Differences in DNA methylation, DNA structure and embryogenesis-related gene expression between embryogenic and non embryogenic lines of Pinus radiata D. don

Pinus radiata is the most important conifer species for commercial forestry in countries such as Australia, New Zeeland and Chile. Nowadays, SE (somatic embryogenesis) is considered the most promising in vitro method for large scale vegetative propagation of woody plants. The understanding of the molecular basis of SE is in its very beginning and a number of embryogenesis-related genes have been identified in conifers. Among the molecular mechanisms involved in regulation of SE, DNA methylation, which is an epigenetic modification associated with transcriptional silencing, has shown to be a pivotal factor controlling gene expression. In this work, we studied the morphological and molecular differences between cell lines previously characterized in terms of their embryogenic potential as embryogenic (E) and non embryogenic (NE), obtained from immature zygotic embryos of P. radiata. In contrast to E lines, NE lines were composed of multicellular aggregates lacking polarity, and they were characterized by the presence of significantly lower transcript levels of embryogenesis-related genes and higher global DNA methylation. Furthermore, the detection of vibrational markers of DNA conformation indicated that DNA samples obtained from E lines presented the common B-DNA conformation, while NE samples presented Z-conformation. Taken together, our results highlight the role of epigenetic mechanisms such as DNA methylation in regulating the expression of embryogenesis- related genes, having impact on the embryo patterning and cell differentiation.