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Professor of Plant Biology
Department of Plant Biology
Plant Biology Department
Selected Publications; Current Funding; Teaching; Lab Members |
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Research
CHLOROPLAST DIVISION IN PLANTS
Our research centers on elucidating the mechanisms powering chloroplast division in plant cells. Plastid division is orchestrated by a dynamic macromolecular machine composed of several ring-shaped sub-complexes that function in concert to constrict the organelle (Fig. 1A). The recruitment, assembly and biochemical activities of these subcomplexes must be coordinated across the two envelope membranes to achieve organelle fission (Fig. 1B). We are combining the powerful genetic and genomic resources of Arabidopsis with the tools of biochemistry and cell biology to identify the components of the plastid division machinery, define their functions within the division complex, and discover how chloroplast division is regulated. Because key features of plastid division are derived from the cell division machinery in the cyanobacterial endosymbiont from which chloroplasts evolved, we are also strategically incorporating experiments on cyanobacterial cell division into our work, as well as pursuing comparative genomic and other computational strategies to uncover the full network of genes and proteins controlling plastid division in plants.
Fig. 1. The plastid division machinery. (A) The tubulin-like FtsZ ring (Z-ring), inner plastid-dividing ring, dynamin-like ARC5 ring and outer plastid-dividing ring assemble sequentially and function together to constrict and sever the envelope membranes. The inner and outer plastid-dividing rings are distinct from the FtsZ and ARC5/dynamin rings (reviewed by Osteryoung and Nunnari, 2003; Miyagishima et al., 2003, Trends Plant Sci. 8: 432-438), but their compositions are not currently known. (B) Working model of the coordinated division machinery in Arabidopsis showing the topologies, interactions and hypothesized functional relationships among a subset of plastid division proteins. Formation of the stromal Z-ring, composed of FtsZ1 (Z1) and FtsZ2 (Z2), occurs first. Z-ring assembly and dynamics are antagonistically regulated by ARC6, which promotes assembly through direct interaction with FtsZ2, and PARC6, which promotes FtsZ disassembly through ARC3. Once the Z-ring is established, ARC6 interacts directly with and recruits PDV2 to the division site, and PARC6 recruits PDV1 to the division site. PDV1 and PDV2 recruit ARC5 independently from the cytosol to the division site, though both PDV1 and PDV2 are required for full ARC5 contractile activity. Dashed lines emphasize regions of PARC6 whose topology remains uncertain. Double-sided arrows with question marks indicate protein-protein interactions not yet demonstrated. The PD rings and other division components have been omitted for simplicity. Many aspects of this model remain to be elucidated. IEM, inner envelope membrane; OEM, outer envelope membrane; IMS, intermembrane space; N, N-terminus; C, C-terminus. Adapted from Glynn et al., 2009.
A sampling of chloroplast division proteins studied in our laboratory (all nuclear-encoded):
FtsZ1 and FtsZ2: Tubulin-like proteins related to bacterial FtsZ, a cytoskeletal GTPase that forms a ring at the midcell during bacterial cytokinesis. In plants, FtsZ1 and FtsZ2 are endosymbiotic in origin and colocalize to a ring (the Z-ring) at the chloroplast division site inside the chloroplast stroma (Fig. 2). FtsZ1 and FtsZ2 interact with different assembly regulators and both proteins are required for full plastid-division activity. Mutations that reduce the levels of either FtsZ1 or FtsZ2 protein cause dose-dependent defects in chloroplast division (Fig. 3), suggesting their stoichiometry is important for their in vivo activities. The plastidic FtsZ ring probably functions both to constrict the inner envelope membrane and to position other components of the division complex.
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ARC5*: A member of the dynamin family of large GTPases, which oligomerize to function as membrane “pinchases.” ARC5 is localized at the division site on the cytosolic surface of the outer envelope membrane where it constricts chloroplasts from the outside. Plants with mutations in ARC5 exhibit enlarged, dumbbell-shaped chloroplasts (Fig. 4). ARC5 has no obvious homologues in bacteria, indicating it is eukaryotic in origin. |
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PDV1 and PDV2: Plant-specific proteins of the chloroplast outer envelope that recruit ARC5 from the cytosol to the surface of the chloroplast at the division site. PDV1 localizes to a punctate mid-plastid ring prior to and during constriction and persists as a spot at the pole of one of the daughter chloroplasts following division (Fig. 5). PDV2 also localizes to the chloroplast division site, but forms a continuous ring and is not retained at the pole following division (Glynn et al, 2008). |
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ARC6 and PARC6: Proteins of the chloroplast inner envelope that both regulate FtsZ ring assembly and dynamics inside the chloroplast (Fig. 5) and position PDV1 and PDV2 to the mid-plastid division site in the outer envelope (Fig. 6), resulting in ARC5 recruitment to the chloroplast surface. ARC6 is cyanobacterial in origin whereas its paralogue PARC6 is unique to vascular plants. ARC6 and PARC6 have divergent functions, but both play critical roles in coordinating the contractile activities of the FtsZ and ARC5 rings across the two envelope membranes (Fig. 1B)
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Fig. 7. ARC6 is required for PDV1 and PDV2 positioning. Merged images showing YFP or GFP (green) and chlorophyll autofluorescence (red) in leaf cells of wild type and an arc6 T-DNA mutant. Arrows show midplastid YFP-PDV2 or GFP-PDV1 rings. PDV1 and PDV2 are distributed diffusely over the chloroplast surface in the arc6 mutant (from Glynn et al., 2008). Similar experiments have shown that PARC6 is required for PDV1 but not PDV2 positioning (Glynn et al, 2009). |
Schmitz A.J., J.M. Glynn, B.J.S.C. Olson, K.D. Stokes and K.W. Osteryoung. 2009. Arabidopsis FtsZ2-1 and FtsZ2-2 are functionally redundant, but FtsZ-based plastid division is not essential for chloroplast partitioning or plant growth and development. Mol. Plant, in press.
Glynn J. M., Y. Yang , S. Vitha, A.J. Schmitz, M. Hemmes, S. Miyagishima and K.W. Osteryoung. 2009. PARC6, a novel chloroplast division factor, influences FtsZ assembly and is required for recruitment of PDV1 during chloroplast division in Arabidopsis. Plant J. 59: 700-711.
Suzuki, K., H. Nakanishi, J. Bower, D.W. Yoder, K.W. Osteryoung and S. Miyagishima. 2009. Plastid chaperonin proteins Cpn60α and Cpn60b are required for plastid division in Arabidopsis thaliana. BMC Plant Biology 9: 38-49.
Yang, Y., J.M. Glynn, B.J.S.C. Olson, A.J. Schmitz, and K.W. Osteryoung. 2008. Plastid division: across time and space. Curr. Opin. Plant Biol. 11: 577-84.
Glynn, J. M., J.E. Froehlich and K.W. Osteryoung. 2008. Arabidopsis ARC6 coordinates the division machineries of the inner and outer chloroplast membranes through interaction with the PDV2 in the intermembrane space. Plant Cell 20: 2460-2470.
McAndrew, R.S., B.J.S.C. Olson, C.L. Chi-Ham, S. Vitha, J.E. Froehlich and K.W. Osteryoung. 2008. In vivo quantitative relationship between plastid division proteins FtsZ1 and FtsZ2 and identification of ARC6 and ARC3 in a native FtsZ complex. Biochem. J. 412: 367-378.
Lu Y., L.J. Savage, I. Ajjawi, K.M. Imre, D.W. Yoder, C. Benning, D. Dellapenna, J.B. Ohlrogge, K.W. Osteryoung, A.P. Weber, C.G. Wilkerson, R.L. Last. 2008. New connections across pathways and cellular processes: industrialized mutant screening reveals novel associations between diverse phenotypes in Arabidopsis. Plant Physiol. 46:1482-500.
Shimada, H., Mochizuki, M., Ogura, K., Froehlich, J.E., Osteryoung, K.W., Shirano, Y., Shibata, D., Masuda, S., Mori, K., and Takamiya, K.I. 2007. Arabidopsis cotyledon-specific chloroplast biogenesis factor CYO1 is a protein disulfide isomerase. Plant Cell 19: 3157-69.
Glynn, J. M., S. Miyagishima and K.W. Osteryoung. 2007. Structure and dynamics of the chloroplast division complex. Traffic 8: 451-461.
Yoder, D.W., D. Kadirjan-Kalbach, B.J.S.C. Olson, S. Miyagishima, S.L. DeBlasio, R.P. Hangarter and K.W. Osteryoung. 2007. Effects of mutations in Arabidopsis FtsZ1 on plastid division, FtsZ ring formation and positioning, and FtsZ filament morphology in vivo. Plant Cell Physiol. 48: 775–791.
Miyagishima, S., J.E. Froehlich, and K.W. Osteryoung. 2006. PDV1 and PDV2 mediate recruitment of the dynamin-related protein ARC5 to the plastid division site. Plant Cell 18: 2506-2516.
Gao, H., T.L. Sage and K.W. Osteryoung. 2006. FZL, an FZO-like protein in plants, is a determinant of thylakoid and chloroplast morphology. Proc. Natl. Acad. Sci. USA. 103: 6759-6764.
Miyagishima, S., C.P. Wolk and K.W. Osteryoung. 2005. Identification of cyanobacterial cell division genes by comparative and mutational analyses. Mol. Microbiol. 56: 126-143.
Osteryoung, K.W. and Nunnari, J. 2003. The division of endosymbiotic organelles. Science 302: 1698-1704.
Vitha, S., Froehlich, J.E., O. Koksharova, K.A. Pyke, H. van Erp and K.W.Osteryoung. 2003. ARC6 is a J-domain plastid division protein and evolutionary descendant of the cyanobacterial cell division protein Ftn2. Plant Cell 15: 1918-1933
Gao, H., D. Kadirjan-Kalbach, J.E. Froehlich and K.W. Osteryoung. 2003. ARC5, a cytosolic dynamin-like protein from plants, is part of the chloroplast division machinery. Proc. Natl. Acad. Sci. USA 100: 4328–4333.
C.G. Wilkerson, W.K. Ray, R.S. McAndrew, K.W. Osteryoung, D.A. Gage and B.S. Phinney. 2003. Proteomic study of the Arabidopsis thaliana chloroplastic envelope membrane utilizing alternatives to traditional two-dimensional electrophoresis. J. Proteome Res. 2: 42-425.
Stokes, K.D., and K.W. Osteryoung, 2003. Early evolutionary divergence of the FtsZ1 and FtsZ2 plastid division gene families in photosynthetic eukaryotes. Gene 320: 97-108.
Osteryoung, K.W. and R.S. McAndrew. 2001. The plastid division machine. Annu. Rev. Plant Physiol. Plant Mol. Biol. 52: 315-333.
Vitha, S., R.S. McAndrew and K.W. Osteryoung. 2001. FtsZ ring formation at the chloroplast division site in plants. J. Cell Biol. 153: 111-119.
McAndrew, R.S., J.E. Froehlich, S. Vitha, K.D. Stokes and K.W. Osteryoung. 2001. Colocalization of plastid division proteins to the chloroplast stromal compartment establishes a new functional relationship between FtsZ1 and FtsZ2 in higher plants. Plant Physiol. 127: 1656-1666.
Colletti, K.S., E.A. Tattersall, K.A. Pyke, J.E.Froelich, K.D.Stokes, and K.W Osteryoung. 2000. A homologue of the bacterial cell division site-determining factor MinD mediates placement of the chloroplast division apparatus. Curr. Biol. 10: 507-16.
Osteryoung, K.W., K.D. Stokes, S.M. Rutherford, A.L. Percival and W.Y. Lee. 1998. Chloroplast division in higher plants requires members of two functionally divergent FtsZ gene families. Plant Cell 10: 1991-2004.
Osteryoung, K.W. and E. Vierling. 1995. Conserved cell and organelle division. Nature 376: 473-474.
US Department of Energy. Mechanisms of Chloroplast Division in Plants, K.W. Osteryoung, PI, 8/1/09-7/31/12.
National Science Foundation, Towards a Model for FtsZ Structure and Dynamics in Chloroplast Division, K.W. Osteryoung, PI, 7/1/06-6/30/10.
National Science Foundation, Arabidopsis 2010: Understanding Chloroplast Function, PI R. Last; co-PIs K. Osteryoung, C. Benning, D. DellaPenna, J. Ohlrogge, Y. Shachar-Hill, A. Weber, W. Wedemeyer. 12/01/05- 11/30/09.
Introductory Biology: Cells and Molecules, MSU (Biological Sciences 111, undergraduate lecture, ~450 students, 3 credits).
June 2009 at MSU Dairy Store, left to right:
Qiang Wang, postdoc
Yue Yang, postdoc
Aaron Schmitz, graduate student (Cell & Moloecular Biology)
Joyce Bower, technician
John Sherbeck, undergraduate researcher

 (mutant screen machine)
Jonathan Glynn, graduate student (Genetics)
Kathy Osteryoung, PI
Afiqah Ahmadhisham, undergraduate researcher
Not shown:
Austin Be, undergraduate researcher
Natalie Mokris, lab assistant
