Premium
Constitutive, light‐responsive and circadian clock‐responsive factors compete for the different I box elements in plant light‐regulated promoters
Author(s) -
Borello Ugo,
Ceccarelli Elena,
Giuliano Giovanni
Publication year - 1993
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1993.04040611.x
Subject(s) - promoter , circadian clock , circadian rhythm , biology , transcription factor , e box , transcription (linguistics) , genetics , microbiology and biotechnology , gene , gene expression , endocrinology , linguistics , philosophy
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 I box 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 diurnally 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.