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Ploidy and size in the Arabidopsis sepal

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Abstract

Ploidy and size phenomena have been correlated across several biological scales, from subcellular to organismal. Whole-genome multiplication increases ploidy in whole plants and is broadly associated with increases in cell and organism size. Endoreduplication, which increases ploidy in individual cells, is strongly correlated with increased cell size and nuclear volume. We use the Arabidopsis sepal as a model to study these phenomena. In my first study, I investigated scaling relationships between ploidy and size by simultaneously quantifying nuclear size, cell size, and organ size in sepals in an isogenic series of diploid, tetraploid, and octoploid plants. We found that pavement cell size increases linearly with ploidy across this series, but organ area increases more modestly due to a compensatory decrease in cell number. Cellular growth rates are similar at all ploidy levels. Likewise, transcriptome size increases with ploidy, and while most genes retain their proportional expression pattern, expression of cell wall-associated genes increases disproportionately with ploidy. We observed that cell size and nuclear size are maintained at a constant ratio; the value of this constant is similar in diploid and tetraploid plants, and slightly lower in octoploid plants. However, cell size is maintained when nuclear size is reduced in the crwn1 mutant, indicating that cell size scales to ploidy rather than nuclear size. These results shed light on how size is regulated in plants and how cells and organisms of differing sizes are generated by ploidy change. In my second study, I imaged promoter and protein expression for the SIAMESE-like CDK inhibitor LGO, which controls the entry into endocycles in sepal pavement cells. I found that LGO is broadly transcribed, but that post-transcriptional regulation limits LGO protein to a small number of cells. This expression pattern is consistent with the scattered pattern of endopolyploid cells observed in mature sepals. In my third study, I explored variation in sepal cell size patterning in a panel of Brassicaceae species. I found that some, but not all, species had an interspersed pattern of small and large cells on the sepal’s abaxial surface; sepals with homogeneous cell size did not modulate curvature during anthesis.

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Supplemental file(s) description: RNA-seq data, Gene ontology enrichment by expression response bin

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Date Issued

2018-05-30

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cell size; endoreduplication; nuclear size; organ size; polyploidy; whole-genome multiplication; Botany; Biology; Plant sciences

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Committee Chair

Roeder, Adrienne H.K.

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Doyle, Jeffrey J.
Scanlon, Michael J.

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Plant Biology

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Ph. D., Plant Biology

Degree Level

Doctor of Philosophy

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Government Document

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dissertation or thesis

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