Discovery of Ethyl 2-Nitro-3-Arylacrylates Molecules as T3SS Inhibitor Reducing the Virulence of Plant Pathogenic Bacteria Xanthomonas

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.

Research Progress on Small Molecular Inhibitors of the Type 3 Secretion System

“…Ethyl 2-nitro-3-arylacrylates ( Figure 8 ) were another group of Xoo T3SS inhibitors screened by Jiang et al [ 122 ]. Molecules I-9, I-12, and I-13 showed good frontal inhibition of Xoo T3SS and exhibited strong inhibition against the hpa1 promoter, with a reduction of over 80% at 100 μM.…”

“…Molecules I-9, I-12, and I-13 showed good frontal inhibition of Xoo T3SS and exhibited strong inhibition against the hpa1 promoter, with a reduction of over 80% at 100 μM. Three inhibitors at a concentration of 100 µM were co-cultured with Xoo PXO99 and did not inhibit bacterial growth [ 122 ]. At the same concentration, the three inhibitors effectively blocked Xoo T3SS hypersensitivity to tobacco.…”

“…At the same concentration, the three inhibitors effectively blocked Xoo T3SS hypersensitivity to tobacco. Further studies showed that I-9, I-12, and I-13 reduced the mRNA levels of the key regulatory genes hrpG and hrpX [ 122 ]. All three of these molecules have potential to alleviate the occurrence of Xoo in rice and Xcc in radish [ 122 ].…”

Exploiting Natural Maltol for Synthesis of Novel Hydroxypyridone Derivatives as Promising Anti-Virulence Agents in Bactericides Discovery

“…The virulence factors of phytopathogenic bacteria, especially Xanthomonas spp., are extremely important in the infection process . For instance, Xoo cells can protect themselves from disadvantageous environmental conditions and beneficially attack host plants by producing a series of virulence factors, including extracellular polysaccharide (EPS), adhesins, extracellular enzymes, and effectors of the type III secretion system (T3SS). , In particular, EPS, as a major virulence factor, can facilitate colonization of the plant by Xoo and prevent Xoo from being recognized by host plants . Biofilm formation, which can increase the pathogenicity of plant pathogens in the bacterial infection process, has been recently shown to be an essential factor for producing bactericide resistance .…”

Five Plant Natural Products Are Potential Type III Secretion System Inhibitors to Effectively Control Soft-Rot Disease Caused by Dickeya

“…Previous studies have shown that the plant phenolic compounds and derivatives p-coumaric acid (PCA), cinnamyl alcohol (CA),and trans-4-hydroxycinnamohydroxamic acid play a role in the inhibition of T3SS expression of D. dadantii 3937 ( Li et al, 2009 , 2015 ; Joshi et al, 2021 ). Plant phenolic compounds and derivatives such as o-coumaric acid, trans -2-phenylcyclopropane-1-carboxylic-acid, trans -2-methylcinnamic acid, and trans -2-methoxycinnamic acid as well as synthetic compound ethyl 2-nitro-3-arylacrylates, have been reported to affect the expression of X. oryzae T3SS genes ( Fan et al, 2017 ; Jiang et al, 2019 ). Khokhani et al (2013) found T3SS inhibitors (4-methoxy-cinnamic acid and benzoic acid) and T3SS inducers [ trans -2-(4-hydroxyphenyl)-ethenylsulfonate] change the expression of E. amylovora T3SS through HrpS-HrpL pathway, and salicylic acid (SA) inhibits hrpA promoter activity.…”