UV protectants and antimicrobial compounds phytoalexins. Chalcone synthase (CHS), the key enzyme of flavonoid biosynthesis, is induced by environmental stresses such as UV, mechanical wounding and pathogen attack. Characterization of the cis elements and trans factors involved in CHS expression has enabled delineation of the terminal stage of the signal transduction pathways underlying its induction by environmental stimuli. This review summarizes recent advances in studies of transcriptional activation of CHS following environmental stimuli.