Somers D. E., Quail P. H.
Department of Plant Biology, University of California, Berkeley, Berkeley, California 94720.
Plant Physiol. 1995 Feb;107(2):523-534. doi: 10.1104/pp.107.2.523.
Phytochrome wild-type gene-[beta]-glucuronidase (PHY-GUS) gene fusions were used in transgenic Arabidopsis to compare the activity levels and light regulation of the PHYA and PHYB promoters and to identify the photoreceptors mediating this regulation. In dark-grown seedlings, both promoters are 4-fold more active in shoots than in roots,but the PHYA promoter is nearly 20-fold more active than that of PHYB in both organs. In shoots, white light represses the activities of the PHYA and PHYB promoters 10- and 2-fold, respectively, whereas in roots light has no effect on the PHYA promoter but increases PHYB promoter activity 2-fold. Consequently, PHYA promoter activity remains higher than that of PHYB in light in both shoots (5-fold) and roots (11-fold). Experiments with narrow-waveband light and photomorphogenic mutants suggest that no single photoreceptor is necessary for full white-light-directed PHYA repression in shoots, but that multiple, independent photoreceptor pathways are sufficient alone or in combination. In contrast, phytochrome B appears both necessary and sufficient for a light-mediated decrease in PHYB activity in shoots, and phytochrome A mediates a far-red-light-stimulated increase in PHYB promoter activity. Together, the data indicate that the PHYA and PHYB genes are regulated in divergent fashion at the transcriptional level, both developmentally and by the spectral distribution of the prevailing light, and that this regulation may be important to the photosensory function of the two photoreceptors.
在转基因拟南芥中使用了光敏色素野生型基因与β-葡萄糖醛酸酶（PHY-GUS）基因的融合体，以比较PHYA和PHYB启动子的活性水平及光调节作用，并鉴定介导这种调节的光感受器。在黑暗中生长的幼苗中，两个启动子在地上部分的活性均比根中高4倍，但在两个器官中，PHYA启动子的活性比PHYB启动子高近20倍。在地上部分，白光分别使PHYA和PHYB启动子的活性降低10倍和2倍，而在根中，光对PHYA启动子没有影响，但使PHYB启动子的活性增加2倍。因此，在光照下，地上部分（5倍）和根中（11倍）的PHYA启动子活性仍然高于PHYB启动子。窄带光和光形态建成突变体的实验表明，对于地上部分完全由白光介导的PHYA抑制作用，单一光感受器并非必需，但多个独立的光感受器途径单独或组合起来就足够了。相比之下，光敏色素B似乎对于地上部分光介导的PHYB活性降低既是必需的也是充分的，而光敏色素A介导远红光刺激的PHYB启动子活性增加。总之，数据表明PHYA和PHYB基因在转录水平上以不同方式受到发育调节以及主要光照的光谱分布调节，并且这种调节可能对这两种光感受器的光感功能很重要。
