The plastid division protein AtMinD1 is a Ca2+-ATPase stimulated by AtMinE1

Bacteria and plastids divide symmetrically through binary fission by accurately placing the division site at midpoint, a process initiated by FtsZ polymerization, which forms a Z-ring. In Escherichia coli precise Z-ring placement at midcell depends on controlled oscillatory behavior of MinD and MinE: In the presence of ATP MinD interacts with the FtsZ inhibitor MinC and migrates to the membrane where the MinD-MinC complex recruits MinE, followed by MinD-mediated ATP hydrolysis and membrane release. Although correct Z-ring placement during Arabidopsis plastid division depends on the precise localization of the bacterial homologs AtMinD1 and AtMinE1, the underlying mechanism of this process remains unknown. Here we have shown that AtMinD1 is a Ca2+-dependent ATPase and through mutation analysis demonstrated the physiological importance of this activity where loss of ATP hydrolysis results in protein mislocalization within plastids. The observed mislocalization is not due to disrupted AtMinD1 dimerization, however; the active site AtMinD1(K72A) mutant is unable to interact with the topological specificity factor AtMinE1. We have shown that AtMinE1, but not E. coli MinE, stimulates AtMinD1-mediated ATP hydrolysis, but in contrast to prokaryotes stimulation occurs in the absence of membrane lipids. Although AtMinD1 appears highly evolutionarily conserved, we found that important biochemical and cell biological properties have diverged. We propose that correct intraplastidic AtMinD1 localization is dependent on AtMinE1-stimulated, Ca2+-dependent AtMinD1 ATP hydrolysis, ultimately ensuring precise Z-ring placement and symmetric plastid division.