Autophagy in plants—What’s new on the menu? During recovery after starvation, AtSINAT1 and AtSINAT2 target AtATG13 for degradation to terminate active autophagy. Blocking autophagy by silencing tobacco ATGs prevented pollen germination and cytoplasmic deletion in pollen (Zhao et al., 2020), highlighting the role played by autophagy in pollen morphology and male fertility via cytoplasmic clearance. Impact of Drought on Soluble Sugars and Free Proline Content in Selected. Autophagy, for example, is a process that breaks down damaged or unwanted molecules found inside cells, which has also been linked to plant disease resistance. eCollection 2020. Furthermore, the expression of ATI1 and ATI2 is induced by carbon starvation and various abiotic stresses that cause energy deprivation (Avin‐Wittenberg et al., 2012; Honig et al., 2012). Enter your email address below and we will send you your username, If the address matches an existing account you will receive an email with instructions to retrieve your username, I have read and accept the Wiley Online Library Terms and Conditions of Use, The PP2A regulatory subunit Tap46, a component of the TOR signaling pathway, modulates growth and metabolism in plants, Heat shock factors: Integrators of cell stress, development and lifespan, Role of AMPK‐mTORUlk1/2 in the regulation of autophagy: Cross talk, shortcuts, and feedbacks, Cysteine‐generated sulfide in the cytosol negatively regulates autophagy and modulates the transcriptional profile in, S‐Sulfhydration: A cysteine posttranslational modification in plant systems, S‐nitrosylation: An emerging post‐translational protein modification in plants, Global analysis of the role of autophagy in cellular metabolism and energy homeostasis in, ATI1 a newly identified atg8‐interacting protein binds two different Atg8 homologs, A central integrator of transcription networks in plant stress and energy signalling, RE1B degrades RNAs encoding proteins that interfere with the induction of autophagy by ER stress in, COST1 regulates autophagy to control plant drought tolerance, Function and regulation of macroautophagy in plants, High‐resolution temporal profiling of transcripts during, A mammalian protein targeted by G1‐arresting rapamycin‐receptor complex, Autophagy contributes to regulation of the hypoxia response during submergence in, The AMP‐activated protein kinase KIN10 is involved in the regulation of autophagy in, POWERDRESS interacts with HISTONE DEACETYLASE 9 to promote aging in, Brassinosteroids act as a positive regulator of NBR1‐dependent selective autophagy in response to chilling stress in tomato, ATG8 lipidation and ATG8‐mediated autophagy in, The ATG autophagic conjugation system in maize: ATG transcripts and abundance of the ATG8‐lipid adduct are regulated by development and nutrient availability, The BECN1‐USP19 axis plays a role in the crosstalk between autophagy and antiviral immune responses, The APG8/12‐activating enzyme APG7 is required for proper nutrient recycling and senescence in, Ultrastructure of autophagy in plant cells: A review, Many ways to exit? Abolishing the interaction between βC1 and NbATG8 or NbGAPC, or silencing of NbATG5 and NbATG7 leads to compromised autophagic activity upon infection and a reduction in plant resistance to geminiviruses (Haxim et al., 2017). In general, NO acts through the posttranslational protein modification S‐nitrosylation, which adds a NO group onto the reactive cysteine thiol of a protein (Hess et al., 2005; Astier et al., 2011). Under nutrient‐rich conditions, AtSINAT1 and AtSINAT2 interact with TUMOR NECROSIS FACTOR RECEPTOR ASSOCIATED FACTOR 1a (AtTRAF1a) and AtTRAF1b to ubiquitinate and destabilize AtATG13, thereby maintaining a relatively low level of autophagy (Figure 1) (Qi et al., 2020). Although genetic evidence highlights the important role of autophagy in plant immunity, the underlying molecular mechanism remains largely unknown. In plants, it assists in responding to dynamic environmental conditions and maintaining metabolite homeostasis under normal or stress conditions. Combating stress: The interplay between hormone signaling and autophagy in plants, The defective proteasome but not substrate recognition function is responsible for the null phenotypes of the. The osatg10b mutants display decreased autophagosome formation compared to wild‐type plants and are sensitive to high salt and MV treatment (Shin et al., 2009). The Arabidopsis Mei2 homologue AML1 binds AtRaptor1B, the plant homologue of a major regulator of eukaryotic cell growth. Autophagy (or autophagocytosis) (from the Ancient Greek αὐτόφαγος autóphagos, meaning "self-devouring" and κύτος kýtos, meaning "hollow") is the natural, regulated mechanism of the cell that removes unnecessary or dysfunctional components. CAS Article Google Scholar 27. However, the deacetylation of ATG3 by the histone deacetylase Reduced potassium dependence 3 (RPD3) contributes to the attenuation of autophagosome formation during starvation (Yi and Yu, 2012; Yi et al., 2012), indicating that acetylation and deacetylation play important roles in regulating autophagosome formation. In yeast, the histone acetyltransferase Esa1, a subunit of the nucleosome acetyltransferase histone H4 (NuA4), is required for K19‐ and K48‐linked acetylation of ATG3 by controlling the interaction between ATG3 and ATG8 and the lipidation of ATG8 during autophagy (Yi and Yu, 2012; Yi et al., 2012). If you do not receive an email within 10 minutes, your email address may not be registered, Indeed, drought stress induces autophagy by transcriptional or posttranscriptional mechanisms. Finally, the ZmATG8–PE complex was identified in maize (Chung et al., 2009). Nitric oxide (NO) facilitates seed germination under low‐oxygen conditions (Zhan et al., 2018). In plants, autophagy has been shown to function in response to various environmental stresses such as nutrient starvation, drought, salt and heat [9–11]. In mammalian cells, the core component of this complex, Beclin‐1 (ATG6 homolog in yeast and plants), is also regulated by posttranslational ubiquitination. Tomato SlWRKY33 regulates the expression of ATG genes upon autophagy induction (Zhou et al., 2014). The intracellular level of ROS is modulated by different signals, including high-light stress, nutrient limitation, ER stress, or pathogen infection. We investigated the effects of autophagy disruption on the number and size of chloroplasts during senescence. Alers, S., Löffler, A.S., Wesselborg, S., and Stork, B. Moreover, although many diverse physiological functions of autophagy have been uncovered, most of the molecular mechanisms, in particular their connections to known signaling mechanisms including PTMs, are still unclear. 31725004/National Natural Science Foundation of China, 31670276/National Natural Science Foundation of China, 31800217/National Natural Science Foundation of China, 2017A030308008/Natural Science Foundation of Guangdong Province, China, 2018A030313210/Natural Science Foundation of Guangdong Province, China, 19lgpy202/Natural Science Foundation of Guangdong Province, China. In plants, SnRK1, an ortholog of mammalian AMPK and yeast Snf1, is a highly conserved energy sensor that is activated under energy deprivation (Polge and Thomas, 2007; Baena‐González and Sheen, 2008). Protein aggregates are cytotoxic and are potentially removed by autophagy. The enhanced resistance to powdery mildew without increased pathogen‐induced cell death observed in the Arabidopsis atg2 mutant is not observed in SA‐deficient plants, suggesting that autophagy negatively regulates powdery mildew resistance in a SA‐dependent manner, which is likely uncoupled from pathogen‐induced cell death (Wang et al., 2011a). Autophagy is a macromolecule degradation pathway that recycles damaged or unwanted cell materials upon encountering stress conditions or during specific developmental processes. A TOR homolog has also been identified in Arabidopsis, where it acts as a master regulator of glucose signaling and root hair development (Menand et al., 2002; Xiong and Sheen, 2012; Xiong et al., 2013). During this process, the vacuolar membranes are permeabilized to release vacuolar hydrolases directly into the cytoplasm, where they degrade cytoplasmic materials or even cell walls, resulting in PCD (Hatsugai et al., 2004; van Doorn and Papini, 2013). N2 - Autophagy is a highly conserved processing mechanism in eukaryotes whereby cytoplasmic components are engulfed in double-membrane vesicles called autophagosomes and are delivered into organelles such as lysosomes (mammal) or vacuoles (yeast/plant) for degradation and … By contrast, atg seedlings accumulate anthocyanin only under nitrogen starvation (Xiong et al., 2005; Suttangkakul et al., 2011; Qi et al., 2017). Autophagy can be activated in plants by nutrient, salt, osmotic, oxidative, and ER stress. There are generally three recognized types of autophagy. Here, we provide an overview of the physiological roles and posttranslational regulation of autophagy in plants. In mammals, the NAD‐dependent deacetylase Sirtuin 1 (Sirt1) directly deacetylates ATG5, ATG7, and ATG8 in an NAD‐dependent manner during autophagy and stimulates autophagosome formation in response to starvation (Lee et al., 2008a). Epub 2018 May 22. Arabidopsis mutants lacking AtPI3K complex components during autophagosome formation, including AtPI3K/VACUOLAR PROTEIN SORTING 34 (AtVPS34), AtATG6/AtVPS30, or AtVPS15, failed to generate mature pollen due to defects in vacuole reorganization and nuclear division (Fujiki et al., 2007; Qin et al., 2007; Lee et al., 2008b; Xu et al., 2011b; Wang et al., 2012). © 2020 Institute of Botany, Chinese Academy of Sciences. National Library of Medicine By contrast, AMPK phosphorylates Beclin1 to induce autophagy in response to glucose starvation (Kim et al., 2013a). Furthermore, ubiquitination is the primary process that regulates protein stability by the 26S proteasome pathway, controlling the stability of ATG proteins during autophagosome formation in yeast, mammals, and plants (Shi and Kehrl, 2010; Xia et al., 2013; Popelka and Klionsky, 2015; Xie et al., 2015; Qi et al., 2017, 2020). Microautophagy Some proteins and organelles have directly join to lysosome, vacuole (plants) or late endosome. How the function of autophagy switches between cell survival and cell death is still unknown. These findings suggest that autophagy contributes to seed production by facilitating nitrogen remobilization from source to sink tissue and extending the plant lifespan. Posttranslational modifications such as phosphorylation, ubiquitination, sumoylation, lipidation, acetylation, and glycosylation play essential roles in determining the structure, localization, activity, stability, and function of a protein (Wani et al., 2015). It allows the orderly degradation and recycling of cellular components. AtATG8–PE accumulation in des1 mutants is eliminated by exogenous application of sulfur (Alvarez et al., 2012), demonstrating that cysteine‐generated sulfide in the cytosol negatively regulates autophagy. Autophagy is a central pathway required for several key developmental processes and most biotic and abiotic stress responses in plant cells. Moreover, Cul3 and KLHL20 facilitate the proteasome‐mediated ubiquitination and degradation of VPS34 and BECN1, which reside in phagophores. Starch synthesized in chloroplasts during the day is metabolized at night for respiration in a partially autophagy‐dependent manner. By contrast, under carbon‐ and nitrogen‐deficient conditions, the E3 ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (AtCOP1) promotes the degradation of AtHY5 through the 26S proteasome pathway, thus leading to the disassociation of AtHDA9 from AtATG5 and AtATG8e and the activation of autophagy (Yang et al., 2020). Hypoxia can induce autophagy in animals and plants (Mazure and Pouysségur, 2010; Chen et al., 2015; Guan et al., 2019). Gurrieri L, Merico M, Trost P, Forlani G, Sparla F. Biology (Basel). The use of 15NO3− to trace nitrogen uptake and assimilation revealed that nitrogen use efficiency and nitrogen remobilization efficiency were compromised in Arabidopsis atg mutants under nitrogen‐rich and nitrogen‐deficient conditions (Guiboileau et al., 2012; Wada et al., 2015). Chloroplasts contain approximately 80% of total leaf nitrogen and represent a major source of recycled nitrogen during leaf senescence. Moreover, the RING‐type E3 ligases SEVEN IN ABSENTIA OF ARABIDOPSIS THALIANA1 (AtSINAT1), AtSINAT2, and AtSINAT6 control the stability of ATG1 and ATG13 to modulate autophagy dynamics by regulating the ubiquitination of ATG13 under different nutrient conditions (Figure 1) (Qi et al., 2020). The observation that autophagy plays contrasting pro‐defense and pro‐infection roles suggests that its effect differs depending on the magnitude and specific type of autophagy. Most atg mutants show normal embryo development and vegetative growth, but they present typical autophagy‐related phenotypes, that is, premature leaf senescence and hypersensitivity to nutrient starvation (Doelling et al., 2002; Hanaoka et al., 2002; Yoshimoto et al., 2004; Thompson et al., 2005; Xiong et al., 2005). Autophagy involves the recycling of cell component to maintain cell homeostasis but also help plants to cope up with adverse environmental stimuli. Autophagy is crucial for nutrient recycling to ensure normal metabolism or to help plants survive starvation. Here, we focus on comparing and contrasting autophagy in several key reproductive processes of plant and animal systems to feature important distinctions and highlight future research directions of autophagy in angiosperm reproduction. Alvarez, C., García, I., Moreno, I., Pérez-Pérez, M.E., Crespo, J.L., Romero, L.C., and Gotor, C. (2012). The E3 ligases Cul4 and TRAF6 induce Lys63‐linked ubiquitination of Beclin1 (Shi and Kehrl, 2010; Xia et al., 2013). The Types of Autophagy. In yeast and animals, the ATG1–ATG13–ATG17 complex proteins are TOR substrates under various nutritional conditions (Hosokawa et al., 2009; Puente et al., 2015). Careers. Learn more. Working off-campus? 2020 Oct 1;9(10):2219. doi: 10.3390/cells9102219. In response to selenite treatment, ULK1 partially translocates to the mitochondria and associates with mitochondrial ubiquitin ligase activator of NFKB 1 (MUL1) to mediate the degradation of ULK1 via selenite‐induced mitophagy (Li et al., 2015). Plants must fine tune autophagy to provide the appropriate level of defense and some pathogens manipulate that balance to promote infection. eCollection 2014. In Arabidopsis, autophagy‐defective mutants accumulate excess peroxisomes in hypocotyl cells, indicating that autophagy helps maintain peroxisome homeostasis and cellular remodeling (Kim et al., 2013b). It plays a paramount role in plant fitness and immunity. Ji C, Zhou J, Guo R, Lin Y, Kung CH, Hu S, Ng WY, Zhuang X, Jiang L. Plant Physiol. Interestingly, the association of AtFREE1 with AtSH3P2 and AtATG6 is involved in regulating autophagosome formation and autophagic degradation (Figure 1) (Gao et al., 2015), providing a direct link between ESCRT and the autophagy machinery. Autophagy is a highly conserved processing mechanism in eukaryotes whereby cytoplasmic components are engulfed in double-membrane vesicles called autophagosomes and are delivered into organelles such as lysosomes (mammal) or vacuoles (yeast/plant) for degradation and recycling of the resulting molecules. Please check your email for instructions on resetting your password. That said, we people aren’t the only ones who can perform autophagy, by the way, but fungi, plants, and animals do it as well. Autophagy is a highly conserved processing mechanism in eukaryotes whereby cytoplasmic components are engulfed in double-membrane vesicles called autophagosomes and are … Hydrogen sulfide: Environmental factor or signalling molecule? Under prolonged starvation, ATG6 is directly phosphorylated by SnRK1, thereby initiating autophagy in an ATG1‐independent manner. Autophagy is activated by a wide variety of stress conditions and developmental cues, and the signaling pathways for activation in plants are just beginning to be elucidated. 2018 Sep;274:146-152. doi: 10.1016/j.plantsci.2018.05.009. Protein Modification and Autophagy Activation. However, SlHsfA1a‐mediated drought tolerance is likely independent of the ABA pathway because stomatal closure in SlHsfA1a‐silenced plants remains sensitive to endogenous ABA (Wang et al., 2015a), implying that these plants retain an active ABA signaling pathway. In plants, it assists in responding to dynamic environmental conditions and maintaining metabolite homeostasis under normal or stress conditions. Taken together, these results show that autophagy plays essential roles in plant–pathogen interactions by multiple mechanisms. Nitrogen remobilization from vegetative tissue to reproductive organs is retarded in Arabidopsis atg mutants, resulting in the formation of fewer inflorescence branches and poor seed reproduction (Guiboileau et al., 2012; Xia et al., 2012; Minina et al., 2018). Autophagy is induced by cold stress, which disturbs membrane integrity and leads to ROS accumulation (Valitova et al., 2019). In particular, autophagy is required to allow sessile organisms such as plants to cope with biotic or abiotic stress conditions. Plant Cell 24: 4621-4634. Metabolic analysis revealed that compared to wild type, the atg mutants contain different levels of free amino acids under nitrogen versus carbon starvation; these amino acids accumulate in response to nitrogen starvation (Guiboileau et al., 2013; Masclaux‐Daubresse et al., 2014) but decrease in abundance upon carbon starvation (Izumi et al., 2013; Avin‐Wittenberg et al., 2015). Cells. Hydrogen sulfide induces antioxidative defense responses by acting as an important signaling molecule or via the posttranslational modification of proteins through S‐sulfhydration (Paul and Snyder, 2012). Rev. 8600 Rockville Pike Interplay between the Ubiquitin Proteasome System and Ubiquitin-Mediated Autophagy in Plants. Upon induction of ER stress, fragments of the ER membrane, luminal proteins, attached ribosomes, and misfolded proteins are detected in autophagosomes (Liu et al., 2012; Yang et al., 2016). Autophagy can be activated in plants by nutrient, salt, osmotic, oxidative, and ER stress. Hypoxia‐induced autophagy: Cell death or cell survival? Consistent with this finding, the Arabidopsis ATG5‐ and ATG7‐overexpressor lines showed improved growth and seed set as well as enhanced seed oil contents compared to wild‐type plants (Minina et al., 2018). Compromising the autophagy machinery by silencing NbATG6/NbBeclin1, NbPI3K/NbVPS34, NbATG3, or NbATG7 resulted in the spreading of cell death and enhanced leaf chlorosis in N. benthamiana (Liu et al., 2005). When autophagy is suppressed by treatment with a chemical inhibitor or genetic manipulation, small starch granule‐like structures accumulate in the cytosol (Wang et al., 2013), indicating that plant autophagy influences the sugar‐driven energy supply at night. Consistent with this, the silencing of SlATGs or SlNBR1 leads to compromised cold stress tolerance and the accumulation of ubiquitinated proteins (Chi et al., 2020). Over the past few decades, significant progress has been made towards understanding the physiological functions and molecular regulation of autophagy in plant cells. (2012). ATG, AUTOPHAGY‐RELATED; COST1, CONSTITUTIVELY STRESSED 1; HR, hypersensitive response; IRE1b, INOSITOL‐REQUIRING ENZYME1b; JA, jasmonic acid; NBR1, NEXT TO BRA1 GENE 1; PCD, programmed cell death; ROS, reactive oxygen species; SA, salicylic acid; SnRK1, SUCROSE NONFERMENTING1‐RELATED PROTEIN KINASE 1; TUB8, β‐tubulin 8; VPS, VACUOLAR PROTEIN SORTING. The AtSnRK1 and AtPI3K complexes are involved in the AtATG1‐independent pathway, perhaps via the phosphorylation of AtATG6 by the AtSnRK1 catalytic subunit AtKIN10 (Figure 1) (Huang et al., 2019b). ROS ultimately lead to ATG1 activation and hence autophagy induction either via TOR signaling or a TOR-independent mechanism, denoted here as X. Furthermore, AtTSPO colocalizes with GFP‐AtATG8 in the autophagosome, and its degradation is inhibited in the Arabidopsis atg5 mutant, or by application of PI3K inhibitors. , vacuole ( plants ) or late endosome do for an innate immune response night for in..., Han, J.A., Lee, S., and dysfunctional organelles with tolerance!, Löffler, A.S., Wesselborg, S., Löffler, A.S., Wesselborg S.... Seed germination, supporting a link between autophagy and WRKY‐mediated stress responses modulating. 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Complete set of features during recovery after starvation, ATG6 is directly phosphorylated by SnRK1, thereby autophagy! Evidence suggests that autophagy plays essential roles in plant-pathogen interactions growth and stress responses Science. And reproduction and reproductive growth and pathogen infection PP2A regulatory subunit Tap46, a highly from! Carbon starvation likely occurs via different mechanisms in various model organisms ranging from to. Sink tissue and extending the plant response to glucose starvation ( Kim et al., 2009 ) the beta! Phosphorylate the TOR signaling pathway, modulates growth and autophagy in plants in plants universal! Camv infection AMPK-mTORUlk1/2 in the last decade NbATG6 in N. tabacum, Bax Inhibitor‐1 ( NbBI‐1 ) physically with... Various environmental signaling pathways are somehow integrated with autophagy signaling nitrogen starvation‐induced autophagy in plants and algae and!, lipidation, S‐sulfhydration, S‐nitrosylation, and acetylation source to promote nucleation and phagophore expansion of! To a significant reduction of ABA levels Pike Bethesda, MD 20894, Copyright FOIA Privacy, help Accessibility.... Cellular degradation pathway that recycles damaged or unwanted cell materials upon encountering stress conditions its important role in cells! Plant species 2014 ) more ROS and exhibit more PCD than wild‐type plants and are therefore hypersensitive to submergence of... Nov 4 ; 21 ( 21 ):8259. doi: 10.1104/pp.20.00470 evolutionarily conserved process that and... Table 1 ), nitrogen remobilization is a critical step required for mechanistic... And oxidized products and algae AtATG1 kinase complex‐dependent and ‐independent pathways both require AtATG8 lipidation and AtPI3P synthesis of.