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, 7 (7), 1105-20

The Translational Apparatus of Plastids and Its Role in Plant Development


The Translational Apparatus of Plastids and Its Role in Plant Development

Nadine Tiller et al. Mol Plant.


Chloroplasts (plastids) possess a genome and their own machinery to express it. Translation in plastids occurs on bacterial-type 70S ribosomes utilizing a set of tRNAs that is entirely encoded in the plastid genome. In recent years, the components of the chloroplast translational apparatus have been intensely studied by proteomic approaches and by reverse genetics in the model systems tobacco (plastid-encoded components) and Arabidopsis (nucleus-encoded components). This work has provided important new insights into the structure, function, and biogenesis of chloroplast ribosomes, and also has shed fresh light on the molecular mechanisms of the translation process in plastids. In addition, mutants affected in plastid translation have yielded strong genetic evidence for chloroplast genes and gene products influencing plant development at various levels, presumably via retrograde signaling pathway(s). In this review, we describe recent progress with the functional analysis of components of the chloroplast translational machinery and discuss the currently available evidence that supports a significant impact of plastid translational activity on plant anatomy and morphology.

Keywords: evolution; leaf development; palisade cell.; plastid; plastid transformation; retrograde signaling; ribosomal protein; ribosome; translation.


Figure 1.
Figure 1.
Typical Leaf Phenotypes of Transplastomic Plants Harboring a Knockout Allele for an Essential Component of the Translational Apparatus. Leaves of transplastomic tobacco plants transformed with a knockout construct for the essential plastid gene rps18 (encoding plastid ribosomal protein S18; Rogalski et al., 2006; Table 2) are shown. The plastid transformants are heteroplasmic and, in the absence of antibiotic selection, the plants randomly segregate into homoplasmy for the wild-type plastid genome or homoplasmy for the transplastome. Homoplasmy for the rps18 knockout allele is lethal at the cellular level and results in loss of cell proliferation. Death of cell lineages during leaf development produces aberrantly shaped leaves that lack individual sectors or, in extreme cases, nearly the entire leaf blade (Ahlert et al., 2003). Scale bar = 2 cm.
Figure 2.
Figure 2.
Knockout of a Non-Essential Plastid Gene Involved in Translation. The large ribosomal subunit protein L36 is not essential for plastid translation and, therefore, homoplasmic knockout mutants can be obtained (Fleischmann et al., 2011). Tobacco Δrpl36 plants grow autotrophically in soil, but suffer from severe photo-oxidative damage due to low levels of plastid protein biosynthesis which results in low photosynthetic activity. Moreover, the mutants display striking alterations in leaf morphology and plant architecture (Fleischmann et al., 2011). (A) A young Δrpl36 plant two month after transfer from in vitro culture to the greenhouse. Note the much narrower leaf blade compared to the wild-type shown in (B). Scale bar = 2 cm. (B) Leaf shape of a young wild-type plant at approximately the same developmental stage as the Δrpl36 plant shown in (A). Scale bar = 2 cm. (C) A flowering wild-type plant (after 9 weeks of growth in the greenhouse). Scale bar = 10 cm. (D) A Δrpl36 plant after 1.3 years of growth in the greenhouse. Note the narrow leaves, the extensive atypical shoot branching (indicative of reduced apical dominance), and the lack of floral induction. Scale bar = 10 cm.

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