Originally published as Genetics Published Articles Ahead of Print on August 5, 2005.

Genetics, Vol. 171, 741-752, October 2005, Copyright © 2005
doi:10.1534/genetics.105.045112

Insertional Polymorphism and Antiquity of PDR1 Retrotransposon Insertions in Pisum Species

Runchun Jing^*,1, Maggie R. Knox^,1, Jennifer M. Lee^*, Alexander V. Vershinin^,2, Michael Ambrose, T. H. Noel Ellis and Andrew J. Flavell^*,3

^* Plant Research Unit, University of Dundee at SCRI, Invergowrie, Dundee, DD2 5DA, United Kingdom and Department of Crop Genetics, John Innes Centre, Norwich, NR4 7UH, United Kingdom

³ Corresponding author: Plant Research Unit, Division of Applied and Environmental Biology, School of Life Sciences, University of Dundee at SCRI, Invergowrie, Dundee DD2 5DA, United Kingdom.
E-mail: a.j.flavell{at}dundee.ac.uk

Sequences flanking 73 insertions of the retrotransposon PDR1 have been characterized, together with an additional 270 flanking regions from one side alone, from a diverse collection of Pisum germ plasm. Most of the identified flanking sequences are repetitious DNAs but more than expected (7%) lie within nuclear gene protein-coding regions. The approximate age of 52 of the PDR1 insertions has been determined by measuring sequence divergence among LTR pairs. These data show that PDR1 transpositions occurred within the last 5 MY, with a peak at 1–2.5 MYA. The insertional polymorphism of 68 insertions has been assessed across 47 selected Pisum accessions, representing the diversity of the genus. None of the insertions are fixed, showing that PDR1 insertions can persist in a polymorphic state for millions of years in Pisum. The insertional polymorphism data have been compared with the age estimations to ask what rules control the proliferation of PDR1 insertions in Pisum. Relatively recent insertions (< 1.5MYA) tend to be found in small subsets of the Pisum accessions set, "middle-aged" insertions (between 1.5 and 2.5 MYA) vary greatly in their occurrence, and older insertions (> 2.5 MYA) are mostly found in small subsets of Pisum. Finally, the average age estimate for PDR1 insertions, together with an existing data set for PDR1 retrotransposon SSAP markers, has been used to derive an estimate of the effective population size for Pisum of 7.5 x 10⁵.

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