Phytochrome‐Mediated Regulation of Two mRNAs, Encoded by Nuclei and Chloroplasts of Ribulose‐1,5‐bisphosphate Carboxylase/Oxygenase

Abstract

Etiolated pea seedlings (5 days old) were treated with red light for 5 min and grown for 2 days more in darkness. Effects of the red light on the mRNA levels of two subunits of ribulose-l,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) (ribulose-P2 carboxylase), rate of enzyme synthesis and accumulation of the enzyme were examined for the plants. Increases of the two mRNA levels, encoded in nuclei and chloroplasts were observed. Red light followed by far-red light treatment for 5 min inhibited the increases. An increase parallel with the mRNA levels was found for the rate of the enzyme synthesis and accumulation of the enzyme. These results indicate that the induction of two mRNA levels is mediated by phytochrome and causes the red-light-inducible, far-red-light-reversible increase of ribulose-P2 carboxylase. When white light was irradiated to induce the enzyme, the effects of red light given in darkness were reinforced. These results indicate that light-induction of ribulose-P2 carboxylase is mediated by phytochrome and controlled by the two mRNA levels.Ribulose-1,5-bisphosphate carboxylase/oxygenase (ribulose-P2 carboxylase) is a key enzyme in photosynthesis, and is localized in the chloroplast. This enzyme is composed of eight large and eight small subunits. The large subunit is encoded in chloroplast D N A [l] and synthesized on chloroplast ribosomes [2]. The small subunit is encoded in nuclear DNA [3] and synthesized on cytoplasmic ribosomes in the form of a precursor. The precursor is transported into chloroplasts and results in the small subunit after removal of an extra peptide during transportation [4-71. The large and the small subunits combine in the chloroplast to form ribulose-P2 carboxylase holoenzyme.Production of ribulose-Pz carboxylase is induced by light. We have previously shown that the light induction of the enzyme is pretranslationally controlled, and that the large and the small subunit mRNA levels seem to be coordinately regulated during light induction [8,9]. We want to know whether the pigment-protein phytochrome [lo] is involved in the photoresponses of the two mRNA levels. The present work shows that both the large and the small subunit mRNA levels of ribulose-P2 carboxylase are regulated by phytochrome.

Two phytochrome‐mediated effects of light on transcription of genes encoding the small subunit of ribulose‐1,5‐bisphosphate carboxylase‐oxygenase in dark‐grown pea (Pisum sativum) plants

“…The rbcS mRNA content reaches a maximum and then remains roughly constant at a steady-state level approx. 10070 of that observed in plants illuminated continuously with white light for 48 h. The effect of an immediate far-red light treatment in reversing the effect of red light on rbcS mRNA accumulation has been reported previously [6][7][8]. …”

“…Dark-grown pea seedlings have extremely low rates of rbcS gene transcription and accumulate very small amounts of rbcS mRNA [3,[6][7][8][9][10]13]. (fig.2).…”

“…Light induces a substantial increase in the rbcS mRNA content in leaf tissue [1,2] and this is primarily due to an increase in the rate of rbcS gene transcription [3][4][5]. In pea [6][7][8][9], and other species [4,5], the photoreceptor phytochrome is involved in mediating the effects of light on rbcS gene expression.…”

Immunological Determination of Phosphoenolpyruvate Carboxylase and the Large and Small Subunits of Ribulose 1,5-Bisphosphate Carboxylase in Leaves of the C4 Plant Pearl Millet

“…However, none of these studies quantitated the actual mass of the mRNAs for either of these two polypeptides or the actual quantities of these two proteins in a leaf of a plant. Sasaki et al (17) and Tobin and Suttie (22) have measured the relative ratio of synthesis of these two polypeptides. Sasaki et al ( 17) showed that in etiolated seedlings exposed to light the large subunit was synthesized more rapidly than was the small subunit of RuBPCase.…”

“…Sasaki et al (17) and Tobin and Suttie (22) have measured the relative ratio of synthesis of these two polypeptides. Sasaki et al ( 17) showed that in etiolated seedlings exposed to light the large subunit was synthesized more rapidly than was the small subunit of RuBPCase. Tobin and Suttie (22) also saw in Lemna that the rate of synthesis of the large subunit was more rapid than the rate of synthesis of the small subunit of RuBPCase.…”