Regulation of rDNA Transcription in Spinach Plastids by Transcription Factor CDF2

Abstract

A series of recent-years discoveries has shown that transcription of the plastid genome is highly regulated. Nucleus-encoded (NEP) and plastidencoded (PEP) RNA polymerase(s) in coordination with different types of transcription factors participate in the expression of the about 150 kbp circular DNA molecule. Most of the plastid transcription units and genes are preceded by several types of promoter structures allowing transcription by different RNA polymerases and suggesting a division of labour between these different enzymes (for reviews see Hess and Borner 1999, Liere and Maliga 2000). However, although genes and cDNAs corresponding to potential plastid transcription factors and RNA polymerase subunits are discovered now, the exact function of them and the interaction of the different transcriptional components during genome expression is not at all clear. We have chosen the spinach plastid rrn operon to analyse some of these interactions in more detail. Ribosome biosynthesis is one of the first events taking place during the differentiation of proplastids into photosynthetically active chloroplasts (Harrak et al 1995) and it is tightly coupled to plastid metabolic activities. To better understand plastid transcription regulation we have analysed rDNA expression in different plant tissues (i. e. corresponding to different types of plastids), during germination (i. e. corresponding to differentiation of proplastids into chloroplasts) and during different climatic and growth conditions (i. e. corresponding to changes in metabolic activities).