The existence of a phage-type plastid transcription machinery (NEP), related to the
mitochondrial RNA polymerase, has been recognized only recently. Here we report the
cis sequences required for transcription initiation by the phage-type enzyme. The
promoter chosen for the study, PclpP-53, is well expressed in tobacco leaves, unlike
most NEP promoters, Promoter definition was carried out in vivo, in transplastomic
tobacco plants expressing a uidA reporter gene from PclpP-53 promoter derivatives.
We report here that sequences from -5 to +25 (relative to the transcription initiation
site) are sufficient to support specific transcription initiation, Requirement of
sequences downstream of the transcription initiation site contrasts with mitochondrial
promoters, which have conserved sequences predominantly upstream. The promoter defined
here is conserved in liverworts and conifers, indicating that the phage-type transcription
machinery appeared in plastids early on during the evolution of land plants. The PclpP-53
promoter sequences are present in rice but do not function, suggesting that PclpP-53
recognition specificity is absent in some monocots.