The cyanobacterium Synechocystis sp. PCC 6803 can move directionally on a moist surface toward or away from a light source to reach optimal light conditions for its photosynthetic lifestyle. This behavior, called phototaxis, is mediated by type IV pili (T4P), which can pull a single cell into a certain direction. Several photoreceptors and their downstream signal transduction elements are involved in the control of phototaxis. However, the critical steps of local pilus assembly in positive and negative phototaxis remain elusive. One of the photoreceptors controlling negative phototaxis in Synechocystis is the blue-light sensor PixD. PixD forms a complex with the CheY-like response regulator PixE that dissociates upon illumination with blue light. In this study, we investigate the phototactic behavior of pixE deletion and overexpression mutants in response to unidirectional red light with or without additional blue-light irradiation. Furthermore, we show that PixD and PixE partly localize in spots close to the cytoplasmic membrane. Interaction studies of PixE with the motor ATPase PilB1, demonstrated by in vivo colocalization, yeast two-hybrid and coimmunoprecipitation analysis, suggest that the PixD-PixE signal transduction system targets the T4P directly, thereby controlling blue-light-dependent negative phototaxis. An intriguing feature of PixE is its distinctive structure with a PATAN (PatA N-terminus) domain. This domain is found in several other regulators, which are known to control directional phototaxis. As our PilB1 coimmunoprecipitation analysis revealed an enrichment of PATAN domain response regulators in the eluate, we suggest that multiple environmental signals can be integrated via these regulators to control pilus function.

中文翻译：

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（PATAN）-CheY样反应调节剂PixE与运动ATPase PilB1相互作用，以控制蓝藻属蓝藻中的负趋光性​​。PCC 6803。

蓝藻Synechocystis sp.。PCC 6803可以在潮湿的表面上朝向或远离光源定向移动，以达到其光合作用生活方式的最佳光照条件。这种行为称为趋光性，是由IV型菌毛（T4P）介导的，它可以将单个细胞拉向某个方向。几个控制光感受器及其下游信号转导元件。但是，正向和负向趋光性中局部菌毛组装的关键步骤仍然难以捉摸。控制蓝藻胞中负趋光性的感光器之一是蓝光传感器PixD。PixD与类似CheY的响应调节器PixE形成复合物，后者在蓝光照射下会解离。在这项研究中，我们调查了pixE缺失和过度表达突变体在响应有或没有附加蓝光的情况下对单向红光的光战术行为。此外，我们显示PixD和PixE部分位于靠近细胞质膜的斑点中。通过体内共定位，酵母双杂交和共免疫沉淀分析表明，PixE与电机ATPase PilB1的相互作用研究表明，PixD-PixE信号转导系统直接靶向T4P，从而控制了依赖蓝光的负趋光性​​。PixE的一个有趣特征是其具有PATAN（PatA N末端）结构域的独特结构。在其他几个调节器中也可以找到此域，这些调节器可以控制方向性趋光性。