Genome Biology and Evolution 6(1): 247-259 (2014)
Rapid Genetic and Epigenetic Alterations under Intergeneric Genomic Shock in Newly Synthesized Chrysanthemum morifolium x Leucanthemum paludosum Hybrids (Asteraceae)
Haibin Wang, Jiafu Jiang, Sumei Chen, Xiangyu Qi, Weimin Fang, Zhiyong Guan, Nianjun Teng, Yuan Liao and Fadi Chen

Abstract
The Asteraceae family is at the forefront of the evolution due to frequent hybridization. Hybridization is associated with the induction of widespread genetic and epigenetic changes and has played an important role in the evolution of many plant taxa. We attempted the intergeneric cross Chrysanthemum morifolium x Leucanthemum paludosum. To obtain the success in cross, we have to turn to ovule rescue. DNA profiling of the amphihaploid and amphidiploid was investigated using amplified fragment length polymorphism, sequence-related amplified polymorphism, start codon targeted polymorphism, and methylation-sensitive amplification polymorphism (MSAP). Hybridization induced rapid changes at the genetic and the epigenetic levels. The genetic changes mainly involved loss of parental fragments and gaining of novel fragments, and some eliminated sequences possibly from the noncoding region of L. paludosum. The MSAP analysis indicated that the level of DNA methylation was lower in the amphiploid (45%) than in the parental lines (51.550.6%), whereas it increased after amphidiploid formation. Events associated with intergeneric genomic shock were a feature of C. morifolium x L. paludosum hybrid, given that the genetic relationship between the parental species is relatively distant. Our results provide genetic and epigenetic evidence for understanding genomic shock in wide crosses between species in Asteraceae and suggest a need to expand our current evolutionary framework to encompass a genetic/epigenetic dimension when seeking to understand wide crosses.

Morphology of materials. (A) Chrysanthemum morifolium “Zhongshanzigui,” (B) amphihaploid, (C) amphidiploid, and (D) Leucanthemum paludosum). From left to right of each line: plant morphology; floral morphology, bar: 1 cm; ligulate flower, bar: 2 mm; tubular flower, bar: 2 mm; leaf: 0.5 cm.

Conclusion
The taxonomic relationship between Chrysanthemum and Leucanthemum is relatively distant. Combining such diverse genomes into a single nucleus can be expected to cause genomic shock in the sense of McClintock: “a highly programmed sequence of events within the cell that serves to cushion the effects of the shock.” The induced changes to the genome must occur very early in the development of the hybrid zygote and continue when the amphihaploid is subjected to whole-genome doubling. A further manifestation of the shock is the alteration in the pattern of DNA methylation. These rapid and massive changes in the genome of hybrids may serve as a tolerance of genome shock and might contribute to rapid genetic diploidization of the newly formed allopolyploid. An important question is whether the genomic and epigenomic events observed here are common in wide hybrids within the Asteraceae family. Understanding these genomic changes and epigenetic modifications is a worthy goal to increase understanding of the evolutionary process of the Asteraceae family, which will require the production and analysis of other wide hybridization combinations between members of the Asteraceae family.