Innate antiviral immunity is the first line of the host defense system that rapidly detects invading viruses. Mitochondria function as platforms for innate antiviral signal transduction in mammals through the adaptor protein, MAVS. Excessive activation of MAVS-mediated antiviral signaling leads to dysfunction of mitochondria and cell apoptosis that likely causes the pathogenesis of autoimmunity. However, the mechanism of how MAVS is regulated at mitochondria remains unknown. Here we show that the Cytochrome c Oxidase (CcO) complex subunit COX5B physically interacts with MAVS and negatively regulates the MAVS-mediated antiviral pathway. Mechanistically, we find that while activation of MAVS leads to increased ROS production and COX5B expression, COX5B down-regulated MAVS signaling by repressing ROS production. Importantly, our study reveals that COX5B coordinates with the autophagy pathway to control MAVS aggregation, thereby balancing the antiviral signaling activity. Thus, our study provides novel insights into the link between mitochondrial electron transport system and the autophagy pathway in regulating innate antiviral immunity.

Mitochondrial fragmentation and bioenergetic failure manifest in Huntington’s disease (HD), a fatal neurodegenerative disease. The factors that couple mitochondrial fusion/fission with bioenergetics and their impacts on neurodegeneration however remain poorly understood. Our proteomic analysis identifies mitochondrial protein ATAD3A as an interactor of mitochondrial fission GTPase, Drp1, in HD. Here we show that, in HD, ATAD3A dimerization due to deacetylation at K135 residue is required for Drp1-mediated mitochondrial fragmentation. Disturbance of ATAD3A steady state impairs mtDNA maintenance by disrupting TFAM/mtDNA binding. Blocking Drp1/ATAD3A interaction with a peptide, DA1, abolishes ATAD3A oligomerization, suppresses mitochondrial fragmentation and mtDNA lesion, and reduces bioenergetic deficits and cell death in HD mouse- and patient-derived cells. DA1 treatment reduces behavioral and neuropathological phenotypes in HD transgenic mice. Our findings demonstrate that ATAD3A plays a key role in neurodegeneration by linking Drp1-induced mitochondrial fragmentation to defective mtDNA maintenance, suggesting that DA1 might be useful for developing HD therapeutics.

Ammonium is a preferred source of nitrogen for plants but is toxic at high levels. Plant ammonium transporters (AMTs) play an essential role in NH 4 + uptake, but the mechanism by which AMTs are regulated remains unclear. To study how AMTs are regulated in the presence of ammonium, we used variable-angle total internal reflection fluorescence microscopy and fluorescence crosscorrelation spectroscopy for single-particle fluorescence imaging of EGFP-tagged AMT1;3 on the plasma membrane of Arabidopsis root cells at various ammonium levels. We demonstrated that AMT1;3-EGFP dynamically appeared and disappeared on the plasma membrane as moving fluorescent spots in low oligomeric states under N-deprived and N-sufficient conditions. Under external high-ammonium stress, however, AMT1;3-EGFPs were found to amass into clusters, which were then internalized into the cytoplasm. A similar phenomenon also occurred in the glutamine synthetase mutant gln1;2 background. Single-particle analysis of AMT1;3-EGFPs in the clathrin heavy chain 2 mutant (chc2 mutant) and Flotllin1 artificial microRNA (Flot1 amiRNA) backgrounds, together with chemical inhibitor treatments, demonstrated that the endocytosis of AMT1;3 clusters induced by high-ammonium stress could occur mainly through clathrin-mediated endocytic pathways, but the contribution of microdomain-associated endocytic pathway cannot be excluded in the internalization. Our results revealed that the clustering and endocytosis of AMT1;3 provides an effective mechanism by which plant cells can avoid accumulation of toxic levels of ammonium by eliminating active AMT1;3 from the plasma membrane. VA-TIRFM | FCSA mmonium (NH 4 + ) and nitrate (NO 3 − ) are the primary sources of nitrogen (N) for most plants growing in agricultural soils. Ammonium assimilation requires less energy than nitrate assimilation, and, thus, ammonium is absorbed preferentially when plants are N-deficient. However, high concentrations of ammonium can be toxic (1); therefore, ammonia absorption and metabolism must be strictly controlled. Understanding the mechanisms by which plant cells regulate ammonium uptake and translocation is of critical importance for agricultural improvements in N-use efficiency and avoiding ammonium toxicity.Evidence suggests that membrane ammonium transporters (AMTs) act in NH 4 + uptake into plant cells, serving as the major transporters for high-affinity ammonium uptake (2). In Arabidopsis thaliana, the AMT family comprises six isoforms, of which three (AtAMT1;1, AtAMT1;2, and AtAMT1;3) are responsible for about 90% of the total high-affinity N uptake in roots (3). AMT gene expression in Arabidopsis roots is generally repressed by high N and induced by N deficiency (4). In addition to transcriptional mechanisms, regulation of membrane transporter activity is also involved in the plant's responses to changing nutrient supplies (1). Although posttranscriptional regulation of AMT appears to be N-dependent (5), the question of how ammonium regulates AMT transporter activity, particularly t...