Staneloni Roberto J, Rodriguez-Batiller María José, Legisa Danilo, Scarpin María R, Agalou Adamantia, Cerdán Pablo D, Meijer Annemarie H, Ouwerkerk Pieter B F, Casal Jorge J
Fundación Instituto Leloir, Instituto de Investigaciones Bioquímicas Buenos Aires, Consejo Nacional de Investigaciones Cientificas y Técnicas and Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1405BWE Buenos Aires, Argentina.
Proc Natl Acad Sci U S A. 2009 Aug 11;106(32):13624-9. doi: 10.1073/pnas.0906598106. Epub 2009 Jul 28.
Plant responses mediated by phytochrome A display a first phase saturated by transient light signals and a second phase requiring sustained excitation with far-red light (FR). These discrete outcomes, respectively so-called very-low-fluence response (VLFR) and high-irradiance response (HIR), are appropriate in different environmental and developmental contexts but the mechanisms that regulate the switch remain unexplored. Promoter analysis of a light-responsive target gene revealed a motif necessary for HIR but not for VLFR. This motif is required for binding of the Bell-like homeodomain 1 (BLH1) to the promoter in in vitro and in yeast 1-hybrid experiments. Promoter substitutions that increased BLH1 binding also enhanced HIR. blh1 mutants showed reduced responses to continuous FR and to deep canopy shadelight, but they retained normal responses to pulsed FR or red light and unfiltered sunlight. BLH1 enhanced BLH1 expression and its promotion by FR. We conclude that BLH1 specifically regulates HIR and not VLFR of phytochrome A.
由光敏色素A介导的植物反应表现出一个由瞬时光信号饱和的第一阶段和一个需要远红光（FR）持续激发的第二阶段。这些不同的结果，分别被称为极低光响应（VLFR）和高辐照响应（HIR），在不同的环境和发育背景下是合适的，但调节这种转换的机制仍未被探索。对一个光响应靶基因的启动子分析揭示了一个对HIR而非VLFR必需的基序。在体外和酵母单杂交实验中，这个基序是类Bell同源结构域1（BLH1）与启动子结合所必需的。增加BLH1结合的启动子替换也增强了HIR。blh1突变体对连续FR和深层冠层遮荫光的反应减弱，但它们对脉冲FR或红光以及未过滤的阳光仍保持正常反应。BLH1增强了BLH1的表达及其受FR的促进作用。我们得出结论，BLH1特异性地调节光敏色素A的HIR而非VLFR。
