We demonstrate the scarcity of conserved bacterial-type promoters in plastids of Streptophyta and report widely conserved promoters only for genes psaA, psbA, psbB, psbE, rbcL. Among the reasonable explanations are: evolutionary changes of sigma subunit paralogs and phage-type RNA polymerases possibly entailing the loss of corresponding nuclear genes, de novo emergence of the promoters, their loss together with plastome genes; functional substitution of the promoter boxes by transcription activation factor binding sites.
Lyubetsky, V. A., Rubanov, L. I., & Seliverstov, A. V. (2010). Lack of conservation of bacterial type promoters in plastids of Streptophyta. Biology Direct, 5. https://doi.org/10.1186/1745-6150-5-34