Function
Key regulator of far red / red (FR/R) spectrum-specific responses essential for the adaption to changing light conditions (e.g. de-etiolation), essentially by regulating PHYA shuttling from the cytoplasm to the nucleus and by directly regulating the expression of some target genes, depending on light conditions and phosphorylation status (PubMed:22582101). Binds chromatin at target genes promoters, especially in FR light conditions (PubMed:25071219). Can activate transcription of different genes, some being in a phytochrome A (PHYA)-dependent and other in a PHYA-independent manners (PubMed:15469493, PubMed:11726703, PubMed:25071219). Controls specific aspects of plant development, such as the inhibition of seed germination under FR during salt stress (PubMed:25071219). Essential for light-regulated PHYA nuclear accumulation and subsequent PHYA phototropic signaling processes involved in photomorphogenesis (PubMed:17566111, PubMed:21969386, PubMed:25071219, PubMed:22374392, PubMed:19482971). Mediates the association of PHYA with HFR1 and LAF1 in the nucleus in response to FR conditions (PubMed:19482971). PHYA-specific signal transducer in response to continuous FR lights (PubMed:15469493, PubMed:16045472, PubMed:19482971, PubMed:11711433, PubMed:11726703, PubMed:8364355). Contributes to inhibition of hypocotyl elongation in continuous blue light (B) (PubMed:16045472).