Background
Diseases caused by Xanthomonas species, including rice bacterial leaf blight, rice bacterial leaf streak and citrus bacterial canker, cause substantial losses in major crops. Current control strategies rely heavily on copper-based bactericides and agricultural antibiotics, but their long-term use is constrained by resistance and environmental risk. New chemistry is needed, but so are new biological ideas about where an agrochemical can act. Liquid-liquid phase separation (LLPS) offers such an idea. In cells, proteins and nucleic acids can assemble into dynamic, membraneless condensates that concentrate specific molecules and accelerate biological processes. LLPS is now widely discussed in cell biology and virology, but its use as a practical agrochemical target in plant pathogenic bacteria has remained largely unexplored.
Research progres s
Starting from syringic acid, a natural phenolic acid with favorable safety and biodegradability features, Prof. Runjiang Song's team at the State Key Laboratory of Green Pesticide, Guizhou University, designed a series of derivatives by combining the syringic acid scaffold with an allicin-inspired disulfide unit and a 1,3,4-oxadiazole moiety. Among 34 derivatives, compound C31 emerged as the most potent anti- Xoo molecule, with an EC 50 of 0.86 μg/mL. In rice pot experiments, C31 achieved 59.37% control efficacy against bacterial leaf blight, outperforming syringic acid and the commercial reference thiodiazole copper in this study.
The work then moved from activity discovery to target identification. Using activity-based protein profiling (ABPP), the team designed clickable/photoaffinity probes derived from C31 and captured candidate cellular receptors in Xoo . Genetic and biochemical validation converged on RpoA, the alpha subunit of bacterial RNA polymerase, as a key molecular receptor. Deletion of RpoA strongly attenuated Xoo pathogenicity: lesion length on rice was reduced by 87.4%, and biofilm formation, extracellular polysaccharide production and motility were all impaired. Complementation of RpoA restored these virulence-associated phenotypes, demonstrating that RpoA is a central node in Xoo pathogenicity.
Binding assays further supported direct target engagement. C31 bound RpoA with high affinity, with a KD of 1.61 μM by biolayer interferometry and 0.56 μM by microscale thermophoresis. Molecular docking and molecular dynamics simulations indicated that C31 binds the C-terminal domain of RpoA and restricts the conformational flexibility of key regions, consistent with an allosteric “molecular wedge” mechanism.
The central mechanistic discovery is that RpoA does more than participate in the classical RNA polymerase machinery. RpoA interacts reversibly with the primary sigma factor σ70, and this interaction promotes LLPS to form RpoA-σ70 biomolecular condensates. These condensates act as transcriptional hubs, enriching RpoA/σ70 complexes and DNA templates to facilitate σ70-dependent transcription. C31 disrupts this interface and suppresses condensate assembly, thereby weakening the global virulence transcriptional program ( FIG.1 ). Transcriptomic and RT-qPCR analyses connected this physical disruption to biological outcomes. RpoA deletion or C31 treatment down-regulated genes involved in extracellular polysaccharide biosynthesis, motility and chemotaxis, the type III secretion system and energy metabolism. The result is a broad reduction in virulence capacity rather than inhibition of a single downstream pathway.
Future prospect s
Several translational directions follow naturally. First, C31 can serve as a starting point for structure-guided optimization around the RpoA-σ70 interface, with the goal of improving potency, formulation compatibility, plant uptake and field stability. Second, the conservation of RpoA supports broader testing across Xanthomonas -associated diseases and other phytopathogenic bacteria. Third, C31-like LLPS inhibitors could be integrated with existing bactericides, plant immunity activators or biological control agents to reduce copper use and manage resistance.
More broadly, the study provides a workflow for discovering agrochemicals that target pathogenic condensates: chemical probe design, proteomic target identification, LLPS validation, virulence-network analysis and in planta efficacy testing. This pipeline may help uncover additional noncanonical targets hidden in the dynamic organization of plant pathogens. By dismantling a bacterial transcriptional hub, the study opens a new route toward mechanism-based, next-generation plant disease control.
Sources: https://spj.science.org/doi/10.34133/research.1222
Research
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Inhibiting Transcriptional Hub: A Phase-Separating RNA Polymerase Alpha Subunit as a First-in-Class Agrochemical Target against Xanthomonas
31-Mar-2026