LAUSR

Rhododendron is well-known for its beauty and colorful corolla. Although some high-quality whole-genome sequencing of Rhododendron has been completed, there is lack of studies on long terminal repeat (LTR) retrotransposons in Rhododendron, which limits our ability to elucidate the causes of genetic variations in Rhododendron species. The properties of the intact Rhododendron LTR retrotransposon were investigated at the genome-wide level. Based on the available data, the high-quality genomes from five species, i.e., R. griersonianum, R. simsii, R. henanense subsp. lingbaoense, R. mucronatum var. ripense and R. ovatum were selected as the identification targets with good assembly continuity. A total of 17,936 intact LTR retrotransposons were identified; they belong to the superfamilies Copia and Gypsy with 17 clades. The insertion time of these transposons was later than 120 million years ago, and the outbreak period was concentrated more recently than 30 million years ago. Phylogenetic analysis revealed that many LTR retrotransposons might originate from intraspecific duplication. The current evidences also suggests that most of the LTR retrotransposons were inserted in the interstitial part of the genes in R. griersonianum, R. simsii, R. henanense, and R. ovatum, and the functions of the inserted genes are mainly involved in starch metabolism and proteolysis etc. The effect of LTR retrotransposon on gene expression depends on its insertion site and activation. Highly expressed LTR retrotransposons tended to be younger. The activity of LTR retrotransposons may affect some stage-specific expression genes of flower development, such as leucine-rich repeat receptor-like kinase. The available results herein improve our knowledge of LTR retrotransposons in Rhododendron genomes and facilitate the further study of genetic variation and trait evolution in Rhododendron.