Roles of TOR signaling in nutrient deprivation and abiotic stress

Role of autophagy in plant growth and adaptation to salt stress

MAIN CONCLUSION

Under salt stress, autophagy regulates ionic balance, scavenges ROS, and supports nutrient remobilization, thereby alleviating osmotic and oxidative damage. Salt stress is a major environmental challenge that significantly impacts plant growth and agricultural productivity by disrupting nutrient balance, inducing osmotic stress, and causing the accumulation of toxic ions like Na+. Autophagy, a key cellular degradation and recycling pathway, plays a critical role in enhancing plant salt tolerance by maintaining cellular homeostasis and mitigating stress-induced damage. While autophagy has traditionally been viewed as a response to nutrient starvation, recent research has highlighted its importance under various environmental stresses, particularly salt stress. Under such conditions, plants activate autophagy through distinct signaling pathways involving autophagy-related genes (ATGs), Target of Rapamycin (TOR) proteins, and reactive oxygen species (ROS). Salt stress induces the expression of ATG genes and promotes the formation of autophagosomes, which facilitate the degradation of damaged organelles, denatured proteins, and the sequestration of Na+ into vacuoles, thereby improving stress tolerance. Recent studies have also suggested that autophagy may play a direct role in salt stress signaling, linking it to the regulation of metabolic processes. This review discusses the molecular mechanisms underlying autophagy induction in plants under salt stress, including the roles of ATGs and TOR, as well as the physiological significance of autophagy in mitigating oxidative damage, maintaining ion balance, and enhancing overall salt tolerance. In addition, we discussed the metabolic changes related to autophagy in stressed plants and examined the broader implications for managing plant stress and improving crops.

Starch metabolism in guard cells: At the intersection of environmental stimuli and stomatal movement

Starch metabolism in guard cells plays a central role in regulating stomatal movement in response to light, elevated ambient CO2 and potentially other abiotic and biotic factors. Here, we discuss how various guard cell signal transduction pathways converge to promote rearrangements in guard cell starch metabolism for efficient stomatal responses, an essential physiological process that sustains plant productivity and stress tolerance. We suggest manipulation of guard cell starch dynamics as a previously overlooked strategy to improve stomatal behavior under changing environmental conditions.

Target of rapamycin coordinates auxin are involved in exogenous melatonin regulated low temperature tolerance in cucumber seedlings

Low temperature (LT) is an important environmental factor affecting the growth and yield of plants. Melatonin (MT) can effectively enhance the LT tolerance of cucumber. This study found that LT stress induced the expression of Comt1 (caffeic acid O-methyltransferase 1), with the highest expression being about 2-times that of the control. Meanwhile, the content of MT was found to be roughly 63.16% of that in the control samples. Compared with LT treatment alone, exogenous MT pretreatment upregulated the expression levels of TOR (Target of rapamycin), PIN1 (Pin-formed 1), and YUC4 (YUCCA 4), with maximum upregulations reaching approximately 66.67%, 79.32%, and 42.86%, respectively. These results suggest that MT may modulate the tolerance of cucumber seedlings to LT stress by regulating the expression of TOR, PIN1, and YUC4. In addition, co-treatment with AZD-8055 (a TOR inhibitor) or NPA (N-1-naphthylphthalamic acid, an auxin polar transport inhibitor) and MT attenuated MT-induced resistance to LT stress, leading to higher levels of reactive oxygen species (ROS), reduced antioxidant defense capacity, and increased damage to the membrane system in cucumber seedlings. Concurrently, the content of osmoregulatory substances and the photosynthesis decreased. These results demonstrate that both TOR and auxin were required for MT to alleviate LT-induced damage in cucumber. In summary, the present study demonstrates that TOR and auxin signaling synergistically contribute to alleviating LT damage in cucumber seedlings by exogenous MT. These findings help us understand the function of MT and provide insights into the regulatory network of MT that regulates the LT tolerance of plants.

Thermal adaptation in plants: understanding the dynamics of translation factors and condensates

Plants, as sessile organisms, face the crucial challenge of adjusting growth and development with ever-changing environmental conditions. Protein synthesis is the fundamental process that enables growth of all organisms. Since elevated temperature presents a substantial threat to protein stability and function, immediate adjustments of protein synthesis rates are necessary to circumvent accumulation of proteotoxic stress and to ensure survival. This review provides an overview of the mechanisms that control translation under high-temperature stress by the modification of components of the translation machinery in plants, and compares them to yeast and metazoa. Recent research also suggests an important role for cytoplasmic biomolecular condensates, named stress granules, in these processes. Current understanding of the role of stress granules in translational regulation and of the molecular processes associated with translation that might occur within stress granules is also discussed.

TOR in plants: Multidimensional regulators of plant growth and signaling pathways

Target Of Rapamycin (TOR) represents a ubiquitous kinase complex that has emerged as a central regulator of cell growth and metabolism in nearly all eukaryotic organisms. TOR is an evolutionarily conserved protein kinase, functioning as a central signaling hub that integrates diverse internal and external cues to regulate a multitude of biological processes. These processes collectively exert significant influence on plant growth, development, nutrient assimilation, photosynthesis, fruit ripening, and interactions with microorganisms. Within the plant domain, the TOR complex comprises three integral components: TOR, RAPTOR, and LST8. This comprehensive review provides insights into various facets of the TOR protein, encompassing its origin, structure, function, and the regulatory and signaling pathways operative in photosynthetic organisms. Additionally, we explore future perspectives related to this pivotal protein kinase.

Effect of interfering TOR signaling pathway on the biosynthesis of terpenoids in Salvia miltiorrhiza Bge

The TOR (Target of Rapamycin) signaling pathway, which takes TOR kinase as the core, regulates the absorption, distribution, and recycling of nutrients by integrating metabolic network and other signaling pathways, thus participating in the plant growth-defense trade-off. While terpenoids play an important role in plant growth, development, stress response, and signal transduction. The effect of the TOR signaling pathway on terpenoid biosynthesis in plants has yet to be studied in detail. In this study, the tissue culture seedlings of Salvia miltiorrhiza were treated with the TOR inhibitor AZD8055. The results show that the roots of the control group had begun to grow on the 8th day, while the seedlings treated with AZD8055 had no rooting signs. Combined with the expression changes of genes related to the TOR signaling pathway in the first 8 days, samples on the 3rd, 6th, and 8th days were selected for RNA-Seq analysis. Through RNA-Seq analysis, a total of 50,689 unigenes were obtained from the samples of these three periods, of which 4088 unigenes showed differential expression. The function enrichment and time-series analysis of differentially expressed genes (DEGs) showed that the main influence of the TOR signal pathway on plant growth-related processes was gradually transmitted with treatment time after TOR was inhibited. Pathway enrichment analysis of DEGs showed that the genes in the biosynthesis of terpenoids, such as diterpenoid and carotenoid biosynthetic pathways, could be regulated. Compared with other stages, DEGs related to terpenoid biosynthesis were mainly regulated in the S2 stage. In addition, the genes involved in terpenoid skeleton biosynthesis was also considerably enriched in the S2 stage, according to the results of gene set enrichment analysis (GSEA) of unigenes. Inhibition of the TOR signaling pathway may affect the biosynthesis of terpenoid signaling molecules, inhibit gibberellin's biosynthesis, and promote abscisic acid's biosynthesis. This study has discussed the effect of interfering with the TOR pathway on terpenoid biosynthesis in S. miltiorrhiza from the perspective of omics and provides new insight into the interaction between the terpenoid biosynthesis pathway and the growth-defense trade-off of medicinal plants.

Starch deficiency in tomato causes transcriptional reprogramming that modulates fruit development, metabolism, and stress responses

Tomato (Solanum lycopersicum) fruit store carbon as starch during early development and mobilize it at the onset of ripening. Starch accumulation has been suggested to buffer fluctuations in carbon supply to the fruit under abiotic stress, and contribute to sugar levels in ripe fruit. However, the role of starch accumulation and metabolism during fruit development is still unclear. Here we show that the tomato mutant adpressa (adp) harbors a mutation in a gene encoding the small subunit of ADP-glucose pyrophosphorylase that abolishes starch synthesis. The disruption of starch biosynthesis causes major transcriptional and metabolic remodeling in adp fruit but only minor effects on fruit size and ripening. Changes in gene expression and metabolite profiles indicate that the lack of carbon flow into starch increases levels of soluble sugars during fruit growth, triggers a readjustment of central carbohydrate and lipid metabolism, and activates growth and stress protection pathways. Accordingly, adp fruits are remarkably resistant to blossom-end rot, a common physiological disorder induced by environmental stress. Our results provide insights into the effects of perturbations of carbohydrate metabolism on tomato fruit development, with potential implications for the enhancement of protective mechanisms against abiotic stress in fleshy fruit.

Finding Balance in Adversity: Nitrate Signaling as the Key to Plant Growth, Resilience, and Stress Response

To effectively adapt to changing environments, plants must maintain a delicate balance between growth and resistance or tolerance to various stresses. Nitrate, a significant inorganic nitrogen source in soils, not only acts as an essential nutrient but also functions as a critical signaling molecule that regulates multiple aspects of plant growth and development. In recent years, substantial advancements have been made in understanding nitrate sensing, calcium-dependent nitrate signal transmission, and nitrate-induced transcriptional cascades. Mounting evidence suggests that the primary response to nitrate is influenced by environmental conditions, while nitrate availability plays a pivotal role in stress tolerance responses. Therefore, this review aims to provide an overview of the transcriptional and post-transcriptional regulation of key components in the nitrate signaling pathway, namely, NRT1.1, NLP7, and CIPK23, under abiotic stresses. Additionally, we discuss the specificity of nitrate sensing and signaling as well as the involvement of epigenetic regulators. A comprehensive understanding of the integration between nitrate signaling transduction and abiotic stress responses is crucial for developing future crops with enhanced nitrogen-use efficiency and heightened resilience.

Genome-wide analysis of WD40 protein family and functional characterization of BvWD40-82 in sugar beet

Sugar beet is one of the most important sugar crops in the world. It contributes greatly to the global sugar production, but salt stress negatively affects the crop yield. WD40 proteins play important roles in plant growth and response to abiotic stresses through their involvement in a variety of biological processes, such as signal transduction, histone modification, ubiquitination, and RNA processing. The WD40 protein family has been well-studied in Arabidopsis thaliana, rice and other plants, but the systematic analysis of the sugar beet WD40 proteins has not been reported. In this study, a total of 177 BvWD40 proteins were identified from the sugar beet genome, and their evolutionary characteristics, protein structure, gene structure, protein interaction network and gene ontology were systematically analyzed to understand their evolution and function. Meanwhile, the expression patterns of BvWD40s under salt stress were characterized, and a BvWD40-82 gene was hypothesized as a salt-tolerant candidate gene. Its function was further characterized using molecular and genetic methods. The result showed that BvWD40-82 enhanced salt stress tolerance in transgenic Arabidopsis seedlings by increasing the contents of osmolytes and antioxidant enzyme activities, maintaining intracellular ion homeostasis and increasing the expression of genes related to SOS and ABA pathways. The result has laid a foundation for further mechanistic study of the BvWD40 genes in sugar beet tolerance to salt stress, and it may inform biotechnological applications in improving crop stress resilience.

Fine Tuning of ROS, Redox and Energy Regulatory Systems Associated with the Functions of Chloroplasts and Mitochondria in Plants under Heat Stress

Heat stress severely affects plant growth and crop production. It is therefore urgent to uncover the mechanisms underlying heat stress responses of plants and establish the strategies to enhance heat tolerance of crops. The chloroplasts and mitochondria are known to be highly sensitive to heat stress. Heat stress negatively impacts on the electron transport chains, leading to increased production of reactive oxygen species (ROS) that can cause damages on the chloroplasts and mitochondria. Disruptions of photosynthetic and respiratory metabolisms under heat stress also trigger increase in ROS and alterations in redox status in the chloroplasts and mitochondria. However, ROS and altered redox status in these organelles also activate important mechanisms that maintain functions of these organelles under heat stress, which include HSP-dependent pathways, ROS scavenging systems and retrograde signaling. To discuss heat responses associated with energy regulating organelles, we should not neglect the energy regulatory hub involving TARGET OF RAPAMYCIN (TOR) and SNF-RELATED PROTEIN KINASE 1 (SnRK1). Although roles of TOR and SnRK1 in the regulation of heat responses are still unknown, contributions of these proteins to the regulation of the functions of energy producing organelles implicate the possible involvement of this energy regulatory hub in heat acclimation of plants.