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Investigations on the influence of cellular sugar and endoplasmic reticulum dynamics on plastid pleomorphy in Arabidopsis thaliana

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Title: Investigations on the influence of cellular sugar and endoplasmic reticulum dynamics on plastid pleomorphy in Arabidopsis thaliana
Author: Barton, Kiah Ainsley
Department: Department of Molecular and Cellular Biology
Program: Molecular and Cellular Biology
Advisor: Mathur, Jaideep
Abstract: Plastids exhibit continuous changes in shape over time, seen either as alterations in the form of the entire plastid or as the extension of thin stroma-filled tubules (stromules). Live-imaging of fluorescently-highlighted organelles was used to assess the role of cellular sugar status and endoplasmic reticulum (ER) rearrangement in this behaviour. Plastids in the pavement cells of Arabidopsis are shown to be chloroplasts and a brief summary of their physical relationship with other cellular structures, their development, and their stromule response to exogenous sucrose is presented. Of the several sugars and sugar alcohols tested, plastid elongation in response to exogenously applied sugars is specific to glucose, sucrose and maltose, indicating that the response is not osmotic in nature. Sugar analogs, used to assess the contribution of sugar signalling to a process, and the sucrose signalling component trehalose-6-phosphate have no effect on stromule formation. Stromule frequency increases in response to multiple nutrient stresses in a sugar-dependent manner. Mutants with increased sugar accumulation show corresponding increases in stromule frequencies, though plastid swelling as a result of excessive starch accumulation negatively affects stromule formation. The elongation and retractions of plastids is seen to correlate with the rearrangement of the ER. Transient dilations in tubular portions of plastids, as well as gaps in stromal fluorescence, are associated with regions of spatial interaction with the ER. The degree of plastid elongation correlates with the size of the ER polygons both regionally and at the level of individual plastids, with more elongated etioplasts seen alongside smaller ER polygons. The disruption of ER structure or rearrangement through treatment with Latrunculin B, Brefeldin A or cold temperatures corresponds with a decrease in general plastid elongation and the inhibition of stromule induction by sucrose. The endoplasmic reticulum morphology 1-1 mutant has compromised ER structure and this correlates with a general reduction in plastid tubulation. The evidence presented here suggests that cellular sugar has a pivotal role in inducing plastid pleomorphy in an ER-mediated manner.
Date: 2020
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Embargoed Until: 2021-04-03

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