Studies on chloroplast-dependent expression of some nuclear genes

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Chloroplast development depends on coordinate expression of nuclear and chloroplast genomes. Based on genetic and physiological studies, some of nuclear genes are known to be expressed only when chloroplasts are functional. It has been proposed that functional chloroplasts send a signal to the nuclus. This study has forcused on the elucidation of such a possible chloroplast signal.1. Identification of chloroplast-dependent nuclear genesFourteen cDNAs so far isolated are all expressed in a chloroplast-dependent manner. Furthermore, 100 additional cDNAs whose expression is chloroplast-dependent have been identified by differential display assay. These include psaD,psaF,rbcS and cab.2. A system for searching a chloroplast signalAn in vitro transcription system has been developed from tobacco cultured BY-2 cells (containing non photosynthetic plastids). This supports a low level transcription of rbcS while the level increases with extracts from tobacco leaves (containing functional chloroplasts).