Molecular Mechanisms of Enhancement of Plant Growth by phototropins.

适当的叶片位置对于优化光合作用和植物生长是至关重要的。我们在这里展示了蓝光刺激下叶片位置的调节。白光下生长的一周龄拟南芥幼苗转移到红光(25μmolm-2 S-1)下5d后，出现的新叶柄几乎是水平的，叶片卷曲并向下倾斜。然而，当从上方发出的弱蓝光(0.1molmolm-2 S-1)叠加在红光上时，新的叶柄倾斜向上生长，叶片平坦而水平。叶片的定位既需要光敏素1(PHI1)，也需要非光性下胚轴3(NPH3)，从而促进了植物的生长。在nph3突变体中，既没有发现最佳的叶片位置，也没有发现蓝光使叶片变平，蓝光诱导的生长促进作用显著减弱。当蓝光从0.1μm~(-2)S~(-1)增加到5μm~(-2)S~(-1)时，两个突变体都能诱导正常的叶位和叶片扁平，表明光信号开始发挥作用，并且光信号不依赖于光和NPH3。当植物受到来自侧面的蓝光(0.1molmolm-2 S-1)和来自上方的红光的照射时，新叶开始朝向蓝光源。我们显示了NPH3的组织表达及其通过盘绕结构域和C-末端区域的质膜定位。我们的结论是，NPH3介导的光刺激信号通过诱导最佳的叶片位置和叶片扁平来优化光感知效率，并促进植物的生长。

Appropriate leaf positioning is essential for optimizing photosynthesis and plant growth. We show here the regulation of leaf positioning under blue light stimuli. When one-week-old Arabidopsis seedlings grown under white light were transferred to red light (25 μmol m-2 s-1) for 5 days, new petioles that appeared were almost horizontal and their leaves were curled and slanted downward. However, when a weak blue light from above (0.1 μmol m-2 s-1) was superimposed on red light, the new petioles grew obliquely upward and the leaves were flat and horizontal. The leaf positioning required both phototropin1 (phot1) and non-phototropic hypocotyl 3 (NPH3), and resulted in enhanced plant growth. In an nph3 mutant, neither optimal leaf positioning nor leaf flattening by blue light was found, and blue light-induced growth enhancement was drastically reduced. When blue light was increased from 0.1 μmol m-2 s-1 to 5 μmol m-2 s-1,normal leaf positioning and leaf flattening were induced in both phot1 and nph3 mutants, suggesting that phot2 signaling became functional and that the signaling was independent of phot1 and NPH3 in these responses. When plants were irradiated with blue light (0.1 μmol m-2 s-1) from the side and red light from above, the new leaves became oriented toward the source of blue light. We showed the tissue expression of NPH3 and its plasma membrane localization via the coiled-coil domain and the C-terminus region. We conclude that NPH3-mediated phototropin signaling optimizes the efficiency of light perception by inducing both optimal leaf positioning and leaf flattening, and enhances plant growth.