Petnicki-Ocwieja et al, 2005)
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