Comparison of Strength of Endogenous and Exogenous Gene Promoters in Arabidopsis Chloroplasts

We have focused on possible stronger promoters in the chloroplast: those of psbA encoding D1 protein of photosystem II reaction center, 16S rDNA in rrn operon, the bacterial fused promoter tac, and the bacteriophage T7 gene φ10 in combination with transgenic T7 RNA polymerase (RNAP). Arabidopsis plants were made transgenic in the nuclear genome with the construct of a chimeric gene for T7 RNAP fused to a chloroplast transit peptide at its N-terminus placed under the control of CaMV 35S promoter. We have transiently expressed gene for β-glucuronidase (GUS) under control of the above promoters in the Arabidopsis chloroplast followed by particle bombardment. Expression in the chloroplast but not in the nucleus was confirmed histochemically and by treatment with α-amanitin. T7 promoter was the strongest among the examined promoters in the Arabidopsis chloroplast, being applicable to higher expression of foreign genes in the chloroplast with managed expression of T7 RNAP.