Somers D E, Quail P H
Department of Plant Biology, University of California, Berkeley 94720.
Plant J. 1995 Mar;7(3):413-27. doi: 10.1046/j.1365-313x.1995.7030413.x.
Phytochromes A and B have discrete photosensory functions in Arabidopsis. To determine whether differential temporal or spatial expression patterns of the PHYA and PHYB genes contribute to this phenomenon the expression of PHYA-GUS and PHYB-GUS reporter genes has been examined in transgenic Arabidopsis. Histochemical and quantitative biochemical analyses indicate that both transgenes are expressed extensively throughout the plant, including roots, shoots and flowers, during the entire life cycle, but with strong differences between the two in expression level and photoregulation, and more limited differences in spatial expression patterns. The data indicate that regulation is at the transcriptional level. In dry seed, PHYB-GUS is expressed throughout the embryo at three-fold higher levels than PHYB-GUS, which is confined primarily to the embryonic root tip. By contrast, PHYA promoter activity, despite strong negative regulation in shoots by light, is consistently higher than PHYB (two- to 20-fold) in both the light and dark in most tissues during all subsequent developmental phases, from seedling to mature adult. At the tissue level, most cells appear to express both transgenes at some level at all stages examined, with highest apparent activity in vascular tissue and root tips. With the notable exception of pollen, where high PHYB-GUS but not PHYA-GUS expression occurs, few major differences are observed in the quantitative spatial distribution pattern between the two transgenes. The strongly similar spatial and temporal expression patterns of PHYA-GUS and PHYB-GUS transgenes suggest that the differential photosensory activity of these two phytochromes occurs largely through differences in their (i) intrinsic biochemical activities, (ii) relative abundances, and/or (iii) independent and separate reaction partners, rather than through discrete, developmentally controlled expression patterns.
光敏色素A和B在拟南芥中具有不同的光感受功能。为了确定PHYA和PHYB基因的差异时空表达模式是否导致了这一现象，我们检测了转基因拟南芥中PHYA-GUS和PHYB-GUS报告基因的表达。组织化学和定量生化分析表明，这两个转基因在整个生命周期中都在植物的各个部位广泛表达，包括根、茎和花，但两者在表达水平和光调节方面存在显著差异，在空间表达模式上的差异则较为有限。数据表明调控发生在转录水平。在干种子中，PHYB-GUS在整个胚中表达，其水平比主要局限于胚根尖端的PHYA-GUS高3倍。相比之下，尽管PHYA启动子活性在茎中受到光的强烈负调控，但在从幼苗到成熟植株的所有后续发育阶段，在大多数组织中，无论光照还是黑暗条件下，其活性始终高于PHYB（2至20倍）。在组织水平上，在所有检测阶段，大多数细胞似乎都在一定程度上表达这两个转基因，在维管组织和根尖中表现出最高的活性。除了花粉中出现高PHYB-GUS表达而无PHYA-GUS表达这一显著例外，在这两个转基因的定量空间分布模式上几乎没有观察到重大差异。PHYA-GUS和PHYB-GUS转基因在时空表达模式上的高度相似表明，这两种光敏色素的差异光感受活性很大程度上是通过它们（i）内在生化活性、（ii）相对丰度和/或（iii）独立且分离的反应伙伴的差异产生的，而不是通过离散的、发育控制的表达模式。
