FUSCA3

FUSCA3, commonly written as FUSCA3 or FUS3, is a plant-specific transcription factor that plays a central role in seed development and maturation. It belongs to the B3-domain family of transcription factors within the AFL group that governs the seed maturation program. FUSCA3 functions as a regulator of late embryogenesis and seed storage programs, activating genes involved in storage protein synthesis, lipid metabolism, and desiccation tolerance, including seed storage proteins and late embryogenesis abundant (LEA) proteins. It acts in concert with other seed regulators such as LEC1, LEC2, and ABI3, forming a network known as the LAFL module that integrates hormonal signals, particularly abscisic acid (ABA) and gibberellins, to control the timing and extent of maturation.

Expression of FUSCA3 is predominantly in the embryo during mid to late embryogenesis, where its activity helps establish the maturation program and embryo identity. The protein binds DNA sequences recognized by B3-domain transcription factors, including RY elements, to regulate transcription of maturation-related genes. In addition to promoting maturation, FUSCA3 participates in regulatory interactions that refine the maturation program and coordinate developmental timing with hormonal cues.

Loss-of-function mutants (fusca3) exhibit defects in embryo development and seed maturation, including altered accumulation of storage compounds and changes in desiccation tolerance and germination behavior. Overexpression or ectopic expression of FUSCA3 can promote embryonic characteristics in vegetative tissues, illustrating its role in maintaining embryonic identity and the integrity of the seed maturation program.

FUSCA3 is conserved across flowering plants, and understanding its function contributes to seed biology and crop improvement, particularly regarding seed dormancy, storage reserve composition, and stress tolerance.