SENSITIVE TO FREEZING 6 (SFR6) integrates cellular and environmental inputs to the plant circadian clock

Heather Knight , Adrian J.W. Thomson , and Harriet G. McWatters ^*

School of Biological & Biomedical Sciences, Durham University, Durham, DH1 3LE, United Kingdom; Institute of Molecular Plant Sciences, University of Edinburgh, Edinburgh, EH9 3JH, United Kingdom; Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, United Kingdom

^* Corresponding author; email: Harriet.McWatters{at}plants.ox.ac.uk.

The sensitive to freezing 6 (sfr6) mutant of Arabidopsis thalianais late flowering in long days due to reduced expression ofcomponents in the photoperiodic flowering pathway in long dayphotoperiods. Microarray analysis of gene expression showedthat a circadian clock-associated motif, the evening element,was over-represented in promoters of genes down-regulated insfr6 plants. Analysis of leaf movement rhythms found sfr6 plantsshowed a sucrose-dependent long period phenotype; unlike wildtype Arabidopsis, the clock in sfr6 plants did not have a shorterrhythm in the presence of sucrose. Other developmental responsesto sucrose were unaltered in sfr6 plants, suggesting insensitivityto sucrose is restricted to the clock. We investigated the effectof sfr6 and sucrose upon clock gene expression over twenty-fourhours. The sfr6 mutation resulted in reduced expression of theclock components CIRCADIAN CLOCK ASSOCIATED 1, GIGANTEA andTIMING OF CAB1. These changes occurred independently of sucrose-supplementation.Wild type plants showed small increases clock gene expressionin the presence of sucrose; this response to sucrose was reducedin sfr6 plants. This study shows that large changes in leveland timing of clock gene expression may have little effect uponclock outputs. Moreover, although sucrose influences the periodand accuracy of the Arabidopsis clock it results in relativelyminor changes in clock gene expression.