Conifer genome sizes of 172 species, covering 64 of 67 genera, range from 8 to 72 picogram

Abstract

Nuclear genome size of conifers as measured by fl ow cytometry with propidium iodide was investigated, striving to collect at least a single species from each genus. 64 out of 67 genera and 172 species were measured. Of the 67 genera, 21 are reported here for the fi rst time and the same is true for 76 species. Th is nearly doubles the number of measured genera and adds 50% to the number of analyzed species. Conifers have chromosome numbers in the range of n ϭ (7)10 -12(19). However, the nuclear DNA content (2C-value) is shown here to range from 8.3 to 71.6 picogram. Th e largest genome contains roughly 6 ϫ 10 10 more base pairs than the smallest genome. Genome sizes are evaluated and compared with available taxonomic treatments. For the mainly (sub)tropical Podocarpaceae small genome sizes were found with a 2C-value of only 8 -28 pg, with 13.5 pg on average. For the Taxaceae 2C-values from 23 -60 pg were determined. Not surprisingly, the genus Pinus with 97 species (39 species measured here) has a broad range with 2C ϭ 38 -72 pg. A factor of 2 difference is also found in the Cupressaceae (136 species) with nuclear DNA contents in the range 18 -35 pg. Apart from the allohexaploid Sequoia , ploidy plays a role only in Juniperus and some new polyploids are found. Th e data on genome size support conclusions on phylogenetic relationships obtained by DNA sequencing. Flow cytometry is applicable even to young plants or seeds for the monitoring of trade in endangered species.

Epigenetic Variability in the Genetically Uniform Forest Tree Species Pinus pinea L

“…Due to the large genome size of conifers [35] several steps of the technique were optimized for pine species. The initial amount of DNA digested with the two restriction enzyme combinations ( Eco RI/ Hpa II and Eco RI/ Msp I), was increased up to 500 ng [52].…”

“…Therefore, these species must cope with very variable environments through their life spans. Conifer genomes are very large, with genome sizes ranging between 20,000 and 30,000 Mbp, which on average is 200-fold larger than Arabidopsis genome and 6–10-fold larger than the human genome [34], [35]. Thus, regulatory machinery for gene expression and genome stability must be a key factor for these species in order to survive under changing environmental conditions.…”

Draft genome of the living fossil Ginkgo biloba

“…Furthermore, a complete ginkgo genome will facilitate the assembly and annotation of the published genome drafts of Picea abies [19], Picea glauca [20, 21] and Pinus taeda [22–26], along with other newly-reported gymnosperm genomes, as well as the transcriptomes of Cycas revoluta , Ephedra trifurca and Pinus canariensis [27]. Despite the rapid advance in the publication of complete genome sequences for diverse plant species, the belated publication of the ginkgo genome may in part result from its large size, which was estimated to be 11.75 Gb [28]. The vast amount of repeated sequences in gymnosperm genomes, as illustrated in the genome draft of P. abies [19], further hampers ambitions to address this issue.…”

Genome sizes of all 19 Araucaria species are correlated with their geographical distribution

“…Araucariaceae. Assuming an increase in DNA with time, the small genome sizes for the Podocarpaceae, with, on average, 13 pg (Zonneveld 2012, in press) (but not for the Araucariaceae) points indeed to an ancient position for the Podocarpaceae.…”