Abstract

The ability of P. syringae pv. phaseolicola to cause halo blight in bean cultivars is mainly determined by pathogenicity and virulence factors. An important pathogenicity component of P. syringae pv. phaseolicola is the type III secretion system (T3SS) that allows the secretion of effector proteins within the host cells, suppressing and modulating the host defense system. The hrpL gene encodes an alternative sigma factor, HrpL, essential for expressing genes involved in forming the T3SS. In several P. syringae pathovars, the biosynthesis of T3SS, siderophores, and some phytotoxins are coordinated by the GacS/GacA system. However, the regulatory connection between the GacS/GacA system, hrp intermediary regulators, and genes involved in synthesizing virulence factors is not fully described. In this study, the participation of HrpL in the production of phaseolotoxin and siderophores in P. syringae pv. phaseolicola NPS3121 was evaluated. An effective knockout strategy allowed the mutating of the hrpL gene. The mutation abolished the transcription of hrpL; consequently, the mutant was unable to cause disease on bean pods. Phaseolotoxin and siderophore analysis revealed that in P. syringae pv. phaseolicola NPS3121, HrpL does not regulate the phaseolotoxin synthesis but is necessary to control siderophore biosynthesis. HrpL controls siderophore biosynthesis by the fur gene regulation. These results reveal a new transcriptional regulatory connection between HrpL and the control of siderophore biosynthesis. The study of these regulatory systems becomes significant in strengthening the understanding of bacterial pathogenesis.

中文翻译：

---

在 Pseudomonas syringae pv。phaseolicola NPS3121 铁载体生物合成需要调节剂 HrpL

摘要

丁香假单胞菌的能力。phaseolicola 引起豆类品种光枯病主要由致病性和毒力因子决定。丁香假单胞菌光伏的重要致病成分。phaseolicola 是 III 型分泌系统 (T3SS)，它允许宿主细胞内分泌效应蛋白，从而抑制和调节宿主防御系统。hrpL基因编码另一种 sigma 因子 HrpL，它是表达参与形成 T3SS 的基因所必需的。在几种P. syringae pathovars 中，T3SS、铁载体和一些植物毒素的生物合成由 GacS/GacA 系统协调。然而，GacS/GacA 系统、 hrp之间的监管联系中间调节器和参与合成毒力因子的基因没有得到充分描述。在这项研究中，HrpL 参与P. syringae pv 中菜豆毒素和铁载体的生产。phaseolicola NPS3121 进行了评估。有效的敲除策略允许hrpL基因发生突变。该突变取消了hrpL的转录；因此，突变体无法在豆荚上引起疾病。Phaseolotoxin 和铁载体分析表明，在P. syringae pv。phaseolicola NPS3121，HrpL 不调节菜豆毒素的合成，但对于控制铁载体生物合成是必需的。HrpL 通过皮毛控制铁载体生物合成基因调控。这些结果揭示了 HrpL 与铁载体生物合成控制之间新的转录调控联系。对这些调节系统的研究对于加强对细菌发病机制的理解具有重要意义。