Repeatome landscapes and cytogenetics of hortensias provide a framework to traceHydrangeaevolution and domestication

Abstract

Background and AimsOrnamental hortensias are bred from a reservoir of over 200 species in the genusHydrangeas.l. and are valued in gardens, households and landscapes across the globe. The phenotypic diversity of hortensia cultivars, hybrids and wild relatives is mirrored by their genomic variation, with differences in genome size, base chromosome numbers and ploidy level. We aim to understand the genomic and chromosomal basis of hortensia genome variation. Therefore, we analyze six hortensias with different origins and chromosomal setups for repeatome divergence, the genome fraction with the highest sequence turnover. This holds information from the hortensia’s evolutionary paths and can inform breeding initiatives.MethodsWe compiled a hortensia genotype panel representing members of the sectionsMacrophyllae,Hydrangea, Asperae, andHeteromallaeand reconstructed a plastome-based phylogenetic hypothesis as evolutionary basis for all our analyses. We comprehensively characterized the repeatomes by whole genome sequencing and comparative repeat clustering. Major tandem repeats were localized by multi-color FISH.Key ResultsTheHydrangeaspecies show differing repeat profiles reflecting their separation into the two majorHydrangeaclades: DiploidHydrangeaspecies from Japan show a conserved repeat profile, distinguishing them from Japanese polyploids as well as Chinese and American hortensias. These results are in line with plastome-based phylogenies. The presence of specific repeats indicates thatH. paniculatawas not polyploidized directly from the common ancestor of JapaneseHydrangeaspecies, but evolved from a distinct progenitor. Major satellite DNAs were detected over allH. macrophyllachromosomes.ConclusionsRepeat composition among theHydrangeaspecies varies in congruence with their origins and phylogeny. Identified species-specific satDNAs may be used as cytogenetic markers to identifyHydrangeaspecies and cultivars, and to infer parental species of oldHydrangeavarieties. This repeatome and cytogenetics information helps to expand the genetic toolbox for tracing hortensia evolution and informing future hortensia breeding.