Abstract
One of the most unique promoters in the plastid genome is the psbD light responsive promoter (psbD LRP). The psbD LRP is transcribed by a eubacteria-type PEP and contains conserved AAG-box and -10 elements. We analyzed the upstream sequences of the psbD among 9 ferns and 17 gymnosperms. The psbD LRP sequences are found in Cycadopsida, Ginkgoopsida and Conferopsida of gymnosperms, but not in ferns and in Gnetopsida (gymnosperm), suggesting that the psbD LRP sequences probably emerged early during the evolution of the gymnosperms. We subsequently examined expression of the light-inducible psbD transcripts in several plants. The psbD gene is constitutively expressed at high levels irrespective of light condition in Adiantum (fern), Cycas (gymnosperm) and Black Pine (gymnosperm), whereas psbD gene expression is induced by light in Arabidopsis (angiosperm). These results may suggest that the evolution of the psbD LRP sequences preceded the establishment of the light-responsive psbD transcription system.
