Nuclear DNA amounts in angiosperms: targets, trends and tomorrow

Annals of Botany 107: 467 –590, 2011 doi:10.1093/aob/mcq258, available online at www.aob.oxfordjournals.org Nuclear DNA amounts in angiosperms: targets, trends and tomorrow M. D. Bennett* and I. J. Leitch Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, UK * For correspondence. E-mail: Received: 25 August 2010 Returned for revision: 18 October 2010 Accepted: 24 November 2010 Published electronically: 21 January 2011 CONTENTS 468 469 470 470 470 471 472 472 473 473 473 474 474 474 474 474 475 475 475 479 480 481 481 482 485 485 587 † Background and Aims The amount of DNA in an unreplicated gametic chromosome complement is known as the C-value and is a key biodiversity character of fundamental significance with many practical and predictive uses. Since 1976, Bennett and colleagues have assembled eight compilations of angiosperm C-values for reference purposes and subsequently these have been pooled into the Angiosperm DNA C-values Database (http://data.kew.org/ cvalues/). Since the last compilation was published in 2005, a large amount of data on angiosperm genome size has been published. It is therefore timely to bring these data together into a ninth compilation of DNA amounts. † Scope The present work lists DNA C-values for 2221 species from 151 original sources (including first values for 1860 species not listed in previous compilations). Combining these data with those published previously shows that C-values are now available for 6287 angiosperm species. † Key Findings Analysis of the dataset, which is by far the largest of the nine compilations published since 1976, shows that angiosperm C-values are now being generated at the highest rate since the first genome sizes were estimated in the 1950s. The compilation includes new record holders for the smallest (1C ¼ 0.0648 pg in Genlisea margaretae) and largest (1C ¼ 152.23 pg in Paris japonica) genome sizes so far reported, extending the range encountered in angiosperms to nearly 2400-fold. A review of progress in meeting targets set at the Plant Genome Size meetings shows that although representation for genera, geographical regions and some plant life forms (e.g. island floras and parasitic plants) has improved, progress to increase familial representation is still slow. In terms of technique it is now clear that flow cytometry is soon likely to become the only method available for plant genome size estimations. Fortunately, this has been accompanied by numerous careful studies to improve the quality of data generated using this technique (e.g. design of new buffers, increased awareness and understanding of problems caused by cytosolic inhibitors). It is also clear that although the speed of DNA sequencing continues to rise dramatically with the advent of next-generation and third-generation sequencing technologies, ‘complete genome sequencing’ projects are still unable to generate accurate plant genome size estimates. Key words: DNA C-value, nuclear genome size, Plant DNA C-values Database, flow cytometry. # The Author 2011. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: INTRODUCTION Extending the range of genome sizes encountered in angiosperms The need for reference lists TARGETS IN GENOME SIZE RESEARCH Meeting targets for species representation Progress towards targets for familial representation Improved systematic representation for genera Improved representation of other groups TRENDS IN TECHNIQUES USED TO ESTIMATE GENOME SIZE The rise in flow cytometry as the technique of choice for genome size estimations Development of different isolation buffers for flow cytometry The application of flow cytometry to plant systematics Recent developments in the application of flow cytometry to genome size studies (i) The use of seeds (ii) Ease of access to methodological data (iii) New equipment Are there any new techniques for estimating genome size on the horizon? (i) Can real time PCR be used for estimating plant genome sizes? (ii) Will ‘complete’ genome sequencing give useable genome size estimates? TOMORROW Uncovering and collating genome size data from diverse published sources Screening ex situ and in situ collections as sources of target taxa DEDICATION LITERATURE CITED APPENDIX Notes to the Appendix Original references for DNA values 468 Bennett & Leitch – Nuclear DNA amounts in angiosperms IN TROD UC TIO N TA B L E 1. Total numbers of first estimates for angiosperm species and of original references from which they come in nine compilations of nuclear genome size estimates collated for reference purposes since 1976 Original compilation 1. Bennett and Smith (1976) 2. Bennett et al. (1982) 3. Bennett and Smith (1991) 4. Bennett and Leitch (1995) 5. Bennett and Leitch (1997) 6. Bennett et al. (2000) 7. Bennett and Leitch (2005a) 8. Zonneveld et al. (2005) 9. Present work Total No. of first estimates for ‘species’ in abstract of compilation No. of prime estimates for species in the Plant DNA C-values Database (release 5.0) No. of original references in compilation No. of first estimates per original reference (column 2/4) 753 240 588 899 471 691 628 308 1860 6438* 596† 195† 552† 868 † 481† 686† 636† 308 1974† 6287* 54 53 56 106 37 71 88 1 151 617 13.9 4.5 10.5 8.5 12.7 9.7 7.7 308.0 13.1 – * The total number of taxa in the Plant DNA C-values Database (i.e. 6287) is lower by 151 than the total for paper compilations (i.e. total ¼ 6438) because several types of entry included in the latter are omitted from the former. These include: 87 DNA per cell values, 35 genus sp. values where other values for named species in the same genus are included, and 29 values for some varieties of species where values for other varieties of the same species are included. † The number of prime estimates for species in the Plant DNA C-values Database (release 5.0) (Bennett and Leitch, 2010) may differ from the number of first estimates for species listed in the abstract of paper compilations (column 2) owing to the reallocation of prime status from the first estimate published for a taxon to an estimate published later. It has been possible to estimate the amount of DNA in plant and animal nuclei using various methods for over 60 years. Following the discovery of the key role of DNA in biology in 1953 (Watson and Crick, 1953) such research has increased in each successive decade, and this trend has further intensified in the 21st century. These decades saw the loss of many who played key roles in founding and developing this interest [including Hewson Swift (1920– 2004), John McLeish (1929 – 1971), Arnold Sparrow (1914– 1976) and Hugh Rees (1923 – 2009)]. Yet until now the remarkable birth and explosion of genome size data in ‘the DNA age’ occurred in the scientific lifetime of some individuals who witnessed or experienced the entire development of this field. However, the death of Jim Price (1944– 2005 (...truncated)