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Control of cytoplasmic translation in plants

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Abstract Translational control provides cells with a mechanism to rapidly control gene expression in a reversible manner in response to environmental and developmental cues. It involves the dynamic, coordinated activity of numerous factors that direct the synthesis of proteins with precision in space and time. Translational control is primarily regulated at the level of initiation, and as such, mechanisms that regulate translation most often target the initiation machinery. Translation in plants is fundamentally similar to that of other eukaryotes. However, there are significant differences in translation factor isoforms and their associated proteins, and the types of regulation that can act upon these factors. Regulation of translation in plants can involve protein phosphorylation, variable associations of initiation factor isoforms, RNA sequence element interactions, and small RNAs. The assembly of large mRNA‐ribonucleoprotein complexes, called processing bodies and stress granules, also influences the translatability of an mRNA. mRNA–cytoskeleton interactions, as well as subcellular and intercellular transport of mRNAs, also appear to regulate translation in plants. Often working together, these control mechanisms finely tune translational expression within the cell. WIREs RNA 2012, 3:178–194. doi: 10.1002/wrna.1104 This article is categorized under: Translation > Translation Mechanisms Translation > Translation Regulation RNA Export and Localization > RNA Localization

Cap‐dependent translation initiation complex assembly. eIF4E binds to the 5′ cap in association with the other members of the eIF4F complex, eIF4G, and eIF4A. eIF4B then joins eIF4A and the cap‐binding complex to unwind secondary structure in the leader. The formation of the 43S preinitiation complex begins with the assembly of the ternary complex (eIF2, GTP, and Met‐tRNAi), followed by its interaction with eIF3, eIF1, eIF1A, and the 40S ribosomal subunit. Interactions between the cap‐binding complex and the 43S preinitiation complex recruit the 40S subunit to the 5′ end of the mRNA to form the 48S initiation complex. Circularization of the mRNA is achieved through the interaction of eIF4G and eIF4B with PABP. Scanning is initiated, and once the 48S initiation complex locates the initiation codon, eIF5 triggers the hydrolysis of ternary complex‐associated GTP. Recruitment of the 60S ribosome is then followed by translation initiation. Interactions between eIF3c and eIF5, as well as eIF3 and eIF2 in the 43S preinitiation complex as indicated18 in Figure 2 are not shown here. (Reprinted with permission from Ref 14. Copyright 2009 Informa Healthcare)

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Localized translation in plant cells. Several examples of localized mRNAs and cytoskeleton‐associated polysomes are identified in a somatic cell (left cell). A developing cell plate is drawn to represent a dividing cell and demonstrate the localization of Ran2 mRNA at the phragmoplast. A companion cell (center) and sieve element (right) show cell‐to‐cell and long‐distance transport via plasmodesmata. See text for details.

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Plant Puf proteins demonstrate sequence divergence at amino acids that contact RNA. Ribbon and stick models of Arabidopsis Puf proteins APum2 (a) and APum13 (b) bound to the core Nanos Response Element RNA (NRE, UUGUAUAU) (top panel). APum2 represents a conserved plant Puf protein, whereas APum13 is divergent in the amino acids located at its binding interface. Individual Puf repeats (R2–R8) consist of a triple α‐helix, with the central helix positioned on the concave surface of the protein and interacting with a single RNA base (blue). In the ribbon models (left), amino acids that contact the Watson–Crick edge of the base are indicated in green, and those that form stacking interactions are indicated in magenta. The stick models (right) show only the amino acids that provide binding interactions. Thin lines on stick models identify hydrogen bonds or van der Waals. Puf repeat 1 could not be modeled because of significant sequence divergence in the corresponding human Puf reference repeat. The amino acid sequence of each of the eight Puf repeats (lower panel) highlights amino acids 12, 13, and 16 that normally interact with RNA bases. (Reprinted with permission from Ref 66. Copyright 2010 BioMed Central)

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Phosphorylation enhances the interactions between components of the multifactor complex. In vitro evidence for interactions between initiation factor components in the absence of 40S ribosomal subunit are identified by solid lines. Dotted lines indicate interactions that were enhanced by CK2 phosphorylation of initiation factors. (Reprinted with permission from Ref 18. Copyright 2009 The American Society for Biochemistry and Molecular Biology, Inc)

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RNA Export and Localization > RNA Localization
Translation > Translation Mechanisms
Translation > Translation Regulation

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