Identification of a sequence-specific DNA binding factor required for transcription of the barley chloroplast blue light-responsive psbD-psbC promoter.

Abstract

The plastid gene psbD encodes the photosystem II reaction center chlorophyll protein D2. psbD is located in a complex operon that includes psbC, psbK, psbl, orf62, and tmG. The operon is transcribed from at least three different promoters. One of the psbD promoters is differentially activated when plants are exposed t o blue light. In this study, the psbD blue light-responsive promoter was accurately transcribed in vitro in high-salt extracts of barley plastids. Transcription required supercoiled templates and was inhibited by tagetitoxin, an inhibitor of plastid transcription. Escherichia coli RNA polymerase did not recognize the psbD light-responsive promoter with the same specificity as plastid RNA polymerase.Deletion analyses demonstrated that sequences between -39 and -68, upstream of the transcription initiation site, were required for transcription of the psbD blue light-responsive promoter. This DNA region is highly conserved among plant species and contains multiple AAG sequences. Gel shift assays and DNase I footprinting experiments demonstrated that the AAG-rich DNA sequence interacts with a sequence-specific DNA binding factor termed AGF. Point mutations in the AAG c i s element decreased binding of AGF and inhibited transcription from the psbD light-responsive promoter. We concluded that AGF is an essential factor required for transcription of the psbD light-responsive promoter.

Involvement of Protein Kinase and Extraplastidic Serine/Threonine Protein Phosphatases in Signaling Pathways Regulating Plastid Transcription and the psbD Blue Light- Responsive Promoter in Barley

“…5). The 5' ends of subclass I correspond exactly to the 5' ends detected in vitro when the BLRP is transcribed by the purified Esckerichia coli core RNA polymerase (Kim and Mullet, 1995). This suggests that in the absence of blue light-induced transcription factors ("specificity factors"), the core E. coli-like RNA polymerase of plastids initiates transcription from additional upstream sites in the BLRP.…”

“…Protein factors have been shown to bind to the AAG element in the BLRP of barley (Kim and Mullet, 1995) and tobacco (Alljson and Maliga, 1995) in a light-independent manner. The presence of this element and its interacting proteins suggests a complex regulatory mechanism for transcription of the BLRP.…”

Unique Architecture of the Plastid Ribosomal RNA Operon Promoter Recognized by the Multisubunit RNA Polymerase in Tobacco and Other Higher Plants

“…Thus, PrrnP1, like all characterized plastid promoters, is remarkably compact, lacking regulatory sequences far upstream or downstream of the Ϫ35/Ϫ10 promoter core. The only exception is the blue light-regulated psbD promoter: the AAG box is located between Ϫ36 and Ϫ64, and the PGT box is located between Ϫ71 and Ϫ100 (Allison and Maliga, 1995;Kim and Mullet, 1995;Kim et al, 1999;Thum et al, 2001). Lack of regulatory sequences extending far upstream of the plastid promoter core in higher plants is in contrast to the E. coli rrnB P1 promoter, which has two distinct sets of regulatory elements: the UP element (Ϫ40 to Ϫ60), which is part of the promoter recognition domain, and the Fis binding sites (Ϫ64 to Ϫ150).…”

“…Transcription from the psbA and psbD promoters, at least in some species and at certain developmental stages, is dependent only on the Ϫ10 promoter element. Interaction of the PEP with the Ϫ35 element probably is replaced by interaction with the extended Ϫ10 sequence (the psbA promoter in wheat) (Satoh et al, 1999), the TATAlike sequence between the Ϫ35 and Ϫ10 elements (the psbA promoter in mustard) (Eisermann et al, 1990), or factors binding to sequences upstream of a degenerate Ϫ35 element (the psbD promoter in barley and tobacco) (Allison and Maliga, 1995;Kim and Mullet, 1995;Kim et al, 1999;Thum et al, 2001). PrrnP1 is the first plastid promoter in higher plants in which the Ϫ10 sequence seems to play a minor role.…”

“…Promoter elements that regulate transcription, at least in the case of the plastid psbD promoter, are localized upstream of the Ϫ 35 promoter core (Allison and Maliga, 1995;Kim and Mullet, 1995;Kim et al, 1999;Thum et al, 2001). Therefore, we searched for potential regulatory elements between the plastid trnV gene and the rrn coding region.…”