Blue-light-induced chloroplast movements play an important role in maximizing light utilization for photosynthesis in plants. Under a weak light condition, chloroplasts accumulate to the cell surface to capture light efficiently (chloroplast accumulation response). Conversely, chloroplasts escape from strong light and move to the side wall to reduce photodamage (chloroplast avoidance response). The blue light receptor phototropin (phot) regulates these chloroplast movements and optimizes leaf photosynthesis by controlling other responses in addition to chloroplast movements. Seed plants such as Arabidopsis (Arabidopsis thaliana) have phot1 and phot2. They redundantly mediate phototropism, stomatal opening, leaf flattening, and the chloroplast accumulation response. However, the chloroplast avoidance response is induced by strong blue light and regulated primarily by phot2. Phots are localized mainly on the plasma membrane. However, a substantial amount of phot2 resides on the chloroplast outer envelope. Therefore, differentially localized phot2 might have different functions. To determine the functions of plasma membrane- and chloroplast envelope-localized phot2, we tethered it to these structures with their respective targeting signals. Plasma membrane-localized phot2 regulated phototropism, leaf flattening, stomatal opening, and chloroplast movements. Chloroplast envelope-localized phot2 failed to mediate phototropism, leaf flattening, and the chloroplast accumulation response but partially regulated the chloroplast avoidance response and stomatal opening. Based on the present and previous findings, we propose that phot2 localized at the interface between the plasma membrane and the chloroplasts is required for the chloroplast avoidance response and possibly for stomatal opening as well.

中文翻译：

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Phototropin2有助于叶绿体-血浆膜界面处的叶绿体回避反应。

蓝光诱导的叶绿体运动在最大限度地利用植物光合作用的光中起着重要作用。在弱光条件下，叶绿体积聚到细胞表面以有效捕获光（叶绿体积聚响应）。相反，叶绿体从强光中逸出并移至侧壁以减少光损伤（避免叶绿体响应）。蓝光受体光养蛋白（phot）通过控制除叶绿体运动之外的其他响应来调节这些叶绿体运动并优化叶片的光合作用。诸如拟南芥（Arabidopsis thaliana）的种子植物具有phot1和phot2。它们多余地介导了向光性，气孔开放，叶片变平和叶绿体积累反应。然而，叶绿体回避反应是由强蓝光引起的，并且主要受phot2调控。照片主要位于质膜上。但是，大量的phot2驻留在叶绿体外壳上。因此，差异本地化的phot2可能具有不同的功能。为了确定质膜和叶绿体包膜定位的phot2的功能，我们将其与各自的靶向信号绑定到这些结构。质膜定位的phot2调节了向光性，叶片变平，气孔开口和叶绿体运动。叶绿体包膜定位的phot2不能介导向光性，叶片变平和叶绿体积累反应，但部分调节了叶绿体回避反应和气孔开放。根据目前和以前的发现，