Unexpected roles for cryptochrome 2 and phototropin revealed by high-resolution analysis of blue light-mediated hypocotyl growth inhibition

Folta, KM Spalding, EP

Km. Folta et Ep. Spalding, Unexpected roles for cryptochrome 2 and phototropin revealed by high-resolution analysis of blue light-mediated hypocotyl growth inhibition, PLANT J, 26(5), 2001, pp. 471-478

33

INGLESE

Article

Plant Sciences","Animal & Plant Sciences

PLANT JOURNAL

0960-7412 → ACNP

26

5

2001

471 - 478

ISI

0960-7412(200106)26:5<471:URFC2A>2.0.ZU;2-1

Blue light (BL) rapidly and strongly inhibits hypocotyl elongation during t he photomorphogenic response known as de-etiolation, the transformation of a dark-grown seedling into a pigmented, photoautotrophic organism. In Arabi dopsis thaliana, high-resolution studies of hypocotyl growth accomplished b y computer-assisted electronic image capture and analysis revealed that inh ibition occurs in two genetically independent phases, the first beginning w ithin 30 sec of illumination. The present work demonstrates that phototropi n (nph1), the photoreceptor responsible for phototropism, is largely respon sible for the initial, rapid inhibition. Signaling from phototropin during the curvature response is dependent upon interaction with NPH3, but the res ults presented here demonstrate that NPH3 is not necessary for phototropin- dependent growth inhibition. Activation of anion channels, which transientl y depolarizes the plasma membrane within seconds of BL, is an early event i n the cryptochrome signaling pathway leading to a phase of growth inhibitio n that replaces the transient phototropin-dependent phase after approximate ly 30 min of BL. Surprisingly, cry1 and cry2 were found to contribute equal ly and non-redundantly to anion-channel activation and to growth inhibition between 30 and 120 min of BL. Inspection of the inhibition kinetics displa yed by nph1 and nph1cry1 mutants revealed that the cryptochrome phase of in hibition is delayed in seedlings lacking phototropin. This result indicates that BL-activation of phototropin influences cryptochrome signaling leadin g to growth inhibition. Mutations in the NPQ1 gene, which inhibit BL-induce d stomatal opening, do not affect any aspect of the growth inhibition withi n the first 120 min examined here, and NPQ1 does not affect the activation of anion channels.