Abstract Eukaryotic cells have evolved membrane-bound organelles, including the endoplasmic reticulum (ER), Golgi, mitochondria, peroxisomes, chloroplasts (in plants and green algae) and lysosomes/vacuoles, for specialized functions. Organelle quality control and their proper interactions are crucial both for normal cell homeostasis and function and for environmental adaption. Dynamic turnover of organelles is tightly controlled, with autophagy playing an essential role. Autophagy is a programmed process for efficient clearing of unwanted or damaged macromolecules or organelles, transporting them to vacuoles for degradation and recycling and thereby enhancing plant environmental plasticity. The specific autophagic engulfment of organelles requires activation of a selective autophagy pathway, recognition of the organelle by a receptor, and selective incorporation of the organelle into autophagosomes. While some of the autophagy machinery and mechanisms for autophagic removal of organelles is conserved across eukaryotes, plants have also developed unique mechanisms and machinery for these pathways. In this review, we discuss recent progress in understanding autophagy regulation in plants, with a focus on autophagic degradation of membrane-bound organelles. We also raise some important outstanding questions to be addressed in the future.
more »
« less
Coordination and Crosstalk between Autophagosome and Multivesicular Body Pathways in Plant Stress Responses
In eukaryotic cells, autophagosomes and multivesicular bodies (MVBs) are two closely related partners in the lysosomal/vacuolar protein degradation system. Autophagosomes are double membrane-bound organelles that transport cytoplasmic components, including proteins and organelles for autophagic degradation in the lysosomes/vacuoles. MVBs are single-membrane organelles in the endocytic pathway that contain intraluminal vesicles whose content is either degraded in the lysosomes/vacuoles or recycled to the cell surface. In plants, both autophagosome and MVB pathways play important roles in plant responses to biotic and abiotic stresses. More recent studies have revealed that autophagosomes and MVBs also act together in plant stress responses in a variety of processes, including deployment of defense-related molecules, regulation of cell death, trafficking and degradation of membrane and soluble constituents, and modulation of plant hormone metabolism and signaling. In this review, we discuss these recent findings on the coordination and crosstalk between autophagosome and MVB pathways that contribute to the complex network of plant stress responses.
more »
« less
- Award ID(s):
- 1758767
- NSF-PAR ID:
- 10229826
- Date Published:
- Journal Name:
- Cells
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2073-4409
- Page Range / eLocation ID:
- 119
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Edelstein-Keshet, Leah (Ed.)Macroautophagy is a homeostatic process required to clear cellular waste. Neuronal autophagosomes form constitutively in the distal tip of the axon and are actively transported toward the soma, with cargo degradation initiated en route. Cargo turnover requires autophagosomes to fuse with lysosomes to acquire degradative enzymes; however, directly imaging these fusion events in the axon is impractical. Here we use a quantitative model, parameterized and validated using data from primary hippocampal neurons, to explore the autophagosome maturation process. We demonstrate that retrograde autophagosome motility is independent of fusion and that most autophagosomes fuse with only a few lysosomes during axonal transport. Our results indicate that breakdown of the inner autophagosomal membrane is much slower in neurons than in nonneuronal cell types, highlighting the importance of this late maturation step. Together, rigorous quantitative measurements and mathematical modeling elucidate the dynamics of autophagosome–lysosome interaction and autophagosomal maturation in the axon.more » « less
-
Plants balance their competing requirements for growth and stress tolerance via a sophisticated regulatory circuitry that controls responses to the external environments. We have identified a plant-specific gene, COST1 ( constitutively stressed 1 ), that is required for normal plant growth but negatively regulates drought resistance by influencing the autophagy pathway. An Arabidopsis thaliana cost1 mutant has decreased growth and increased drought tolerance, together with constitutive autophagy and increased expression of drought-response genes, while overexpression of COST1 confers drought hypersensitivity and reduced autophagy. The COST1 protein is degraded upon plant dehydration, and this degradation is reduced upon treatment with inhibitors of the 26S proteasome or autophagy pathways. The drought resistance of a cost1 mutant is dependent on an active autophagy pathway, but independent of other known drought signaling pathways, indicating that COST1 acts through regulation of autophagy. In addition, COST1 colocalizes to autophagosomes with the autophagosome marker ATG8e and the autophagy adaptor NBR1, and affects the level of ATG8e protein through physical interaction with ATG8e, indicating a pivotal role in direct regulation of autophagy. We propose a model in which COST1 represses autophagy under optimal conditions, thus allowing plant growth. Under drought, COST1 is degraded, enabling activation of autophagy and suppression of growth to enhance drought tolerance. Our research places COST1 as an important regulator controlling the balance between growth and stress responses via the direct regulation of autophagy.more » « less
-
Various intracellular degradation organelles, including autophagosomes, lysosomes, and endosomes, work in tandem to perform autophagy, which is crucial for cellular homeostasis. Altered autophagy contributes to the pathophysiology of various diseases, including cancers and metabolic diseases. This paper aims to describe an approach to reproducibly identify and distinguish subcellular structures involved in macroautophagy. Methods are provided that help avoid common pitfalls. How to distinguish between lysosomes, lipid droplets, autolysosomes, autophagosomes, and inclusion bodies are also discussed. These methods use transmission electron microscopy (TEM), which is able to generate nanometer-scale micrographs of cellular degradation components in a fixed sample. Serial block face-scanning electron microscopy is also used to visualize the 3D morphology of degradation machinery using the Amira software. In addition to TEM and 3D reconstruction, other imaging techniques are discussed, such as immunofluorescence and immunogold labeling, which can be used to classify cellular organelles, reliably and accurately. Results show how these methods may be used to accurately quantify cellular degradation machinery under various conditions, such as treatment with the endoplasmic reticulum stressor thapsigargin or ablation of the dynamin-related protein 1.more » « less
-
more » « less
Abstract Various intracellular degradation organelles, including autophagosomes, lysosomes, and endosomes, work in tandem to perform autophagy, which is crucial for cellular homeostasis. Altered autophagy contributes to the pathophysiology of various diseases, including cancers and metabolic diseases. This paper aims to describe an approach to reproducibly identify and distinguish subcellular structures involved in macroautophagy. Methods are provided that help avoid common pitfalls. How to distinguish between lysosomes, lipid droplets, autolysosomes, autophagosomes, and inclusion bodies are also discussed. These methods use transmission electron microscopy (TEM), which is able to generate nanometer‐scale micrographs of cellular degradation components in a fixed sample. Serial block face‐scanning electron microscopy is also used to visualize the 3D morphology of degradation machinery using the Amira software. In addition to TEM and 3D reconstruction, other imaging techniques are discussed, such as immunofluorescence and immunogold labeling, which can be used to classify cellular organelles, reliably and accurately. Results show how these methods may be used to accurately quantify cellular degradation machinery under various conditions, such as treatment with the endoplasmic reticulum stressor thapsigargin or ablation of the dynamin‐related protein 1.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/cells9010119
