Escherichia coli MinE is required for placement of a division septum. A nucleus-encoded and plastidtargeted MinE homologue, CrMinE, was identified from Chlamydomonas reinhardtii. Similar to the Arabidopsis nucleus-encoded AtMinE, the CrMinE protein possesses extra N-terminal and C-terminal extensions relative to the eubacterial and other algal plastid-encoded MinE proteins. The CrMinE protein functions in plastids, as revealed by a transient expression assay using a full-length CrMinE protein fused to enhanced green fluorescent protein. In addition, the overexpressed CrMinE:EGFP in wild-type E. coli with clear coiled structures could still recognize the cell division site of the host cell, which suggests evolutionary conservation of the MinE mode of action. No MinE homologue was found in a search of all researched plastid genome sequences of land plants; moreover, the researched MinEs of land plants are encoded by nuclear genomes. Thus, the identification of the CrMinE located in the nuclear genome implies that the transfer events of MinE from plastid to nucleus might have occurred before the evolution of land plants and during the evolution of green algae.