Since their identification as organelles in the 19th century, lipid droplets (LDs) have undergone various nomenclature changes. They were once referred to as lipid bodies, adiposomes, oil bodies, sphaerosomes and oleosomes, but are now commonly known as LDs (Walther and Farese, 2012). LDs are lipid-rich organelles, which possess a core of neutral lipids, predominantly triacylglycerols (TAGs) and steryl/wax esters, which is encased by a monolayer of phospholipids (PLs).

LDs are derived from the endoplasmic reticulum (ER), and the biogenesis of LDs includes the following key steps: neutral lipid synthesis at the ER; formation of a lipid lens; budding of LDs; LD growth and maturation (Mathiowetz and Olzmann, 2024). In the last decade, proteins involved in these steps have been well characterized in plants, especially model plant Arabidopsis thaliana. These proteins include TAG-synthesizing enzymes and the proteins responsible for the LDs generation, such as SEIPIN, VESICLE-ASSOCIATED MEMBRANE PROTEIN-ASSOCIATED PROTEIN 27 (VAP27) and LD-ASSOCIATED PROTEIN-INTERACTING PROTEIN (LDIP) (Barneda and Christian, 2017; Man et al., 2024). The degradation of LDs in plants is also a tightly regulated process, mainly mediated by lipolysis and lipophagy. Among the key players in lipolysis, a conserved patatin domain containing protein SUGAR-DEPENDENT1 (SDP1) stands out (Eastmond, 2006; Huang et al., 2022). In A. thaliana leaves, lipophagy occurs through microautophagy, relying on the core components of the macroautophagy pathway (Fan et al., 2019a).

The role of LDs in carbon reserve storage is fundamental to the survival and growth of plants. However, over the past decade, a paradigm shift has occurred in the perception of LDs in plant biology. Except acting as static storage organelles, LDs are now recognized as dynamic subcellular structures actively involved in multiple physiological processes. Mounting evidence has shown that LDs play a crucial role in stress adaptation. Under abiotic stress conditions such as drought, cold, and heat stress, the abundance of LDs increases in plant cells (Yang et al., 2011; Kong et al., 2013; Kim et al., 2016; Yang et al., 2024). This new understanding has highlighted the importance of lipid metabolism, lipid transport, and stress responses in plants.

Given the significance of LDs in plant physiology, this review aims to provide a comprehensive overview of the latest research advancements in the biogenesis and degradation of LDs in plants. It will also explore the importance of LDs in the stress response of plants. By integrating findings from recent studies, we hope to shed light on the complex molecular and physiological processes associated with LDs in plants, which may have implications for crop improvement, bioenergy production, and understanding plant responses to environmental changes.

LD biogenesis in plant cells shares conserved mechanisms with other eukaryotes, relying on ER-localized protein machinery to initiate LD formation and on LD surface proteins to ensure proper cytoplasmic packaging. The process begins with the synthesis of neutral lipids within the ER, where they accumulate into lens-like structures between the ER membrane leaflets (Scholz et al., 2022). Key proteins, such as SEIPIN and VAP27, facilitate the budding of nascent LDs into the cytoplasm (Guzha et al., 2023). During this step, the phospholipid monolayer of the LD becomes continuous with the outer ER membrane leaflet. Subsequently, additional proteins, including lipins and LD coat proteins, are recruited to promote LD growth. However, the mechanism underlying LD dissociation from the ER remains poorly understood (Bouchnak et al., 2023).

In yeast, Drosophila, plants, and humans, stored TAGs are typically degraded by lipases, a conserved protein family with a patatin domain (Xu and Shanklin, 2016). As mentioned previously, lipolysis refers to the process of TAG degradation in LDs mediated by lipases, whereas lipophagy denotes an autophagic mechanism for LD degradation. The stored lipids are hydrolyzed by these lipases, leading to the breakdown of TAGs into components such as diacylglycerols (DAGs), monoacylglycerols (MAGs), fatty acids (FAs), and glycerol. Subsequent to this process, the hydrolytic byproducts enter diverse metabolic pathways, thereby playing pivotal roles in cellular growth, energy balance, and other physiological processes, occurring at the opportune moment (Kretzschmar et al., 2020). SDP1, the patatin-like acyl-hydrolase domain protein encoding gene, was discovered using forward genetic screening in A. thaliana ( Figure 1 ) (Eastmond, 2006). Subsequent evidence suggests that this protein also serves as a primary enzyme for TAG hydrolysis in the leaves and roots of mature plants (Kelly et al., 2013a; Fan et al., 2014). During the early stages of seed germination in A. thaliana, SDP1 initially localizes to the surface of peroxisomes in an inactive form and subsequently extends to the surface of LDs within peroxisomes to hydrolyze TAGs (Thazar-Poulot et al., 2015). Further investigations have revealed that FYVE DOMAIN PROTEIN REQUIRED FOR ENDOSOMAL SORTING 1 (FREE1), within the ENDOSOMAL SORTING COMPLEX REQUIRED FOR TRANSPORT (ESCRT), directly interacts with both PEROXIN 11e (PEX11e) and SDP1, thereby facilitating the transport of SDP1 from peroxisomes to LDs (Huang et al., 2022). In addition to SDP1, A. thaliana possesses other patatin domain-containing lipases, such as SDP1-LIKE (SDP1L), which exhibit lipase activity and can release FAs from TAGs (Kelly et al., 2011, 2013a). Both SDP1 and SDP1L proteins are involved in the hydrolysis of TAGs during seed germination and also vegetative growth (Kelly et al., 2013a; Huang et al., 2022). In addition, the AtOBL1 gene in A. thaliana encodes for an enzyme known as OIL BODY LIPASE 1, which is associated with LDs. AtOBL1 represents the only described TAG lipase from A. thaliana that is associated with LDs, as SDP1 is regarded as a peroxisome-associated protein (Müller and Ischebeck, 2018).

Besides, biochemical analysis indicates that SDP1 and SDP1L preferentially hydrolyze TAGs over DAGs and monoacylglycerols (MAGs). The purification of oil body membranes from sdp1 sdp1L double mutant seedlings revealed a deficiency in TAG lipase activity. However, the hydrolysis of DAGs and MAGs was still observed, indicating the presence of other lipid enzymes that function in synergy with patatin-like acyl-hydrolases to complete the hydrolysis of TAG (Eastmond, 2006; Kelly et al., 2011, 2013a).

Following the liberation of FAs into the cytoplasm by SDP1, these FAs are converted into CoA esters through the action of currently unidentified Acyl-CoA synthetases (Li et al., 2016). The subsequent translocation of FAs across the peroxisomal membrane is facilitated by PXA1, an ABCD transporter belonging to the ATP-binding cassette (ABC) transporter family. Notably, PXA1 exhibits a unique intrinsic Acyl-CoA thioesterase activity (De Marcos Lousa et al., 2013). This distinctive property enables PXA1 to first bind fatty Acyl-CoAs on the cytosolic face of the peroxisomal membrane, then cleave the CoA moiety, and ultimately mediate the import of free FAs into the peroxisomal matrix for β-oxidation - a metabolic process that yields Acetyl-CoA as the end product (Kunz et al., 2009; Li et al., 2016; Fan et al., 2017). In the case of impaired β-oxidation function, pxa1 mutants exhibit delayed germination and reduced germination rate due to insufficient ATP supply required for the germination process. However, this defect can be alleviated by supplementing external carbon sources (Kunz et al., 2009). In addition, compared to the wild type, pxa1 mutant shows increased sensitivity to dark conditions and exhibits early plant death due to the compromised β-oxidation (Fan et al., 2017).

In addition, COMPARATIVE GENE IDENTIFICATION-58 (CGI-58) protein positively regulates lipid metabolism through β-oxidation-related pathway. Chapman et al. identified the homologous gene of human CGI58 in A. thaliana, referred to as CGI58-like (Yamaguchi and Osumi, 2009; James et al., 2010). In the A. thaliana mutant of this gene, plant leaves display a significantly increased TAG content of over tenfold compared to the wild type. However, unlike the sdp1 mutants, germination and growth of cgi-58 mutants do not show obvious defects (Yamaguchi and Osumi, 2009). Subsequent studies by Park et al. demonstrated that CGI-58 interacts with PXA1 to coregulate lipid homeostasis and signaling in A. thaliana (Park et al., 2013).

In the context of seedling establishment, the rapid breakdown of TAGs in planta, predominantly within four days, is particularly noteworthy. This phenomenon is further compounded by the accelerated degradation of LD-associated proteins, which may contribute to the enlargement of LDs during this critical phase. Studies have demonstrated that several LD proteins, including oleosins and steroleosins, have been observed to undergo polyubiquitination, a process associated with protein degradation (Deruyffelaere et al., 2018). This pathway, which is dependent on the removal of proteins from membranes, involves the action of the ubiquitin-proteasome system. Intriguingly, the analysis highlights the potential role of CELL DIVISION CYCLE PROTEIN 48 (CDC48) unfoldases, conserved in eukaryotes, in facilitating the unfolding and removal of membrane proteins. In planta, CDC48 has been observed to collaborate with PUX10, a scaffold protein residing at the LDs, to facilitate the degradation of ubiquitinated proteins (Kretzschmar et al., 2018; Liu et al., 2024). pux10 mutants exhibit a reduced rate of LD protein degradation and an accumulation of ubiquitinated proteins (Deruyffelaere et al., 2018). However, to date, no known degradation mechanism has been identified for LD membrane lipids.

Lipophagy, a selective autophagic process, first described in mammals, is a process that involves the selective uptake of LDs into the vacuole or lysosome, followed by their degradation ( Figure 1 , Table 1 ). Notably, mammalian lipophagy is a form of macroautophagy, in which autophagosomes engulf LDs, distinguishing it from microlipophagy observed in yeast. Autophagy, a self-degradative and highly conserved process, plays a crucial role in various developmental processes within cellular organisms (Zhao et al., 2020). Autophagy primarily functions through vacuolar degradation and recycling of harmful or obsolete cellular components, thereby maintaining cellular homeostasis and facilitating adaptation to environmental changes (Avin-Wittenberg et al., 2012; Couso et al., 2018; Sun et al., 2018; Bao et al., 2020). The identification of AUTOPHAGY-RELATED (ATG) genes in Saccharomyces cerevisiae revolutionized our understanding of autophagy, revealing a highly conserved eukaryotic mechanism (Marshall and Vierstra, 2018). Subsequent studies identified homologous ATG genes in plants, including A. thaliana, Oryza sativa, and Zea mays, through sequence alignment analyses (Li et al., 2015). These studies uncovered over 40 evolutionarily conserved ATG proteins that orchestrate autophagosome biogenesis and autophagy regulation across kingdoms, from yeast to mammals and plants (Marshall and Vierstra, 2018).

In A. thaliana, two independent studies, Fan et al. and Havé et al., reached the same conclusion through different approaches, thereby demonstrating the involvement of autophagy in the degradation of lipids (Fan et al., 2019a; Havé et al., 2019). Their findings suggest that, in A. thaliana leaves, basal autophagy contributes to TAG synthesis, whereas inducible autophagy under starvation contributes to LD degradation (Fan et al., 2019a). Besides, direct evidence through ultrastructural analysis has demonstrated that LDs are degraded in autophagic vacuoles (Fan et al., 2019a). In the parallel study, Havé et al. utilized protein and lipid profiling analyses on atg5 mutant, demonstrating that autophagy plays a pivotal role in the lipid metabolism of the ER and peroxisome in A. thaliana leaves (Fan et al., 2019a; Havé et al., 2019). Fan et al. investigated the role of autophagy in lipid metabolism by using mutants with auto (Havé et al., 2019). In addition to its role in A. thaliana, autophagy has been observed to contribute to the degradation of LD in other plant species. In rice, investigating osatg7 mutants has demonstrated autophagy’s crucial role during the late stages of pollen meiosis. As LDs are critical for energy supply, osatg7 mutants exhibit reduced levels of autophagy, and such deficiency leads to impaired pollen maturation (Kurusu et al., 2014).

This review offers a detailed examination of the processes involved in the formation and breakdown of LDs in plants, emphasizing crucial enzymes, regulatory pathways, and physiological contexts. A more profound understanding of the regulatory mechanisms governing LD-associated pathways holds considerable potential for enhancing crop yield and promoting bioenergy production. Manipulating the genes and proteins involved in LD biogenesis and turnover may lead to the development of crops with higher oil yields and improved stress resilience.

Many studies have demonstrated that LDs play a crucial role in cellular lipid homeostasis. While much attention has been paid to how LD size and number are determined in plants (Doner et al., 2025), the regulation of lipolysis and lipophagy-mediated lipid turnover, particularly during nutrient deprivation when plants rely on lipid catabolism for energy production, remains poorly understood. In mammals, the process of lipolysis is subject to stringent regulation, with the rate-limiting enzyme Adipose Triglyceride Lipase (ATGL) being subject to enhancement of up to 20-fold through its interaction with the activator CGI-58 (ABHD5) (Mathiowetz and Olzmann, 2024). Concurrently, PLIN proteins function as a regulatory mechanism, sequestering CGI-58 and thereby impeding ATGL activity (Mathiowetz and Olzmann, 2024). In contrast, plants employ SDP1 as their functional ATGL homolog, but lack both PLIN proteins and CGI-58-mediated activation of SDP1, despite the presence of a CGI-58 homolog that instead regulates PXA1 (Park et al., 2013). The current understanding of plant lipolysis regulation remains incomplete, particularly regarding whether energy-sensing pathways modulate SDP1 activity. The energy-sensing central regulators include the low-energy sensor SnRK1, the high-energy sensor TOR kinase and the sucrose-signaling metabolite T6P. These components form an intricate regulatory network where SnRK1 promotes lipolysis during energy deficit while TOR suppresses it under energy-replete conditions, with T6P fine-tuning this balance by inhibiting SnRK1 (Figueroa and Lunn, 2016; Liu and Xiong, 2022; Van Leene et al., 2022). Critical areas for future investigation include investigating the possible direct phosphorylation of SDP1 by SnRK1/TOR kinases, characterizing the functional relationship between the energy sensing module and SDP1 during lipid mobilization, and identifying potential novel components that facilitate communication between SDP1 and energy-sensing pathways. Resolution of these questions will significantly advance our understanding of the molecular mechanisms controlling LD degradation and overall plant lipid homeostasis.

Current research indicates that plants may dynamically regulate the functions of LD-associated proteins through post-translational modifications (PTMs) in response to environmental stresses. Despite extensive characterization of LD protein PTMs in animal systems (Zhang et al., 2022; Loix et al., 2024), their functional validation and molecular mechanisms remain largely unexplored in plants. Ubiquitination may regulate LD protein turnover through either proteasomal degradation or selective autophagy (e.g., lipophagy), maintaining cellular homeostasis under stress conditions. Furthermore, oxidative modifications and SUMOylation likely participate in mediating LD-organelle interactions (e.g., with peroxisomes), affecting membrane remodeling and ROS scavenging. Future investigations should integrate subcellular proteomics, PTM site-directed mutagenesis, and super-resolution imaging to systematically decipher stress-specific PTM dynamics on LD proteins and their physiological relevance. Such advances would not only elucidate the regulatory mechanisms of plant lipid metabolism under stress but may also provide novel strategies for improving crop stress tolerance.

LDs serve as critical organelles in stress response mechanisms. Numerous abiotic stressors have been shown to induce LD biogenesis (Zhao et al., 2023; Coulon et al., 2024). During senescence or stress conditions, TAG accumulation is closely linked to lipid catabolic processes. However, several key aspects remain poorly understood: the functional significance of fatty acids derived from membrane lipids like Monogalactosyldiacylglycerol (MGDG) (Fan et al., 2017); the specific roles of various lipases in stress adaptation; and the degradation mechanisms of stress-induced LDs during post-stress recovery. While LD degradation during seed germination has been well characterized (Kelly et al., 2011), the catabolic pathways of stress-induced LDs and their contributions to cellular homeostasis restoration remain elusive. Particularly, the relative importance of lipolysis versus lipophagy in TAG remobilization, the metabolic fates of neutral lipids, and the subsequent utilization of released fatty acids all require systematic investigation (Coulon et al., 2024). Elucidating these processes will not only advance our understanding of plant stress responses but also provide a theoretical framework for developing stress-resistant crops through LD manipulation.

Research has shown that the proteome of LDs in plants undergoes extensive dynamic remodeling under diverse stress conditions (Krawczyk et al., 2022). This is evidenced by the specific upregulation of stress-responsive LD-associated proteins, such as CLO3 and α-DOX1, in both wild-type plants and the tgd1–1 sdp1–4 mutant (Shimada et al., 2014). Notably, different stresses exhibit distinct regulatory effects on LD proteins: CLO3 responds to both heat stress and pathogen infection, whereas α-DOX1 is selectively activated only under pathogen infection and drought stress conditions (Scholz et al., 2025). These findings suggest that plants have evolved a stress-specific LD reprogramming mechanism, fine-tuning protein expression to adapt to different environmental threats. However, the molecular mechanisms governing LD remodeling under various stress conditions remain poorly understood and warrant further investigation.