EID1, an F-box protein involved in phytochrome A-specific light signaling

Abstract

To perceive red and far-red light, plants have evolved specific photoreceptors called phytochromes. Even though the spectral properties of all phytochromes are very similar, they show a distinct mode of action. Here we describe EID1, a negatively acting component of the signaling cascade that shifts the responsiveness of the phytochrome A (phyA) signaling system associated with hypocotyl elongation from red to far-red wavelengths. EID1 is a novel nuclear F-box protein that contains a leucine zipper whose integrity is necessary for its biological function. EID1 most probably acts by targeting activated components of the phyA signaling pathway to ubiquitin-dependent proteolysis.

The Negatively Acting Factors EID1 and SPA1 Have Distinct Functions in Phytochrome A-Specific Light Signaling

“…Compared with the large number of mutants with reduced phyA responses, only two mutants, spa1 and eid1, showed enhanced phyA-specific light responses (Hoecker et al, 1998;Bü che et al, 2000;Dieterle et al, 2001). Both mutants accumulate normal levels of phyA, and phyA degradation in the mutants was not altered.…”

“…Under these light conditions, the wild type remained almost completely etiolated, whereas hypersensitive mutants should exhibit a clear photomorphogenic development with expanded cotyledons, an open hook, and a reduced hypocotyl elongation (Dieterle et al, 2001). In total, eight independent mutant lines were isolated after screening approximately 20,000 T-DNA and approximately 30,000 EMS lines obtained in a WS background and approximately 10,000 T-DNA lines in a Col background.…”

“…The resulting SPA1 protein should be terminated at this position instead of reaching its full length of 1,029 amino acids. The phenotype of the spa1 allele was compared with the phenotypes of the strong eid1-3 and the weak eid1-5 allele (Dieterle et al, 2001). The eid1-3 allele carries an insertion of a single basepair that leads to a frame shift at the 3Ј end of the open reading frame.…”

“…F-box proteins are components of so-called SCF (Skp1/Cdc53/F-box protein) complexes that function as ubiquitin ligases. Thus, EID1 most probably acts by targeting activated components of phyA-signaling pathway to ubiquitin-dependent proteolysis (Dieterle et al, 2001).…”

“…Thus, the HIR sensory system must be able to detect the amount of photons that reach the plant in a given time period. The action spectra of HIR show a maximum at approximately 720 nm, a wavelength that completely inhibits responses of the light-stable phytochromes (Mancinelli, 1994;Furuya and Schäfer, 1996;Neff et al, 2000;Dieterle et al, 2001).…”