Plant growth and phenotypic analyses

The Arabidopsis thaliana plants used in this study were of the Col-0 ecotype. The T-DNA insertion mutant erf (Stock No: {"type":"entrez-nucleotide","attrs":{"text":"CS849696","term_id":"162808119","term_text":"CS849696"}}CS849696) was obtained from The Arabidopsis Information Resource (TAIR; https://www.arabidopsis.org/) and confirmed by genotyping, PCR, and RT-PCR (Supplementary Fig. S1 at JXB online). All seeds were surface-sterilised and sown on half-strength Murashige and Skoog (MS) medium containing 1.5% sucrose and 0.7% agar, and incubated at 4 °C under dark conditions for 3 d. The plates were then irradiated with white light for 6 h to promote germination and subsequently kept either in darkness set periods of time or under continuous red light (60 µmol m^–2 s^–1), far-red light (5 µmol m^–2 s^–1), blue light (7 µmol m^–2 s^–1), or white light (60 µmol m^–2 s^–1) for 5 d. For the light-to-dark transition experiments, seedlings were grown under continuous light or dark conditions for 7 d, and then transferred to the opposite conditions for set periods of time. For cycloheximide (CHX) treatment, seedlings were grown in continuous light for 7 d, transferred to plates containing half-strength MS medium with or without 100 μM CHX, and then placed in the light or darkness for set periods of time. The seedlings were then collected for experimental use.

Images of the hook and hypocotyl phenotypes of seedlings were obtained using an EOS60D digital camera (Canon, Japan). Cell length was determined using a confocal laser-scanning microscope (LSM700; Zeiss, Germany). Hypocotyl length and cell length were measured using the ImageJ software (https://imagej.nih.gov/ij/).