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Mutations in the NPH1 locus of Arabidopsis disrupt the perception of phototropic stimuli

By Emmanuel Liscum and Winslow R. Briggs


The phototropic response is an important component of seedling establishment in higher plants because it orients the young seedlings for maximal photosynthetic light capture. Despite their obvious impoftance, little is known about the mechanisms underlying the perception and transduction of the light signals that induce phototropic curvatures. Here, we report the isolation of eight mutants of Arabidopsis that lack or have severely impaired phototropic responses. These nph (for Conphototropic hypocotyl) mutants comprise four genetic loci: nphl, nph2, nph3, and nph4. Physiological and biochemical characterization of the nphl allele series indicated that the NPHl locus may encode the apoprotein for a dualchromophoric or multichromophoric holoprotein photoreceptor capable of absorbing UV-A, blue, and green light and that this photoreceptor regulates all the phototropic responses of Arabidopsis. It appears that the NPHl protein is most likely a 120-kD plasma membrane-associated phosphoprotein because all of the nphl mutations negatively affected the abundance of this protein. In addition, the putative NPHl photoreceptor protein is genetically and biochemically distinct from the HY4 protein, which most likely acts as a photoreceptor for blue light-mediated hypocotyl growth inhibition. Furthermore, the NPHl and HY4 proteins are not functionally redundant because mutations in either gene alone affect only one physiological response but not the other, thus providing strong support for the hypothesis that more than one blue light photoreceptor is required for the normal growth and development of a seedling

Year: 1995
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