Mol Gen Genet (1996) 252:631-639 © Springer-Verlag t996 Victor Kusnetsov • Cordelia Bolle • Thomas Liibberstedt Sudhir Sopory • Reinhold G. Herrmann • Raif Oelmiiller Evidence that the plastid signal and light operate via the same cis.acting elements in the promoters of nuclear genes for plastid proteins Received: 22 March 1996/Accepted: 28 June 1996 Abstract Nuclear-encoded genes for proteins of the photosynthetic maschinery represent a particular subset of genes. Their expression is cooperatively stimulated by discrete factors including the developmental stage of plastids and light. We have analyzed in transgenic tobacco the plastid- and light-dependent expression of a series of 5' promoter deletions of various nuclear genes from spinach, of fusions of defined promoter segments with the 90-bp 35S RNA CaMV minimal promoter, as well as with mutations in sequences with homologies to characterized cis-elements, to address the question of whether the plastid signal and light operate via the same or different cis-acting ele- ments. In none of the 160 different transgenic lines (representing 32 promoter constructs from seven genes) analyzed, could significant differences be identified in the responses to the two regula- tory pathways. The data are compatible with the idea that both signals control the expression of nuclear genes for plastid proteins via the same cis- acting elements. Key words Gene expression - Light regulation • Photosynthesis' Plastid signal Communicated by R. Hagemann V. Kusnetsov • C. Bolle 1 - T. Ltibberstedt - S. Sopory 2 R. G. Herrmann • R. Oelmiiller (I~) Botanisches Institut der Ludwig-Maximilians-Universit~it, Menzingerstrasse 67, D-80638 Munich, Germany Present address: 1 Rockefeller University Plant Laboratory, 1230 York Avenue, NY 10021-6399, USA Permanen~ address: 2 Plant Research Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Dehli 110 067, India Introduction Light is one of the most crucial factors for plant growth and development (Kendrick and Kronenberg 1994). Among the most intensively studied effects of this factor are its influence on the regulation of nuclear gene transcription (Thompson and White t991; Bowler and Chua 1994; Terzaghi and Cashmore 1995) and on the differentiation of etioplasts or proplastids into chloro- plasts (Herrmann et al. 1992). Microinjection studies in particular have recently facilitated the identification of components involved in light-signal transduction (Neuhaus et al. 1993; Bowler et at. 1994a, b). Light (phytochrome) activates heterotrimeric G protein(s) (Ma 1994), which, in turn, appear to trigger three sub- sequent pathways: one involving cGMP, a second Ca2+/calmodulin, and a third route that seems to re- quire both components. Refined studies indicate that this separation is not strict and that the two pathways interact considerably (summarized in Barnes et al. 1995). In addition to the stimulation of nuclear gene expression, injection of phytochrome and non- hydrolyzable GTP analogs, which activate G proteins, also stimulate plastid biogenesis (Shacklock et al. 1992; Neuhaus et al. 1993). Activation of the Ca2+/cal - modulin pathway alone directs only partial chloroplast development; complete development of the organetle also requires the activation of the cGMP-dependent pathway. The partially developed chloroplasts contain photosystem II and antenna components, while other components of the photosynthetic membrane, such as photosystem I, are missing. In agreement with these observations, activation of the Ca 2 ÷/calmodulin path- way alone suffices to stimulate Lhcb gene expression, while activation of both pathways is required for the expression of Peril, which encodes the photo- system I-associated ferredoxin-NADP ÷ oxidoreduc- tase (Barnes et al. 1995). This suggests a tight coupling between light-induced developmental processes in the plastid and the expression of the required nuclear genes.