We have monitored changes in the chlorophyll a/b-binding protein (Cab) mRNA levels in etiolated wheat leaves exposed to light of different wavelengths by Northern blot hybridizations and 5' S1 nuclease protection assays. Accumulation of the Cab mRNA and the specific Cab-1 transcript is regulated by phytochrome. Transcript levels are elevated by red light and the red enhancement can be partially reversed by far-red light. Moreover, far-red light alone can elicit a small increase in the transcript levels. These characteristic features of the wheat Cab-1 phytochrome response can be recapitulated in etiolated seedlings of transgenic tobacco containing the Cab-1 gene. Analyses of a chimeric construct revealed that a 1.8-kb 5'-flanking fragment (-1816 to +31) of the Cab-1 gene can confer phytochrome response as well as leaf-specific expression on a heterologous coding sequence.