Brassica oleracea displays a high level of DNA methylation polymorphism

Abstract

Brassica oleracea is a species displaying a high level of phenotypic variability. In order to evaluate the extent of genome methylation and to relate methylation polymorphism to phenotypic variability, we used the methylation-sensitive amplification polymorphism (MSAP) technique on 30 B. oleracea populations and lines representing the species diversity. We first observed that most MSAP fragments were inherited from one generation to the next one and were mainly additive in a progeny. A high mean rate of methylation estimated by MSAP was revealed in this species (range of 52–60% depending on the accessions), 30–41% of MSAP fragments being detected by MspI and 17–27% by HpaII. Most of the MSAP-methylated fragments (95%) were polymorphic between the populations and lines analysed. We performed a phenetic analysis to group populations/lines by using MSAP-methylated fragments. The phenetic relationships revealed showed a populations/lines classification that did not correlate completely with a classification by morphotype as obtained using AFLP fragments insensitive to methylation polymorphism. The high methylation level and polymorphism reported in this study could be related with the high structural genome plasticity already reported in the Brassica species to explain the phenotypic variability of this species.