PT - JOURNAL ARTICLE AU - Larkin, Robert M. AU - Alonso, Jose M. AU - Ecker, Joseph R. AU - Chory, Joanne TI - GUN4, a Regulator of Chlorophyll Synthesis and Intracellular Signaling AID - 10.1126/science.1079978 DP - 2003 Feb 07 TA - Science PG - 902--906 VI - 299 IP - 5608 4099 - http://science.sciencemag.org/content/299/5608/902.short 4100 - http://science.sciencemag.org/content/299/5608/902.full SO - Science2003 Feb 07; 299 AB - Nuclear genes control plastid differentiation in response to developmental signals, environmental signals, and retrograde signals from plastids themselves. In return, plastids emit signals that are essential for proper expression of many nuclear photosynthetic genes. Accumulation of magnesium-protoporphyrin IX (Mg-Proto), an intermediate in chlorophyll biosynthesis, is a plastid signal that represses nuclear transcription through a signaling pathway that, inArabidopsis, requires the GUN4 gene. GUN4 binds the product and substrate of Mg- chelatase, an enzyme that produces Mg-Proto, and activates Mg-chelatase. Thus, GUN4 participates in plastid-to-nucleus signaling by regulating Mg-Proto synthesis or trafficking.