INVESTIGATION OF SIGNALING FROM THE SENSORY PLASTID GENOME IN ARABIDOPSIS THALIANA
Restricted (Penn State Only)
- Author:
- Dopp, Isaac
- Graduate Program:
- Plant Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 24, 2024
- Committee Members:
- Sally Mackenzie, Chair & Dissertation Advisor
Cristina Rosa, Outside Unit & Field Member
Sarah Assmann, Major Field Member
Gabriele Monshausen, Major Field Member
Teh-Hui Kao, Program Head/Chair - Keywords:
- plastid
signaling
epigenetic
reactive oxygen species
plant - Abstract:
- Plastids are endosymbiotic organelles in plants that have retained part of their ancestral genome over evolution and adopted diverse metabolic functions. Maintenance of the plastid genome is essential for autotrophic development, and the plastid genome is under constant assault from light-dependent damage and photosynthesis-derived reactive oxygen species. Consequently, plants have evolved extensive mechanisms for surveillance and repair of this genome. Characterizations of mutant plants defective in DNA repair pathways have demonstrated considerable reprogramming of nuclear gene expression following damage and instability of the plastid genome, suggesting an intricate process of retrograde signaling from the plastid genome to affect nuclear gene expression. One such protein, MutS-Homolog 1 (MSH1), is nuclear-encoded, organelle-targeted, and involved in maintenance of the plastid and mitochondrial genomes. Our lab has demonstrated developmental pleiotropy in msh1 that is largely attributed to depletion of msh1 from the plastid. Likewise, msh1 mutants (and plastid-depleted mutants, specifically) can imbue heritable, epigenetic phenotypes that can be separated from cytoplasmic mutations arising from organellar genome instability. The central questions of this dissertation are: how do plastids signal genome instability, and is plastid genome instability sufficient to explain the msh1 phenotypes? Based off an MSH1 cell type-specific gene expression data set, we have previously identified Ca2+-mediated signaling as a uniquely enriched network of msh1 mutant plants. Consistent with this observation, severe developmental epistasis between double mutants for msh1 and the plastid localized, cytoplasmic Ca2+regulating Calcium Sensing receptor (CaS) was observed. We detected a CaS-dependent cytoplasmic Ca2+ signal following acute organellar genomic stress via application of the DNA gyrase inhibitor, ciprofloxacin (CIP). CIP treatment phenocopied msh1 growth, plastid genome recombination, and plastid stromal redox buffering phenotypes. Whole genomic nuclear DNA methylation analysis of msh1 and CIP-treated Arabidopsis seedlings demonstrated striking correspondence in gene-associated differential cytosine methylation. Taken together, these data support a model where Ca2+ mediates retrograde signaling from the plastid genome, revealing a previously uncharacterized link between the role of msh1 in maintaining plastid genome stability and the subsequent nuclear, epigenetic reprogramming. These findings have important implications for implementation of msh1-dependent epigenetic breeding programs in agriculturally relevant species.