Journal Article

A Mechanism for Light-Induced Translation of the <i>rbcL</i> mRNA Encoding the Large Subunit of Ribulose-1,5-bisphosphate Carboxylase in Barley Chloroplasts

Jungmook Kim and John E. Mullet

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 44, issue 5, pages 491-499
Published in print May 2003 | ISSN: 0032-0781
Published online May 2003 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcg061
A Mechanism for Light-Induced Translation of the rbcL mRNA Encoding  the Large Subunit of Ribulose-1,5-bisphosphate Carboxylase in Barley Chloroplasts

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  • Biochemistry
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Translational regulation plays a key role in light-induced expression of photosynthesis-related genes at various levels in chloroplasts. We here present the results suggesting a mechanism for light-induced translation of the rbcL mRNA encoding the large subunit (LS) of ribulose-1,5-bisphosphate carboxylase (Rubisco). When 8-day-old dark-grown barley seedlings that have low plastid translation activity were illuminated for 16 h, a dramatic increase in synthesis of large subunit of Rubisco and global activation of plastid protein synthesis occurred. While an increase in polysome-associated rbcL mRNA was observed upon illumination for 16 h, the abundance of translation initiation complexes bound to rbcL mRNA remained constant, indicating that translation elongation might be controlled during this dark-to-light transition. Toeprinting of soluble rbcL polysomes after in organello plastid translation showed that ribosomes of rbcL translation initiation complexes could read-out into elongating ribosomes in illuminated plastids whereas in dark-grown plastids, read-out of ribosomes of translation initiation complexes was inhibited. Moreover, new rounds of translation initiation could also occur in illuminated plastids, but not in dark-grown plastids. These results suggest that translation initiation complexes for rbcL are normally formed in the dark, but the transition step of translation initiation complexes entering the elongation phase of protein synthesis and/or the elongation step might be inhibited, and this inhibition seems to be released upon illumination. The release of such a translational block upon illumination may contribute to light-activated translation of the rbcL mRNA.

Keywords: Keywords: Hordeum vulgare — Plastids — Polysome — Toeprinting — Translational control — Translation elongation; Abbreviations: LS, large subunit; Rubisco, ribulose-1,5-bisphosphate carboxylase; UTR, untranslated region; P700, P700 chlorophyll apoproteins A and B of PSI; CP47, 47-kDa PSII chlorophyll apoprotein; CP43, 43-kDa PSII chlorophyll apoprotein: D2, 34-kDa PSII reaction center polypeptide; D1, 32-kDa PSII reaction center polypeptide.

Journal Article.  6810 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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