Premium
Chromosome number reduction in the sister clade of Carica papaya with concomitant genome size doubling
Author(s) -
Rockinger Alexander,
Sousa Aretuza,
Carvalho Fernanda A.,
Renner Susanne S.
Publication year - 2016
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.3732/ajb.1600134
Subject(s) - biology , carica , genome size , genome , clade , genus , ploidy , karyotype , genetics , evolutionary biology , chromosome , zoology , phylogenetics , botany , gene
PREMISE OF THE STUDY: Caricaceae include six genera and 34 species, among them papaya, a model species in plant sex chromosome research. The family was held to have a conserved karyotype with 2 n = 18 chromosomes, an assumption based on few counts. We examined the karyotypes and genome size of species from all genera to test for possible cytogenetic variation. METHODS: We used fluorescent in situ hybridization using standard telomere, 5S, and 45S rDNA probes. New and published data were combined with a phylogeny, molecular clock dating, and C values (available for ∼50% of the species) to reconstruct genome evolution. KEY RESULTS: The African genus Cylicomorpha, which is sister to the remaining Caricaceae (all neotropical), has 2 n = 18, as do the species in two other genera. A Mexican clade of five species that includes papaya, however, has 2n = 18 (papaya), 2 n = 16 ( Horovitzia cnidoscoloides ), and 2 n = 14 ( Jarilla caudata and J. heterophylla ; third Jarilla not counted), with the phylogeny indicating that the dysploidy events occurred ∼16.6 and ∼5.5 million years ago and that Jarilla underwent genome size doubling (∼450 to 830–920 Mbp/haploid genome). Pericentromeric interstitial telomere repeats occur in both Jarilla adjacent to 5S rDNA sites, and the variability of 5S rDNA sites across all genera is high. CONCLUSIONS: On the basis of outgroup comparison, 2 n = 18 is the ancestral number, and repeated chromosomal fusions with simultaneous genome size increase as a result of repetitive elements accumulating near centromeres characterize the papaya clade. These results have implications for ongoing genome assemblies in Caricaceae.