The phytochrome-controlled accumulation of mRNA sequences encoding the light-harvesting chlorophyll a/b protein of barley (Hordeum vulgare L.).

Double-stranded cDNA was synthesized from polysomal poly(A)-containing RNA of illuminated barley plants and was inserted into the PstI site of the bacterial plasmid pBR322. Two different strategies were used for the screening of the bacterial colonies. Light-regulated sequences were detected by differential hybridization with cDNA of polyadenylated RNA from dark-grown and illuminated barley plants. For a second screening step partially purified mRNAs encoding the light-harvesting chlorophyll a/b protein were used for the synthesis of another cDNA probe. By using these procedures a cDNA clone was isolated which encodes a constitutive polypeptide of the light-harvesting chlorophyll a/b protein. This cloned cDNA has been used to assess the effect of phytochrome on the steady-state level of mRNA sequences encoding the light-harvesting chlorophyll a/b protein. The mRNA is almost undetectable in dark-grown plants. Following treatment with red light, the concentration of this mRNA sequence increases rapidly during the subsequent dark period. This red light effect can be reversed substantially by irradiation with far-red light. These results indicate that not only the amount of mRNA activity as shown previously, but also the steady-state level of mRNA sequences encoding the light-harvesting chlorophyll a/b is controlled by phytochrome.