Abstract
The consensus is that a cyanobacterium with cell wall phagocytosed by a host cell evolved into plastids. However, no wall-like structures including peptidoglycan (PG or murein) were found in plastids of all green plants. Ten Mur genes are associated with PG biosynthesis in bacteria. Recently, we found that the moss Physcomitrella patens has eight homologs related to PG biosynthesis. Gene knockout experiments for the PpMurE or PpPbp (penicillin-binding protein) genes in P. patens showed appearance of macrochloroplasts both in protonema and in leaf cells. Electron microscopic observations showed no obvious differences in the shape or stacking of thylakoid membranes in the transformants. We isolated two genes (PpMraY and PpMurG) that were not found previously by screening the P. patens genomic database. PpMraY and PpMurG encoded a protein of 487 and 400 amino-acids, respectively. Gene disruption of the PpMraY gene in P. patens resulted in the appearance of macrochloroplasts.
