Analysis of transcriptional regulation in chloroplasts by DNA-associated transcrition factors by means of chloroplast transformation

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Chloroplast-encoded photosynthesis genes are transcribed by eubacterial-type RNA polymerase (PEP). Thus it has been considered that transcription factors involved in the regulation of PEP would be homologous to the bacterial factors. Hewever, arabidopsis genome project revealed that neither chloroplast genome nor nuclear genome encoded any prokaryotic transcription factor. In order to identify and characterize the chloroplast transcription factors involved in the regulation of PEP, novel biochemical and/or genetic approaches specific for chloroplasts should be employed. In this study, I identified novel nuclear-encoded chloroplast factors that specifically interact with the region 4of chloroplast sigma factor, Sig1. In vitro transcription analysis of the chloroplast psbA promoter revealed that promoter recognition property of PEP was developmentally regulated in wheat seedlings. In young chloroplasts, the -35 element was essential for transcription initiation from the psbA promoter, but not in mature chloroplasts. It was also suggested that chloroplast sigma factor, Sig5 would be involved in the blue light-dependent activation of transcription at the psbD light-responsive promoter. Furthermore, I employed chloroplast transformation technique to study the trancriptional regulation in chloroplasts and revealed that the transcription initiation at the psbA promoter required the -35 element in tobacco. Finally, I visualized stromules in transplastomic plants expressing GFP in chloroplasts and characterized their physiological functions.