IDENTIFICATION OF AN ARABIDOPSIS-THALIANA RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE ACTIVASE (RCA) MINIMAL PROMOTER REGULATED BY LIGHT AND THE CIRCADIAN CLOCK

Transcription of the Arabidopsis thaliana gene encoding ribulose-1,5-b isphosphate carboxylase/oxygenase (Rubisco) activase (RCA) is organ-sp ecific, light-responsive, and regulated by the circadian clock. RCA is transcribed throughout the green parts of the plant, but not in roots and petals. Responses elicited by short pulses of light indicate that the light response is mediated, at least in part, by phytochrome. Ana lysis of transgenic tobacco and Arabidopsis carrying RCA 5' untranscri bed regions fused to reporter genes (uidA, encoding beta-glucuronidase , or cat, encoding chloramphenicol acetyltransferase) indicate that el ements sufficient to confer organ-specific, light-responsive, and cloc k-regulated transcription are localized within 317 base pairs upstream of the site of transcription initiation. A clock-responsive element s ufficient to confer a low-amplitude (approximately 2-fold) circadian o scillation lies within 317 base pairs of the transcription start, but other elements necessary for high-amplitude (approximately 10-fold) ci rcadian oscillation lie upstream of -317 and are removed by deletion f rom -970 to -317.