VIVIPAROUS/ABSCISIC ACID INSENSITIVE3 (ABI3)-LIKE (VAL) B3 domain proteins orchestrate developmental timing in plants

Developmental phase transitions in plants represent irreversible shifts in growth and identity and must therefore be precisely controlled. These transitions rely heavily on epigenetic mechanisms and are tightly coordinated with environmental cues. The VIVIPAROUS/ABSCISIC ACID INSENSITIVE3 (ABI3)-LIKE (VAL) family of B3 domain transcription factors has emerged as a central regulatory node throughout plant development. VAL proteins act as sequence-specific DNA-binding factors that mediate the assembly of Polycomb Repressive Complexes (PRCs) and associate chromatin modifiers, thereby ensuring stable transcriptional silencing at key developmental regulators. Through this function, VAL proteins specify which genes must be epigenetically repressed to allow transitions from embryogenesis to seedling growth, from juvenile to adult vegetative phases, and ultimately to flowering. Most mechanistic insights into VAL protein function come from Arabidopsis thaliana, although recent studies in other species reinforce VAL conserved role in chromatin silencing and epigenetic integration. Here, we synthesize current knowledge on VAL-mediated regulation and highlight conceptual advances in understanding how sequence-specific repressors interface with chromatin machinery in plants. We further discuss the evolutionary conservation of VAL structural domains and outline open questions surrounding VAL functional roles in chromatin regulation.