Chlorophagy is ATG gene-dependent microautophagy process

The relationship between autophagy and respiratory viruses

Respiratory viruses have caused severe global health problems and posed essential challenges to the medical community. In recent years, the role of autophagy as a critical process in cells in viral respiratory diseases has been noticed. One of the vital catabolic biological processes in the body is autophagy. Autophagy contributes to energy recovery by targeting and selectively directing foreign microorganisms, organelles, and senescent intracellular proteins to the lysosome for degradation and phagocytosis. Activation or suppression of autophagy is often initiated when foreign pathogenic organisms such as viruses infect cells. Because of its antiviral properties, several viruses may escape or resist this process by encoding viral proteins. Viruses can also use autophagy to enhance their replication or prolong the persistence of latent infections. Here, we provide an overview of autophagy and respiratory viruses such as coronavirus, rhinovirus, parainfluenza, influenza, adenovirus, and respiratory syncytial virus, and examine the interactions between them and the role of autophagy in the virus-host interaction process and the resulting virus replication strategy.

New insights into plant autophagy: molecular mechanisms and roles in development and stress responses

Autophagy is an evolutionarily conserved eukaryotic intracellular degradation process. Although the molecular mechanisms of plant autophagy share similarities with those in yeast and mammals, certain unique mechanisms have been identified. Recent studies have highlighted the importance of autophagy during vegetative growth stages as well as in plant-specific developmental processes, such as seed development, germination, flowering, and somatic reprogramming. Autophagy enables plants to adapt to and manage severe environmental conditions, such as nutrient starvation, high-intensity light stress, and heat stress, leading to intracellular remodeling and physiological changes in response to stress. In the past, plant autophagy research lagged behind similar studies in yeast and mammals; however, recent advances have greatly expanded our understanding of plant-specific autophagy mechanisms and functions. This review summarizes current knowledge and latest research findings on the mechanisms and roles of plant autophagy with the objective of improving our understanding of this vital process in plants.

Picky eaters: selective autophagy in plant cells

Autophagy, a fundamental cellular process, plays a vital role in maintaining cellular homeostasis by degrading damaged or unnecessary components. While selective autophagy has been extensively studied in animal cells, its significance in plant cells has only recently gained attention. In this review, we delve into the intriguing realm selective autophagy in plants, with specific focus on its involvement in nutrient recycling, organelle turnover, and stress response. Moreover, recent studies have unveiled the interesting interplay between selective autophagy and epigenetic mechanisms in plants, elucidating the significance of epigenetic regulation in modulating autophagy-related gene expression and finely tuning the selective autophagy process in plants. By synthesizing existing knowledge, this review highlights the emerging field of selective autophagy in plant cells, emphasizing its pivotal role in maintaining nutrient homeostasis, facilitating cellular adaptation, and shedding light on the epigenetic regulation that governs these processes. Our comprehensive study provides the way for a deeper understanding of the dynamic control of cellular responses to nutrient availability and stress conditions, opening new avenues for future research in this field of autophagy in plant physiology.

Lysosomal microautophagy: an emerging dimension in mammalian autophagy

Autophagy is a self-catabolic process through which cellular components are delivered to lysosomes for degradation. There are three types of autophagy, i.e., macroautophagy, chaperone-mediated autophagy (CMA), and microautophagy. In macroautophagy, a portion of the cytoplasm is wrapped by the autophagosome, which then fuses with lysosomes and delivers the engulfed cytoplasm for degradation. In CMA, the translocation of cytosolic substrates to the lysosomal lumen is directly across the limiting membrane of lysosomes. In microautophagy, lytic organelles, including endosomes or lysosomes, take up a portion of the cytoplasm directly. Although macroautophagy has been investigated extensively, microautophagy has received much less attention. Nonetheless, it has become evident that microautophagy plays a variety of cellular roles from yeast to mammals. Here we review the very recent updates of microautophagy. In particular, we focus on the feature of the degradative substrates and the molecular machinery that mediates microautophagy.

Plants' Response to Abiotic Stress: Mechanisms and Strategies

Abiotic stress is the adverse effect of any abiotic factor on a plant in a given environment, impacting plants' growth and development. These stress factors, such as drought, salinity, and extreme temperatures, are often interrelated or in conjunction with each other. Plants have evolved mechanisms to sense these environmental challenges and make adjustments to their growth in order to survive and reproduce. In this review, we summarized recent studies on plant stress sensing and its regulatory mechanism, emphasizing signal transduction and regulation at multiple levels. Then we presented several strategies to improve plant growth under stress based on current progress. Finally, we discussed the implications of research on plant response to abiotic stresses for high-yielding crops and agricultural sustainability. Studying stress signaling and regulation is critical to understand abiotic stress responses in plants to generate stress-resistant crops and improve agricultural sustainability.

Chloroplast Envelopes Play a Role in the Formation of Autophagy-Related Structures in Plants

Autophagy is a degradation process of cytoplasmic components that is conserved in eukaryotes. One of the hallmark features of autophagy is the formation of double-membrane structures known as autophagosomes, which enclose cytoplasmic content destined for degradation. Although the membrane source for the formation of autophagosomes remains to be determined, recent studies indicate the involvement of various organelles in autophagosome biogenesis. In this study, we examined the autophagy process in Bienertia sinuspersici: one of four terrestrial plants capable of performing C₄ photosynthesis in a single cell (single-cell C₄ species). We demonstrated that narrow tubules (stromule-like structures) 30-50 nm in diameter appear to extend from chloroplasts to form the membrane-bound structures (autophagosomes or autophagy-related structures) in chlorenchyma cells of B. sinuspersici during senescence and under oxidative stress. Immunoelectron microscopic analysis revealed the localization of stromal proteins to the stromule-like structures, sequestering portions of the cytoplasm in chlorenchyma cells of oxidative stress-treated leaves of B. sinuspersici and Arabidopsis thaliana. Moreover, the fluorescent marker for autophagosomes GFP-ATG8, colocalized with the autophagic vacuole maker neutral red in punctate structures in close proximity to the chloroplasts of cells under oxidative stress conditions. Together our results implicate a role for chloroplast envelopes in the autophagy process induced during senescence or under certain stress conditions in plants.

Genome-Wide Identification of ATG Gene Family Members in Fagopyrum tataricum and Their Expression during Stress Responses

Abiotic stresses such as drought and salinity are major environmental factors limiting plant productivity. Autophagy-related genes are extensively involved in plant growth, development, and adverse stress responses, which have not yet been characterized in Tartary buckwheat (Fagopyrum tataricum, TB). In this study, we verified that drought stress could induce autophagy in TB roots. Next, 49 FtATGs in the whole genome of TB were identified. All FtATGs were randomly distributed in 8 known chromosomes, while 11 FtATGs were predictably segmental repeats. As the core component of autophagy, there were 8 FtATG8s with similar gene structures in TB, while FtATG8s showed high expression at the transcription level under drought and salt stresses. The cis-acting element analysis identified that all FtATG8 promoters contain light-responsive and MYB-binding elements. FtATG8s showed a cell-wide protein interaction network and strongly correlated with distinct stress-associated transcription factors. Furthermore, overexpression of FtATG8a and FtATG8f enhanced the antioxidant enzyme activities of TB under adverse stresses. Remarkably, FtATG8a and FtATG8f may be vital candidates functioning in stress resistance in TB. This study prominently aids in understanding the biological role of FtATG genes in TB.

Autophagy: a game changer for plant development and crop improvement

Manipulation of autophagic pathway represents a tremendous opportunity for designing climate-smart crops with improved yield and better adaptability to changing environment. For exploiting autophagy to its full potential, identification and comprehensive characterization of adapters/receptor complex and elucidation of its regulatory network in crop plants is highly warranted.  Autophagy is a major intracellular trafficking pathway in eukaryotes involved in vacuolar degradation of cytoplasmic constituents, mis-folded proteins, and defective organelles. Under optimum conditions, autophagy operates at a basal level to maintain cellular homeostasis, but under stressed conditions, it is induced further to provide temporal stress relief. Our understanding of this highly dynamic process has evolved exponentially in the past few years with special reference to several plant-specific roles of autophagy. Here, we review the most recent advances in the field of autophagy in plants and discuss its potential implications in designing crops with improved stress and disease-tolerance, enhanced yield potential, and improved capabilities for producing metabolites of high economic value. We also assess the current knowledge gaps and the possible strategies to develop a robust module for biotechnological application of autophagy to enhance bioeconomy and sustainability of agriculture.

Chloroplasts Protein Quality Control and Turnover: A Multitude of Mechanisms

As the organelle of photosynthesis and other important metabolic pathways, chloroplasts contain up to 70% of leaf proteins with uniquely complex processes in synthesis, import, assembly, and turnover. Maintaining functional protein homeostasis in chloroplasts is vitally important for the fitness and survival of plants. Research over the past several decades has revealed a multitude of mechanisms that play important roles in chloroplast protein quality control and turnover under normal and stress conditions. These mechanisms include: (i) endosymbiotically-derived proteases and associated proteins that play a vital role in maintaining protein homeostasis inside the chloroplasts, (ii) the ubiquitin-dependent turnover of unimported chloroplast precursor proteins to prevent their accumulation in the cytosol, (iii) chloroplast-associated degradation of the chloroplast outer-membrane translocon proteins for the regulation of chloroplast protein import, (iv) chloroplast unfolded protein response triggered by accumulated unfolded and misfolded proteins inside the chloroplasts, and (v) vesicle-mediated degradation of chloroplast components in the vacuole. Here, we provide a comprehensive review of these diverse mechanisms of chloroplast protein quality control and turnover and discuss important questions that remain to be addressed in order to better understand and improve important chloroplast functions.

Autophagy in plant viral infection

Autophagy is a conserved degradation pathway that delivers dysfunctional cellular organelles or other cytosol components to degradative vesicular structures (vacuoles in plants and yeasts, lysosomes in mammals) for degradation and recycling. Viruses are intracellular parasites that hijack their host to live. Research on regulation of the trade-off between plant cells and viruses has indicated that autophagy is an integral part of the host responses to virus infection. Meanwhile, plants have evolved a diverse array of defense responses to counter pathogenic viruses. In this review, we focus on the roles of autophagy in plant virus infection and offer a glimpse of recent advances about how plant viruses evade autophagy or manipulate host autophagy pathways to complete their replication cycle.

Coordination of Chloroplast Activity with Plant Growth: Clues Point to TOR

Photosynthesis is the defining function of most autotrophic organisms. In the plantae kingdom, chloroplasts host this function and ensure growth. However, these organelles are very sensitive to stressful conditions and the photosynthetic process can cause photooxidative damage if not perfectly regulated. In addition, their function is energivorous in terms of both chemical energy and nutrients. To coordinate chloroplast activity with the cell’s need, continuous signaling is required: from chloroplasts to cytoplasm and from nucleus to chloroplasts. In this opinion article, several mechanisms that ensure this communication are reported and the many clues that point to an important role of the Target of Rapamycin (TOR) kinase in the coordination between the eukaryotic and prokaryotic sides of plants are highlighted.

Diallyl disulfide and diallyl trisulfide in garlic as novel therapeutic agents to overcome drug resistance in breast cancer

Breast cancer is one of the leading causes of cancer-related deaths in women worldwide. It is a cancer that originates from the mammary ducts and involves mutations in multiple genes. Recently, the treatment of breast cancer has become increasingly challenging owing to the increase in tumor heterogeneity and aggressiveness, which gives rise to therapeutic resistance. Epidemiological, population-based, and hospital-based case-control studies have demonstrated an association between high intake of certain Allium vegetables and a reduced risk in the development of breast cancer. Diallyl disulfide (DADS) and diallyl trisulfide (DATS) are the main allyl sulfur compounds present in garlic, and are known to exhibit anticancer activity as they interfere with breast cancer cell proliferation, tumor metastasis, and angiogenesis. The present review highlights multidrug resistance mechanisms and their signaling pathways in breast cancer. This review discusses the potential anticancer activities of DADS and DATS, with emphasis on drug resistance in triple-negative breast cancer (TNBC). Understanding the anticancer activities of DADS and DATS provides insights into their potential in targeting drug resistance mechanisms of TNBC, especially in clinical studies.

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The review describes the causes of drug resistance in TNBC.

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The effects of DADS and DATS on drug resistance mechanisms in TNBC are presented.

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The impacts of DADS and DATS on metastasis of TNBC are discussed.

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Antitumor immune activities of DADS and DATS against TNBC are illustrated.

The Autophagy Machinery in Human-Parasitic Protists; Diverse Functions for Universally Conserved Proteins

Autophagy is a eukaryotic cellular machinery that is able to degrade large intracellular components, including organelles, and plays a pivotal role in cellular homeostasis. Target materials are enclosed by a double membrane vesicle called autophagosome, whose formation is coordinated by autophagy-related proteins (ATGs). Studies of yeast and Metazoa have identified approximately 40 ATGs. Genome projects for unicellular eukaryotes revealed that some ATGs are conserved in all eukaryotic supergroups but others have arisen or were lost during evolution in some specific lineages. In spite of an apparent reduction in the ATG molecular machinery found in parasitic protists, it has become clear that ATGs play an important role in stage differentiation or organelle maintenance, sometimes with an original function that is unrelated to canonical degradative autophagy. In this review, we aim to briefly summarize the current state of knowledge in parasitic protists, in the light of the latest important findings from more canonical model organisms. Determining the roles of ATGs and the diversity of their functions in various lineages is an important challenge for understanding the evolutionary background of autophagy.

Ultrastructural characterization of microlipophagy induced by the interaction of vacuoles and lipid bodies around generative and sperm cells in Arabidopsis pollen

During pollen maturation, various organelles change their distribution and function during development as male gametophytes. We analyzed the behavior of lipid bodies and vacuoles involved in lipophagy in Arabidopsis pollen using serial section SEM and conventional TEM. At the bicellular pollen stage, lipid bodies in the vegetative cells lined up at the surface of the generative cell. Vacuoles then tightly attached, drew in, and degraded the lipid bodies and eventually occupied the space of the lipid bodies. Degradation of lipid began before transfer of the entire contents of the lipid body. At the tricellular stage, vacuoles instead of lipid bodies surrounded the sperm cells. The degradation of lipid bodies is morphologically considered microautophagy. The atg2-1 Arabidopsis mutant is deficient in one autophagy-related gene (ATG). In this mutant, the assembly of vacuoles around sperm cells was sparser than that in wild-type pollen. The deficiency of ATG2 likely prevents or slows lipid degradation, although it does not prevent contact between organelles. These results demonstrate the involvement of microlipophagy in the pollen development of Arabidopsis.

Microautophagy - distinct molecular mechanisms handle cargoes of many sizes

Autophagy is fundamental for cell and organismal health. Two types of autophagy are conserved in eukaryotes: macroautophagy and microautophagy. During macroautophagy, autophagosomes deliver cytoplasmic constituents to endosomes or lysosomes, whereas during microautophagy lytic organelles take up cytoplasm directly. While macroautophagy has been investigated extensively, microautophagy has received much less attention. Nonetheless, it has become clear that microautophagy has a broad range of functions in biosynthetic transport, metabolic adaptation, organelle remodeling and quality control. This Review discusses the selective and non-selective microautophagic processes known in yeast, plants and animals. Based on the molecular mechanisms for the uptake of microautophagic cargo into lytic organelles, I propose to distinguish between fission-type microautophagy, which depends on ESCRT proteins, and fusion-type microautophagy, which requires the core autophagy machinery and SNARE proteins. Many questions remain to be explored, but the functional versatility and mechanistic diversity of microautophagy are beginning to emerge.

Microautophagy in Plants: Consideration of Its Molecular Mechanism

Microautophagy is a type of autophagy. It is characterized by direct enclosing with the vacuolar/lysosomal membrane, which completes the isolation and uptake of cell components in the vacuole. Several publications present evidence that plants exhibit microautophagy. Plant microautophagy is involved in anthocyanin accumulation in the vacuole, eliminating damaged chloroplasts and degrading cellular components during starvation. However, information on the molecular mechanism of microautophagy is less available than that on the general macroautophagy, because the research focusing on microautophagy has not been widely reported. In yeast and animals, it is suggested that microautophagy can be classified into several types depending on morphology and the requirements of autophagy-related (ATG) genes. This review summarizes the studies on plant microautophagy and discusses possible techniques for a future study in this field while taking into account the information on microautophagy obtained from yeast and animals.

Interactions between Autophagy and DNA Viruses

Autophagy is a catabolic biological process in the body. By targeting exogenous microorganisms and aged intracellular proteins and organelles and sending them to the lysosome for phagocytosis and degradation, autophagy contributes to energy recycling. When cells are stimulated by exogenous pathogenic microorganisms such as viruses, activation or inhibition of autophagy is often triggered. As autophagy has antiviral effects, many viruses may escape and resist the process by encoding viral proteins. At the same time, viruses can also use autophagy to enhance their replication or increase the persistence of latent infections. Here, we give a brief overview of autophagy and DNA viruses and comprehensively review the known interactions between human and animal DNA viruses and autophagy and the role and mechanisms of autophagy in viral DNA replication and DNA virus-induced innate and acquired immunity.