Key Laboratory of Plant Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
Plant Cell. 2012 Feb;24(2):551-65. doi: 10.1105/tpc.111.094284. Epub 2012 Feb 28.
Under blue light (BL) illumination, Arabidopsis thaliana roots grow away from the light source, showing a negative phototropic response. However, the mechanism of root phototropism is still unclear. Using a noninvasive microelectrode system, we showed that the BL sensor phototropin1 (phot1), the signal transducer NONPHOTOTROPIC HYPOCOTYL3 (NPH3), and the auxin efflux transporter PIN2 were essential for BL-induced auxin flux in the root apex transition zone. We also found that PIN2-green fluorescent protein (GFP) localized to vacuole-like compartments (VLCs) in dark-grown root epidermal and cortical cells, and phot1/NPH3 mediated a BL-initiated pathway that caused PIN2 redistribution to the plasma membrane. When dark-grown roots were exposed to brefeldin A (BFA), PIN2-GFP remained in VLCs in darkness, and BL caused PIN2-GFP disappearance from VLCs and induced PIN2-GFP-FM4-64 colocalization within enlarged compartments. In the nph3 mutant, both dark and BL BFA treatments caused the disappearance of PIN2-GFP from VLCs. However, in the phot1 mutant, PIN2-GFP remained within VLCs under both dark and BL BFA treatments, suggesting that phot1 and NPH3 play different roles in PIN2 localization. In conclusion, BL-induced root phototropism is based on the phot1/NPH3 signaling pathway, which stimulates the shootward auxin flux by modifying the subcellular targeting of PIN2 in the root apex transition zone.
在蓝光（BL）照射下，拟南芥根会背离光源生长，表现出负向向光性反应。然而，根向光性的机制仍不清楚。我们利用一种非侵入性微电极系统，表明 BL 传感器光受体 1（phot1）、信号转导非光形态发生矮化 3（NPH3）和生长素外排转运蛋白 PIN2 是 BL 诱导根尖过渡区生长素流所必需的。我们还发现，PIN2-绿色荧光蛋白（GFP）在黑暗生长的根表皮和皮层细胞中定位于液泡样小泡（VLCs），而 phot1/NPH3 介导了 BL 起始的途径，导致 PIN2 重新分布到质膜。当黑暗生长的根暴露于布雷菲德菌素 A（BFA）时，PIN2-GFP 在黑暗中仍保留在 VLCs 中，而 BL 导致 PIN2-GFP 从小泡中消失，并诱导 PIN2-GFP-FM4-64 在扩大的小泡内共定位。在 nph3 突变体中，黑暗和 BL BFA 处理都导致 PIN2-GFP 从小泡中消失。然而，在 phot1 突变体中，黑暗和 BL BFA 处理下 PIN2-GFP 仍保留在小泡内，这表明 phot1 和 NPH3 在 PIN2 定位中发挥不同的作用。总之，BL 诱导的根向光性是基于 phot1/NPH3 信号通路，该通路通过改变根尖过渡区中 PIN2 的亚细胞靶向来刺激向光侧生长素流。
