Sugimoto Yuki, Nakamura Hiroshi, Ren Shukun, Hori Koichi, Masuda Shinji
Graduate School of Bioscience & Biotechnology, Tokyo Institute of Technology, Yokohama, Japan.
Center for Biological Resources & Informatics, Tokyo Institute of Technology, Yokohama, USA.
Plant Cell Physiol. 2017 Mar 1;58(3):458-465. doi: 10.1093/pcp/pcw218.
The Synechocystis sp. PCC6803 can move on a solid surface in response to light, a phenomenon called phototaxis. Although many of the photoreceptors involved in phototaxis have been identified, the mechanisms that regulate directional motility of Synechocystis are not well understood. Previous studies showed that a mutant lacking the blue light-using flavin (BLUF) photoreceptor PixD exhibits negative phototaxis under conditions where the wild type responds positively. PixD interacts with the pseudo-response regulator-like protein PixE in a light-dependent manner, suggesting that this intermolecular interaction is important for phototaxis regulation, although genetic evidence has been lacking. To gain further insight into phototaxis regulation by PixD-PixE signaling, we constructed the deletion mutants ΔPixE and ΔPixD-ΔPixE, and characterized their phenotypes, which matched those of the wild type (positive phototaxis). Because ΔPixD exhibited negative phototaxis, PixE must function downstream of PixD. Under intense blue light (>100 μmol m-2 s-1; 470 nm) the wild type exhibited negative phototaxis, but ΔPixD-PixE exhibited positive phototaxis toward low-intensity blue light (∼0.8 μmol m-2 s-1; 470 nm). These results suggest that an unknown light-sensing system(s), that is necessary for directional cell movement, can be activated by low-intensity blue light; on the other hand, PixD needs high-intensity blue light to be activated. We also isolated spontaneous mutants that compensated for the pixE deletion. Genome-wide sequencing of the mutants revealed that the uncharacterized gene sll2003 regulates positive and negative phototaxis in response to light intensity.
集胞藻PCC6803能够响应光照在固体表面移动，这种现象称为趋光性。尽管已经鉴定出许多参与趋光性的光感受器，但集胞藻定向运动的调控机制仍未完全了解。先前的研究表明，缺乏利用蓝光的黄素（BLUF）光感受器PixD的突变体在野生型做出正向反应的条件下表现出负趋光性。PixD以光依赖的方式与类假反应调节蛋白PixE相互作用，这表明这种分子间相互作用对趋光性调节很重要，尽管缺乏遗传学证据。为了进一步深入了解PixD - PixE信号对趋光性的调控，我们构建了缺失突变体ΔPixE和ΔPixD - ΔPixE，并对它们的表型进行了表征，其表型与野生型（正趋光性）相符。由于ΔPixD表现出负趋光性，所以PixE必定在PixD的下游发挥作用。在强蓝光（>100 μmol m-2 s-1；470 nm）下，野生型表现出负趋光性，但ΔPixD - ΔPixE对低强度蓝光（~0.8 μmol m-2 s-1；470 nm）表现出正趋光性。这些结果表明，一种未知的光感应系统，它是细胞定向运动所必需的，可被低强度蓝光激活；另一方面，PixD需要高强度蓝光才能被激活。我们还分离出了补偿pixE缺失的自发突变体。对这些突变体进行全基因组测序发现，未表征的基因sll2003可根据光强度调节正趋光性和负趋光性。
