Acts as a negative regulator of abscisic acid (ABA) response during germination through the ubiquitin-mediated proteolysis of ABI5/DPBF1. Forms a homodimer and heterodimer with AFP1 and AFP3. Interacts with ABI5/DPBF1, DPBF2, AREB3/DPBF3, EEL/DPBF4, ABF1, ABF3/DPBF5 and ABF4/AREB2. Up-regulated by abscisic acid (ABA), glucose and salt. Exhibits hypersensitivity to salt, glucose and osmotic stress and slight hypersensitivity to abscisic acid (ABA). Belongs to the Ninja family.