Rapid genome change in synthetic polyploids of Brassica and its implications for polyploid evolution.

TLDR

Polyploidy is evolutionarily successful in higher plants, yet little is known about post‑formation genome evolution, which may have driven diversification in natural polyploids. The study used synthetic Brassica polyploids to investigate early‑generation genome evolution after polyploidization. Synthetic homozygous Brassica polyploids were self‑fertilized and monitored with 89 nuclear DNA clone probes from F2 to F5 to detect genome changes. Genome analysis revealed rapid, extensive changes—including fragment loss/gain and novel fragments—in every generation from F2 to F5, with frequency tied to parental divergence and evidence of directional shifts, demonstrating that synthetic polyploids generate substantial genetic diversity in a short time.

Abstract

Although the evolutionary success of polyploidy in higher plants has been widely recognized, there is virtually no information on how polyploid genomes have evolved after their formation. In this report, we used synthetic polyploids of Brassica as a model system to study genome evolution in the early generations after polyploidization. The initial polyploids we developed were completely homozygous, and thus, no nuclear genome changes were expected in self-fertilized progenies. However, extensive genome change was detected by 89 nuclear DNA clones used as probes. Most genome changes involved loss and/or gain of parental restriction fragments and appearance of novel fragments. Genome changes occurred in each generation from F2 to F5, and the frequency of change was associated with divergence of the diploid parental genomes. Genetic divergence among the derivatives of synthetic polyploids was evident from variation in genome composition and phenotypes. Directional genome changes, possibly influenced by cytoplasmic-nuclear interactions, were observed in one pair of reciprocal synthetics. Our results demonstrate that polyploid species can generate extensive genetic diversity in a short period of time. The occurrence and impact of this process in the evolution of natural polyploids is unknown, but it may have contributed to the success and diversification of many polyploid lineages in both plants and animals.