Functional symmetry of the B3 network controlling seed development.

Two subfamilies of plant-specific B3 domain transcription factors regulate the fundamental transition between seed and vegetative phases of development. The AFL B3 genes activate the embryo maturation program, while the closely related VAL B3 genes shutdown the AFL network before germination. VP8/AMP1 signaling most probably acts upstream of the AFL network. Key downstream AFL targets elaborate seed-specific abscisic acid (ABA), gibberellin (GA), and auxin signaling. ABA feeds back into network via ABI3 interaction with ABI5. GA promotes repression of the AFL network by the VAL repressors and the PICKLE (PKL) chromatin-remodeling factor before germination. Strikingly, the functional symmetry of the AFL and VAL B3 genes is mirrored in patterns of chromatin modification.