J Syst Evol

• Research Articles •    

Polyploidy in Cupressaceae: Discovery of a new naturally occurring tetraploid, Xanthocyparis vietnamensis

Perla Farhat1,2*, Sonja Siljak-Yakovlev2, Oriane Hidalgo3,4, Keith Rushforth5, Jim A. Bartel6, Nicolas Valentin7, Ilia J. Leitch3, and Robert P. Adams8   

  1. 1 Laboratoire Biodiversité et Génomique Fonctionnelle, Faculté des Sciences, Université Saint‐Joseph, Campus Sciences et Technologies, Mar Roukos, Mkalles, BP: 1514 Riad el Solh, Beirut 1107 2050, Lebanon
    2 Université Paris‐Saclay, CNRS, AgroParisTech, Ecologie Systématique Evolution, Orsay 91405, France
    3 Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK
    4 Institut Botànic de Barcelona (IBB, CSIC‐Ajuntament de Barcelona), Passeig del Migdia s.n., Parc de Montjuïc, Barcelona, Catalonia 08038, Spain
    5 The Shippen, Ashill, Cullompton, Devon EX15 3NL, UK
    6 San Diego Botanic Garden, P.O. Box 230005, Encinitas, CA 92023, USA
    7 Institute of Integrative Biology of the Cell (I2BC), Plateforme de Cytométrie, CEA, CNRS, Université Paris‐Saclay, Gif‐sur‐Yvette 91198, France
    8 Biology Department, Baylor University, Box 97388, Waco, TX 76798, USA
  • Received:2020-12-10 Accepted:2021-04-08 Online:2021-04-19

Abstract: While polyploidy (whole-genome multiplication) is generally considered rare in extant gymnosperms (with the exception of Ephedra, Ephedraceae), the occurrence of sporadic polyploid individuals belonging to various genera in the conifer family Cupressaceae has been reported in the literature. In addition, recent studies have revealed that polyploidy is not uncommon in the genus Juniperus (Cupressaceae), with tetraploid and hexaploid individuals reported in individuals collected from wild populations. Given these findings, we undertook a comprehensive screening of ploidy levels in 32 species belonging to the four genera that are phylogenetically closest to Juniperus (i.e., Callitropsis, Hesperocyparis, Xanthocyparis, and Cupressus), referred to as the CaHXCu complex. In addition, we also determined the ploidy level of two accessions in the poorly studied tetraploid, Fitzroya cupressoides. Using flow cytometry together with published chromosome counts to assign ploidy levels, we show that all species of the CaHXCu complex are diploid except Xanthocyparis vietnamensis, which is tetraploid, with a genome size of 44.60 pg/2 C. This study opens up new opportunities for studying the impact and consequences of polyploidy on the evolution and adaptation of species in Cupressaceae.

Key words: conifers, evolution, flow cytometry, genome size, gymnosperms, ploidy level