The moment the growing seedling emerges, the Sun acts as both power and poison. Precursors of chlorophyll lie ready to be converted to functioning chlorophyll, but the precursor form can do more harm than good if exposed to light. Huq et al. have now identified a transcription factor, PIF1, that interacts with light-sensing phytochromes and regulates chlorophyll biosynthesis. PIF1 negotiates the balance between chlorophyll synthesis and the sensing of light such that emergent seedlings become photoautotrophic before they would otherwise burn up.
E. Huq, B. Al-Sady, M. Hudson, C. Kim, K. Apel, P. H. Quail, PHYTOCHROME-INTERACTING FACTOR 1 is a critical bHLH regulator of chlorophyll biosynthesis. Science 305, 1937-1941 (2004). [Abstract] [Full Text]