Sex-specific DNA methylation and gene expression in andromonoecious poplar

The andromonoecious poplar is an exceptional model system for studying sex-specific flower development in dioecious plants. There is increasing evidence that epigenetic regulation, particularly DNA methylation, is an important regulatory factor during flower development. Here, methylation-sensitive amplified polymorphism (MSAP) was used to screen for sex-specific DNA methylation alterations in the andromonoecious poplar. The sequences of 27 sex-specific amplified fragments were obtained from DNA prepared from sex-specific flower tissues. PtGT2, PtPAL3, and PtCER4, which are homologous to MF26, MF29, and MF35, respectively, were cloned as candidate genes. Expression analysis and DNA methylation pattern profiling of the three candidate genes revealed that gene expression upregulation was always associated with gene body methylation. The results suggested that DNA methylation sites have the potential to regulate the genes' transcript levels. These three genes were shown to play important roles during different phases of flower development. This study will help to provide candidates for future experiments aimed at understanding the mechanism, whereby DNA methylation regulates gene expression in poplar. We report the first screen for sex-specific DNA methylation alterations in the andromonoecious poplar. 27 sex-specific methylation sites were identified. The gene expression levels and DNA methylation patterns were detected for three candidate genes.