Abstract
Mitochondria fulfill some basic roles in all plant cells. They supply the cell with energy in the form of ATP and reducing equivalents [NAD(P)H] and they provide the cell with intermediates for a range of biosynthetic pathways. In addition to this, mitochondria contribute to a number of specialized functions depending on the tissue and cell type, as well as environmental conditions. We will here review the biochemistry and proteomics of mitochondria from non-green cells and organs, which differ from those of photosynthetic organs in a number of respects. We will briefly cover purification of mitochondria and general biochemical properties such as oxidative phosphorylation. We will then mention a few adaptive properties in response to water stress, seed maturation and germination, and the ability to function under hypoxic conditions. The discussion will mainly focus on Arabidopsis cell cultures, etiolated germinating rice seedlings and potato tubers as model plants. It will cover the general proteome as well as the posttranslational modification protein phosphorylation. To date 64 phosphorylated mitochondrial proteins with a total of 103 phosphorylation sites have been identified.
Highlights
All living plant cells contain mitochondria, the organelle where organic molecules are oxidized to produce energy, in the form of ATP and reducing equivalents, as well as metabolic intermediates for use in biosynthetic processes
Mitochondria have a number of other important functions depending on the cell and tissue type, as well as environmental conditions
In anticipation and preparation for this époque we review critical aspects of the field including: (1) methods for isolation of ultra-pure mitochondria; (2) properties of mitochondria; and (3) the current status of mitochondrial proteome investigations
Summary
All living plant cells contain mitochondria, the organelle where organic molecules are oxidized to produce energy, in the form of ATP and reducing equivalents, as well as metabolic intermediates for use in biosynthetic processes. Proteomic comparisons of mitochondria from non-photosynthetic Arabidopsis suspension cells and developing photosynthetic shoots (Lee et al, 2008) as well as developing Arabidopsis roots and photosynthetic shoots (Lee et al, 2011) collectively revealed differences in TCA cycle and photorespiratory enzymes In both instances, most of the component enzymes of the glycine decarboxylase complex, except for the lipoamide dehydrogenase (E3) subunit, which is shared with the PDC, were highly upregulated in green shoot mitochondria compared to the two non-photosynthetic counterparts. Three subunits of the PDC complex including E3 were more prominently expressed in root and suspension cell mitochondria These and other changes to TCA and amino acid metabolism between mitochondria from green and non-green sources confirmed previous observations (e.g., upregulation of GDC in photorespiring tissues) and suggested previously unknown differences in both carbon import/export and oxidative metabolism for this organelle as a direct result of photosynthetic capacity. Both protein phosphorylation and other PTMs such as acetylation are important in mammalian mitochondria (Guan and Xiong, 2011; Koc and Koc, 2012), but in plant mitochondria only protein phosphorylation has been studied in any detail
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