Seminars

Many plants measure changes in day length in order to coordinate their development with the most favorable seasons. In Arabidopsis thaliana, precise timing of CONSTANS (CO) gene expression is necessary for day-length measurement for photoperiodic flowering. The FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1) and GIGANTEA (GI) proteins regulate CO transcription by regulating the stability of CO transcriptional repressor, CYCLING DOF FACTOR 1 (CDF1). Currently, the CDF family is the only known transcription factor family that directly regulates the CO expression. It is improbable that CDFs are the only transcription factors that regulate CO expression. Therefore, we performed yeast one-hybrid screening to search for additional transcriptional regulators and isolated a bHLH transcription factor named FLOWERING BHLH 1 (FBH1). Overexpressors of FBH1 increased CO expression levels and caused early flowering regardless of day-length. In addition, FBH1 associated with the CO chromatin in vivo, indicating that FBH1 directly regulates CO transcription. Our data suggest that both repressors and an activator precisely control the timing of daily CO expression.
 
References:
Song, Ito, and Imaizumi (2010) Curr Opin Plant Biol 5:594-603
Sawa, Nusinow, Kay, and Imaizumi (2007) Science 318:261-265
Imaizumi, Schultz, Harmon, Ho, and Kay (2005) Science 309:293-297