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Biochemical Characterization of Arabidopsis Wild-Type and Mutant Phytochrome B Holoproteins

Tedd D. Elich and Joanne Chory
The Plant Cell
Vol. 9, No. 12 (Dec., 1997), pp. 2271-2280
DOI: 10.2307/3870584
Stable URL: http://www.jstor.org/stable/3870584
Page Count: 10
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Biochemical Characterization of Arabidopsis Wild-Type and Mutant Phytochrome B Holoproteins
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Abstract

Although phytochrome B (phyB) plays a particularly important role throughout the life cycle of a plant, it has not been studied in detail at the molecular level due to its low abundance. Here, we report on the expression, assembly with chromophore, and purification of epitope-tagged Arabidopsis phyB. In addition, we have reconstructed two missense mutations, phyB-4 and phyB-101, isolated in long hypocotyl screens. We show that mutant proteins phyB-4 and phyB-101 exhibit altered spectrophotometric and biochemical properties relative to the wild-type protein. In particular, we demonstrate that phyB-101 Pfr exhibits rapid nonphotochemical (dark) reversion to Pr that results in a lower photoequilibrium level of the active Pfr form. We conclude that this occurs in vivo as well because phyB-101 mutants are shown to lack an end-of-day-far-red hypocotyl elongation response that requires a stable Pfr species. We propose that this Pfr instability may be the primary molecular mechanism underlying the phyB-101 mutant phenotype.

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