Coordination of Phospholipid-Based Signaling and Membrane Trafficking in Plant Immunity

Exploring lipid signaling in plant physiology: From cellular membranes to environmental adaptation

Lipids have evolved as versatile signaling molecules that regulate a variety of physiological processes in plants. Convincing evidence highlights their critical role as mediators in a wide range of plant processes required for survival, growth, development, and responses to environmental conditions such as water availability, temperature changes, salt, pests, and diseases. Understanding lipid signaling as a critical process has helped us expand our understanding of plant biology by explaining how plants sense and respond to environmental cues. Lipid signaling pathways constitute a complex network of lipids, enzymes, and receptors that coordinate important cellular responses and stressing plant biology's changing and adaptable traits. Plant lipid signaling involves a wide range of lipid classes, including phospholipids, sphingolipids, oxylipins, and sterols, each of which contributes differently to cellular communication and control. These lipids function not only as structural components, but also as bioactive molecules that transfer signals. The mechanisms entail the production of lipid mediators and their detection by particular receptors, which frequently trigger downstream cascades that affect gene expression, cellular functions, and overall plant growth. This review looks into lipid signaling in plant physiology, giving an in-depth look and emphasizing its critical function as a master regulator of vital activities.

Exploration the interaction of cadmium and copper toxic effects in pakchoi (Brassica chinensis L) roots through combinatorial transcriptomic and weighted gene co-expression network analysis

The interaction between cadmium(Cd) and copper(Cu) during combined pollution can lead to more complex toxic effects on humans and plants.However, there is still a lack of sufficient understanding regarding the types of interactions at the plant molecular level and the response strategies of plants to combined pollution. To assess this, we investigated the phenotypic and transcriptomic patterns of pakchoi (Brassica chinensis L) roots in response to individual and combined pollution of Cd and Cu. The results showed that compared to single addition, the translocation factor of heavy metals in roots significantly decreased (p < 0.05) under the combined addition, resulting in higher accumulation of Cd and Cu in the roots. Transcriptomic analysis of pakchoi roots revealed that compared to single pollution, there were 312 and 1926 differentially expressed genes (DEGs) specifically regulated in the Cd2Cu20 and Cd2Cu100 combined treatments, respectively. By comparing the expression of these DEGs among different treatments, we found that the combined pollution of Cd and Cu mainly affected the transcriptome of the roots in an antagonistic manner. Enrichment analysis indicated that pakchoi roots upregulated the expression of genes involved in glucosetransferase activity, phospholipid homeostasis, proton transport, and the biosynthesis of phenylpropanoids and flavonoids to resist Cd and Cu combined pollution. Using weighted gene co-expression network analysis (WGCNA), we identified hub genes related to the accumulation of Cd and Cu in the roots, which mainly belonged to the LBD, thaumatin-like protein, ERF, MYB, WRKY, and TCP transcription factor families. This may reflect a transcription factor-driven trade-off strategy between heavy metal accumulation and growth in pakchoi roots. Additionally, compared to single metal pollution, the expression of genes related to Nramp, cation/H+ antiporters, and some belonging to the ABC transporter family in the pakchoi roots was significantly upregulated under combined pollution. This could lead to increased accumulation of Cd and Cu in the roots. These findings provide new insights into the interactions and toxic mechanisms of multiple metal combined pollution at the molecular level in plants.

DGK5 phosphorylation finetunes PA homeostasis in plant immunity

Phosphatidic acid (PA) as a universal second messenger is transiently and rapidly produced upon immune activation in plants. A recent study by Kong et al. elucidated a mechanism for maintaining PA homeostasis via two uncoupled phosphorylation events of DIACYLGLYCEROL KINASE 5 (DGK5) at different phosphorylation sites by two distinct kinases.

Lipid mediated plant immunity in susceptible and tolerant soybean cultivars in response to Phytophthora sojae colonization and infection

BACKGROUND

Soybean is one of the most cultivated crops globally and a staple food for much of the world's population. The annual global crop losses due to infection by Phytophthora sojae is currently estimated at $20B USD, yet we have limited understanding of the role of lipid mediators in the adaptative strategies used by the host plant to limit infection. Since root is the initial site of this infection, we examined the infection process in soybean root infected with Phytophthora sojae using scanning electron microscopy to observe the changes in root morphology and a multi-modal lipidomics approach to investigate how soybean cultivars remodel their lipid mediators to successfully limit infection by Phytophthora sojae.

RESULTS

The results reveal the presence of elevated biogenic crystals and more severe damaged cells in the root morphology of the infected susceptible cultivar compared to the infected tolerant cultivars. Furthermore, induced accumulation of stigmasterol was observed in the susceptible cultivar whereas, induced accumulation of phospholipids and glycerolipids occurred in tolerant cultivar.

CONCLUSION

The altered lipidome reported in this study suggest diacylglycerol and phosphatidic acid mediated lipid signalling impacting phytosterol anabolism appears to be a strategy used by tolerant soybean cultivars to successfully limit infection and colonization by Phytophthora sojae.

Dual phosphorylation of DGK5-mediated PA burst regulates ROS in plant immunity

Phosphatidic acid (PA) and reactive oxygen species (ROS) are crucial cellular messengers mediating diverse signaling processes in metazoans and plants. How PA homeostasis is tightly regulated and intertwined with ROS signaling upon immune elicitation remains elusive. We report here that Arabidopsis diacylglycerol kinase 5 (DGK5) regulates plant pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). The pattern recognition receptor (PRR)-associated kinase BIK1 phosphorylates DGK5 at Ser-506, leading to a rapid PA burst and activation of plant immunity, whereas PRR-activated intracellular MPK4 phosphorylates DGK5 at Thr-446, which subsequently suppresses DGK5 activity and PA production, resulting in attenuated plant immunity. PA binds and stabilizes the NADPH oxidase RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD), regulating ROS production in plant PTI and ETI, and their potentiation. Our data indicate that distinct phosphorylation of DGK5 by PRR-activated BIK1 and MPK4 balances the homeostasis of cellular PA burst that regulates ROS generation in coordinating two branches of plant immunity.

Stress- and phospholipid signalling responses in Arabidopsis PLC4-KO and -overexpression lines under salt- and osmotic stress

Several drought and salt tolerant phenotypes have been reported when overexpressing (OE) phospholipase C (PLC) genes across plant species. In contrast, a negative role for Arabidopsis PLC4 in salinity stress was recently proposed, showing that roots of PLC4-OE seedlings were more sensitive to NaCl while plc4 knock-out (KO) mutants were more tolerant. To investigate this apparent contradiction, and to analyse the phospholipid signalling responses associated with salinity stress, we performed root growth- and phospholipid analyses on plc4-KO and PLC4-OE seedlings subjected to salinity (NaCl) or osmotic (sorbitol) stress and compared these with wild type (WT). Only very minor differences between PLC4 mutants and WT were observed, which even disappeared after normalization of the data, while in soil, PLC4-OE plants were clearly more drought tolerant than WT plants, as was found earlier when overexpressing Arabidopsis PLC2, -3, -5, -7 or -9. We conclude that PLC4 plays no opposite role in salt-or osmotic stress and rather behaves like the other Arabidopsis PLCs.

Editing a rice CDP-DAG synthase confers broad-spectrum resistance

Lesion mimic mutations (LMMs) often confer broad-spectrum resistance (BSR) in plants, but with significant yield penalties. Sha et al. recently demonstrated that genome editing of the rice BSR gene RESISTANCE TO BLAST1 (RBL1), encoding a cytidine diphosphate diacylglycerol (CDP-DAG) synthase involved in phospholipid biosynthesis, confers multipathogen resistance without an obvious trade-off in yield.

Membrane microdomains: Structural and signaling platforms for establishing membrane polarity

Cell polarity results from the asymmetric distribution of cellular structures, molecules, and functions. Polarity is a fundamental cellular trait that can determine the orientation of cell division, the formation of particular cell shapes, and ultimately the development of a multicellular body. To maintain the distinct asymmetric distribution of proteins and lipids in cellular membranes, plant cells have developed complex trafficking and regulatory mechanisms. Major advances have been made in our understanding of how membrane microdomains influence the asymmetric distribution of proteins and lipids. In this review, we first give an overview of cell polarity. Next, we discuss current knowledge concerning membrane microdomains and their roles as structural and signaling platforms to establish and maintain membrane polarity, with a special focus on the asymmetric distribution of proteins and lipids, and advanced microscopy techniques to observe and characterize membrane microdomains. Finally, we review recent advances regarding membrane trafficking in cell polarity establishment and how the balance between exocytosis and endocytosis affects membrane polarity.

Arabidopsis Tubby domain-containing F-box proteins positively regulate immunity by modulating PI4Kβ protein levels

The Tubby domain, named after the TUBBY protein in mice, binds to phosphatidylinositol 4,5-bisphosphate. Arabidopsis has 11 Tubby domain-containing proteins referred to as Tubby-Like Proteins (TLPs). Of the 11 TLPs, 10 possess the N-terminal F-box domain, which can interact with SKP-like proteins and form SKP1-Cullin-F-box E3 ligase complexes. Although mice TUBBY has been extensively studied, plant TLPs' functions are scarcely detailed. In this study, we show that the Arabidopsis Tubby-like protein 6 (TLP6) and its redundant homologs, TLP1, TLP2, TLP5, and TLP10, positively regulate Arabidopsis immune responses. Furthermore, in an immunoprecipitation mass spectrometry analysis to search for ubiquitination substrates of the TLPs, we identified two redundant phosphoinositide biosynthesis enzymes, phosphatidylinositol 4-kinase β proteins (PI4Kβs), PI4Kβ1 and PI4Kβ2, as TLP interactors. Importantly, TLP6 overexpression lines fully phenocopy the phenotypes of the pi4kβ1,2 mutant, while TLP6 overexpression also leads to increased PI4Kβ2 ubiquitination and reduction in its protein level in a proteasome-dependent manner. Most significantly, TLP6 overexpression does not further enhance the autoimmunity of the pi4kβ1,2 double mutant, supporting the hypothesis that TLP6 targets the PI4Kβs for ubiquitination and degradation. Thus, our study reveals a novel mechanism where TLPs promote plant immune responses by modulating the PI4Kβs protein levels.

Dynamics of nucleic acid mobility

Advances in sequencing technologies and bioinformatic analyses are accelerating the quantity and quality of data from all domains of life. This rich resource has the potential to reveal a number of important incidences with respect to possible exchange of nucleic acids. Ancient events have impacted species evolution and adaptation to new ecological niches. However, we still lack a full picture of processes ongoing within and between somatic cells, gametes, and different organisms. We propose that events linked to acceptance of alien nucleic acids grossly could be divided into 2 main routes in plants: one, when plants are exposed to extreme challenges and, the second level, a more everyday or season-related stress incited by biotic or abiotic factors. Here, many events seem to comprise somatic cells. Are the transport and acceptance processes of alien sequences random or are there specific regulatory systems not yet fully understood? Following entrance into a new cell, a number of intracellular processes leading to chromosomal integration and function are required. Modification of nucleic acids and possibly exchange of sequences within a cell may also occur. Such fine-tune events are most likely very common. There are multiple questions that we will discuss concerning different types of vesicles and their roles in nucleic acid transport and possible intracellular sequence exchange between species.

Genome editing of a rice CDP-DAG synthase confers multipathogen resistance

The discovery and application of genome editing introduced a new era of plant breeding by giving researchers efficient tools for the precise engineering of crop genomes1. Here we demonstrate the power of genome editing for engineering broad-spectrum disease resistance in rice (Oryza sativa). We first isolated a lesion mimic mutant (LMM) from a mutagenized rice population. We then demonstrated that a 29-base-pair deletion in a gene we named RESISTANCE TO BLAST1 (RBL1) caused broad-spectrum disease resistance and showed that this mutation caused an approximately 20-fold reduction in yield. RBL1 encodes a cytidine diphosphate diacylglycerol synthase that is required for phospholipid biosynthesis2. Mutation of RBL1 results in reduced levels of phosphatidylinositol and its derivative phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). In rice, PtdIns(4,5)P2 is enriched in cellular structures that are specifically associated with effector secretion and fungal infection, suggesting that it has a role as a disease-susceptibility factor3. By using targeted genome editing, we obtained an allele of RBL1, named RBL1Δ12, which confers broad-spectrum disease resistance but does not decrease yield in a model rice variety, as assessed in small-scale field trials. Our study has demonstrated the benefits of editing an LMM gene, a strategy relevant to diverse LMM genes and crops.

Dynamic responses of PA to environmental stimuli imaged by a genetically encoded mobilizable fluorescent sensor

Membrane fluidity, permeability, and surface charges are controlled by phospholipid metabolism and transport. Despite the importance of phosphatidic acid (PA) as a bioactive molecule, the mechanical properties of PA translocation and subcellular accumulation are unknown. Here, we used a mobilizable, highly responsive genetically encoded fluorescent indicator, green fluorescent protein (GFP)-N160_RbohD, to monitor PA dynamics in living cells. The majority of GFP-N160_RbohD accumulated at the plasma membrane and sensitively responded to changes in PA levels. Cellular, pharmacological, and genetic analyses illustrated that both salinity and abscisic acid rapidly enhanced GFP-N160_RbohD fluorescence at the plasma membrane, which mainly depended on hydrolysis of phospholipase D. By contrast, heat stress induced nuclear translocation of PA indicated by GFP-N160_RbohD through a process that required diacylglycerol kinase activity, as well as secretory and endocytic trafficking. Strikingly, we showed that gravity triggers asymmetric PA distribution at the root apex, a response that is suppressed by PLDζ2 knockout. The broad utility of the PA sensor will expand our mechanistic understanding of numerous lipid-associated physiological and cell biological processes and facilitate screening for protein candidates that affect the synthesis, transport, and metabolism of PA.

Genome-wide identification and expression analysis of the cotton patatin-related phospholipase A genes and response to stress tolerance

Patatin-related phospholipase A genes were involved in the response of Gossypium hirsutum to drought and salt tolerance. pPLA (patatin-related phospholipase A) is a key enzyme that catalyzes the initial step of lipid hydrolysis, which is involved in biological processes, such as drought, salt stress, and freezing injury. However, a comprehensive analysis of the pPLA gene family in cotton, especially the role of pPLA in the response to drought and salt tolerance, has not been reported so far. A total of 33 pPLA genes were identified in this study using a genome-wide search approach, and phylogenetic analysis classified these genes into three groups. These genes are unevenly distributed on the 26 chromosomes of cotton, and most of them contain a few introns. The results of the collinear analysis showed that G. hirsutum contained 1-5 copies of each pPLA gene found in G. arboreum and G. raimondii. The subcellular localization analysis of Gh_D08G061200 showed that the protein was localized in the nucleus. In addition, analysis of published upland cotton transcriptome data revealed that six GhPLA genes were expressed in various tissues and organs. Two genes (Gh_A04G142100.1 and Gh_D04G181000.1) were highly expressed in all tissues under normal conditions, showing the expression characteristics of housekeeping genes. Under different drought and salt tolerance stresses, we detected four genes with different expression levels. This study helps to clarify the role of pPLA in the response to drought and salt tolerance.

The Role of ABA in the Interaction between Citrus Fruit and Penicillium digitatum

Abscisic acid (ABA) protects citrus fruit against Penicillium digitatum infection. The global mechanisms involved in the role of ABA in the P. digitatum-citrus fruit interaction are unknown. Here, we determine the transcriptome differences between the Navelate (Citrus sinensis (L.) Osbeck) orange and its ABA-deficient mutant Pinalate, which is less resistant to infection. Low ABA levels may affect both the constitutive mechanisms that protect citrus fruit against P. digitatum and early responses to infection. The repression of terpenoid, phenylpropanoid and glutation metabolism; of oxidation-reduction processes; and of processes related to the defense response to fungus and plant hormone signal transduction may be one part of the constitutive defense reduced in the mutant against P. digitatum. Our results also provide potential targets for developing P. digitatum-citrus fruit-resistant varieties. Of those up-regulated by ABA, a thaumatin protein and a bifunctional inhibitor/LTP, which are relevant in plant immunity, were particularly remarkable. It is also worth highlighting chlorophyllase 1 (CLH1), induced by infection in Pinalate, and the OXS3 gene, which was down-regulated by ABA, because the absence of OXS3 activates ABA-responsive genes in plants.

Visualizing the Spatial Distribution of Arctium lappa L. Root Components by MALDI-TOF Mass Spectrometry Imaging

This study is aimed at developing novel analytical methods to accurately visualize the spatial distribution of various endogenous components in Arctium lappa L. (A. lappa) roots, and to precisely guide the setting of pre-treatment operations during processing technologies and understand plant metabolism process. The matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) imaging technology was used for visual demonstration of the in situ spatial distribution in A. lappa roots. This work consisted of four steps: matrix selection, section preparation, matrix coating, and MALDI-TOF MS imaging analysis. Consequently, eight saccharides, four caffeoylquinic acids, four flavonoids, six amino acids, one choline, and one phospholipid were imaged and four unidentified components were found. Saccharides were distributed in the center, whereas caffeoylquinic acids and flavonoids were mainly present in the epidermis and cortex. Furthermore, amino acids were mainly detected in the phloem, and choline in the cambium, while phosphatidylserine was found in the secondary phloem and cambium. This study demonstrated that MALDI-TOF MS imaging technology could provide a technical support to understand the spatial distribution of components in A. lappa roots, which would promote the processing technologies for A. lappa roots and help us to understand the plant metabolism process.

Regulation of immune complex formation and signalling by FERONIA, a busy goddess in plant-microbe interactions

Being sessile in soil, plant cells rely on cell-surface receptors to sense and transduce environmental stimulus signals into intracellular responses. FERONIA (FER), a Catharanthus roseus receptor-like kinase 1-like protein, has emerged as a versatile regulator of plant growth, development, and stress responses. In recent years, accumulating studies have witnessed rapid advances in dissecting the mechanisms underlying the interaction between FER and its partners in response to pathogen invasion, particularly regulation of immune complex formation and signalling. Moreover, hormonal signalling, rhizosphere microbiota and other constituents are also extensively involved in these processes.

Plasma membrane-to-organelle communication in plant stress signaling

Intracellular compartments engage in extensive communication with one another, an essential ability for cells to respond and adapt to changing environmental and developmental conditions. The plasma membrane (PM), as the interface between the cellular and the outside media, plays a central role in the perception and relay of information about external stimuli, which needs to be ultimately addressed to the relevant subcellular organelles. Interest in PM-organelle communication has increased dramatically in recent years, as examples arise that illustrate different strategies through which information from the PM can be transmitted. In this review, we will discuss mechanisms enabling PM-to-organelle communication in plants, specifically in biotic and abiotic stress signaling.

Spatiotemporal dynamics of FERONIA reveal alternative endocytic pathways in response to flg22 elicitor stimuli

The plant receptor-like kinase FERONIA (FER) functions in the response to multiple extracellular signals, thereby regulating diverse cellular processes, such as polarized cell growth, hormone signaling and responses to pathogens. Here, we reported that in Arabidopsis thaliana, flagellin peptide flg22 stimulus significantly promoted the lateral mobility and dissociation of FER from the plasma membrane by inducing the association of FER with membrane microdomain components. FER underwent constitutive endocytosis and recycling in a brefeldin A (BFA)-sensitive manner via a clathrin-mediated pathway. Following flg22 elicitation, FER localized to bona fide endosomes via two distinct endocytic routes, showing differential sensitivity to BFA. These results at the single-particle level confirm that FER acts as an essential regulator during flg22 perception and immune activation, thus broadening our understanding of location-specific protein dynamics and membrane trafficking in receptor/receptor kinase signaling.

Membrane trafficking functions of the ANTH/ENTH/VHS domain-containing proteins in plants

Subcellular localization of proteins acting on the endomembrane system is primarily regulated via membrane trafficking. To obtain and maintain the correct protein composition of the plasma membrane and membrane-bound organelles, the loading of selected cargos into transport vesicles is critically regulated at donor compartments by adaptor proteins binding to the donor membrane, the cargo molecules, and the coat-protein complexes, including the clathrin coat. The ANTH/ENTH/VHS domain-containing protein superfamily generally comprises a structurally related ENTH, ANTH, or VHS domain in the N-terminal region and a variable C-terminal region, which is thought to act as an adaptor during transport vesicle formation. This protein family is involved in various plant processes, including pollen tube growth, abiotic stress response, and development. In this review, we provide an overview of the recent findings on ANTH/ENTH/VHS domain-containing proteins in plants.

Imaging the living plant cell: From probes to quantification

At the center of cell biology is our ability to image the cell and its various components, either in isolation or within an organism. Given its importance, biological imaging has emerged as a field of its own, which is inherently highly interdisciplinary. Indeed, biologists rely on physicists and engineers to build new microscopes and imaging techniques, chemists to develop better imaging probes, and mathematicians and computer scientists for image analysis and quantification. Live imaging collectively involves all the techniques aimed at imaging live samples. It is a rapidly evolving field, with countless new techniques, probes, and dyes being continuously developed. Some of these new methods or reagents are readily amenable to image plant samples, while others are not and require specific modifications for the plant field. Here, we review some recent advances in live imaging of plant cells. In particular, we discuss the solutions that plant biologists use to live image membrane-bound organelles, cytoskeleton components, hormones, and the mechanical properties of cells or tissues. We not only consider the imaging techniques per se, but also how the construction of new fluorescent probes and analysis pipelines are driving the field of plant cell biology.

The plasma membrane-associated Ca2+ -binding protein, PCaP1, is required for oligogalacturonide and flagellin-induced priming and immunity

Early signalling events in response to elicitation include reversible protein phosphorylation and re-localization of plasma membrane (PM) proteins. Oligogalacturonides (OGs) are a class of damage-associated molecular patterns (DAMPs) that act as endogenous signals to activate the plant immune response. Previous data on early phosphoproteome changes in Arabidopsis thaliana upon OG perception uncovered the immune-related phospho-regulation of several membrane proteins, among which PCaP1, a PM-anchored protein with actin filament-severing activity, was chosen for its potential involvement in OG- and flagellin-triggered responses. Here, we demonstrate that PCaP1 is required for late, but not early, responses induced by OGs and flagellin. Moreover, pcap1 mutants, unlike the wild type, are impaired in the recovery of full responsiveness to a second treatment with OGs performed 24 h after the first one. Localization studies on PCaP1 upon OG treatment in plants expressing a functional PCaP1-GFP fusion under the control of PCaP1 promoter revealed fluorescence on the PM, organized in densely packed punctate structures, previously reported as microdomains. Fluorescence was found to be associated also with endocytic vesicles, the number of which rapidly increased after OG treatment, suggesting both an endocytic turnover of PCaP1 for maintaining its homeostasis at the PM and an OG-induced endocytosis.

Unravelling Plant Responses to Stress-The Importance of Targeted and Untargeted Metabolomics

Climate change and an increasing population, present a massive global challenge with respect to environmentally sustainable nutritious food production. Crop yield enhancements, through breeding, are decreasing, whilst agricultural intensification is constrained by emerging, re-emerging, and endemic pests and pathogens, accounting for ~30% of global crop losses, as well as mounting abiotic stress pressures, due to climate change. Metabolomics approaches have previously contributed to our knowledge within the fields of molecular plant pathology and plant-insect interactions. However, these remain incredibly challenging targets, due to the vast diversity in metabolite volatility and polarity, heterogeneous mixtures of pathogen and plant cells, as well as rapid rates of metabolite turn-over. Unravelling the systematic biochemical responses of plants to various individual and combined stresses, involves monitoring signaling compounds, secondary messengers, phytohormones, and defensive and protective chemicals. This demands both targeted and untargeted metabolomics approaches, as well as a range of enzymatic assays, protein assays, and proteomic and transcriptomic technologies. In this review, we focus upon the technical and biological challenges of measuring the metabolome associated with plant stress. We illustrate the challenges, with relevant examples from bacterial and fungal molecular pathologies, plant-insect interactions, and abiotic and combined stress in the environment. We also discuss future prospects from both the perspective of key innovative metabolomic technologies and their deployment in breeding for stress resistance.

Phospholipases C and D and Their Role in Biotic and Abiotic Stresses

Plants, as sessile organisms, have adapted a fine sensing system to monitor environmental changes, therefore allowing the regulation of their responses. As the interaction between plants and environmental changes begins at the surface, these changes are detected by components in the plasma membrane, where a molecule receptor generates a lipid signaling cascade via enzymes, such as phospholipases (PLs). Phospholipids are the key structural components of plasma membranes and signaling cascades. They exist in a wide range of species and in different proportions, with conversion processes that involve hydrophilic enzymes, such as phospholipase-C (PLC), phospholipase-D (PLD), and phospholipase-A (PLA). Hence, it is suggested that PLC and PLD are highly conserved, compared to their homologous genes, and have formed clusters during their adaptive history. Additionally, they generate responses to different functions in accordance with their protein structure, which should be reflected in specific signal transduction responses to environmental stress conditions, including innate immune responses. This review summarizes the phospholipid systems associated with signaling pathways and the innate immune response.