Blue and UV-A light-regulated CHS expression in Arabidopsis independent of phytochrome A and phytochrome B

Light plays a fundamental role in the development of higher plants. It influences the activity of many genes and is sensed through at least three different photoreceptor systems (phytochromes, blue/UV-A- and UV-B photoreceptors). In contrast to UV-B and blue/UV-A photoreceptors, phytochromes absorb both in the long-wavelength (red and far-red) and short-wavelength region of light, making it extremely difficult to differentiate the exact function of different photoreceptors in the blue/UV region. The availability of phytochrome mutants in combination with a transgenic approach has enabled clarification of the question whether or not phytochromes are a prerequisite for the action of blue/UV-A photoreceptors on gene expression. This paper reports that the light-responsive element of a gene encoding chalcone synthase, the key enzyme of the flavonoid pathway, mediates blue-and UV-A-induced transcription in the absence of phytochrome A and phytochrome B.