Abstract
GRIM-19 (Gene associated with Retinoid-Interferon-induced Mortality 19) is a subunit of mitochondrial respiratory complex I in mammalian systems, and it has been demonstrated to be a multifunctional protein involved in the cell cycle, cell motility and innate immunity. However, little is known about the molecular functions of its homologues in plants. Here, we characterised GhMCS1, an orthologue of human GRIM-19 from cotton (Gossypium hirsutum L.), and found that it was essential for maintaining complex integrity and mitochondrial function in cotton. GhMCS1 was detected in various cotton tissues, with high levels expressed in developing fibres and flowers and lower levels in leaves, roots and ovules. In fibres at different developmental stages, GhMCS1 expression peaked at 5–15 days post anthesis (dpa) and then decreased at 20 dpa and diminished at 25 dpa. By Western blot analysis, GhMCS1 was observed to be localised to the mitochondria of cotton leaves and to colocalise with complex I. In Arabidopsis, GhMCS1 overexpression enhanced the assembly of complex I and thus respiratory activity, whereas the GhMCS1 homologue (At1g04630) knockdown mutants showed significantly decreased respiratory activities. Furthermore, the mutants presented with some phenotypic changes, such as smaller whole-plant architecture, poorly developed seeds and fewer trichomes. More importantly, in the cotton fibres, both the GhMCS1 transcript and protein levels were correlated with respiratory activity and fibre developmental phase. Our results suggest that GhMCS1, a functional ortholog of the human GRIM-19, is an essential subunit of mitochondrial complex I and is involved in cotton fibre development. The present data may deepen our knowledge on the potential roles of mitochondria in fibre morphogenesis.
Highlights
Mitochondria in plants, similar to other eukaryotes, are highly specialised and dynamic double membranous organelles that play a pivotal role in energy production through oxidative phosphorylation (OXPHOS) [1]
Our results suggest that GhMCS1, a functional ortholog of the human GRIM-19, is an essential subunit of mitochondrial complex I and is involved in cotton fibre development
No alternative transcript was detected in the RT-PCR sequencing, suggesting that alternative splicing might not occur during GhMCS1 transcription, or the expression of alternative transcripts was too low to be detected
Summary
Mitochondria in plants, similar to other eukaryotes, are highly specialised and dynamic double membranous organelles that play a pivotal role in energy production through oxidative phosphorylation (OXPHOS) [1]. The OXPHOS system is localised to the mitochondrial inner membrane, and it is composed of five complexes (I to V) that work in concert to drive the aerobic synthesis of ATP [2]. Of these complexes, complex I or NADH:ubiquinone oxidoreductase (E.C. 1.6.5.3) is the first and largest enzyme of the OXPHOS system that contains over 40 different subunits in eukaryotes, including mammals and plants [3,4,5]. Mutations have been found in both mitochondrial and nuclear genes, such as GRIM-19 (gene associated with retinoid-interferon-induced mortality-19), which leads to the complete abolishment of complex I assembly when deleted; its knockout causes early embryonic lethality in mice [4, 7]
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