Abstract
BackgroundNon-photosynthetic plastids of plants are known to be involved in a range of metabolic and biosynthetic reactions, even if they have been difficult to study due to their small size and lack of color. The morphology of root plastids is heterogeneous and also the plastid size, density and subcellular distribution varies depending on the cell type and developmental stage, and therefore the functional features have remained obscure. Although the root plastid proteome is likely to reveal specific functional features, Arabidopsis thaliana root plastid proteome has not been studied to date.ResultsIn the present study, we separated Arabidopsis root protein fraction enriched with plastids and mitochondria by 2D-PAGE and identified 84 plastid-targeted and 77 mitochondrion-targeted proteins using LC-MS/MS. The most prevalent root plastid protein categories represented amino acid biosynthesis, carbohydrate metabolism and lipid biosynthesis pathways, while the enzymes involved in starch and sucrose metabolism were not detected. Mitochondrion-targeted proteins were classified mainly into the energetics category.ConclusionsThis is the first study presenting gel-based map of Arabidopsis thaliana root plastid and mitochondrial proteome. Our findings suggest that Arabidopsis root plastids have broad biosynthetic capacity, and that they do not play a major role in a long-term storage of carbohydrates. The proteomic map provides a tool for further studies to compare changes in the proteome, e.g. in response to environmental cues, and emphasizes the role of root plastids in nitrogen and sulfur metabolism as well as in amino acid and fatty acid biosynthesis. The results enable taking a first step towards an integrated view of root plastid/mitochondrial proteome and metabolic functions in Arabidopsis thaliana roots.
Highlights
Non-photosynthetic plastids of plants are known to be involved in a range of metabolic and biosynthetic reactions, even if they have been difficult to study due to their small size and lack of color
It has been shown that the morphology of root plastids is very heterogeneous and the plastid shape, size, density and subcellular distribution varies depending on the cell type and the stage of development [19]
The most prevalent categories represented amino acid biosynthesis (31%) and carbohydrate metabolism (20%), while in mitochondria the proteins involved in energetics (41%) formed the largest category (Fig. 2)
Summary
Non-photosynthetic plastids of plants are known to be involved in a range of metabolic and biosynthetic reactions, even if they have been difficult to study due to their small size and lack of color. The morphology of root plastids is heterogeneous and the plastid size, density and subcellular distribution varies depending on the cell type and developmental stage, and the functional features have remained obscure. All plastid types are enclosed by a double envelope membrane and they contain several copies of a semiautonomous circular genome encoding circa 100 proteins, which are involved in photosynthesis, transcription and translation. Chloroplasts are the sites of photosynthesis and contain an elaborate internal membrane system called the thylakoids, in which the large pigment-protein complexes involved in photosynthetic electron transfer reactions are embedded. Chloroplasts are able to capture light energy and convert it into chemical form as ATP and reducing equivalents of NADPH, while the non-photosynthetic plastids are dependent on the import of external sugar phosphates and ATP to the plastid
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