Chloroplasts

InPhyscomitrella patens, chloronemal and leaf cells contain numerous large round chloroplasts while caulonemal cells contain fewer and smaller spindle‐shaped chloroplasts. Unlike seed plants, plastid differentiation is not usually observed inP. patensand the gametophytes always contain chloroplasts that develop even in the dark. TheP. patensplastid genome (122 890 bp) possesses at least 118 genes. The most interesting feature is that therpoAgene encoding the α subunit of the plastid‐encoded plastid RNA polymerase (PEP) is absent from the plastid genome ofP. patens. Instead, two nuclear counterparts encode the α subunits of PEP enzyme and modulate transcription of the plastid genes. WhetherP. patenschloroplasts contain a second RNA polymerase, the nuclear‐encoded plastid RNA polymerase (NEP), continues to be debated. Here, we provide biochemical evidence supporting the existence of NEP activity inP. patens. Plastid transformation, which has been achieved inP. patens, allows further investigation of the regulation of plastid gene expression and over‐production of foreign polypeptides in the moss chloroplasts. Molecular techniques with the complete genome informatics open a way to study the molecular basis of plastid division and movement, chloroplast import, or circadian rhythm inP. patens.