FIN219 has been demonstrated to be involved in phytochromes A-mediated inhibition of hypocotyl elongation in far-red light (FR) and its overexpressed transgenic Arabidopsis seedlings display a hypersensitive phenotype under FR, blue and white light conditions, which suggests that FIN219 may play a role in blue light signaling. To explore this possibility, a yeast two-hybrid interaction approach was utilized to examine whether FIN219 can interact with blue light photoreceptors, cryptochrome 1 (cry1) and 2 (cry2). The result indicated that the C-terminus of FIN219 can interact with CRY1 and CRY2. As well, FIN219 overexpression in cry1, cry2, or cry1cry2 mutant backgrounds did not show obvious phenotype, which implies that FIN219 may function only in the presence of CRYs proteins. Overexpression of FIN219 in GUS-CCT1 transgenic plants can rescue the constitutive photomorphogenic phenotype of GUS-CCT1 in darkness, which indicates that the interaction between FIN219 and GUS-CCT1 may exclude the binding of GUS-CCT1 to COP1
Microarray data revealed that fin219 mutation resulted in the upregulation of 4 different ethylene signaling components. This findings lead us to test whether FIN219 regulates ethylene response or signaling. The FIN219 overexpression in the cry1cry2 mutant background can rescue the defect of cry1cry2 mutants in response to 1-aminocyclopropane-1-carboxylic acid (ACC, a precursor of ethylene). Histochemical GUS staining indicated that ACC induced FIN219 expression in the exaggerated apical hook. ACC might promotes the downward transport of FIN219-GUS fusion proteins. In addition, FIN219 promoter activity was regulated by the addition of methyl jasmonate and auxin under FR light, which indicates that the photomorphogenic phenotype triggered by FR may be the result of combinatory interactions among multiple hormones and FR, where FIN219 may play a vital function to fine tune the process.