Control of hypocotyl elongation in Arabidopsis thaliana by photoreceptor interaction

Abstract

In order to test the interaction of different phytochromes and blue-light receptors, etiolated seedlings of wild-type Arabidopsis thaliana (L.) Heynh., a phytochrome (phy) B-overexpressor line (ABO), and the photoreceptor mutants phyA-201, phyB-5, hy4-2.23n, fha-1, phyA-201/phyB-5, and phyA-201/hy4-2.23n were exposed to red and far-red light pulses after various preirradiations. The responsiveness to the inductive red pulses is primarily mediated by phyB which is rather stable in its far-red-absorbing form as demonstrated by a very slow loss of reversibility. Without preirradiation the red pulses had an impact on hypocotyl elongation only in PHYA mutants but not in the wild type. This indicates a suppression of phyB function by the presence of phyA. Preirradiation with either far-red or blue light resulted in an inhibition of hypocotyl elongation by red pulses in the wild type. Responsiveness amplification by far-red light is mediated by phyA and disappears slowly in the dark. The extent of responsiveness amplification by blue light was identical in the wild type and in the absence of phyA, or the cryptochromes cryl (hy4-2.23n) or cry2 (fha-1). Therefore, we conclude that stimulation of phyB by blue light preirradiation is either mediated by an additional still-unidentified blue-light-absorbing pigment or that phyA, cry1 and cry2 substitute for each other completely. Both blue and red preirradiation established responsiveness to red pulses in phyA-201/phyB-5 double mutants. These results demonstrate that inhibition of hypocotyl elongation by red pulses is not only mediated by phyB but also by a phytochrome(s) other than phyA and phyB.

Photobody Localization of Phytochrome B Is Tightly Correlated with Prolonged and Light-Dependent Inhibition of Hypocotyl Elongation in the Dark

“…It is well known that the Pfr of phyB has a relatively slow dark reversion rate and that it can persist into darkness; these properties of phyB play a pivotal role in hypocotyl growth inhibition under diurnal conditions (Hennig et al, 1999;Rausenberger et al, 2010). This is best demonstrated by end-of-day FR treatment, in which an FR light pulse is applied at dusk to inactivate phyB to its Pr.…”

“…The circadian clock mediates an increase in PIF4 and PIF5 gene expression at the end of the night (Nozue et al, 2007;Leivar et al, 2012a;Soy et al, 2012). In parallel, because of the slow dark reversion rate of phyB (Hennig et al, 1999;Rausenberger et al, 2010), photoactivated phyB persists into the night to inhibit the accumulation of PIFs (Nozue et al, 2007;Soy et al, 2012Soy et al, , 2014. Based on these recent results, it would be interesting to investigate whether photobodies are required for phyB-mediated hypocotyl growth inhibition and PIF stability in the dark.…”

The Mediator Complex Subunit PFT1 Interferes with COP1 and HY5 in the Regulation of Arabidopsis Light Signaling

“…8A): first, PFT1 mainly functions as a positive factor in light signaling downstream of phyA; second, PFT1 mediates phyA-dependent inhibition of phyB-controlled light responses that have been described in several studies (Hennig et al, 1999(Hennig et al, , 2001Cerdán and Chory, 2003); and third, phyB should be able to stimulate light-dependent gene expression on at least two separate pathways, one of which should be negatively regulated by PFT1 in a phyA-dependent manner, whereas the second should have a stimulatory effect on PFT1-dependent light signaling. The first pathway might be related to the phyB-dependent degradation of phytochrome-interacting factors (negative regulators of light signaling) or another positively acting pathway functioning on the level of transcriptional regulation.…”

BAS1 : A gene regulating brassinosteroid levels and light responsiveness in Arabidopsis

“…All affect gross morphological changes in the seedling as it makes the transition from heterotrophic growth in the dark to photoautotrophic growth in the light (1). Genetic analyses demonstrate a complex web of interactions between these photoreceptor signaling pathways (2)(3)(4)(5).…”