TheArabidopsis SRR1gene mediates phyB signaling and is required for normal circadian clock function

Abstract

Plants possess several photoreceptors to sense the light environment. In Arabidopsis cryptochromes and phytochromes play roles in photomorphogenesis and in the light input pathways that synchronize the circadian clock with the external world. We have identified SRR1 (sensitivity to red light reduced), a gene that plays an important role in phytochrome B (phyB)-mediated light signaling. The recessive srr1 null allele and phyB mutants display a number of similar phenotypes indicating that SRR1 is required for normal phyB signaling. Genetic analysis suggests that SRR1 works both in the phyB pathway but also independently of phyB. srr1 mutants are affected in multiple outputs of the circadian clock in continuous light conditions, including leaf movement and expression of the clock components, CCA1 and TOC1. Clock-regulated gene expression is also impaired during day-night cycles and in constant darkness. The circadian phenotypes of srr1 mutants in all three conditions suggest that SRR1 activity is required for normal oscillator function. The SRR1 gene was identified and shown to code for a protein conserved in numerous eukaryotes including mammals and flies, implicating a conserved role for this protein in both the animal and plant kingdoms.

The evolutionary conserved BER1 gene is involved in microtubule stability in yeast

“…This is in agreement with observations made during large-scale analyses of protein localization (Huh et al 2003). A similar subcellular localisation was reported for SRR1-GFP in Arabidopsis (Staiger et al 2003). However, no enrichment of the signal was seen on microtubules or at kinetochores.…”

“…Future experiments will address this hypothesis biochemically and hopefully identify the targets of Ber1p activity. Such experiments may allow us to shed light on the biochemical function of other members of the SRR1 family, in particular Arabidopsis SRR1 for which genetic studies have shown that it is involved in light perception and circadian rhythms (Staiger et al 2003). Proteasome subunits are heavily N-acetylated (Csank et al 2002) and the proteasome is very important for light perception and circadian rhythms in Arabidopsis (Hellmann and Estelle 2002;Mas 2005).…”

“…shows synthetic lethality with kinetochore and spindle checkpoint genes SRR1-related proteins encoded by single copy genes can be identiWed in most eukaryotes for which genome information is available (Staiger et al 2003). All the proteins presented on our alignment ( Fig.…”

“…It is also required for normal circadian rhythms (Staiger et al 2003). Remarkably, this gene is conserved in eukaryotes, where it is found as single copy gene without any recognizable functional domain.…”

Signalling for developmental plasticity

“…The sensitivity to red light reduced 1 (srr1) mutant (SRR1, GenBank Accession number NM125348) shows a de-etiolation phenotype that is weaker and a leaf rhythm phenotype that is stronger than that of the phyB mutant [21]. One possibility is that SRR1 is involved in two different but connected molecular functions, one in light signalling and the other in circadian rhythms.…”