21001:

Molecular dissection of the plastid division machinery: FtsZ and MinD function in Arabidopsis.

Authors:	Vitha, Stanislav(A)
Affiliations:	(A): Dept. of Biochemistry/200, University of Nevada, Reno, NV 89557
Presenter:	Vitha, Stanislav , oster_k@med.unr.edu

The division of plastids by binary fission is critical for the maintenance of plastid populations in plant cells and the accumulation of green chloroplasts in photosynthetic tissues. Our aim is to identify and functionally dissect the components of the plastid division apparatus, and establish the processes that control their activity. To date, we have identified four nuclear-encoded proteins from Arabidopsis thaliana with homology to bacterial cell division proteins. Three share 40-50% identity with FtsZ, a prokaryotic cytoskeletal protein that localizes to a ring at the division site during cell septation. The other shares about 40% identity with bacterial MinD, which is involved in specifying the site of FtsZ ring formation in E. coli. We have shown previously that one of the Arabidopsis FtsZ proteins, AtFtsZ1-1, is targeted to chloroplasts, while two, AtFtsZ2-1 and AtFtsZ2-2, are proposed to be cytosolic. AtMinD also contains a putative chloroplast transit peptide. Antisense suppression of either AtFtsZ1-1, AtFtsZ2-1, or AtMinD expression in transgenic plants results in dramatically reduced numbers of enlarged chloroplasts. Plants overexpressing either AtFtsZ1-1 or AtFtsZ2-1 have mostly similar phenotypes. These results indicate that AtFtsZ1-1, AtFtsZ2-1 and AtMinD all function as plastid division proteins, and suggest that prokaryotically derived plastid division components may function on both sides of the plastid envelope membranes during constriction of the organelle. To correlate FtsZ protein levels with the transgenic phenotypes and provide sensitive probes for expression and localization studies, antisera are being raised against peptides designed to mimic optimal FtsZ epitopes. Epitope-tagging strategies and fusions to green fluorescent protein (GFP) are also being employed for localization studies. An AtFtsZ2-1-GFP fusion protein causes filamentation when expressed in E. coli and localizes to presumptive division sites along the bacterial filament, similar to the effects of bacterial ftsZ overexpression. This suggests that AtftsZ2-1 can interact with the bacterial division apparatus. Our data collectively imply that plastid and prokaryotic cell division are evolutionarily and mechanistically related, but that the processes mediating plastid division are inherently more complex.