Figure 4.

HY5 regulates CBF3 expression in response to the plastid signal. A, Plants were grown in short-day conditions (9/15 h light/dark), and 3-week-old plants were analyzed for CBF1 to CBF3 (At4g25490, At4g25470, and At4g25480) expression following 12 h of feeding with 50 µm Mg-ProtoIX. B, CBF3 (At4g25480) expression 6 h into the light period in wild-type Col, crd, hy5, and hy5 crd. CBF3 expression was significantly different in crd and hy5 compared with Col and in hy5 crd compared with crd. C, Plants were kept in constant light for 27 h, and then samples were collected 9 h after the subjective dawn at ZT 57 and analyzed for CBF3 (At4g25480) expression. Following constant light treatment, no significant difference could be observed between Col, crd, and hy5 gene expression. All gene expression data were normalized to ubiquitin-like protein (UBI; At4g36800) and related to the amount present in wild-type Col. Each data point represents the mean ± sd of at least three biological replicates. Statistical differences were calculated using Student’s t test: ***, P < 0.001.