pTAC2, -6, and -12 Are Components of the Transcriptionally Active Plastid Chromosome That Are Required for Plastid Gene Expression

Abstract

Transcription in plastids is mediated by a plastid-encoded multimeric (PEP) and a nuclear-encoded single-subunit RNA polymerase (NEP) and a still unknown number of nuclear-encoded factors. By combining gel filtration and affinity chromatography purification steps, we isolated transcriptionally active chromosomes from Arabidopsis thaliana and mustard (Sinapis alba) chloroplasts and identified 35 components by electrospray ionization ion trap tandem mass spectrometry. Eighteen components, called plastid transcriptionally active chromosome proteins (pTACs), have not yet been described. T-DNA insertions in three corresponding genes, ptac2, -6, and -12, are lethal without exogenous carbon sources. Expression patterns of the plastid-encoded genes in the corresponding knockout lines resemble those of Drpo mutants. For instance, expression of plastid genes with PEP promoters is downregulated, while expression of genes with NEP promoters is either not affected or upregulated in the mutants. All three components might also be involved in posttranscriptional processes, such as RNA processing and/or mRNA stability. Thus, pTAC2, -6, and -12 are clearly involved in plastid gene expression.

Modified Clp Protease Complex in the ClpP3 Null Mutant and Consequences for Chloroplast Development and Function in Arabidopsis

“…Thus, the loss of Clp protease capacity specifically affects a subset of chloroplast proteases, indicative of a controlled protease network. pTAC11 (WHY3) and pTAC17, initially identified in transcriptionally active chromosome (TAC) fractions (Pfalz et al, 2006), were 7-and 3-fold up-regulated in clpp3-1, respectively. In particular, pTAC11, but not pTAC17, is strongly enriched in nucleoids Huang et al, 2013).…”

Combined Large-Scale Phenotyping and Transcriptomics in Maize Reveals a Robust Growth Regulatory Network

“…of ATP for photosynthesis (Endo et al, 2008); and genes involved in plastid gene expression, such as the ribosomal proteins, components of the plastid-encoded RNA polymerase complex, the pfkB-type carbohydrate kinase FRUCTOKINASE-LIKE PROTEIN (Gilkerson et al, 2012), MurE (Garcia et al, 2008), and PLASTID TRANSCRIPTIONALLY ACTIVE CHROMOSOME6 (Pfalz et al, 2006), CIA2 , genes involved in chloroplast protein import (Chiu and Li, 2008), and pentatricopeptide repeat proteins (Liu et al, 2013a). As a consequence, many mutants in these genes are chlorotic, white, or pale green due to abnormal plastid development and reduced photosynthetic competence.…”

New insights into plastid nucleoid structure and functionality

“…The DNA containing fraction prepared by gel filtration was called TAC, because it has been used initially to determine the activity and composition of the transcriptional apparatus (see reviews of Gruissem and Tonkyn 1993;Igloi and Kössel 1992;Sakai et al 2004, and references therein). The TAC fraction is prepared from plastid membranes by release of the nucleoids with detergents and by subsequent purification involving sepharose gel filtration and other steps (Krause and Krupinska 2000;Pfalz et al 2006). Recent proteomic analyses of these (Pfalz et al 2006;Melonek et al 2012) and other nucleoid-enriched fractions (Phinney and Thelen 2005;Majeran et al 2012) have revealed that several of the newly identified DNA binding proteins were not inherited from the prokaryotic ancestors.…”

“…The TAC fraction is prepared from plastid membranes by release of the nucleoids with detergents and by subsequent purification involving sepharose gel filtration and other steps (Krause and Krupinska 2000;Pfalz et al 2006). Recent proteomic analyses of these (Pfalz et al 2006;Melonek et al 2012) and other nucleoid-enriched fractions (Phinney and Thelen 2005;Majeran et al 2012) have revealed that several of the newly identified DNA binding proteins were not inherited from the prokaryotic ancestors. Plastid proteins homologous to the abundant prokaryotic HU protein, on the other hand, were not detected in higher plants which stands in contrast to their identification in some algal plastids (Karcher et al 2009), in the apicoplasts of apicomplexans (Sato et al 2003) as well as in some dinoflagellates (Chan et al 2006).…”