Phototropin, RPT2, NPH3 and stomatal opening.


RPT2 is a signal transducer involved in phototropic response and stomatal opening by association with phototropin 1 in Arabidopsis thaliana

by Inada S., Ohgishi M., Mayama T., Okada K., Sakai T. (2004)

RIKEN Plant Science Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan.

in Plant Cell 16, 887–896 (2004). –

Stomatal Opening under Blue Light in Wild-Type Plants (Ler and WS) and Mutants. Stomatal apertures were measured after 1-h incubation in the dark (Dark) and then after 2-h incubation under red light (50 μmol·m−2·s−1; RL) or under blue light (10 μmol·m−2·s−1) in a red light background (RL + BL). Each bar represents an average of three experiments (20 measurements each) ±sd. –


Phototropin 1 (phot1) and phot2, which are blue light receptor kinases, function in blue light-induced hypocotyl phototropism, chloroplast relocation, and stomatal opening in Arabidopsis (Arabidopsis thaliana).

Previous studies have shown that the proteins RPT2 (for ROOT PHOTOTROPISM2) and NPH3 (for NONPHOTOTROPIC HYPOCOTYL3) transduce signals downstream of phototropins to induce the phototropic response. However, the involvement of RPT2 and NPH3 in stomatal opening and in chloroplast relocation mediated by phot1 and phot2 was unknown.

Genetic analysis of the rpt2 mutant and of a series of double mutants indicates that RPT2 is involved in the phot1-induced phototropic response and stomatal opening but not in chloroplast relocation or phot2-induced movements.

Biochemical analyses indicate that RPT2 is purified in the crude microsomal fraction, as well as phot1 and NPH3, and that RPT2 makes a complex with phot1 in vivo.

On the other hand, NPH3 is not necessary for stomatal opening or chloroplast relocation. Thus, these results suggest that phot1 and phot2 choose different signal transducers to induce three responses: phototropic response of hypocotyl, stomatal opening, and chloroplast relocation.


Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.

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