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Review Examines the Impact of Genome Doubling on Biology of the Cell; Considers Polyploidy, Nucleotype, and Novelty

In an open-access review article titled "Polyploidy, the Nucleotype, and Novelty: The Impact of Genome Doubling on the Biology of the Cell," that was published in the January 2019 print issue of the International Journal of Plant Sciences(180: 1-52), Dr. Jeff J. Doyle and Dr. Jeremy E. Coate examine the effects of genome doubling on cell biology and the generation of novelty in plants. Polyploid organisms are those containing more than two paired (homologous) sets of chromosomes, and polyploidy is common across many plant species. This "genome doubling" generates evolutionary novelty and is a prime facilitator of new species. How polyploidy alters cells to generate novelty, however, is complex, and, as Dr. Doyle (School of Integrative Plant Science, Plant Breeding and Genetics Section, Cornell University) and Dr. Coate (Biology Department, Reed College) illustrate, not well understood, even on a fundamental level. Rapidly developing technology, however, will enable researchers to shed light, not only on this integral part of plant evolution and biology, but also on the function of cells in general. Many of the documented effects of genome doubling on cells, such as increases in cell size, nuclear volume, and cell cycle duration, are hypothesized to be "nucleotypic" – i.e., effects induced by changes in bulk DNA amount, irrespective of genotype. Dr. Doyle and Dr. Coate update our understanding of the nucleotype and other mechanisms by which genome doubling can alter cell biology, highlighting insights gained from studies of synthetic autopolyploids and relating these to the current state of knowledge in the field of cell biology. Cell size, in particular, was of great interest to the authors, because it is strongly associated with genome doubling. Though it has long been known that genome size and cell size correlate, recent work shows that this correlation is cell-type-specific, and the factors that control cell size, polyploidy or otherwise, remain mysterious.

Dr. Doyle and Dr. Coate write that they had hoped that the long-running literature of cell biology would hold the answers to how polyploidy operates at the cellular level. "Instead, we discovered that these questions, as well as a host of other issues needed to address the question of what polyploidy "does," have yet to be answered satisfactorily," they write.

"In many cases, there are competing theories, and often there exists a dearth of compelling data, even in mature model systems, such as human and yeast, or in the best plant models, such as Arabidopsis and maize, let alone in non-model plant species."

The authors go on to suggest that in order to understand polyploidy, as well as cellular function in general, researchers must shift their focus to quantitative data, such as time resolution, rate constants, and local molecule concentrations, when analyzing polyploids against their diploid progenitors.

Dr. Doyle and Dr. Coate outline questions on polyploidy research going forward. These include how nuclear crowdedness varies with nuclear size across cell types and species, whether protein stability is affected by polyploidy, and whether changes in transcriptome size associated with polyploidy are a response to increased nuclear volume or vice versa.

"The technology exists to address such questions quantitatively, with ever-increasing precision and at ever-decreasing scales down to individual cells and molecules," they write. "We are now poised to address these questions and to understand what polyploidy 'does.'"

[Press release] [International Journal of Plant Sciences review article (open-acces)]