RESUMO
Transcription of the Arabidopsis thaliana gene encoding ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) is organ-specific, 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. Analysis of transgenic tobacco and Arabidopsis carrying RCA 5' untranscribed regions fused to reporter genes (uidA, encoding beta-glucuronidase, or cat, encoding chloramphenicol acetyltransferase) indicate that elements sufficient to confer organ-specific, light-responsive, and clock-regulated transcription are localized within 317 base pairs upstream of the site of transcription initiation. A clock-responsive element sufficient to confer a low-amplitude (approximately 2-fold) circadian oscillation lies within 317 base pairs of the trascription start, but other elements necessary for high-amplitude (approximately 10-fold) circadian oscillation lie upstream of -317 and are removed by deletion from -970 to -317.
