Overexpression of rice sphingosine-1-phoshpate lyase gene OsSPL1 in transgenic tobacco reduces salt and oxidative stress tolerance

Transcriptomic and Lipidomic Analysis Reveals Complex Regulation Mechanisms Underlying Rice Roots' Response to Salt Stress

Rice (Oryza sativa L.), a crucial food crop that sustains over half the world's population, is often hindered by salt stress during various growth stages, ultimately causing a decrease in yield. However, the specific mechanism of rice roots' response to salt stress remains largely unknown. In this study, transcriptomics and lipidomics were used to analyze the changes in the lipid metabolism and gene expression profiles of rice roots in response to salt stress. The results showed that salt stress significantly inhibited rice roots' growth and increased the roots' MDA content. Furthermore, 1286 differentially expressed genes including 526 upregulated and 760 downregulated, were identified as responding to salt stress in rice roots. The lipidomic analysis revealed that the composition and unsaturation of membrane lipids were significantly altered. In total, 249 lipid molecules were differentially accumulated in rice roots as a response to salt stress. And most of the major phospholipids, such as phosphatidic acid (PA), phosphatidylcholine (PC), and phosphatidylserine (PS), as well as major sphingolipids including ceramide (Cer), phytoceramide (CerP), monohexose ceramide (Hex1Cer), and sphingosine (SPH), were significantly increased, while the triglyceride (TG) molecules decreased. These results suggested that rice roots mitigate salt stress by altering the fluidity and integrity of cell membranes. This study enhances our comprehension of salt stress, offering valuable insights into changes in the lipids and adaptive lipid remodeling in rice's response to salt stress.

PtoMPO1, a negative mediator, functions in poplar drought tolerance

Drought, as one of the most severe abiotic stresses in nature, adversely affects plant growth and development. Poplar is a woody plant which is prone to water-deficit sensitivity. Therefore, it is important to improve our understanding of how poplar responds to drought stress. Here, we cloned a gene from Populus tomentosa, namely PtoMPO1. PtoMPO1 encodes a DUF962 domain protein that is a homolog of yeast dioxygenase Mpo1 and Arabidopsis MHP1. The transcripts of PtoMPO1 were repressed by drought stress and ABA. Atmhp1-1 was a T-DNA insertion mutant lacking AtMHP1, and heteroexpression of PtoMPO1 in Atmhp1-1 significantly alleviated the sensitivity of Atmhp1-1 to ABA and NaCl, implying the functional replacement of PtoMPO1 to AtMHP1. PtoMPO1 overexpression decreased but PtoMPO1 mutation enhanced poplar drought tolerance. Furthermore, the expression of drought-related gene PtoRD26 is markedly lower in PtoMPO1-overexpressing plants and notably higher in Ptompo1 mutants compared to that in the wild type. Overall, these results suggested that PtoMPO1 functions as a novel negative mediator for drought tolerance in poplar.

Overexpression of TaLAX3-1B alters the stomatal aperture and improves the salt stress resistance of tobacco

BACKGROUND

Stomata, which play important roles in both optimizing photosynthesis efficiency and adapting to stress, are closely related to IAA and ABA. In plants, the auxin influx carrier LAX3 has been found to play roles in development and stress tolerance. However, the function of LAX3 in stomata and in response to salt stress remains largely unknown.

METHODS AND RESULTS

Here, we show that overexpression of wheat TaLAX3-1B in tobacco results in a decrease in stomatal aperture and a relatively closed state of the stomata. In addition, the stomatal movement of the OxTaLAX3-1B lines was less sensitive to ABA than that of the WT. Consistently, compared with the WT, the OxTaLAX3-1B lines showed significantly higher expression of stomate-, IAA- and ABA-related genes and endogenous IAA and ABA contents. Furthermore, compared with the WT, the OxTaLAX3-1B lines exhibited higher proline content, salt stress-related gene expression and ROS antioxidant enzyme activity but lower MDA content and ROS accumulation after salt treatment.

CONCLUSIONS

The present results suggest that TaLAX3-1B plays a positive role in regulating stomatal closure and enhancing salt stress tolerance.

Detailed sphingolipid profile responded to salt stress in cotton root and the GhIPCS1 is involved in the regulation of plant salt tolerance

Sphingolipids are major structural components of membrane and active signaling molecules and play an important role in plant developmental processes and stress responses. As land salinization has increased globally, salinity has compromised the growth and productivity of crops such as cotton. Understanding the mechanisms of plant adaptation to salt stress is essential for breeding salt-tolerant crops. In this study, we explored the comprehensive metabolic profile of sphingolipids in cotton root under salt stress using lipidomics. 118 sphingolipid molecular species were identified, of which PhytoSph, PhytoCer, PhytoCer-OHFA, IPC, and GIPC were relatively high in content, and PhytoSph, PhytoCer, PhytoCer-OHFA, Phyto-GluCer, and IPC showed significant changes after salt stress, especially inositol phosphatidyl ceramide (IPC), which was significantly upregulated after salt treatment. Subsequently, we identified the genes encoding IPC synthase (IPCS), and ectopic expression of GhIPCS1 enhanced salt sensitivity in Arabidopsis, which might result from the disruption on the balance between various sphingolipid classes and/or molecular species. Overall, this study reveals key lipids and genes response to salt stress in cotton and provides a theoretical basis for the use of genetic engineering to improve cotton stress resistance.

Phytosphingosine induces systemic acquired resistance through activation of sphingosine kinase

Phytosphingosine (PHS) is a naturally occurring bioactive sphingolipid molecule. Intermediates such as sphingolipid long-chain bases (LCBs) in sphingolipid biosynthesis have been shown to have important roles as signaling molecules. PHS treatment caused rapid cell damage and upregulated the generation of reactive oxygen species (ROS) and ethylene in tobacco plants. These events were followed by the induction of sphingosine kinase (SphK) in a biphasic manner, which metabolized PHS to phytosphingosine-1-phosphate (PHS-1-P). On the other hand, a PHS treatment with a virulent pathogen, Phytophthora parasitica var. nicotianae (Ppn), alleviated the pathogen-induced cell damage and reduced the growth of Ppn. A Ppn infection increased the PHS and PHS-1-P levels significantly in the upper part of the leaves at the infection site at the later stage. In addition, Ppn increased the transcription levels of serine palmitoyltransferase (LCB1 and LCB2) for sphingolipid biosynthesis at the later stage, which was enhanced further by PHS. Moreover, the PHS treatment increased the transcription and activity of SphK, which was accompanied by prominent increases in the transcription levels of ROS-detoxifying enzymes and PR proteins in the later phase of the pathogen infection. Overall, the PHS-induced resistant effects were prominent during the necrotic stage of this hemibiotrophic infection, indicating that it is more beneficial for inhibiting the pathogenicity on necrotic cell death. Phosphorylated LCBs reduced the pathogen-induced cell damage significantly in this stage. These results suggest that the selective channeling of sphingolipids into phosphorylated forms has a pro-survival effect on plant immunity.

Link between Lipid Second Messengers and Osmotic Stress in Plants

Plants are subject to different types of stress, which consequently affect their growth and development. They have developed mechanisms for recognizing and processing an extracellular signal. Second messengers are transient molecules that modulate the physiological responses in plant cells under stress conditions. In this sense, it has been shown in various plant models that membrane lipids are substrates for the generation of second lipid messengers such as phosphoinositide, phosphatidic acid, sphingolipids, and lysophospholipids. In recent years, research on lipid second messengers has been moving toward using genetic and molecular approaches to reveal the molecular setting in which these molecules act in response to osmotic stress. In this sense, these studies have established that second messengers can transiently recruit target proteins to the membrane and, therefore, affect protein conformation, activity, and gene expression. This review summarizes recent advances in responses related to the link between lipid second messengers and osmotic stress in plant cells.

Sphingolipids: towards an integrated view of metabolism during the plant stress response

Plants exist in an environment of changing abiotic and biotic stresses. They have developed a complex set of strategies to respond to these stresses and over recent years it has become clear that sphingolipids are a key player in these responses. Sphingolipids are not universally present in all three domains of life. Many bacteria and archaea do not produce sphingolipids but they are ubiquitous in eukaryotes and have been intensively studied in yeast and mammals. During the last decade there has been a steadily increasing interest in plant sphingolipids. Plant sphingolipids exhibit structural differences when compared with their mammalian counterparts and it is now clear that they perform some unique functions. Sphingolipids are recognised as critical components of the plant plasma membrane and endomembrane system. Besides being important structural elements of plant membranes, their particular structure contributes to the fluidity and biophysical order. Sphingolipids are also involved in multiple cellular and regulatory processes including vesicle trafficking, plant development and defence. This review will focus on our current knowledge as to the function of sphingolipids during plant stress responses, not only as structural components of biological membranes, but also as signalling mediators.

Emerging Roles of Sphingolipid Signaling in Plant Response to Biotic and Abiotic Stresses

Plant sphingolipids are not only structural components of the plasma membrane and other endomembrane systems but also act as signaling molecules during biotic and abiotic stresses. However, the roles of sphingolipids in plant signal transduction in response to environmental cues are yet to be investigated in detail. In this review, we discuss the signaling roles of sphingolipid metabolites with a focus on plant sphingolipids. We also mention some microbial sphingolipids that initiate signals during their interaction with plants, because of the limited literatures on their plant analogs. The equilibrium of nonphosphorylated and phosphorylated sphingolipid species determine the destiny of plant cells, whereas molecular connections among the enzymes responsible for this equilibrium in a coordinated signaling network are poorly understood. A mechanistic link between the phytohormone-sphingolipid interplay has also not yet been fully understood and many key participants involved in this complex interaction operating under stress conditions await to be identified. Future research is needed to fill these gaps and to better understand the signal pathways of plant sphingolipids and their interplay with other signals in response to environmental stresses.

S1P Lyase Regulation of Thymic Egress and Oncogenic Inflammatory Signaling

Sphingosine-1-phosphate (S1P) is a potent lipid signaling molecule that regulates pleiotropic biological functions including cell migration, survival, angiogenesis, immune cell trafficking, inflammation, and carcinogenesis. It acts as a ligand for a family of cell surface receptors. S1P concentrations are high in blood and lymph but low in tissues, especially the thymus and lymphoid organs. S1P chemotactic gradients are essential for lymphocyte egress and other aspects of physiological cell trafficking. S1P is irreversibly degraded by S1P lyase (SPL). SPL regulates lymphocyte trafficking, inflammation and other physiological and pathological processes. For example, SPL located in thymic dendritic cells acts as a metabolic gatekeeper that controls the normal egress of mature T lymphocytes from the thymus into the circulation, whereas SPL deficiency in gut epithelial cells promotes colitis and colitis-associated carcinogenesis (CAC). Recently, we identified a complex syndrome comprised of nephrosis, adrenal insufficiency, and immunological defects caused by inherited mutations in human SGPL1, the gene encoding SPL. In the present article, we review current evidence supporting the role of SPL in thymic egress, inflammation, and cancer. Lastly, we summarize recent progress in understanding other SPL functions, its role in inherited disease, and SPL targeting for therapeutic purposes.

Overexpression of human peroxisomal enoyl-CoA delta isomerase2 HsPECI2, an ortholog of bamboo expressed during gregarious flowering alters salinity stress responses and polar lipid content in tobacco

Peroxisomal enoyl-CoA delta isomerase2 (PECI2) is one of the key enzymes that has critical role in lipid metabolism and plant development during salt stress. Seven out of ten tobacco plants overexpressing human PECI2 (HsPECI2) with PTS1-sequence showed hypersensitivity to salt. Under salt-stress, T2 transformed plants (HsPECI2) displayed reduced primary root, delayed shoot-growth, and visibly smaller rosette leaves turning pale yellow as compared to the pKYLX71 vector control plant. Also, we found altered reactive oxygen species (ROS) levels and reduced catalase activity in 100mM sodium chloride (NaCl) treated HsPECI2 transformed plant compared with the pKYLX71 counterpart. ESI-MS/MS data showed that the polar lipids were differentially modulated upon salt treatment in HsPECI2 transformed and pKYLX71 plants as compared with the respective untreated counterpart. Notably, the levels of monogalactosyldiacylglycerol and phosphatidic acid varied significantly, whereas phosphatidylcholine, phosphatidylserine and digalactosyldiacylglycerol contents were moderately upregulated. In parallel, abscisic acid (ABA) responsiveness assay confirmed insensitivity of HsPECI2 transformed plant towards ABA. Overall our data proclaim that HsPECI2 play multifunctional role in normal development and response to salinity stress apart from its primary role in β-oxidation.

The Arabidopsis ceramidase AtACER functions in disease resistance and salt tolerance

Ceramidases hydrolyze ceramide into sphingosine and fatty acids. In mammals, ceramidases function as key regulators of sphingolipid homeostasis, but little is known about their roles in plants. Here we characterize the Arabidopsis ceramidase AtACER, a homolog of human alkaline ceramidases. The acer-1 T-DNA insertion mutant has pleiotropic phenotypes, including reduction of leaf size, dwarfing and an irregular wax layer, compared with wild-type plants. Quantitative sphingolipid profiling showed that acer-1 mutants and the artificial microRNA-mediated silenced line amiR-ACER-1 have high ceramide levels and decreased long chain bases. AtACER localizes predominantly to the endoplasmic reticulum, and partially to the Golgi complex. Furthermore, we found that acer-1 mutants and AtACER RNAi lines showed increased sensitivity to salt stress, and lines overexpressing AtACER showed increased tolerance to salt stress. Reduction of AtACER also increased plant susceptibility to Pseudomonas syringae. Our data highlight the key biological functions of ceramidases in biotic and abiotic stresses in plants.

Nitric oxide-sphingolipid interplays in plant signalling: a new enigma from the Sphinx?

Nitric oxide (NO) emerged as one of the major signaling molecules operating during plant development and plant responses to its environment. Beyond the identification of the direct molecular targets of NO, a series of studies considered its interplay with other actors of signal transduction and the integration of NO into complex signaling networks. Beside the close relationships between NO and calcium or phosphatidic acid signaling pathways that are now well-established, recent reports paved the way for interplays between NO and sphingolipids (SLs). This mini-review summarizes our current knowledge of the influence NO and SLs might exert on each other in plant physiology. Based on comparisons with examples from the animal field, it further indicates that, although SL-NO interplays are common features in signaling networks of eukaryotic cells, the underlying mechanisms and molecular targets significantly differ.