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Universität Bielefeld > Fakultät für Biologie > Chair of Molecular Cell Physiology > Research

The Role of SRR1 in the circadian system

SRR1 is a regulator of the circadian clock and esstential for flowering time control in non-inductive conditions

The endogenous clock not only serves as a daily timer but also as a calender.
Plants adjust the onset of flowering to the appropriate time of the year. For that, the endogenous clock keeps track of daylength that changes with seasons. Other important flowering signals are ambient temperature, length of the winter cold period, age of the plant and phytohormones such as gibberelic acid (GA). These environmental signals are mediated in a hierarchical manner through molecular signaling pathways that in the end either promotes or represses the expression of key floral integrator genes, called florigens.

SENSITIVITY TO RED LIGHT REDUCED (SRR1) is a protein that is involved in the mediation of red light signals as well as in regulation of the circadian clock. Core clock genes show a shortened period of expression in srr1-1 loss-of-function mutants, suggesting that the SRR1 protein is important for correct clock function.

The srr1 mutant shows altered circadian transcript oscillations.

In addition, srr1-1 mutants flower earlier than wt plants in a photoperiod-independent manner, meaning that they have a problem discriminating between non-inductive and inductive photoperiods.

Srr1-1 plants grown in non-inductive short days flower much earlier than the wildtype, due to upregulation of the florigen FT.

Flowering in Arabidopsis is triggered by the expression of the florigen FT. Expression of FT is tightly controlled by proteins that act as promoters or repressors to ensure that it is only expressed when the surrounding environment is suitable for flowering.

The role of SRR1 in this process is to prevent flowering until photoperiodic conditions are suitable for reproduction, by promoting the expression of genes that code for direct repressors of FT. These target genes are involved in different pathways regulating flowering, suggesting that SRR1 may act as a focal point to synchronize the flowering response.

SRR1 promotes expression of flowering regulators that directly repress the florigen FT.

SRR1 is thus a key protein in the regulation of flowering time, necessary to prevent plants from flowering prematurely under noninductive conditions.

We are now studying how SRR1 acts on the molecular level to integrate these signals. In addition, we are interested in how SRR1 acts to set the correct circadian period of the clock.

Project-related publications:
Johansson M, Staiger D (2014). SRR1 is essential to repress flowering in non-inductive conditions in Arabidopsis thaliana.
Journal of Experimental Botany 65, 5811-5822.

Johansson M, Staiger D (2015) Time to flower – Interplay between photoperiod and the circadian clock. Journal of Experimental Botany 66, 719-730.

Staiger D, Allenbach L, Salathia N, Fiechter V, Davis SJ, Millar AJ, Chory J, Fankhauser C (2003) The Arabidopsis SRR1 gene mediates phyB signaling and is important for normal circadian clock function. Genes and Development 17, 256-268.