Trends in Plant Science
Volume 4, Issue 4, 1 April 1999, Pages 125-126
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Phytochromes, pif3 and light signalling go nuclear

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Components of phytochrome A- and B-controlled signalling

The regulation of photomorphogenesis and physiological responses is achieved by fine tuning the expression of a large number of genes. One of the key aims of research into photomorphogenesis has been to unravel the molecular mechanism by which the photoreceptors convert the light signal into inductive or repressive signals. Several approaches have been adopted to obtain a more detailed insight into these processes, especially those in which phyA and phyB exert control at the level of gene

Isolation of pif3, the first phytochrome interacting protein

The research group led by Peter Quail used a different approach to tackle this problem. Previous studies had shown that the C-terminal regions of phyA and phyB, containing two PAS-like domains, are interchangeable and might be involved in signal transmission from phytochrome to a putative partner molecule11. To identify this hypothetical signal-receiving protein they performed a yeast two-hybrid screen using the C-terminal domain of phyB as bait and identified a new type of basic

PIF3 is nuclear localized but what about phyA and phyB?

Apart from the question of how this interaction occurs, additional experiments performed with PIF3 created a degree of controversy regarding the question of where this interaction takes place. Peter Quail's group showed that PIF3 is apparently constitutively localized in the nuclei (Fig. 1). They, therefore, suggested that PIF3 interacts with phyA or phyB in the nucleus and that early events in the phyA- and phyB-mediated signalling pathway take place in the nuclei. However, this scenario

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