Mutations in a plastid-localized elongation factor G alter early stages of plastid development in Arabidopsis thaliana

Department of Biology, Indiana University, Bloomington, IN 47405, USA.
BMC Plant Biology (Impact Factor: 3.81). 02/2007; 7(1):37. DOI: 10.1186/1471-2229-7-37
Source: PubMed


Proper development of plastids in embryo and seedling tissues is critical for plant development. During germination, plastids develop to perform many critical functions that are necessary to establish the seedling for further growth. A growing body of work has demonstrated that components of the plastid transcription and translation machinery must be present and functional to establish the organelle upon germination.
We have identified Arabidopsis thaliana mutants in a gene that encodes a plastid-targeted elongation factor G (SCO1) that is essential for plastid development during embryogenesis since two T-DNA insertion mutations in the coding sequence (sco1-2 and sco1-3) result in an embryo-lethal phenotype. In addition, a point mutation allele (sco1-1) and an allele with a T-DNA insertion in the promoter (sco1-4) of SCO1 display conditional seedling-lethal phenotypes. Seedlings of these alleles exhibit cotyledon and hypocotyl albinism due to improper chloroplast development, and normally die shortly after germination. However, when germinated on media supplemented with sucrose, the mutant plants can produce photosynthetically-active green leaves from the apical meristem.
The developmental stage-specific phenotype of the conditional-lethal sco1 alleles reveals differences in chloroplast formation during seedling germination compared to chloroplast differentiation in cells derived from the shoot apical meristem. Our identification of embryo-lethal mutant alleles in the Arabidopsis elongation factor G indicates that SCO1 is essential for plant growth, consistent with its predicted role in chloroplast protein translation.

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    • "The involvement and general importance of photoreceptors in this process, including both phytochromes and cryptochromes, also has been described (Chun et al., 2001; Thum et al., 2001; Wellburn and Wellburn, 1973), and in some plant species, specific contributions of blue and red light have been quantified (eg. in Cucumis,Hogewoning et al., 2010). Development of plastids in both embryonic development and post-germination is still poorly understood, but involve many transcriptional and translation mechanisms, including plastidspecific elongation factor G (SCO1), required for embryonic survival and seedling plastid development and subsequent survival (Ruppel and Hangarter, 2007). A limited number of factors that function downstream of the photoreceptors have been identified. "
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    ABSTRACT: Plants exhibit sensitivity to dynamic or changing environments and respond to such fluctuations through short- and long-term adaptive responses. The transition from seed to established seedling is a critical phase of the plant life cycle. This brief, but highly important, phase is linked to species persistence and impacts long-term population dynamics. During the seed-to-seedling transition, key factors that modulate plant form and function are light, hormones, and integrated signaling at the light-hormone interface. During this stage of early plant development, germination, seedling development and the critical heterotrophic-to-autotrophic conversion, the latter of which includes chloroplast development and differentiation, are modulated by external light parameters and homeostasis of several plant hormones. Specific mechanisms used to mediate responses to light and/or hormones during the seed-to-seedling transition include the regulation of gene expression, protein dynamics, and metabolites (including sugars and reactive oxygen species). In this review, we highlight key mechanistic factors and components that are especially linked to integrating responses to light and hormones during germination and the post-germinative seed-to-seedling transition. These light-/hormone-dependent mechanisms have implications for short- and long-term dynamics and diversity of natural plant species and communities.
    Environmental and Experimental Botany 05/2015; 83. DOI:10.1016/j.envexpbot.2015.05.004 · 3.36 Impact Factor
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    • "Thus, our results establish a link between PEP activity and embryo development. Previously compromised translational and post-translational activities in the chloroplasts, such as mutations in elongation factor G and PPR proteins, have been shown to lead to embryo lethality (Ruppel and Hangarter, 2007; Khrouchtchova et al., 2012; Sosso et al., 2012). Interestingly, in tobacco and barley neither of the knockouts completely lacking PEP activity exhibits an embryo lethal phenotype (Allison et al., 1996; De Santis-MacIossek et al., 1999; Zhelyazkova et al., 2012). "
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    ABSTRACT: Chloroplast biogenesis and function is essential for proper plant embryo and seed development but the molecular mechanisms underlying the role of plastids during embryogenesis are poorly understood. Expression of plastid encoded genes is dependent on two different transcription machineries; a plastid-encoded bacterial-type RNA polymerase (PEP) and a nuclear-encoded phage-type RNA polymerase (NEP), which recognize distinct types of promoters. However, the division of labor between PEP and NEP during plastid development and in mature chloroplasts is unclear. We show here that PLASTID REDOX INSENSITIVE 2 (PRIN2) and CHLOROPLAST STEM-LOOP BINDING PROTEIN 41 kDa (CSP41b), two proteins identified in plastid nucleoid preparations, are essential for proper plant embryo development. Using Co-IP assays and native PAGE we have shown a direct physical interaction between PRIN2 and CSP41b. Moreover, PRIN2 and CSP41b form a distinct protein complex in vitro that binds DNA. The prin2.2 and csp41b-2 single mutants displayed pale phenotypes, abnormal chloroplasts with reduced transcript levels of photosynthesis genes and defects in embryo development. The respective csp41b-2prin2.2 homo/heterozygote double mutants produced abnormal white colored ovules and shrunken seeds. Thus, the csp41b-2prin2.2 double mutant is embryo lethal. In silico analysis of available array data showed that a large number of genes traditionally classified as PEP dependent genes are transcribed during early embryo development from the pre-globular stage to the mature-green-stage. Taken together, our results suggest that PEP activity and consequently the switch from NEP to PEP activity, is essential during embryo development and that the PRIN2-CSP41b DNA binding protein complex possibly is important for full PEP activity during this process.
    Frontiers in Plant Science 08/2014; 5:385. DOI:10.3389/fpls.2014.00385 · 3.95 Impact Factor
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    • "A key class of mutations has been identified that specifically disrupts chloroplast biogenesis in cotyledons: sigma factor 6 (sig6), delayed greening 1 (dg1), white cotyledon (wco1), cyo1 (shi-o-u, means cotyledon in Japanese) and the snowy cotyledon (sco) loci (Yamamoto et al., 2000; Ishizaki et al., 2005; Albrecht et al., 2006, 2008, 2010; Ruppel and Hangarter , 2007; Shimada et al., 2007; Chi et al., 2010). These mutations have different functions: the sig6 and dg1 mutations have an impact on chloroplast gene transcription (Ishizaki et al., 2005; Chi et al., 2010); wco1 and sco1 both affect chloroplast protein translation (Yamamoto et al., 2000; Albrecht et al., 2006; Ruppel and Hangarter, 2007); sco3 encodes a protein of unknown function that is not located in chloroplasts but to the periphery of peroxisomes, associated with the cytoskeleton (Albrecht et al., 2010); and cyo1 and sco2 are allelic mutations in a gene that encodes a chloroplast protein disulphide isomerase that was shown to be capable of renaturation of denatured RNase A (Shimada et al., 2007; Albrecht et al., 2008). Intriguingly, despite showing bleached or chlorotic cotyledons, these mutants exhibit very few, if any, defects in the chloroplasts of rosette leaves; this situation suggests distinct complementary processes and/or proteins function in the two different types of photosynthetic leaves. "
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    ABSTRACT: The process of chloroplast biogenesis requires a multitude of pathways and processes to establish chloroplast function. In cotyledons of seedlings, chloroplasts develop either directly from proplastids (also named eoplasts) or, if germinated in the dark, via etioplasts, whereas in leaves chloroplasts derive from proplastids in the apical meristem and are then multiplied by division. The snowy cotyledon 2, sco2, mutations specifically disrupt chloroplast biogenesis in cotyledons. SCO2 encodes a chloroplast-localized protein disulphide isomerase, hypothesized to be involved in protein folding. Analysis of co-expressed genes with SCO2 revealed that genes with similar expression patterns encode chloroplast proteins involved in protein translation and in chlorophyll biosynthesis. Indeed, sco2-1 accumulates increased levels of the chlorophyll precursor, protochlorophyllide, in both dark grown cotyledons and leaves. Yeast two-hybrid analyses demonstrated that SCO2 directly interacts with the chlorophyll-binding LHCB1 proteins, being confirmed in planta using bimolecular fluorescence complementation (BIFC). Furthermore, ultrastructural analysis of sco2-1 chloroplasts revealed that formation and movement of transport vesicles from the inner envelope to the thylakoids is perturbed. SCO2 does not interact with the signal recognition particle proteins SRP54 and FtsY, which were shown to be involved in targeting of LHCB1 to the thylakoids. We hypothesize that SCO2 provides an alternative targeting pathway for light-harvesting chlorophyll binding (LHCB) proteins to the thylakoids via transport vesicles predominantly in cotyledons, with the signal recognition particle (SRP) pathway predominant in rosette leaves. Therefore, we propose that SCO2 is involved in the integration of LHCB1 proteins into the thylakoids that feeds back on the regulation of the tetrapyrrole biosynthetic pathway and nuclear gene expression.
    The Plant Journal 03/2012; 69(5):743-54. DOI:10.1111/j.1365-313X.2011.04833.x · 5.97 Impact Factor
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