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 en coding 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 d issecting 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) r eporter gene mediate high-amplitude circadian oscillations of the GUS trans cript in transgenic Arabidopsis. 5' deletion to -490 greatly reduces overal l transcript abundance while retaining a basal oscillation. Further deletio n to -299 abolishes preferential GUS expression in the evening. Taken toget her, these data indicate that clock-response elements contributing to high- amplitude Atger3 oscillations largely reside between -299 and -967. Histoch emical staining for GUS activity indicates that the Atger3 promoter is acti ve in cotyledons, young leaves, petioles, the inflorescence axis, pedicels, sepals, ovary, style and siliques but not in roots, petals and anthers.