Sullivan Stuart, Hart Jaynee E, Rasch Patrick, Walker Catriona H, Christie John M
Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow Glasgow, UK.
Front Plant Sci. 2016 Mar 11;7:290. doi: 10.3389/fpls.2016.00290. eCollection 2016.
Hypocotyl phototropism of etiolated Arabidopsis seedlings is primarily mediated by the blue-light receptor kinase phototropin 1 (phot1). Phot1-mediated curvature to continuous unilateral blue light irradiation (0.5 μmol m(-2) s(-1)) is enhanced by overhead pre-treatment with red light (20 μmol m(-2) s(-1) for 15 min) through the action of phytochrome (phyA). Here, we show that pre-treatment with blue light is equally as effective in eliciting phototropic enhancement and is dependent on phyA. Although blue light pre-treatment was sufficient to activate early phot1 signaling events, phot1 autophosphorylation in vivo was not found to be saturated, as assessed by subsequently measuring phot1 kinase activity in vitro. However, enhancement effects by red and blue light pre-treatment were not observed at higher intensities of phototropic stimulation (10 μmol m(-2) s(-1)). Phototropic enhancement by red and blue light pre-treatments to 0.5 μmol m(-2) s(-1) unilateral blue light irradiation was also lacking in transgenic Arabidopsis where PHOT1 expression was restricted to the epidermis. Together, these findings indicate that phyA-mediated effects on phot1 signaling are restricted to low intensities of phototropic stimulation and originate from tissues other than the epidermis.
黄化拟南芥幼苗的下胚轴向光性主要由蓝光受体激酶向光素1（Phot1）介导。通过phytochrome（phyA）的作用，用红光（20 μmol m(-2) s(-1) 处理15分钟）进行顶光预处理可增强Phot1介导的对连续单侧蓝光照射（0.5 μmol m(-2) s(-1)）的弯曲。在此，我们表明蓝光预处理在引发向光性增强方面同样有效，且依赖于phyA。尽管蓝光预处理足以激活早期Phot1信号事件，但通过随后体外测量Phot1激酶活性评估发现，体内Phot1自身磷酸化未达到饱和。然而，在较高强度的向光性刺激（10 μmol m(-2) s(-1)）下未观察到红光和蓝光预处理的增强效应。在Phot1表达仅限于表皮的转基因拟南芥中，对0.5 μmol m(-2) s(-1)单侧蓝光照射的红光和蓝光预处理的向光性增强也不存在。这些发现共同表明，phyA介导的对Phot1信号的影响仅限于低强度的向光性刺激，且起源于表皮以外的组织。
