The Atger3 promoter confers circadian clock-regulated transcription with peak expression at the beginning of the night.

In Arabidopsis thaliana, steady-state abundance of the Atger3 transcript encoding a germin-like cell wall protein follows a circadian rhythm, reaching its highest level at the beginning of the night. As a first step towards dissecting the molecular mechanisms underlying these transcript oscillations, the Atger3 genomic locus was characterised. Transcriptional fusions of 1.8 kb and 967 bp Atger3 promoter fragments to the beta-glucuronidase (GUS) reporter gene mediate high-amplitude circadian oscillations of the GUS transcript in transgenic Arabidopsis. 5' deletion to -490 greatly reduces overall transcript abundance while retaining a basal oscillation. Further deletion to -299 abolishes preferential GUS expression in the evening. Taken together, these data indicate that clock-response elements contributing to high-amplitude Atger3 oscillations largely reside between -299 and -967. Histochemical staining for GUS activity indicates that the Atger3 promoter is active in cotyledons, young leaves, petioles, the inflorescence axis, pedicels, sepals, ovary, style and siliques but not in roots, petals and anthers.