An Eruption of LTR Retrotransposons in the Autopolyploid Genomes of Chrysanthemum nankingense (Asteraceae)

Abstract

Whole genome duplication, associated with the induction of widespread genetic changes, has played an important role in the evolution of many plant taxa. All extant angiosperm species have undergone at least one polyploidization event, forming either an auto- or allopolyploid organism. Compared with allopolyploidization, however, few studies have examined autopolyploidization, and few studies have focused on the response of genetic changes to autopolyploidy. In the present study, newly synthesized C. nankingense autotetraploids (Asteraceae) were employed to characterize the genome shock following autopolyploidization. Available evidence suggested that the genetic changes primarily involved the loss of old fragments and the gain of novel fragments, and some novel sequences were potential long terminal repeat (LTR) retrotransposons. As Ty1-copia and Ty3-gypsy elements represent the two main superfamilies of LTR retrotransposons, the dynamics of Ty1-copia and Ty3-gypsy were evaluated using RT-PCR, transcriptome sequencing, and LTR retrotransposon-based molecular marker techniques. Additionally, fluorescence in situ hybridization(FISH)results suggest that autopolyploidization might also be accompanied by perturbations of LTR retrotransposons, and emergence retrotransposon insertions might show more rapid divergence, resulting in diploid-like behaviour, potentially accelerating the evolutionary process among progenies. Our results strongly suggest a need to expand the current evolutionary framework to include a genetic dimension when seeking to understand genomic shock following autopolyploidization in Asteraceae.

Exploration of incompatible crosses in plants for novel and useful variations

“…Elimination of most male chromosomes and extra duplication of partial chromosomes during meiotic DNA synthesis phase were observed in intertribal crosses between Brassica species (B. rapa, B. napus) and Capsella bursa-pastoris and B. rapa  O. violaceus intergeneric cross (Chen, 2007;Liu & Li, 2007). Genetic changes as the loss of old fragments and the gain of novel fragments and some novel sequences were potential long terminal repeat (LTR) retrotransposons were reported in Chrysanthemum nankingense due to genome shock following autopolyploidization that can contribute abundant raw material in adaptive evolution (He et al, 2022). In the hybrids of synthetic Brassica, Brassica oleracea allohexaploids  O. violaceus, chromosomes of O. violaceus are preferentially eliminated, whereas Brassica genomes showed stability in the order of B > A > C (Ge et al, 2009).…”

“…By isolating the genomic regions flanking the newly transposed retrotransposon Tos17 copies, Han et al (2004) identified preferential insertion of the elements in cellular genes, thereby explaining potential impacts of the transposition on the structure and expression of the targeted genes. LTR retrotransposons such as Ty1-copia and Ty3-gypsy elements are triggered by genome shock during alloploidization leading to array of genetic changes (He et al, 2022).…”