Résumé
PREMISE OF THE STUDY: The genome size of a species (C-value) is associated
with growth, development and adaptation to environmental changes.
Angiosperm C-values range 1200-fold and frequently vary within species,
although little is known about the impacts of domestication on genome
size. Genome size variation among related species of palms is of
evolutionary significance because changes characterize clades and may be
associated with polyploidy, transposon amplifications, deletions, or
rearrangements. Further knowledge of genome size will provide crucial
information needed for planning of whole genome sequencing and accurate
annotations. We studied the genome size of Cocos nucifera and its
variation among cultivars, and compared it to values for related palms
from the Attaleinae subtribe. METHODS: Flow cytometric analysis of
isolated nuclei from young palm leaves was used to estimate genome sizes
of 23 coconut cultivars (Talls, Dwarfs, and hybrids) worldwide and 17
Cocoseae species. Ancestral genome size was reconstructed on a maximum
likelihood phylogeny of Attaleinae from seven WRKY loci. KEY RESULTS: The
coconut genome is large—averaging 5.966 pg—and shows intraspecific
variation associated with domestication. Variation among Tall coconuts was
significantly greater than among Dwarfs. Attaleinae genomes showed
moderate size variation across genera, except polyploids Jubaeopsis
caffra, Voanioala gerardii, Beccariophoenix alfredii, and Allagoptera
caudescens, which had larger genomes. CONCLUSIONS: Our results contribute
to the understanding of the relationship between domestication and genome
size in long-lived tree crops and provide a basis for whole-genome
sequencing of the coconut and other domesticated plants. Polyploidy
evolved independently in two clades within Attaleinae.