A 146 bp fragment of the tobacco Lhcb12 promoter confers very-low-fluence, low-fluence and high-irradiance responses of phytochrome to a minimal CaMV 35S promoter.

摘要

The occurrence of very-low-fluence responses (VLFR), low-fluence responses (LFR) and high-irradiance responses (HIR) of phytochrome was investigated for expression of the beta-glucuronidase gene (gusA) under the control of the tobacco (Nicotiana plumbaginifolia) Lhcb1*2 (a light-harvesting chlorophyll a/b binding protein gene of photosystem II) promoter in etiolated transgenic tobacco (N. sativum cv. SR1) seedlings. The activity of beta-glucuronidase (GUS) showed biphasic responses to the calculated proportion of far-fed light (Pfr) provided by light pulses. The first phase (i.e., the VLFR) showed a maximum for Pfr levels characteristic of far-red light. The second phase (i.e., the LFR) was observed at higher Pfr levels and was reversible by far-red light pulses. The strong effect of continuous far-red light (i.e., HIR) was fluence-rate-dependent and could not be replaced either by hourly pulses of the same spectral composition and total fluence or by very low fluences of red light. Deletion of the Lhcb1*2 promoter to -453 caused little loss of GUS activity. The -453 to -31, -270 to -31 and -176 to -31 fragments of the Lhcb12 promoter conferred proportionally normal VLFR, LFR and HIR to a truncated (-46 to +8) CaMV 35S minimal promoter. This isthe first demonstration of the presence of three phytochrome action modes in the control of the transcriptional activity of a single gene. The cis-acting regulatory elements necessary for VLFR, LFR and HIR are present in a 146 bp fragment of the tobaccoLhcb1*2 promoter. Nucleotide sequence data have been submitted to the EMBL/GenBank/DDBJ databases under the accession number U56861.