College of Resources and Environment, Southwest University, Chongqing, China.
Chongqing Academy of Agricultural Sciences, Chongqing, China.
Mol Plant Pathol. 2022 May;23(5):679-692. doi: 10.1111/mpp.13189. Epub 2022 Feb 4.
A syringe-like type III secretion system (T3SS) plays essential roles in the pathogenicity of Ralstonia solanacearum, which is a causal agent of bacterial wilt disease on many plant species worldwide. Here, we characterized functional roles of a CysB regulator (RSc2427) in R. solanacearum OE1-1 that was demonstrated to be responsible for cysteine synthesis, expression of the T3SS genes, and pathogenicity of R. solanacearum. The cysB mutants were cysteine auxotrophs that failed to grow in minimal medium but grew slightly in host plants. Supplementary cysteine substantially restored the impaired growth of cysB mutants both in minimal medium and inside host plants. Genes of cysU and cysI regulons have been annotated to function for R. solanacearum cysteine synthesis; CysB positively regulated expression of these genes. Moreover, CysB positively regulated expression of the T3SS genes both in vitro and in planta through the PrhG to HrpB pathway, whilst impaired expression of the T3SS genes in cysB mutants was independent of growth deficiency under nutrient-limited conditions. CysB was also demonstrated to be required for exopolysaccharide production and swimming motility, which contribute jointly to the host colonization and infection process of R. solanacearum. Thus, CysB was identified here as a novel regulator on the T3SS expression in R. solanacearum. These results provide novel insights into understanding of various biological functions of CysB regulators and complex regulatory networks on the T3SS in R. solanacearum.
一种类似于注射器的 III 型分泌系统（T3SS）在茄青枯雷尔氏菌的致病性中起着至关重要的作用，茄青枯雷尔氏菌是全球许多植物物种细菌性萎蔫病的病原体。在这里，我们对茄青枯雷尔氏菌 OE1-1 中的一个 CysB 调节剂（RSc2427）的功能作用进行了表征，该调节剂被证明负责半胱氨酸的合成、T3SS 基因的表达以及茄青枯雷尔氏菌的致病性。cysB 突变体是半胱氨酸营养缺陷型，无法在最小培养基中生长，但在宿主植物中生长稍快。补充半胱氨酸可大大恢复 cysB 突变体在最小培养基和宿主植物中的生长缺陷。cysU 和 cysI 调控子的基因已被注释为参与茄青枯雷尔氏菌半胱氨酸合成的功能；CysB 正向调节这些基因的表达。此外，CysB 通过 PrhG 到 HrpB 途径正向调节 T3SS 基因的表达，无论是在体外还是在体内，而 cysB 突变体中 T3SS 基因的表达受损与营养有限条件下的生长缺陷无关。CysB 还被证明是荚膜多糖产生和泳动运动所必需的，这共同有助于茄青枯雷尔氏菌的宿主定殖和感染过程。因此，CysB 在这里被确定为茄青枯雷尔氏菌 T3SS 表达的新型调节剂。这些结果为深入了解 CysB 调节剂的各种生物学功能以及茄青枯雷尔氏菌 T3SS 的复杂调控网络提供了新的见解。
