Membrane-bound transcription factor required for the plastid-to-nucleus retrograde signaling. Functions in multiple retrograde pathways. The plastid-to-nucleus signal plays an important role in the coordinated expression of both nuclear- and chloroplast-localized genes that encode photosynthesis-related proteins. In the nucleus, activates ABI4 transcription in a PHD-dependent manner associated with histone modifications. Localized primarily in the chloroplast outer membrane as dormant form and, in response to retrograde signals, is released from the membrane through proteolytic cleavage and its cleaved fragment containing the transcription factor domain is redistributed to the nucleus, where it regulates the expression of particular nuclear genes. Interacts (via the DDT domain) with CHR11 (via C-terminus). Localized primarily in the chloroplast outer membrane as dormant form and, upon specific stimulation, is released from the membrane through proteolytic cleavage, and its cleaved fragment containing the transcription factor domain is redistributed to the nucleus, where it regulates the expression of particular nuclear genes. No visible phenotype under normal growth conditions. Truncated N-terminus.