Visualization of the chloroplast MinE ring in living mesophyll cells of <i>Arabidopsis thaliana</i>

Chloroplast division is a complex process influenced by various proteins, among which bacteria-derived MinE plays a vital role in correctly placing the FtsZ-based division apparatus and initiating the division. This study aimed to elucidate the intrachloroplastic localization of MinE in the living mesophyll cells of Arabidopsis thaliana using the MinE-yellow fluorescent protein (YFP) fusion. Fluorescence microscopy of the complemented A. thaliana minE mutant, expressing MinE-YFP under the native MinE promoter, showed normal chloroplast division and revealed a mid-chloroplast MinE ring composed of array-of-dots and filaments, as well as other distinct localization patterns of MinE during chloroplast division. The MinE ring relatively maintained its configuration during chloroplast constriction, as does the FtsZ ring, suggesting a dynamic protein dissociation correlating with division progression. We also observed a unique “twin dot” structure and one-sided distribution of MinE in chloroplasts with slight over-accumulation of MinE-YFP in transgenic tissues. These observations deviate from the well-accepted model of the MinE behavior during Escherichia coli cytokinesis, suggesting fundamental differences in the division mechanisms between chloroplasts and bacteria. The present findings deepen our understanding of the protein organization at the chloroplast division site and highlight the distinctive nature of the MinE protein’s behavior in plants.