LIGHT-REGULATED CHANGES IN ABUNDANCE AND POLYRIBOSOME ASSOCIATION OF FERREDOXIN MESSENGER-RNA ARE DEPENDENT ON PHOTOSYNTHESIS

In transgenic tobacco plants containing a pea ferredoxin transcribed r egion (Fed-1) driven by the cauliflower mosaic virus 35S promoter (P-3 5S), light acts at a post-transcriptional level to control the abundan ce of Fed-1 mRNA in green leaves. To determine whether the light signa l for this response involves photosynthesis, we treated transgenic see dlings with or without 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosynthetic electron transport. DCMU prevented the normal light response by blocking reaccumulation of Fed-1 transcripts when dark-adapted green plants were returned to the light. In contras t, reaccumulation of light-harvesting complex B (Lhcb) transcripts was unaffected by DCMU treatment, Because Fed-1 light regulation requires translation, we also examined polyribosome profiles. We found that Fe d-1 transcripts accumulated on polyribosomes in the light but were fou nd primarily in non-polyribosomal fractions in dark-adapted plants or in illuminated plants exposed to lower than normal light intensity or treated with DCMU. Surprisingly, although Lhcb mRNA abundance was not affected by DCMU, its polyribosomal loading pattern was altered in muc h the same way as was that of Fed-1 mRNA. In contrast, DCMU had no eff ect on either the abundance or the polyribosome profiles of endogenous histone H1 or transgenic P-35S::CAT transcripts. Thus, our results ar e consistent with the hypothesis that a process coupled to photosynthe sis affects the polyribosome loading of a subset of cytoplasmic mRNAs.