Molecular mechanisms underlying the maintenance of terminal differentiation in Arabidopsis guard cells

In many plant species, guard cells retain their distinctive morphology and physiological function for extended periods after differentiation and maturation. How this terminally differentiated state is actively maintained over time is not fully understood, but recent studies have begun to reveal the underlying mechanisms. Elucidating the underlying mechanisms in Arabidopsis guard cells may provide valuable insights into the maintenance of differentiated identities in other plant cell types. In this review, we synthesize recent findings showing that guard cell identity is secured by two interconnected layers: PRC2-mediated H3K27me3 deposition silences stomatal stem cell genes, while sustained expression of FAMA, supported by SWI/SNF and HAC1-dependent chromatin remodeling, reinforces the mature transcriptional program. Permanent cell cycle exit may serve as an additional safeguard against dedifferentiation, as aberrant cell cycle reactivation triggers fate resetting. This framework highlights the combined action of two interconnected layers: repression of stomatal stem cell genes, coupled with sustained expression of the mature transcriptional program, with cell cycle exit providing additional protection. Such a framework may serve as a useful reference for studying terminal differentiation maintenance in guard cells and other post-mitotic cell types.