Dataset Information

Unravelling hidden components of the chloroplast envelope proteome

ABSTRACT: Chloroplast is a major plant cell organelle that fulfills essential metabolic and biosynthetic functions. Located at the interface between the chloroplast and other cell compartments, the chloroplast envelope system is a strategic barrier controlling exchanges of ions, metabolites and proteins, thus regulating essential metabolic functions (synthesis of hormones precursors, amino acids, pigments, sugars, vitamins, lipids, nucleotides…) of the plant cell. However, chloroplast envelope membranes remain the hidden part of the chloroplast proteome and many envelope proteins remain to be characterized (known but uncharacterized envelope proteins) or identified (orphan known envelope-associated functions carried by unidentified proteins) Indeed, the envelope contains only 1% of the chloroplast proteins (i.e. 0.25% of the whole cell proteome). When comparing the composition crude leaf extract and purified envelope vesicles, a high theoretical enrichment factor (EF) of specific envelope proteins is thus expected. This is especially true for minor envelope proteins (e.g. representing 1/100 or 1/1000 of the envelope protein content). Sensitivity of MS technique has been greatly improved during the last decade. Today, thanks to the continuous improvement of MS techniques, we are able to detect more components in a complex sample, to generate quantitative data and to statistically validate above-cited enrichment factor. Here, we have taken advantage of present-days better MS sensitivity towards a better definition (differentiate genuine envelope proteins from contaminants) of the chloroplast envelope proteome. This MS- and statistical-based analysis relied on an enrichment factor calculated for each protein identified in purified envelope fractions when compared to the value obtained for the same protein in crude cell extracts. Using this approach, a total of 1376 proteins was detected in purified envelope fractions, of which, more than 500 could be assigned an envelope localization combining MS-based statistical analyses and manual annotation using data from the literature or prediction tools. Interestingly, many of such proteins being unknown or unexpected envelope components, these data constitute a new resource of significant value to the broader plant science community aiming to define principles and molecular mechanisms controlling fundamental aspects of plastid biogenesis and functions.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Arabidopsis Thaliana (mouse-ear Cress)

TISSUE(S): Photosynthetic Cell, Rosette

SUBMITTER: Marianne Tardif

LAB HEAD: Norbert Rolland

PROVIDER: PXD010545 | Pride | 2019-04-15

REPOSITORIES: Pride

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Unraveling Hidden Components of the Chloroplast Envelope Proteome: Opportunities and Limits of Better MS Sensitivity.

Bouchnak Imen I Brugière Sabine S Moyet Lucas L Le Gall Sophie S Salvi Daniel D Kuntz Marcel M Tardif Marianne M Rolland Norbert N

Molecular & cellular proteomics : MCP 20190408 7

The chloroplast is a major plant cell organelle that fulfills essential metabolic and biosynthetic functions. Located at the interface between the chloroplast and other cell compartments, the chloroplast envelope system is a strategic barrier controlling the exchange of ions, metabolites and proteins, thus regulating essential metabolic functions (synthesis of hormones precursors, amino acids, pigments, sugars, vitamins, lipids, nucleotides etc.) of the plant cell. However, unraveling the conten ...[more]

PMID: 30962257

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Project description:Aim: To identify regulatory factors that control: (1) chloroplast protein importand (2) chloroplast-to-nucleus signalling. This project is a joint proposal from the Jarvis lab which is interested in chloroplast protein import [1] and the Moller lab which is interested in plastid-to-nucleus signalling [2]. Background: The majority of chloroplast proteins are encoded in the nucleus and imported post-translationally into chloroplasts. The abundance of chloroplast proteins may therefore be regulated at multiple levels. It is well documented that the nuclear gene expression is responsive to (largely unknown) signals from the chloroplast [23] and evidence is now emerging that protein import is also a regulated process [1]. Protein import into chloroplasts is mediated by protein complexes in the outer and inner envelope membranes called Toc and Tic respectively. Biochemical studies of pea chloroplasts identified several Toc/Tic components. These proteins are mechanistic or structural components of the import apparatus. Arabidopsis homologues of the pea Toc/Tic proteins were identified by the AGI. Pea Toc34 is represented in Arabidopsis by two genes "Toc33 and Toc34" and pea Toc75 is represented by three genes. These different Tocs have different expression patterns and are proposed to have different precursor protein recognition specificities. The factors that regulate Toc expression in concert with the needs of plastids in developmentally different cells are unknown. Proposal: Two Arabidopsis mutants will be analysed. The ppi1 mutant is null for the putative precursor protein receptor Toc33 [1]and the ppi3 mutant is null for a putative component of the protein import channel Toc75-IV (on chromosome IV). ppi1 plants are yellow-green in appearance but remarkably healthy and grow only slightly more slowly than wild type. By contrast ppi3 plants are indistinguishable from wild type by eye although analysis of the mutant's chloroplast proteome is beginning to reveal some differences (K. Lilley personal communication). Gene expression changes in ppi1 are likely to be quite extensive. Retardation of chloroplast development in ppi1 will activate retrograde signalling pathways so that many nuclear photosynthetic genes are down-regulated. Changes in the expression of photosynthetic genes and of the genes responsible for mediating these responses may therefore be observed. Any regulatory and signalling genes identified will be of interest to the Moller lab. The expression of factors that regulate Toc/Tic gene expression may also be altered in ppi1. It should be possible to distinguish these factors from those involved in the general control of chloroplast gene expression by comparing the results from the two mutants. Genes affected in both mutants are more likely to be involved in regulating chloroplast import since it is unlikely that widespread changes in gene expression will be observed in ppi3. Changes in the expression of factors that regulate import post-translationallyand of the Toc/Tic genes themselves (many are on the RNA) may also be observed. References: 1. Jarvis P. et al. (1998) Science 282: 100-103. 2. Moller S.G. et al. (2001) Genes Dev. 15:90-103. 3. Jarvis P. (2001) Curr. Biol. 11: R307-R310.

			Action	DRS
	Arabidopsis-CCE-Env.pride.mgf.gz	Mgf
	Arabidopsis-CCE-Env.xml.gz	Xml
	F108008_CCE1.dat	Other
	F108009_CCE2.dat	Other
	F108010_CCE3.dat	Other