The I box is a conserved regulatory motif which is found upstream of plant genes (rbcS, cab and nia) whose transcription is regulated by light and the circadian clock. Gel retardation and UV cross-linking assays were used to resolve two different groups of I box binding factors (IBFs) in tomato nuclear extracts. Active components of the first group (IBF-1) recognize the I box of the light-responsive rbcS promoter; one factor within this group, IBF-1a, also recognizes the adjacent G box, which has been shown previously to bind a different class of plant transcription factors, the G box binding factors (GBFs). To the limit of experimental resolution, IBF-1a and GBF compete for the same nucleotides on the G box. Nevertheless, these two activities are biochemically and immunologically distinct. The relative abundance of IBF-1a shows a vast decrease in dark-adapted plants. Factors in the second group (IBF-2), recognize the I box of the nia promoter, which is regulated both by light and the circadian clock; one factor within this group, IBF-2a, also binds the Ibox of a second promoter showing similar regulation, the cab promoter. The IBF-2a binding sites on the cab and nia promoters show extensive homology to a circadian clock-responsive promoter element from wheat. The abundance of IBF-2a is diumally regulated and shows a dramatic induction around the onset of the light period. Transfer of the plants in continuous darkness demonstrates that this induction is under the control of a circadian clock. These data suggest that I box binding factors may be involved in regulation of transcription by light and the circadian clock.
|Pages (from-to)||611 - 619|
|Number of pages||9|
|Publication status||Published - 1993|
All Science Journal Classification (ASJC) codes
- Plant Science
- Cell Biology
Borello, U., Ceccarelli, E., & Giuliano, G. (1993). Constitutive, light-responsive and circadian clock-responsive factors compete for the different I box elements in plant light-regulated promoters. Plant Journal, 4(4), 611 - 619. https://doi.org/10.1046/j.1365-313X.1993.04040611.x