Curr Genet (1991)t9:199 206 Current Genetics 9 Springer-Verlag 1991 Differential expression of the psbB and psbH genes encoding the 47 kDa chlorophyll a-protein and the 10 kDa phosphoprotein of photosystem II during chloroplast development in wheat Scan M. Hird 1,2, Andrew N. Webber 1,,, Rebecca J. Wilson 1, Tristan A. Dyer 2'**, and John C. Gray 1 1 Botany School, University of Cambridge, Downing Street, Cambridge, CB2 3EA, UK 2 Institute of Plant Science Research (Cambridge Laboratory), Marls Lane, Trumpington, Cambridge, CB2 2JB, UK Received October 17/November 14, 1990 Summary. The nucleotide sequence of a region of wheat chloroplast DNA containing the psbB gene for the 47 kDa chlorophyll a-binding protein of photosystem II has been determined. The gene encodes a polypeptide of 508 amino acid residues which is predicted to contain six hydrophobic membrane-spanning regions. The psbB gene is located 562 bp upstream of the psbH gene for the 10 kDa phosphoprotein of photosystem II. A small open reading frame of 38 codons is located between psbB and psbH, and on the opposite strand the psbN gene, encod- ing a photosystem II polypeptide of 43 amino acid residues, is located between orf38 and psbH. $1 nuclease mapping indicated that the 5' ends of transcripts were located 371 and 183 bp upstream of the psbB translation initiation codon. Predominant transcripts of 2.1 kb and 1.8 kb forpsbB and 0.4 kb for psbH were present in RNA isolated from etiolated and greening wheat seedlings. Im- munodecoration of Western blots indicated that the 47 kDa polypeptide was absent, or present in very low amounts, in dark-grown tissue and accumulated on greening, whereas the 10 kDa polypeptide was present in similar amounts in both dark-grown and greening seedlings. The 10 kDa polypeptide was phosphorylated in vitro by incubating wheat etioplast membranes with [732P] ATP. Key words: Light regulation - p s b N - Triticum aestivum - Etioplast Introduction Photosystem II is the most complex of the multi-subunit assemblies of the chloroplast thylakoid membrane and is Present addresses: * Department of Botany, Arizona State University, Tempe, AZ 85287-1601, USA ** Cambridge Laboratory, John Innes Centre for Plant Science Research, Colney Lane, Norwich NR4 7U J, UK Offprint requests to: J.C. Gray composed of more than 20 different polypeptides or- ganised into the light-harvesting complex (LHCII), the reaction centre complex, and the extrinsic water-splitting complex. The assembly of a functional photosystem II requires the integrated expression of a large number of genes distributed between the nuclear and chloroplast genomes. Experiments with several higher plant species indicate that the expression of genes for photosystem II components is regulated at a variety of different stages, including transcription (Apel 1979; Cuming and Bennett 1981; Lamppa et al. 1985) and translation (Klein and Mullet 1987; Klein et al. 1988), and at post-translational steps (Apel and Kloppstech 1980; Bennett 1981; Fromm et al. 1985). The presence of chlorophyll appears to be an important factor in the expression of many of the photo- system II genes. In the absence of chlorophyll, the tran- scripts of the chloroplast-encoded chlorophyll a-binding proteins are not translated (Klein and Mullet 1987; Klein et al. 1988) and newly-synthesised LHCII polypeptides are degraded (Apel and Kloppstech 1980; Bennett 198l). Destruction of chlorophyll by photobleaching in norflu- razon-treated plants results in decreased transcription of several nuclear genes for photosystem II components (Mayfield and Taylor 1984, 1987; Batschauer et al. 1986; Burgess and Taylor 1987). The chloroplast genome encodes a number of photo- system II components whose synthesis is regulated by light. We wished to study the effect of light on the expres- sion of two co-transcribed genes, for the 47 kDa chloro- phyll a-protein and the 10kDa phosphoprotein, in wheat. The psbB gene for the 47 kDa polypeptide is locat- ed just upstream of the psbH gene for the 10 kDa polypeptide in wheat chloroplast DNA (Courtice et al. 1985; Hird et al. 1986) and in several plants these genes have been shown to be co-transcribed and to produce a complex pattern of transcripts (Westhoff et al. 1986; Tanaka et al. 1987; Rock et al. 1987; Barkan 1988; West- hoff and Herrmann 1988). We have examined the effect of illumination of dark-grown wheat seedlings on the amounts of transcripts and polypeptides produced from the psbB and psbH genes. Our results indicate that light