Analysis of the leaf methylomes of parents and their hybrids provides new insight into hybrid vigor in Populus deltoides.

backgroundPlants with heterosis/hybrid vigor perform better than their parents in many traits. However, the biological mechanisms underlying heterosis remain unclear. To investigate the significance of DNA methylation to heterosis, a comprehensive analysis of whole-genome DNA methylome profiles of Populus deltoides cl.'55/65' and '10/17' parental lines and their intraspecific F1 hybrids lines was performed using methylated DNA immunoprecipitation (MeDIP) and high-throughput sequencing.

resultsHere, a total of 486.27 million reads were mapped to the reference genome of Populus trichocarpa, with an average unique mapping rate of 57.8%. The parents with similar genetic background had distinct DNA methylation levels. F1 hybrids with hybrid vigor possessed non-additive DNA methylation level (their levels were higher than mid-parent values). The DNA methylation levels in promoter and repetitive sequences and transposable element of better-parent F1 hybrids and parents and lower-parent F1 hybrids were different. Compared with the maternal parent, better-parent F1 hybrids had fewer hypermethylated genes and more hypomethylated ones. Compared with the paternal parent and lower-parent L1, better-parent F1 hybrids had more hypermethylated genes and fewer hypomethylated ones. The differentially methylated genes between better-parent F1 hybrids, the parents and lower-parent F1 hybrids were enriched in the categories metabolic processes, response to stress, binding, and catalytic activity, development, and involved in hormone biosynthesis, signaling pathway.

conclusionsThe methylation patterns of the parents both partially and dynamically passed onto their hybrids, and F1 hybrids has a non-additive mathylation level. A multidimensional process is involved in the formation of heterosis.