Genome sizes for all genera of Cycadales

Abstract

Nuclear DNA content (2C) is reported for all genera of the Cycadales, using flow cytometry with propidium iodide. Nuclear DNA content ranges from 24 to 64 pg in cycads. This implies that the largest genome contains roughly 40 × 10(9) more base pairs than the smallest genome. The narrow range in nuclear DNA content within a genus is remarkable for such an old group. Furthermore, 42 of the 58 plants measured, covering five genera, have 18 chromosomes. They vary from 36.1 to 64.7 pg, covering the whole range of genome sizes (excluding the genome of Cycas). Hence, their does not seem to be a correlation between genome size and the number of chromosomes.

RADseq as a valuable tool for plants with large genomes—A case study in cycads

“…Plant genome sizes are highly plastid (Pellicer, Hidalgo, Dodsworth, & Leitch, ), ranging from 13.2 Megabase pairs (Mbp) in the genome of Ostreococcus lucimarinus to over 149 Gigabase pairs (Gbp) in the octoploid Paris japonica (Pellicer, Fay, & Leitch, ). As a result of whole genome duplication, gymnosperm genomes are generally larger than those found in many angiosperms, ranging from ~8 Gbp in Microstrobus to ~72 Gbp in Pinus and Ceratozamia (Roodt et al, ; Scott, Stenz, Ingvarsson, & Baum, ; Zonneveld, , ; Zonneveld & Lindstrom, ). Typically, as a result of polyploidy, the on‐average large genome size is caused by an inefficiency of gymnosperms at eliminating repeat amplifications in the genome (Pellicer et al, ).…”

“…In order to test the effectiveness of RADseq for taxa with large genomes, we used a RADseq technique across a cohort of samples representing ten known cycad genera (Cycadales). We chose cycads because they have particularly large genomes, ranging from ~25 to 30 Gbp in Cycas L. to ~72 Gbp in Ceratozamia (Zonneveld, ), which appears to be the result of many tandem repeats, pseudogenes, paralogs and possibly whole genome duplication (Roodt et al, ). In addition to having on‐average larger genomes, we also chose cycads because there is need for better methods to find more data‐rich sequences for the purposes of systematic and population genomic studies.…”

“…in Microstrobus to ~72 Gbp in Pinus and Ceratozamia (Roodt et al, 2017;Scott, Stenz, Ingvarsson, & Baum, 2016;Zonneveld, 2012aZonneveld, , 2012bZonneveld & Lindstrom, 2016). Typically, as a result of polyploidy, the on-average large genome size is caused by an inefficiency of gymnosperms at eliminating repeat amplifications in the genome (Pellicer et al, 2018).…”

“…Gbp in Cycas L. to ~72 Gbp in Ceratozamia (Zonneveld, 2012a), which appears to be the result of many tandem repeats, pseudogenes, paralogs and possibly whole genome duplication (Roodt et al, 2017).…”

Evolutionary developmental biology in cycad phenology

“…21). Similarly, Lynch and Conery 22 hypothesized that large genome size, which we see in cycads, 20 , 23 may be maladaptive. Thus developmental rates of different plant parts may be nothing more that what Gould and Lewontin 24 mistakenly called spandrels.…”