Abstract
Flowering time of summer annual Arabidopsis thaliana accessions is largely determined by the timing of FLOWERING LOCUS T (FT) expression in the leaf vasculature. To understand the complex interplay between activating and repressive inputs controlling flowering through FT, cis-regulatory sequences of FT were identified in this study. A proximal and an approximately 5-kb upstream promoter region containing highly conserved sequence blocks were found to be essential for FT activation by CONSTANS (CO). Chromatin-associated protein complexes add another layer to FT regulation. In plants constitutively overexpressing CO, changes in chromatin status, such as a decrease in binding of LIKE HETEROCHROMATIN PROTEIN1 (LHP1) and increased acetylation of H3K9 and K14, were observed throughout the FT locus, although these changes appear to be a consequence of FT upregulation and not a prerequisite for activation. Binding of LHP1 was required to repress enhancer elements located between the CO-controlled regions. By contrast, the distal and proximal promoter sequences required for FT activation coincide with locally LHP1 and H3K27me3 depleted chromatin, indicating that chromatin status facilitates the accessibility of transcription factors to FT. Therefore, distant regulatory regions are required for FT transcription, reflecting the complexity of its control and differences in chromatin status delimit functionally important cis-regulatory regions.
Highlights
The transition to flowering is controlled by genetic pathways that integrate environmental cues and the developmental state of the plant
Expanding the alignment with homologous sequences of Sisymbrium polyceratum, Brassica oleracea, Capsella rubella, and Arabis hirsuta revealed highly conserved sequence stretches within block A of the Aa FT2 and Aa FT3 genes and in the promoter sequence of A. thaliana TWIN SISTER OF FT (TSF) (Figure 1C)
Block B is located around 1.8 kb upstream of FLOWERING LOCUS T (FT) and contains two highly conserved sequence stretches that include an E-box, which is a binding site for many basic-helix-loop-helix proteins like Cryptochromeinteracting bHLH 1 (CIB1), which has been shown to enhance FT expression in response to blue light (Liu et al, 2008; Figure 1D)
Summary
The transition to flowering is controlled by genetic pathways that integrate environmental cues and the developmental state of the plant. In Arabidopsis thaliana, several floral signals, including response to photoperiod, converge at the level of transcriptional regulation of the FLOWERING LOCUS T (FT) gene. Under inductive long-day (LD) conditions, the floral integrator FT is transcribed in the leaf vasculature (Takada and Goto, 2003; Notaguchi et al, 2008). Misexpression of FT causes early flowering independent of environmental and endogenous stimuli, whereas loss of function of FT results in a severe late-flowering phenotype in LDs and has just a minor effect on flowering under noninductive short-day (SD) conditions (Koornneef et al, 1991; Kardailsky et al, 1999; Kobayashi et al, 1999).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
