Rapid Transcriptional Regulation of the Cab and PEA207 Gene Families in Peas by Blue Light in the Absence of Cytoplasmic Protein Synthesis

We have analyzed the fluence-response and time-course characteristics, and the requirements for protein synthesis, for the blue-light (BL) regulated transcription of the nuclear-coded Cab, pEA207, and pEA25 gene families in pea (Pisum sativum L.). Fluence-response curves indicate two BL responses: a blue low-fluence (BLF) response with a threshold at or below 10(-1) μmol·m(-2) of BL and a blue high-fluence (BHF) response with a threshold between 10(1) and 10(3) μmol·m(-2) of BL. Excitation of the photomorphogenic system responsible for the BLF response results in increased Cab, and decreased pEA25, transcription. Excitation of the photomorphogenic system responsible for the BHF response results in decreased pEA207 transcription and induction of turnover for Cab RNA and pEA207 RNA. Altered rates of transcription for the Cab and pEA207 gene families are apparent within 15 min of BL treatment and remain in effect for at least 24 h. The effect of BL on pEA25 transcription is not apparent until 3-5 h after the BL treatment. Cycloheximide, an inhibitor of cytoplasmic protein synthesis, has no effect on the altered rates of pEA207 and Cab transcription. We conclude from these results that the BLF response for Cab transcription and the BHF response for pEA207 transcription probably occurs without the expression of intervening regulatory genes coded within the nucleus or the translation of pre-existing transcripts derived from nuclear-coded genes.