Center for Bioscience Research and Education, Utsunomiya University, Tochigi, Japan.
Graduate School of Agriculture, Utsunomiya University, Tochigi, Japan.
Physiol Plant. 2021 Nov;173(3):775-787. doi: 10.1111/ppl.13473. Epub 2021 Jun 17.
Changes in the subcellular localisation of chloroplasts help optimise photosynthetic activity under different environmental conditions. In many plants, this movement is mediated by the blue-light photoreceptor phototropin. A model organism with simple phototropin signalling that allows clear observation of chloroplasts would facilitate the study of chloroplast relocation movement. Here, we examined this process in the simple thalloid liverwort Apopellia endiviifolia. Transverse sections of the thallus tissue showed uniformly developed chloroplasts and no air chambers; these characteristics enable clear observation of chloroplasts and analysis of their movements under a fluorescence stereomicroscope. At 22°C, the chloroplasts moved to the anticlinal walls of cells next to the neighbouring cells in the dark (dark-positioning response), whereas they moved towards weak light (accumulation response) and away from strong light (avoidance response). When the temperature was reduced to 5°C, the chloroplasts moved away from weak light (cold-avoidance response). Hence, both light- and temperature-dependent chloroplast relocation movements occur in A. endiviifolia. Notably, the accumulation, avoidance and cold-avoidance responses were induced under blue-light but not under red-light. These results suggest that phototropin is responsible for chloroplast relocation movement in A. endiviifolia and that the characteristics are similar to those in the model liverwort Marchantia polymorpha. RNA sequencing and Southern blot analysis identified a single copy of the PHOTOTROPIN gene in A. endiviifolia, indicating that a simple phototropin signalling pathway functions in A. endiviifolia. We conclude that A. endiviifolia has great potential as a model system for elucidating the mechanisms of chloroplast relocation movement.
叶绿体的亚细胞定位变化有助于在不同环境条件下优化光合作用。在许多植物中，这种运动是由蓝光光受体向光素介导的。具有简单向光素信号传导的模式生物可以清楚地观察到叶绿体，从而促进叶绿体重定位运动的研究。在这里，我们研究了简单叶状地钱 Apopellia endiviifolia 中的这个过程。叶组织的横切片显示出均匀发育的叶绿体和没有气室；这些特征使得能够清楚地观察叶绿体并在荧光立体显微镜下分析它们的运动。在 22°C 下，叶绿体在黑暗中移动到邻近细胞的细胞的垂周壁（暗定位响应），而在弱光下（积累响应）并远离强光（回避响应）。当温度降低到 5°C 时，叶绿体远离弱光（冷回避响应）。因此，光和温度依赖性叶绿体重定位运动都发生在 A. endiviifolia 中。值得注意的是，积累、回避和冷回避反应是在蓝光下而不是在红光下诱导的。这些结果表明，向光素是 A. endiviifolia 叶绿体重定位运动的原因，其特征与模型地钱 Marchantia polymorpha 相似。RNA 测序和 Southern blot 分析鉴定出 A. endiviifolia 中存在单个 PHOTOTROPIN 基因的拷贝，表明简单的向光素信号通路在 A. endiviifolia 中起作用。我们得出结论，A. endiviifolia 作为阐明叶绿体重定位运动机制的模型系统具有很大的潜力。
