Xanthomonas campestris pv. campestris is the causative agent of black rot disease in crucifer plants. This Gram-negative bacterium utilizes the type III secretion system (T3SS), encoded by the hrp gene cluster, to aid in its resistance to host defenses and the ability to cause disease. The T3SS injects a set of proteins known as effectors into host cells that come into contact with the bacterium. The T3SS is essential for the virulence and hypersensitive response (HR) of X. campestris pv. campestris, making it a potential target for disease control strategies. Using a unique and straightforward high-throughput screening method, we examined a large collection of diverse small molecules for their potential to modulate the T3SS without affecting the growth of X. campestris pv. campestris. Screening of 13,129 different compounds identified 10 small molecules that had a significant inhibitory influence on T3SS. Moreover, reverse transcription-quantitative PCR (qRT-PCR) assays demonstrated that all 10 compounds repress the expression of the hrp genes. Interestingly, the effect of these small molecules on hrp genes may be through the HpaS and ColS sensor kinase proteins that are key to the regulation of the T3SS in planta. Five of the compounds were also capable of inhibiting X. campestris pv. campestris virulence in a Chinese radish leaf-clipping assay. Furthermore, seven of the small molecules significantly weakened the HR in nonhost pepper plants challenged with X. campestris pv. campestris. Taken together, these small molecules may provide potential tool compounds for the further development of antivirulence agents that could be used in disease control of the plant pathogen X. campestris pv. campestris.

IMPORTANCE The bacterium Xanthomonas campestris pv. campestris is known to cause black rot disease in many socioeconomically important vegetable crops worldwide. The management and control of black rot disease have been tackled with chemical and host resistance methods with variable success. This has motivated the development of alternative methods for preventing this disease. Here, we identify a set of novel small molecules capable of inhibiting X. campestris pv. campestris virulence, which may represent leading compounds for the further development of antivirulence agents that could be used in the control of black rot disease.

Xanthomonas campestris pv。樟脑是十字花科植物黑腐病的病原体。这种革兰氏阴性细菌利用由hrp基因簇编码的III型分泌系统（T3SS）来增强其对宿主防御的抵抗力和引起疾病的能力。T3SS将一组称为效应子的蛋白质注射到与细菌接触的宿主细胞中。T3SS对于X. campestris pv的毒力和超敏反应（HR）至关重要。樟脑，使其成为疾病控制策略的潜在目标。使用独特而直接的高通量筛选方法，我们检查了多种多样的小分子的大集合，这些小分子具有调节T3SS而不影响其生长的潜力。X.campestris pv。桔梗。对13,129种不同化合物的筛选确定了10种对T3SS具有明显抑制作用的小分子。此外，逆转录定量PCR（qRT-PCR）分析表明，所有10种化合物均抑制hrp基因的表达。有趣的是，这些小分子上的效果HRP基因可以通过杂多酸和cols传感器是关键T3SS的调节激酶的蛋白质在植物中。其中的五种化合物也能够抑制喜树耶尔森氏菌。萝卜切叶测定中的樟脑毒力。此外，七个小分子显着削弱了非宿主辣椒植物的HR，这些植物受到X.campestris pv。桔梗。这些小分子合在一起可为进一步开发抗毒剂提供潜在的工具化合物，这些抗毒剂可用于植物病原体X. campestris pv的病害控制。桔梗。

重要细菌黄单胞菌（Xanthomonas campestris） pv。众所周知，樟脑在全球许多具有社会经济意义的蔬菜作物中都会引起黑腐病。黑腐病的控制和控制已经通过化学和宿主抗性方法获得了成功。这激发了预防该疾病的替代方法的发展。在这里，我们确定了一组能够抑制X. campestris pv的新型小分子。樟脑毒力，可能代表了进一步开发可用于控制黑腐病的抗毒剂的主要化合物。