Phytochrome activation of two nuclear genes requires cytoplasmic protein synthesis.

Abstract

We have investigated the effects of protein synthesis inhibitors on light-induced expression of two plant nuclear genes, Cab and rbcS, in wheat, pea and transgenic tobacco. Light activation of these two genes is very sensitive to cycloheximide, an inhibitor of cytoplasmic protein synthesis but not to chloramphenicol, an inhibitor of organeliar protein synthesis. Studies with chimeric gene constructs in transgenic tobacco seedlings show that cycloheximide exerts its effect at the transcriptional level. As a control, we show that the expression of the cauliflower mosaic virus (CaMV) 35S promoter is enhanced by cycloheximide treatment, irrespective of the coding sequence used. Escape-time analyses with green wheat seedlings show that the cycloheximide block for Cab gene expression is after the primary signal transduction step linked to phytochrome photoconversion. Our results suggest that phytochrome activation of Cab and rbcS is mediated by a labile protein factor(s) synthesized on cytoplasmic ribosomes.

Guanine nucleotide binding protein involvement in early steps of phytochrome-regulated gene expression.

“…Previous reports (15,23), as well as this work, have shown that phytochrome activation of cab and rbcS shows relatively slow kinetics with a maximal level of mRNA accumulation reached within 6-10 h after onset of irradiation. In the present work, we found <5% of the light-inducible cab transcript 0.5 h after illumination.…”

Metabolic Repression of Transcription in Higher Plants

“…The metabolic repression of photosynthetic genes apparently overrides other forms of regulation, e.g., light, tissue type, and developmental stage (Simpson et al, 1986;Kuhlemeier et al, 1987;Schell, 1987;Ha and An, 1988;Benfey and Chua, 1989;Ueda et al, 1989) because it is executed in young leaf cells under light. In this study, the young leaf cells (greening mesophyll protoplasts) were isolated from illuminated dark-grown seedlings, which is a well-established system for the study of the photosynthetic gene expression at an early developmental stage (Nelson et al, 1984;Sheen and Bogorad, 1986a, 1986bSimpson et al, 1986;Mosinger et al, 1988;Lam et al, 1989). The greening mesophyll protoplasts of maize provide an abundant and homogeneous cell population, synchronized in photosynthetic gene induction and expression, for the study of photosynthetic gene regulation.…”

Fungal Elicitor-Induced Bean Proline-Rich Protein mRNA Down-Regulation Is Due to Destabilization That Is Transcription and Translation Dependent.

“…The efficacies of protein synthesis inhibitors may differ among plant species. Emetine and anisomycin treatment of wheat seedlings provided O and 40% inhibition, respectively (Lam et al, 1989). In contrast, both inhibitors blocked protein synthesis in pea seedlings by 85% (Theologis et al, 1985).…”