An inverse control by phytochrome of the expression of two nuclear genes in barley (Hordeum vulgare L.).

During the light-dependent transformation of etioplasts to chloroplasts a rapid decrease of the NADPH-protochlorophyllide oxidoreductase is induced. At the same time the mRNA activity coding for this enzyme protein also declines rapidly under the influence of phytochrome (Pfr). On the other hand the apoprotein of the light-harvesting chlorophyll a/b protein and its mRNA activity are inversely affected by the same photoreceptor. Cloned cDNA sequences which are complementary to these mRNAs have been used to assess the effect of phytochrome (Pfr) on the concentration of the two transcripts. The phytochrome-induced changes of the two translatable mRNAs are paralleled by corresponding changes in the steady-state concentration of the mRNA sequences. This inverse relationship between the light-dependent regulation of the NADPH-protochlorophyllide oxidoreductase and the light-harvesting chlorophyll a/b protein suggests that a single reversible triggering event can increase the transcription of certain genes and decrease the transcription of others.