The molecular biology and regulation of plastid division
Min proteins mediate plastid division site selection by controlling the formation of the Z-ring, the initial event of plastid division. The Z-ring is formed by the polymerisation of the FtsZ proteins into a contractile ring at the future division site and acts as a scaffold for the assembly of the rest of the divisions machinery. This study aims to elucidate AtMinD1 function in Arabidopsis thaliana and demonstrates that AtMinD1 has Ca2+-dependent ATPase activity that is stimulated by AtMinE1. Site directed mutagenesis was used to create an active site mutant of AtMinD1, analysis of this mutant revealed loss of interaction with AtMinE1 and mis-localisation. The interaction of the stromal plastid division components was also investigated. Co-localisation and biomolecular fluorescence complementation assays revealed that AtFtsZ1-1 and AtFtsZ2-1 are capable of forming both homopolymeric and heteropolymeric filaments, AtMinD1 and AtMinE1 interact both with themselves and each other and ARC6 interacts specifically with AtFtsZ2-1. Many of the components involved in plastid division have yet to be identified. To identify novel plastid division components, yeast two-hybrid screening and co-immunoprecipitation were used to hunt for novel interacting partners of FtsZ proteins. Although much work has been dedicated to unravelling the machinery of plastid division, very little is known about the regulation of plastid division. DNA microarrays were used to investigate changes in nuclear gene expression upon chloroplast division inhibition. Quantitative PCR experiments demonstrate that the expression of AtFtsZ1-1, AtFtsZ2-1, AtMinD1 and AtMinE1 is light regulated and yeast one-hybrid screening was used to hunt for transcriptional activators/enhancers of AtMinD1 and AtMinE1.