Eyespot-dependent determination of the phototactic sign in Chlamydomonas reinhardtii
Eyespot-dependent determination of the phototactic sign in Chlamydomonas reinhardtii
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DOI：
10.1073/pnas.1525538113
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发表时间：
2016-05-10
影响因子：
11.1
通讯作者：
Wakabayashi, Ken-ichi
中科院分区：
文献类型：
--
作者：
Ueki, Noriko;Ide, Takahiro;Wakabayashi, Ken-ichi
双鞭毛绿色衣藻莱茵衣藻在适宜光照条件下具有正向和负向趋光性。已经表明，用活性氧（ROS）试剂处理细胞使趋光性标志偏向阳性，而用ROS清除剂处理细胞使趋光性标志偏向阴性。利用这一特性，我们分离出一个突变体，lts 1 -211，它显示了一个还原-氧化（氧化还原）依赖趋光信号相反的野生型。该突变体在八氢番茄红素合成酶中具有单个氨基酸取代，八氢番茄红素合成酶是在类胡萝卜素生物合成途径中起作用的酶。眼斑含有大量的类胡萝卜素，对趋光性至关重要。大多数lts 1 -211细胞没有可检测到的眼斑和减少的类胡萝卜素水平。有趣的是，lts 1 -211的反向趋光信号表型被其他无眼点突变体共享。此外，我们直接表明，细胞体作为一个凸透镜。在缺乏类胡萝卜素层的情况下，细胞体的透镜效应将来自后部的光聚集到感光器上，这可以解释突变体的反向趋光性符号表型。这些结果表明，眼斑的遮光特性是决定趋光信号的必要条件。
The biflagellate green alga Chlamydomonas reinhardtii exhibits both positive and negative phototaxis to inhabit areas with proper light conditions. It has been shown that treatment of cells with reactive oxygen species (ROS) reagents biases the phototactic sign to positive, whereas that with ROS scavengers biases it to negative. Taking advantage of this property, we isolated a mutant, lts1-211, which displays a reduction-oxidation (redox) dependent phototactic sign opposite to that of the wild type. This mutant has a single amino acid substitution in phytoene synthase, an enzyme that functions in the carotenoid-biosynthesis pathway. The eyespot contains large amounts of carotenoids and is crucial for phototaxis. Most lts1-211 cells have no detectable eyespot and reduced carotenoid levels. Interestingly, the reversed phototactic-sign phenotype of lts1-211 is shared by other eyespot-less mutants. In addition, we directly showed that the cell body acts as a convex lens. The lens effect of the cell body condenses the light coming from the rear onto the photoreceptor in the absence of carotenoid layers, which can account for the reversed-phototactic-sign phenotype of the mutants. These results suggest that light-shielding property of the eyespot is essential for determination of phototactic sign.