Presenter: Robert Martienssen, Cold Spring Harbor Laboratory, USA
From the EMBO|EMBL Symposium: The Mobile Genome: Genetic and Physiological Impacts of Transposable Elements
EMBL Advanced Training Centre Heidelberg, Germany 11 - 14 October 2017
Germline reprogramming and epigenetic inheritance of transposable elements in plants: how to avoid BadKarma
Epigenetic inheritance is more widespread in plants than in mammals, in part because mammals erase epigenetic information each generation by germline reprogramming. To assess the extent of germline reprogramming in plants, we sequenced the methylome from sperm cells (SC), the vegetative nucleus (VN), and the precursor microspore from developing haploid pollen. We found that asymmetric CHH methylation is lost in microspores and sperm cells, but restored in the VN and in fertilized seed, while CG methylation is partially lost in the VN but fully retained in the germline. Transposons are activated in pollen, as they are in
DECREASE IN DNA METHYLATION 1 (DDM1) mutants and in tissue culture. Targeting by miRNA triggers accumulation of 21nt epigenetically activated” small RNAs, which promote chromosome segregation. In pollen, targeting of retrotransposons by a highly conserved pollen specific microRNA mediates chromosome dosage response (imprinting) in the next generation. Thus genome reprogramming in pollen contributes to epigenetic inheritance, transposon silencing, and imprinting, guided by small RNA. If reprogramming is avoided altogether through somatic cloning in oil palm, activation of Karma transposons results in heritable epigenetic variation with real-world consequences.
