Phototropins are light-activated protein kinases, which contribute to photosynthesis optimization both through enhancement of photon absorption when light is limiting and avoidance responses in high light. This duality is in part endowed by the presence of phototropins with different photosensitivity (phot1 and phot2). Here we show that phot1, which senses low light to promote positive phototropism (growth towards the light), also limits the response in high light. This response depends in part on phot1-mediated phosphorylation of Phytochrome Kinase Substrate 4 (PKS4). This light-regulated phosphorylation switch changes PKS4 from a phototropism enhancer in low light to a factor limiting the process in high light. In such conditions phot1 and PKS4 phosphorylation prevent phototropic responses to shallow light gradients and limit phototropism in a natural high light environment. Hence, by modifying PKS4 activity in high light the phot1-PKS4 regulon enables appropriate physiological adaptations over a range of light intensities.

中文翻译：

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磷酸化开关将光致性的正调节剂转变为该过程的抑制剂。

光养蛋白是光激活的蛋白激酶，通过增强光受限时的光子吸收和强光下的回避响应，有助于光合作用的最优化。这种双重性部分归因于光敏蛋白具有不同的光敏性（phot1和phot2）。在这里，我们显示phot1可以感知弱光以促进正向光性（向光的生长），它也限制了强光下的响应。该响应部分取决于植物色素激酶底物4（PKS4）的phot1介导的磷酸化。该光调节的磷酸化开关将PKS4从弱光下的光致增光剂改变为限制高光下的过程的因素。在这种情况下，phot1和PKS4磷酸化会阻止对浅光梯度的光致反应，并限制自然高光环境中的光致性。因此，通过在高光下修改PKS4活性，phot1-PKS4调节剂可以在一定的光强度范围内进行适当的生理适应。