Inheritance of vernalization memory at FLOWERING LOCUS C during plant regeneration.

Specific gene states can be transmitted to subsequent cell generations through mitosis involving particular chromatin (epigenetic) states. During reproduction of plants and animals, however, most epigenetic states are reset to allow development to start anew. Flowering is one of the critical developmental steps by which plants acquire their reproductive capacity. This phase transition is controlled by environmental signals and autonomous regulation. The FLOWERING LOCUS C (FLC) gene is a flowering repressor that is epigenetically silenced after long-term exposure to cold, ensuring flowering in the spring season. In Arabidopsis thaliana, epigenetically silenced FLC expression is reset during sexual reproduction. Plants have a remarkable potential to regenerate from somatic cells. However, little is known about whether the regeneration process is similar to sexual reproduction in terms of affecting chromatin states. Here, we tested whether FLC silencing is reset during in vitro regeneration. Transcriptional repression and high H3K27me3 at FLC were both stably transmitted, resulting in early flowering in regenerated shoots. Thus, the silenced epigenetic state of FLC is reset only during sexual reproduction and not during in vitro regeneration. In contrast, the active epigenetic state of FLC was only partially maintained through in vitro reproduction, suggesting that regeneration causes stochastic FLC silencing.