Abstract Detail

Classical Genetics

Robinson, Dana [1], Coate, Jeremy [2], Doyle, Jeff [3], Roeder, Adrienne [1].

Endopolyploidy and whole-genome duplication similarly affect cell size in the Arabidopsis thaliana sepal.

Cell size variation in Arabidopsis is largely driven by endopolyploidy, a system in which cell ploidy (2C-32C) and cell size are strongly correlated. Whereas endopolyploidy (EPP) occurs in single cells during differentiation, stable whole-genome duplication (WGD) constitutively increases the ploidy of all cells. Here we ask whether these distinct forms of polyploidy (EPP and WGD) have comparable effects on cell size. The Arabidopsis sepal epidermis is patterned with endopolyploid cells and is amenable to imaging. We manipulated WGD and EPP in the sepal to explore the relationships among cell ploidy, cell size, and organ size. We first assessed the relationship between nuclear and cell size. Paired measurements of cell area and nuclear volume were made for roughly 700 cells per sepal. Nuclear volume was positively correlated with cell area (R²=0.78). The karyoplasmic ratio (KR) was calculated as cell area/nuclear volume. Average KR was ca. 4.0 in diploid and tetraploid sepals, indicating remarkable consistency in the scaling of cell and nuclear size. Average nuclear volume increased linearly with WGD ploidy. Cell area also increased with genome duplication, 1.76-fold between diploid and tetraploid and 1.71-fold between tetraploid and octoploid. Patterns of endoreduplication were near-identical in diploid, tetraploid, and octoploid plants. WGD also had a significant, but less pronounced effect on total organ size: sepal area increased 1.28-fold between diploid and tetraploid and 1.26-fold between tetraploid and octoploid. In contrast, changes in level of endopolyploidy have a very minor effect on organ size. Such changes can be made by misexpression of the CDK inhibitor LGO, which affects entry into endocycles. Loss of LGO expression reduced average cell area by 1.24-fold, whereas overexpression increased average cell area by 3.28-fold; total sepal area changed by only 1.07-fold. These data suggest a strong organ-level mechanism compensating for changes in endopolyploidy and a weaker compensation method for changes in WGD. Together, these results suggest that the scaling relationship between cell ploidy and cell size is conserved between EPP and WGD; this offers a cell-level mechanism that may partially explain observed size differences between polyploid lineages and their diploid progenitors. We are performing genome-normalized RNA-Seq to determine how transcriptome size scales with ploidy and to identify candidate genes involved in regulating cell size response to ploidy. Preliminary estimates in leaf tissue indicate that transcriptome size is ca. 1.5-fold larger in a synthetic Arabidopsis tetraploid than in its diploid parent; we hypothesize that transcription scales predictably with cell size.

1 - Cornell University, Plant Biology Section, School of Integrative Plant Science, Ithaca, NY, 14853, USA
2 - Reed College, Plant Biology, 3203 SE Woodstock Blvd., Portland, OR, 97202, USA
3 - Cornell University, Plant Breeding & Genetics Section, School of Integrative Plant Science, Ithaca, NY, 14853, USA

Keywords:
Polyploidy
cell size
nuclear volume
endopolyploidy.

Presentation Type: Oral Paper
Session: 4, Classical Genetics & Molecular Ecology
Location: Fort Worth Ballroom 8/Omni Hotel
Date: Monday, June 26th, 2017
Time: 8:45 AM
Number: 4003
Abstract ID:220
Candidate for Awards:None