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Division Ring Placement, Osmotic Stress Response, and Plant Development: The Many Roles of Membrane Tension in the Life of a Plastid
Date of Award
Doctor of Philosophy (PhD)
All living organisms sense and respond to mechanical stimuli such as touch, gravity, and osmotic pressure. One instrument of mechanoperception is mechanosensitive (MS) channels. Two Arabidopsis thaliana homologs of the well-characterized bacterial MS channel MscS, MscS-Like (MSL)2 and 3, localize to the inner envelope of plastids (plant-specific organelles), where they serve as osmotic release valves. msl2 msl3 mutants exhibit several distinct phenotypes including enlarged chloroplasts, enlarged, spherical non-green plastids, abnormal leaf morphology, and stunted growth. Characterization of these mutants has allowed me to: (1) Establish a role for MS channels in chloroplast division site placement. In both chloroplasts and bacteria, the division site is specified by FtsZ-ring formation, which is regulated by the Min system. My analyses determined that msl2 msl3 mutant chloroplasts contain multiple FtsZ rings and place MSL2 and MSL3 in the same regulatory pathway as several Min system components. Additionally, a bacterial strain lacking MS channels displayed aberrant FtsZ ring placement, suggesting that the role for MS channels in FtsZ ring placement is evolutionarily conserved. (2) Provide evidence that plastids are capable of communicating their osmotic status to the rest of the cell. I have shown that msl2 msl3 mutants exhibit several hallmarks of osmotically stressed plants including osmotic adjustment, proline and ABA accumulation, and transcriptional responses as a result of plastid hypoosmotic stress rather than external environmental stress. These results establish that plastids are capable of sensing cytoplasmic osmotic imbalance and triggering the same osmotic responses as osmosensors present at the plasma membrane. (3) Begin evaluating the cellular, whole-plant, and developmental defects stemming from organelle dysfunction in plants lacking functional versions of MSL2, MSL3, and MSL1, a mitochondrial-localized MscS homolog. The abnormal leaf morphology and root defects observed in msl1 msl2 msl3 mutants are shared among a diverse group of mutants with impaired plastid and/or mitochondrial function. This suggests that organelle stress results in a general transcriptional response, possibly through organelle-to-nucleus signaling. In summary, MS channels are required for proper division site placement, and plants lacking organelle localized MS channels are powerful tools for exploring the impact of organelle osmotic stress on plant growth and development.
Chair and Committee
Elizabeth S Haswell
Ram Dixit, Barbara Kunkel, Robert Kranz, Petra Levin, Sona Pandey
Wilson, Margaret E., "Division Ring Placement, Osmotic Stress Response, and Plant Development: The Many Roles of Membrane Tension in the Life of a Plastid" (2013). Arts & Sciences Electronic Theses and Dissertations. 153.