Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, NY 14853, USA.
Mol Microbiol. 2012 Jul;85(2):195-200. doi: 10.1111/j.1365-2958.2012.08119.x. Epub 2012 Jun 14.
The assembly of type III secretion systems (T3SSs), which inject bacterial effector proteins into the cytosol of animal and plant hosts, is a highly regulated process. Animal pathogens use a length-control protein to produce T3SS needles of fixed length and then a second regulator, such as YopN in Yersinia spp, to mediate host contact-dependent effector delivery. For Pseudomonas syringae and other plant pathogens, regulation of the assembly process differs because the T3SS pilus must grow through variably thick plant cell walls before contacting the host plasma membrane. In this issue of Molecular Microbiology, Crabill et al. (2012) report evidence that the YopN homologue HrpJ is a multifunctional regulator of T3SS assembly in DC3000. A hrpJ mutant hyper-secretes pilus protein and no longer secretes four translocator proteins in culture, and it fails to inject effectors in planta. As with other proteins in this class, HrpJ is itself a T3SS substrate, but secretion-incompetent forms retain regulatory function. However, HrpJ is unusual in suppressing innate immune responses within host cells, as demonstrated with transgenic plants. The multiple capabilities of HrpJ appear to couple host contact sensing with pilus length control and translocator secretion while also contributing to immunity suppression early in the interaction.
III 型分泌系统（T3SS）的组装将细菌效应蛋白注入动植物宿主的细胞质中，这是一个高度调控的过程。动物病原体使用长度控制蛋白来产生固定长度的 T3SS 针，然后使用第二个调节剂（例如耶尔森氏菌中的 YopN）来介导宿主接触依赖性效应物传递。对于丁香假单胞菌和其他植物病原体，组装过程的调节方式不同，因为 T3SS 菌毛必须穿过可变厚度的植物细胞壁才能接触宿主质膜。在本期《分子微生物学》中，Crabill 等人（2012 年）报告了证据表明，YopN 同源物 HrpJ 是 DC3000 中 T3SS 组装的多功能调节剂。hrpJ 突变体过度分泌菌毛蛋白，在培养物中不再分泌四种转运蛋白，并且无法在植物体内注射效应物。与该类别的其他蛋白质一样，HrpJ 本身也是 T3SS 的底物，但分泌无能形式保留了调节功能。然而，HrpJ 不同寻常之处在于它在宿主细胞内抑制先天免疫反应，这在转基因植物中得到了证明。HrpJ 的多种功能似乎将宿主接触感应与菌毛长度控制和转运蛋白分泌联系起来，同时也有助于在相互作用的早期抑制免疫。
