Editors' ChoiceCircadian Rhythms

The Flowering Clock

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Science's STKE  10 Sep 2002:
Vol. 2002, Issue 149, pp. tw334-TW334
DOI: 10.1126/stke.2002.149.tw334

Plants respond to changes in the duration of the daylight by altering their reproductive and vegetative growth periods. Doyle et al. specifically investigated how the EARLY FLOWERING 4 (ELF4) gene influences flowering time in the model plant Arabidopsis. Plants in which the elf4 gene is mutated flower early when grown under short-day conditions, compared with wild-type plants that undergo the floral transition. Doyle et al. cloned ELF4 and analyzed its expression, which showed that ELF4 has a periodic expression in plants grown in continuous light, but not in plants grown in continuous dark. Using plants with reporters for the expression of genes involved in the circadian plant cycle, plants with the elf4 mutation were shown to became arrhythmic or only weakly rhythmic with respect to the expression of the reporter containing the chlorophyll a/b-binding protein (CAB) gene promoter and the reporter containing the cold- and circadian-regulated (CCR) gene reporter. The circadian rhythm of the elf4 mutants is lost after one 24-hour cycle, not immediately after transition to continuous dark or continuous light, which occurs in other elf mutants. Furthermore, the expression of a reporter for the CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) gene was repressed compared with that in wild-type plants. CCA1 is normally expressed shortly after dawn. Another gene with disrupted expression was CONSTANS (CO) gene, which was elevated in the elf4 mutants and which is a promoter of floral induction. Whether the floral transition phenotype is solely due to the effects of ELF4 on the CO floral inducer or whether its effects on the circadian oscillator CCA1 are also important remains to be determined.

M. R. Doyle, S. J. Davis, R. M. Bastow, H. G. McWatters, L. Kozma-Bognár, F. Nagy, A. J. Millar, R. M. Amasino, The ELF4 gene controls circadian rhythms and flowering time in Arabidopsis thaliana. Nature 419, 74-77 (2002). [Online Journal]

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