Plants have evolved sophisticated mechanisms to recycle intracellular constituents. One gaining in appreciation is autophagy, which involves specialized vesicles engulfing and delivering unwanted ...cytoplasmic material to the vacuole for breakdown. Central to this process is the ubiquitin-fold protein autophagy (ATG)-8, which becomes tethered to the developing autophagic membranes by lipidation. Here, we review data showing that the ATG8 moiety provides a docking site not only for proteins that help shape the enclosing vesicles and promote their fusion with the tonoplast, but also for a host of receptors that recruit appropriate autophagic cargo. The identity of these receptors has dramatically altered the view of autophagy as being a relatively nonspecific mechanism to one that may selectively sequester aggregated proteins, protein complexes, organelles, and even invading pathogens.
Autophagy-mediated turnover removes damaged organelles and unwanted cytoplasmic constituents and thus plays critical roles in cellular housekeeping and nutrient recycling. This "self eating" is ...tightly regulated by the AUTOPHAGY-RE LATE D1/13 (ATG1/13) kinase complex, which connects metabolic and environmental cues to the vacuolar delivery of autophagic vesicles. Here, we describe the Arabidopsis thaliana accessory proteins ATG11 and ATG101, which help link the ATG1/13 complex to autophagic membranes. ATG11 promotes vesicle delivery to the vacuole but is not essential for synthesizing the ATG12-ATG5 and ATG8-phosphatidylethanolamine adducts that are central to autophagic vesicle assembly. ATG11, ATG101, ATG1, and ATG13 colocalize with each other and with ATG8, with ATG1 tethered to ATG8 via a canonical ATG8-interacting motif. Also, the presence of ATG11 encourages starvation-induced phosphorylation of ATG1 and turnover of ATG1 and ATG13. Like other atg mutants, ATG11-deficient plants senesce prematurely and are hypersensitive to nitrogen and fixed-carbon limitations. Additionally, we discovered that the senescence-induced breakdown of mitochondria-resident proteins and mitochondrial vesicles occurs via an autophagic process requiring ATG11 and other ATG components. Together, our data indicate that ATG11 (and possibly ATG 101) provides important scaffolds connecting the ATG 1/13 complex to both general autophagy and selective mitophagy.
Autophagic turnover of intracellular constituents is critical for cellular housekeeping, nutrient recycling, and various aspects of growth and development in eukaryotes. Here we show that autophagy ...impacts the other major degradative route involving the ubiquitin-proteasome system by eliminating 26S proteasomes, a process we termed proteaphagy. Using Arabidopsis proteasomes tagged with GFP, we observed their deposition into vacuoles via a route requiring components of the autophagy machinery. This transport can be initiated separately by nitrogen starvation and chemical or genetic inhibition of the proteasome, implying distinct induction mechanisms. Proteasome inhibition stimulates comprehensive ubiquitylation of the complex, with the ensuing proteaphagy requiring the proteasome subunit RPN10, which can simultaneously bind both ATG8 and ubiquitin. Collectively, we propose that Arabidopsis RPN10 acts as a selective autophagy receptor that targets inactive 26S proteasomes by concurrent interactions with ubiquitylated proteasome subunits/targets and lipidated ATG8 lining the enveloping autophagic membranes.
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•The Arabidopsis 26S proteasome is degraded by ATG8-mediated autophagy•This degradation is induced by nitrogen starvation and proteasome inhibition•Proteasome inhibition stimulates extensive ubiquitylation of the complex•RPN10 acts as a proteaphagy receptor by binding ubiquitylated proteasomes and ATG8
Marshall et al. have revealed that the 26S proteasome is degraded by ATG8-mediated autophagy in Arabidopsis, a process stimulated separately by nitrogen starvation and chemical or genetic proteasome inhibition. Additionally, they showed that inhibited proteasomes become extensively ubiquitylated and that subsequent autophagic turnover is mediated by the ubiquitin receptor RPN10.
Autophagy is an intracellular recycling route in eukaryotes whereby organelles and cytoplasm are sequestered in vesicles, which are subsequently delivered to the vacuole for breakdown. The process is ...induced by various nutrient-responsive signaling cascades converging on the Autophagy-Related 1 (ATG1)/ATG13 kinase complex. Here, we describe the ATG1/13 complex in Arabidopsis thaliana and show that it is both a regulator and a target of autophagy. Plants missing ATG13 are hypersensitive to nutrient limitations and senesce prematurely similar to mutants lacking other components of the ATG system. Synthesis of the ATG12-ATG5 and ATG8-phosphatidylethanolamine adducts, which are essential for autophagy, still occurs in ATG13-deficient plants, but the biogenesis of ATG8-decorated autophagic bodies does not, indicating that the complex regulates downstream events required for autophagosome enclosure and/or vacuolar delivery. Surprisingly, levels of the ATG 1a and ATG 13a phosphoproteins drop dramatically during nutrient starvation and rise again upon nutrient addition. This turnover is abrogated by inhibition of the ATG system, indicating that the ATG 1/13 complex becomes a target of autophagy. Consistent with this mechanism, ATG 1a is delivered to the vacuole with ATG8-decorated autophagic bodies. Given its responsiveness to nutrient demands, the turnover of the ATG 1/13 kinase likely provides a dynamic mechanism to tightly connect autophagy to a plant's nutritional status.
Metabolic engineering of plant carotenoids in food crops has been a recent focus for improving human health. Pathway manipulation is predicated on comprehensive knowledge of this biosynthetic ...pathway, which has been extensively studied. However, there existed the possibility of an additional biosynthetic step thought to be dispensable because it could be compensated for by light. This step, mediated by a putative Z-ISO, was predicted to occur in the sequence of redox reactions that are coupled to an electron transport chain and convert the colorless 15-cis-phytoene to the red-colored all-trans-lycopene. The enigma of carotenogenesis in the absence of light (e.g. in endosperm, a target for improving nutritional content) argued for Z-ISO as a pathway requirement. Therefore, understanding of plant carotenoid biosynthesis was obviously incomplete. To prove the existence of Z-ISO, maize (Zea mays) and Arabidopsis (Arabidopsis thaliana) mutants were isolated and the gene identified. Functional testing of the gene product in Escherichia coli showed isomerization of the 15-cis double bond in 9,15,9'-tri-cis-ζ-carotene, proving that Z-ISO encoded the missing step. Z-ISO was found to be important for both light-exposed and "dark" tissues. Comparative genomics illuminated the origin of Z-ISO found throughout higher and lower plants, algae, diatoms, and cyanobacteria. Z-ISO evolved from an ancestor related to the NnrU (for nitrite and nitric oxide reductase U) gene required for bacterial denitrification, a pathway that produces nitrogen oxides as alternate electron acceptors for anaerobic growth. Therefore, plant carotenogenesis evolved by recruitment of genes from noncarotenogenic bacteria.
Phosphatidylinositol 3-phosphate (PI3P) is an essential membrane signature for both autophagy and endosomal sorting that is synthesized in plants by the class III phosphatidylinositol 3-kinase (PI3K) ...complex, consisting of the VPS34 kinase, together with ATG6, VPS15, and either VPS38 or ATG14 as the fourth subunit. Although Arabidopsis (
) plants missing the three core subunits are infertile,
mutants are viable but have aberrant leaf, root, and seed development, Suc sensing, and endosomal trafficking, suggesting that VPS38 and ATG14 are nonredundant. Here, we evaluated the role of ATG14 through a collection of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 and T-DNA insertion mutants disrupting the two Arabidopsis paralogs.
double mutants were relatively normal phenotypically but displayed pronounced autophagy defects, including reduced accumulation of autophagic bodies and cargo delivery during nutrient stress. Unexpectedly, homozygous
triple mutants were viable but showed severely compromised rosette development and reduced fecundity, pollen germination, and autophagy, consistent with a need for both ATG14 and VPS38 to fully actuate PI3P biology. However, the triple mutants still accumulated PI3P, but they were hypersensitive to the PI3K inhibitor wortmannin, indicating that the ATG14/VPS38 component is not essential for PI3P synthesis. Collectively, the ATG14/VPS38 mutant collection now permits the study of plants altered in specific aspects of PI3P biology.
Autophagy is a primary route for nutrient recycling in plants by which superfluous or damaged cytoplasmic material and organelles are encapsulated and delivered to the vacuole for breakdown. Central ...to autophagy is a conjugation pathway that attaches AUTOPHAGY-RELATED8 (ATG8) to phosphatidylethanolamine, which then coats emerging autophagic membranes and helps with cargo recruitment, vesicle enclosure, and subsequent vesicle docking with the tonoplast. A key component in ATG8 function is ATG12, which promotes lipidation upon its attachment to ATG5. Here, we fully defined the maize (Zea mays) ATG system transcriptionally and characterized it genetically through atg12 mutants that block ATG8 modification. atg12 plants have compromised autophagic transport as determined by localization of a YFP-ATG8 reporter and its vacuolar cleavage during nitrogen or fixed-carbon starvation. Phenotypic analyses showed that atg12 plants are phenotypically normal and fertile when grown under nutrient-rich conditions. However, when nitrogen-starved, seedling growth is severely arrested, and as the plants mature, they show enhanced leaf senescence and stunted ear development. Nitrogen partitioning studies revealed that remobilization is impaired in atg12 plants, which significantly decreases seed yield and nitrogen-harvest index. Together, our studies demonstrate that autophagy, while nonessential, becomes critical during nitrogen stress and severely impacts maize productivity under suboptimal field conditions.
The strong corrosion behavior at the Al current collector restricts the application range of lithium bis (trifluoromethanesulfonylimide) (LiTFSI), despite its high stability against water and ...thermal. SEM, LSV and Tafel curves proved that adding LiODFB into LiTFSI-based electrolytes could suppress aluminum corrosion caused by LiTFSI-based electrolytes. The cycling stability and rate capability of LiFePO4-based batteries using LiTFSI0.6–LiODFB0.4-based electrolytes is excellent as compared to LiFePO4-based batteries using LiPF6-based electrolytes.
•A novel dual-salts of LiTFSI and LiODFB has been used in LiFePO4-based batteries.•LiTFSI–LiODFB-based electrolyte shows good anti-corrosion performance to Al foil.•Li|LiFePO4 cells using LiTFSI–LiODFB-based electrolyte show good cycling stability and rate performance.•Li|LiFePO4 cells using LiTFSI–LiODFB-based electrolyte has an appropriate conductivity.
Autophagy, a highly conserved quality control mechanism, is essential for maintaining cellular homeostasis and healthy growth of plants. Compared with extensive research in the cytoplasmic control of ...autophagy, studies regarding the nuclear events involved in the regulation of plant autophagy are just beginning to emerge. Accumulating evidence reveals a coordinated expression of plant autophagy genes in response to diverse developmental states and growth conditions. Here, we summarize recent progress in the identification of tightly controlled transcription factors and histone marks associated with the autophagic process in plants, and propose several modules, consisting of transcription regulators and epigenetic modifiers, as important nuclear players that could contribute to both short-term and long-term controls of plant autophagy at the transcriptional and post-transcriptional levels.
Coordinated transcriptional upregulation of ATG genes emerges as a general mechanism of autophagy activation in plants.Recent studies unveil several key transcription factors involved in the transcriptional control of plant autophagy.HDA9 functions as an important epigenetic modifier to modulate plant autophagy in response to developmental or stress cues.Genome-wide studies illustrate the enrichment of specific epigenetic marks or nucleobase modifications on ATG loci in plants.
Autophagy is a highly evolutionarily-conserved catabolic process facilitating the development and survival of organisms which have undergone favorable and/or stressful conditions, in particular the ...plant. Accumulating evidence has implicated that autophagy is involved in growth and development, as well as responses to various stresses in plant. Similarly, phytohormones also play a pivotal role in the response to various stresses in addition to the plant growth and development. However, the relationship between autophagy and phytohormones still remains poorly understood. Here, we review advances in the crosstalk between them upon various environmental stimuli. We also discuss how autophagy coordinates the phytohormones to regulate plant growth and development. We propose that unraveling the regulatory role(s) of autophagy in modulating the homeostasis of phytohormones would benefit crop breeding and improvement under variable environments, in particular under suboptimal conditions.
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