Non-canonical RNA-directed DNA methylation participates in maternal and environmental control of seed dormancy.

Abstract

Seed dormancy is an adaptive trait preventing premature germination out of season. In a previous report (Piskurewicz et al., 2016) we showed that dormancy levels are maternally inherited through the preferential maternal allele expression in the seed endosperm of <i>ALLANTOINASE</i> (<i>ALN</i>), a negative regulator of dormancy. Here we show that suppression of <i>ALN</i> paternal allele expression is imposed by non-canonical RNA-directed DNA methylation (RdDM) of the paternal <i>ALN</i> allele promoter. Dormancy levels are further enhanced by cold during seed development. We show that DNA methylation of the <i>ALN</i> promoter is stimulated by cold in a tissue-specific manner through non-canonical RdDM, involving RDR6 and AGO6. This leads to suppression of <i>ALN</i> expression and further promotion of seed dormancy. Our results suggest that tissue-specific and cold-induced RdDM is superimposed to parental allele imprints to deposit in the seed progeny a transient memory of environmental conditions experienced by the mother plant.