Abstract
To enhance the genomics and genetics of azalea, the whole-genome sequences of two species of Rhododendron were determined and analysed in this study: Rhododendron ripense, the cytoplasmic donor and ancestral species of large-flowered and evergreen azalea cultivars; and Rhododendron kiyosumense, a native of Chiba prefecture (Japan) seldomly bred and cultivated. A chromosome-level genome sequence assembly of R. ripense was constructed by single-molecule real-time sequencing and genetic mapping, while the genome sequence of R. kiyosumense was assembled using the single-tube long fragment read sequencing technology. The R. ripense genome assembly contained 319 contigs (506.7 Mb; N50 length: 2.5 Mb) and was assigned to the genetic map to establish 13 pseudomolecule sequences. On the other hand, the genome of R. kiyosumense was assembled into 32,308 contigs (601.9 Mb; N50 length: 245.7 kb). A total of 34,606 genes were predicted in the R. ripense genome, while 35,785 flower and 48,041 leaf transcript isoforms were identified in R. kiyosumense through Iso-Seq analysis. Overall, the genome sequence information generated in this study enhances our understanding of genome evolution in the Ericales and reveals the phylogenetic relationship of closely related species. This information will also facilitate the development of phenotypically attractive azalea cultivars.
Highlights
Azalea is a popular woody ornamental plant grown all around the world
We report the first genome assembly of R. ripense, which covered 96.1% of the estimated genome size and included 96.9% of the core gene set of Embryophyta represented by Benchmarking Universal Single-Copy Orthologs (BUSCO) (Table 2)
We established a draft genome sequence of R. kiyosumense, with 90.9% complete BUSCOs (Table 2); the assembled sequence contiguity represented by N50 was $10 times less than that of R. ripense contigs
Summary
Azalea is a popular woody ornamental plant grown all around the world. In Japan, evergreen azalea varieties (genus Rhododendron; subgenus Tsutsusi; section Tsutsusi), with high ornamental value, were collected from the natural habitat and have served as founding genotypes for breeding phenotypically attractive cultivars since the 17th century.[1].
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