Photocontrol of subcellular partitioning of phytochrome-B : GFP fusion protein in tobacco seedlings

Photomorphogenesis of higher plants is regulated by photoreceptors includin g the red/far-red light-absorbing phytochromes, blue-UV/A sensing cryptochr omes and as yet uncharacterized UV/B receptors. Specific phototransduction pathways that are controlled by either individual or interacting photorecep tors mediate regulation. Phytochrome B (phyB) is the major red light-sensin g photoreceptor. Phototransduction mediated by this light sensor has been s hown to include light-dependent nuclear import and interaction of phyB with transcription factor-like proteins in the nucleus. Here we report that nuc lear import of phyB and physiological responses regulated by this photorece ptor exhibit very similar wavelength- and fluence rate-dependence. Nuclear import of phyB is insensitive to single red, blue and far-red light pulses. It is induced by continuous red light and to a lesser extent by continuous blue light, whereas far-red light is completely ineffective. The data pres ented indicate that light-dependent partitioning of phyB exhibits features characteristic of blue light responsiveness amplification, a phenomenon tha t is thought to be mediated by interaction of phyB with CRY1.