Nonspecific phospholipase C NPC4 promotes responses to abscisic acid and tolerance to hyperosmotic stress in Arabidopsis

Phosphatidic acid signaling in modulating plant reproduction and architecture

Phosphatidic acid (PA) is an important class of signaling lipids involved in various biological processes in plants. Functional characterization of mutants of PA-metabolizing enzymes, combined with lipidomics and protein-lipid interaction analyses, has revealed the key role of PA signaling in plant responses to biotic and abiotic stresses. Moreover, PA and its metabolizing enzymes influence several reproductive processes, including gametogenesis, pollen tube growth, self-incompatibility, haploid embryo formation, embryogenesis, and seed development. They also play a significant role in shaping plant reproductive and root architecture. Recent studies have shed light on the diverse mechanisms of PA's action, though much remains to be elucidated. Here, we summarize recent advances in the study of PA and its metabolizing enzymes, emphasizing their roles in plant sexual reproduction and architecture. We also explore potential mechanisms underlying PA's functions and discuss future research directions.

The combination of hyperspectral imaging, untargeted metabolomics and lipidomics highlights a coordinated stress-related biochemical reprogramming triggered by polyethylene nanoparticles in lettuce

Polyethylene nanoplastics (NPs) are widely diffused in terrestrial environments, including soil ecosystems, but the stress mechanisms in plants are not well understood. This study aimed to investigate the effects of two increasing concentrations of NPs (20 and 200 mg kg-1 of soil) in lettuce. To this aim, high-throughput hyperspectral imaging was combined with metabolomics, covering both primary (using NMR) and secondary metabolism (using LC-HRMS), along with lipidomics profiling (using ion-mobility-LC-HRMS) and plant performance. Hyperspectral imaging highlighted a reduced plant growth pattern. Several vegetative indexes indicated plant toxicity, with 20 mg kg-1 NPs significantly decreasing lettuce density and vegetation health (as indicated by NDVI and plant senescence reflectance indexes). Consistently, photosynthetic activity also decreased. At the biochemical level, metabolomics and lipidomics pointed out a multi-layered broad biochemical reprogramming of primary and secondary metabolism involving a decrease in sterols, sphingolipids, glycolipids, and glycerophospholipids in response to NPs. The reduction in phosphatidylinositol coincided with an accumulation of diacylglycerols (DAG), suggesting the activation of the phospholipase C lipid signaling pathway. Moreover, nanoplastic treatments down-modulated different biosynthetic pathways, particularly those involved in N-containing compounds and phenylpropanoids. Our mechanistic basis of NPs stress in plants will contribute to a better understanding of their environmental impact.

Anionic phospholipid-mediated transmembrane transport and intracellular membrane trafficking in plant cells

Cellular membranes primarily consist of proteins and lipids. These proteins perform cellular functions such as metabolic regulation, environmental and hormonal signal sensing, and nutrient transport. There is increasing experimental evidence that certain lipids, particularly anionic phospholipids, can act as signaling molecules. Specific examples of functional regulation by anionic phospholipids in plant cells have been reported for transporters, channels, and even receptors. By regulating the structure and activity of membrane-integral proteins, these phospholipids mediate the transport of phytohormones and ions, and elicit physiological responses to developmental and environmental cues. Phospholipids also control membrane protein abundance and lipid composition and abundance by facilitating vesicular trafficking. In this review, we discuss recent research that elucidates the mechanisms by which membrane-integral transporters and channels are controlled via phospholipid signaling, as well as the regulation of membrane protein accumulation by phospholipids through coordinated removal, recycling, and degradation processes.

Non-specific phospholipase C3 is involved in endoplasmic reticulum stress tolerance in Arabidopsis

Non-specific phospholipase C (NPC) is an emerging family of lipolytic enzymes unique to plants and bacteria that play crucial roles in growth and stress responses. Among six copies of NPC isoforms found in Arabidopsis, the role of NPC3 remains elusive to date. Here, we show that NPC3 is a functional non-specific phospholipase C involved in tolerance to tunicamycin (TM)-induced endoplasmic reticulum (ER) stress through the synthesis of phosphocholine (PCho), a reaction product of NPC3. The npc3 mutant exhibited reduced sensitivity to TM treatment. Recombinant NPC3 possessed pronounced phospholipase C activity that hydrolyses phosphatidylcholine (PC). The hyposensitivity of npc3 to TM treatment was complemented by exogenous PCho, suggesting that NPC3-catalysed PCho production is involved in TM-induced ER stress tolerance. NPC3 was localized at the ER and was predominantly expressed in the roots, and it was further induced by TM-induced ER stress. Intriguingly, npc3 mutants showed a markedly reduced PCho content in shoots under ER stress. Our results indicate that ER stress induces NPC3 to produce PCho, which is involved in TM-induced ER stress tolerance.

Non-specific Phospholipase C4 Improves Phosphorus Remobilization From Old to Young Leaves in Camelina

Camelina sativa is regarded as a low-input oilseed crop for versatile food, biofuels and industrial applications with potential production on marginal lands, whereas phosphate (Pi) deficiency greatly reduces camelina seed production. To improve camelina resilience to low P conditions, here we overexpressed the Pi deficiency-induced non-specific phospholipase C4 (NPC4) to test its effect on camelina seed production under different levels of Pi availability. NPC4-overexpressing (OE) plants displayed increased seed yield and oil production, with a greater magnitude of increases under Pi-deficient than Pi-sufficient conditions. NPC4-OE camelina had a higher level of total P and free Pi in young leaves but a lower level in old leaves than in wild-type plants. More Pi was moved from old leaves to young leaves in NPC4-OE than in wild-type plants. NPC4-OE increased the expression of Pi transporter genes, and the increase was greater in old leaves and under Pi-deficient conditions. These data indicate that NPC4 improves camelina growth by promoting Pi remobilization from old to young tissues, revealing a mechanism by which NPC4 mediates plant response to Pi deficiency.

Phospholipase-mediated phosphate recycling during plant leaf senescence

BACKGROUND

Phosphorus is a macronutrient necessary for plant growth and development and its availability and efficient use affect crop yields. Leaves are the largest tissue that uses phosphorus in plants, and membrane phospholipids are the main source of cellular phosphorus usage.

RESULTS

Here we identify a key process for plant cellular phosphorus recycling mediated by membrane phospholipid hydrolysis during leaf senescence. Our results indicate that over 90% of lipid phosphorus, accounting for more than one-third of total cellular phosphorus, is recycled from senescent leaves before falling off the plants. Nonspecific phospholipase C4 (NPC4) and phospholipase Dζ2 (PLDζ2) are highly induced during leaf senescence, and knockouts of PLDζ2 and NPC4 decrease the loss of membrane phospholipids and delay leaf senescence. Conversely, overexpression of PLDζ2 and NPC4 accelerates the loss of phospholipids and leaf senescence, promoting phosphorus remobilization from senescent leaves to young tissues and plant growth. We also show that this phosphorus recycling process in senescent leaves mediated by membrane phospholipid hydrolysis is conserved in plants.

CONCLUSIONS

These results indicate that PLDζ2- and NPC4-mediated membrane phospholipid hydrolysis promotes phosphorus remobilization from senescent leaves to growing tissues and that the phospholipid hydrolysis-mediated phosphorus recycling improves phosphorus use efficiency in plants.

Nonspecific phospholipases C3 and C4 interact with PIN-FORMED2 to regulate growth and tropic responses in Arabidopsis

The dynamic changes in membrane phospholipids affect membrane biophysical properties and cell signaling, thereby influencing numerous biological processes. Nonspecific phospholipase C (NPC) enzymes hydrolyze common phospholipids to release diacylglycerol (DAG), which is converted to phosphatidic acid (PA) and other lipids. In this study, 2 Arabidopsis (Arabidopsis thaliana) tandemly arrayed genes, NPC3 and NPC4, were identified as critical factors modulating auxin-controlled plant growth and tropic responses. Moreover, NPC3 and NPC4 were shown to interact with the auxin efflux transporter PIN-FORMED2 (PIN2). The loss of NPC3 and NPC4 enhanced the endocytosis and vacuolar degradation of PIN2, which disrupted auxin gradients and slowed gravitropic and halotropic responses. Furthermore, auxin-triggered activation of NPC3 and NPC4 is required for the asymmetric PA distribution that controls PIN2 trafficking dynamics and auxin-dependent tropic responses. Collectively, our study reveals an NPC-derived PA signaling pathway in Arabidopsis auxin fluxes that is essential for fine-tuning the balance between root growth and environmental responses.

Dissection of genetic architecture of nine hazardous component traits of mainstream smoke in tobacco (Nicotiana tabacum L.)

Tobacco (Nicotiana tabacum L.) use is the leading cause of preventable death, due to deleterious chemical components and smoke from tobacco products, and therefore reducing harmful chemical components in tobacco is one of the crucial tobacco breeding targets. However, due to complexity of tobacco smoke and unavailability of high-density genetic maps, the genetic architecture of representative hazardous smoke has not been fully dissected. The present study aimed to explore the genetic architecture of nine hazardous component traits of mainstream smoke through QTL mapping using 271 recombinant inbred lines (RILs) derived from K326 and Y3 in multiple environments. The analysis of genotype and genotype by environment interaction (GE) revealed substantially greater heritability over 95% contributed mostly by GE interaction effects. We also observed strong genetic correlations among most studied hazardous smoke traits, with the highest correlation coefficient of 0.84 between carbon monoxide and crotonaldehyde. Based on a published high-density genetic map, a total of 19 novel QTLs were detected for eight traits using a full QTL model, of which 17 QTLs showed significant additive effects, six showed significant additive-by-environment interaction effects, and one pair showed significant epistasis-by-environment interaction effect. Bioinformatics analysis of sequence in QTL region predicted six genes as candidates for four traits, of which Nt21g04598.1, Nt21g04600.1, and Nt21g04601.1 had pleiotropic effects on PHE and TAR.

Lipid phosphorylation by a diacylglycerol kinase suppresses ABA biosynthesis to regulate plant stress responses

Lipid phosphorylation by diacylglycerol kinase (DGK) that produces phosphatidic acid (PA) plays important roles in various biological processes, including stress responses, but the underlying mechanisms remain elusive. Here, we show that DGK5 and its lipid product PA suppress ABA biosynthesis by interacting with ABA-DEFICIENT 2 (ABA2), a key ABA biosynthesis enzyme, to negatively modulate plant response to abiotic stress tested in Arabidopsis thaliana. Loss of DGK5 function rendered plants less damaged, whereas overexpression (OE) of DGK5 enhanced plant damage to water and salt stress. The dgk5 mutant plants exhibited decreased total cellular and nuclear levels of PA with increased levels of diacylglycerol, whereas DGK5-OE plants displayed the opposite effect. Interestingly, we found that both DGK5 and PA bind to the ABA-synthesizing enzyme ABA2 and suppress its enzymatic activity. Consistently, the dgk5 mutant plants exhibited increased levels of ABA, while DGK5-OE plants showed reduced ABA levels. In addition, we showed that both DGK5 and ABA2 are detected in and outside the nuclei, and loss of DGK5 function decreased the nuclear association of ABA2. We found that both DGK5 activity and PA promote nuclear association of ABA2. Taken together, these results indicate that both DGK5 and PA interact with ABA2 to inhibit its enzymatic activity and promote its nuclear sequestration, thereby suppressing ABA production in response to abiotic stress. Our study reveals a sophisticated mechanism by which DGK5 and PA regulate plant stress responses.

Phosphatidic acid signaling and function in nuclei

Membrane lipidomes are dynamic and their changes generate lipid mediators affecting various biological processes. Phosphatidic acid (PA) has emerged as an important class of lipid mediators involved in a wide range of cellular and physiological responses in plants, animals, and microbes. The regulatory functions of PA have been studied primarily outside the nuclei, but an increasing number of recent studies indicates that some of the PA effects result from its action in nuclei. PA levels in nuclei are dynamic in response to stimuli. Changes in nuclear PA levels can result from activities of enzymes associated with nuclei and/or from movements of PA generated extranuclearly. PA has also been found to interact with proteins involved in nuclear functions, such as transcription factors and proteins undergoing nuclear translocation in response to stimuli. The nuclear action of PA affects various aspects of plant growth, development, and response to stress and environmental changes.

Degradation of glycosylinositol phosphoceramide during plant tissue homogenization

A convenient method for the determination of plant sphingolipids (glycosylinositol phosphoceramide, GIPC; glucosylceramide, GluCer; phytoceramide 1-phosphate, PC1P and phytoceramide, PCer) was developed. This method includes the extraction of lipids using 1-butanol, alkali hydrolysis with methylamine and separation by TLC. The amounts of sphingolipids in the sample were determined based on the relative intensities of standard sphingolipids visualized by primulin/UV on TLC. Using this method, we found that almost all GIPCs were degraded in response to tissue homogenization in cruciferous plants (cabbage, broccoli and Arabidopsis thaliana). The decrease in GIPCs was compensated for by increases in PC1P and PCer, indicating that GIPC was degraded by hydrolysis at the D and C positions of GIPC, respectively. In carrot roots and leaves, most of GIPC degradation was compensated for by an increase in PCer. In rice roots, the decrease in GIPCs was not fully explained by the increases in PC1P and PCer, indicating that enzymes other than phospholipase C and D activities operated. As the visualization of lipids on TLC is useful for detecting the appearance or disappearance of lipids, this method will be available for the characterization of metabolism of sphingolipids in plants.

Non-specific phospholipase C4 hydrolyzes phosphosphingolipids and phosphoglycerolipids and promotes rapeseed growth and yield

Phosphorus is a major nutrient vital for plant growth and development, with a substantial amount of cellular phosphorus being used for the biosynthesis of membrane phospholipids. Here, we report that NON-SPECIFIC PHOSPHOLIPASE C4 (NPC4) in rapeseed (Brassica napus) releases phosphate from phospholipids to promote growth and seed yield, as plants with altered NPC4 levels showed significant changes in seed production under different phosphate conditions. Clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9 (Cas9)-mediated knockout of BnaNPC4 led to elevated accumulation of phospholipids and decreased growth, whereas overexpression (OE) of BnaNPC4 resulted in lower phospholipid contents and increased plant growth and seed production. We demonstrate that BnaNPC4 hydrolyzes phosphosphingolipids and phosphoglycerolipids in vitro, and plants with altered BnaNPC4 function displayed changes in their sphingolipid and glycerolipid contents in roots, with a greater change in glycerolipids than sphingolipids in leaves, particularly under phosphate deficiency conditions. In addition, BnaNPC4-OE plants led to the upregulation of genes involved in lipid metabolism, phosphate release, and phosphate transport and an increase in free inorganic phosphate in leaves. These results indicate that BnaNPC4 hydrolyzes phosphosphingolipids and phosphoglycerolipids in rapeseed to enhance phosphate release from membrane phospholipids and promote growth and seed production.

Quantitative Time-Course Analysis of Osmotic and Salt Stress in Arabidopsis thaliana Using Short Gradient Multi-CV FAIMSpro BoxCar DIA

A major limitation when undertaking quantitative proteomic time-course experimentation is the tradeoff between depth-of-analysis and speed-of-analysis. In high complexity and high dynamic range sample types, such as plant extracts, balance between resolution and time is especially apparent. To address this, we evaluate multiple compensation voltage (CV) high field asymmetric waveform ion mobility spectrometry (FAIMSpro) settings using the latest label-free single-shot Orbitrap-based DIA acquisition workflows for their ability to deeply quantify the Arabidopsis thaliana seedling proteome. Using a BoxCarDIA acquisition workflow with a -30 -50 -70 CV FAIMSpro setting, we were able to consistently quantify >5000 Arabidopsis seedling proteins over a 21-min gradient, facilitating the analysis of ∼42 samples per day. Utilizing this acquisition approach, we then quantified proteome-level changes occurring in Arabidopsis seedling shoots and roots over 24 h of salt and osmotic stress, to identify early and late stress response proteins and reveal stress response overlaps. Here, we successfully quantify >6400 shoot and >8500 root protein groups, respectively, quantifying nearly ∼9700 unique protein groups in total across the study. Collectively, we pioneer a short gradient, multi-CV FAIMSpro BoxCarDIA acquisition workflow that represents an exciting new analysis approach for undertaking quantitative proteomic time-course experimentation in plants.

Comparative transcriptome analysis of grafting to improve chilling tolerance of cucumber

Grafting with pumpkin as rootstock could improve chilling tolerance of cucumber; however, the underlying mechanism of grafting-induced chilling tolerance remains unclear. Here, we analyzed the difference of physiological and transcriptional level between own-rooted (Cs/Cs) and hetero-grafted (Cs/Cm) cucumber seedlings under chilling stress. The results showed that grafting with pumpkin significantly alleviated the chilling injury as evidenced by slightly symptoms, lower contents of electrolyte leakage (EL), malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O2-) and higher relative water content in Cs/Cm seedlings compared with Cs/Cs seedlings under chilling stress. RNA-seq data showed that grafting induced more DGEs at 8 °C/5 °C compared with 25 °C/18 °C. In accordance with the increase of the activities of antioxidant enzymes (SOD, POD, CAT, APX), grafting upregulated the expression of the regulated redox-related genes such as GST, SOD, and APX. Moreover, grafting increased the expression of genes participated in central carbon metabolism to promote the conversion and decomposition of sugar, which provided more energy for the growth of Cs/Cm seedlings under chilling stress. In addition, grafting regulated the genes involved in the intracellular signal transduction pathways such as calcium signal (CAML, CML, and CDPK) and inositol phospholipid signal (PLC), as well as changed the gene expression of plant hormone signal transduction pathways (ARF, GAI, ABF, and PYR/PYL). These results provide a physiological and transcriptional basis for the molecular mechanism of grafting-induced chilling tolerance of cucumber seedlings.

Phospholipase C: Diverse functions in plant biotic stress resistance and fungal pathogenicity

Phospholipase C (PLC) generates various second messenger molecules and mediates phospholipid hydrolysis. In recent years, the important roles of plant and fungal PLC in disease resistance and pathogenicity, respectively, have been determined. However, the roles of PLC in plants and fungi are unintegrated and relevant literature is disorganized. This makes it difficult for researchers to implement PLC-based strategies to improve disease resistance in plants. In this comprehensive review, we summarize the structure, classification, and phylogeny of the PLCs involved in plant biotic stress resistance and fungal pathogenicity. PLCs can be divided into two groups, nonspecific PLC (NPC) and phosphatidylinositol-specific PLC (PI-PLC), which present marked differences in phylogenetic evolution. The products of PLC genes in fungi play significant roles in physiological activity and pathogenesis, whereas those encoded by plant PLC genes mediate the immune response to fungi. This review provides a perspective for the future control of plant fungal diseases.

Overexpression of OsERF106MZ promotes parental root growth in rice seedlings by relieving the ABA-mediated inhibition of root growth under salinity stress conditions

BACKGROUND

Roots are essential for plant growth and have a variety of functions, such as anchoring the plant to the ground, absorbing water and nutrients from the soil, and sensing abiotic stresses, among others. OsERF106MZ is a salinity-induced gene that is expressed in germinating seeds and rice seedling roots. However, the roles of OsERF106MZ in root growth remain poorly understood.

RESULTS

Histochemical staining to examine β-glucuronidase (GUS) activity in transgenic rice seedlings harboring OsERF106MZp::GUS indicated that OsERF106MZ is mainly expressed in the root exodermis, sclerenchyma layer, and vascular system. OsERF106MZ overexpression in rice seedlings leads to an increase in primary root (PR) length. The phytohormone abscisic acid (ABA) is thought to act as a hidden architect of root system structure. The expression of the ABA biosynthetic gene OsAO3 is downregulated in OsERF106MZ-overexpressing roots under normal conditions, while the expression of OsNPC3, an AtNPC4 homolog involved in ABA sensitivity, is reduced in OsERF106MZ-overexpressing roots under both normal and NaCl-treated conditions. Under normal conditions, OsERF106MZ-overexpressing roots show a significantly reduced ABA level; moreover, exogenous application of 1.0 µM ABA can suppress OsERF106MZ-mediated root growth promotion. Additionally, OsERF106MZ-overexpressing roots display less sensitivity to ABA-mediated root growth inhibition when treated with 5.0 µM ABA under normal conditions or exposed to NaCl-treated conditions. Furthermore, chromatin immunoprecipitation (ChIP)-qPCR and luciferase (LUC) reporter assays showed that OsERF106MZ can bind directly to the sequence containing the GCC box in the promoter region of the OsAO3 gene and repress the expression of OsAO3.

CONCLUSIONS

OsERF106MZ may play a role in maintaining root growth for resource uptake when rice seeds germinate under salinity stress by alleviating ABA-mediated root growth inhibition.

Biological insights from multi-omics analysis strategies: Complex pleotropic effects associated with autophagy

Research strategies that combine molecular data from multiple levels of genome expression (i.e., multi-omics data), often referred to as a systems biology strategy, has been advocated as a route to discovering gene functions. In this study we conducted an evaluation of this strategy by combining lipidomics, metabolite mass-spectral imaging and transcriptomics data from leaves and roots in response to mutations in two AuTophaGy-related (ATG) genes of Arabidopsis. Autophagy is an essential cellular process that degrades and recycles macromolecules and organelles, and this process is blocked in the atg7 and atg9 mutants that were the focus of this study. Specifically, we quantified abundances of ~100 lipids and imaged the cellular locations of ~15 lipid molecular species and the relative abundance of ~26,000 transcripts from leaf and root tissues of WT, atg7 and atg9 mutant plants, grown either in normal (nitrogen-replete) and autophagy-inducing conditions (nitrogen-deficient). The multi-omics data enabled detailed molecular depiction of the effect of each mutation, and a comprehensive physiological model to explain the consequence of these genetic and environmental changes in autophagy is greatly facilitated by the a priori knowledge of the exact biochemical function of the ATG7 and ATG9 proteins.

Insights into the mechanism of phospholipid hydrolysis by plant non-specific phospholipase C

Non-specific phospholipase C (NPC) hydrolyzes major membrane phospholipids to release diacylglycerol (DAG), a potent lipid-derived messenger regulating cell functions. Despite extensive studies on NPCs reveal their fundamental roles in plant growth and development, the mechanistic understanding of phospholipid-hydrolyzing by NPCs, remains largely unknown. Here we report the crystal structure of Arabidopsis NPC4 at a resolution of 2.1 Å. NPC4 is divided into a phosphoesterase domain (PD) and a C-terminal domain (CTD), and is structurally distinct from other characterized phospholipases. The previously uncharacterized CTD is indispensable for the full activity of NPC4. Mechanistically, CTD contributes NPC4 activity mainly via CTD^α1-PD interaction, which ultimately stabilizes the catalytic pocket in PD. Together with a series of structure-guided biochemical studies, our work elucidates the structural basis and provides molecular mechanism of phospholipid hydrolysis by NPC4, and adds new insights into the members of phospholipase family.

Heterologous expression of the TaPI-PLC1-2B gene enhanced drought and salt tolerance in transgenic rice seedlings

Drought and salt stress are important factors that affect plant growth and development and cause crop yield reductions worldwide. Phospholipase C is a class of enzymes that can hydrolyze phospholipids, and it has been shown to play an important role in plant growth regulation and stress response. We used rice as a model to investigate the function of the wheat TaPI-PLC1-2B gene in salt and drought tolerance. For this purpose, we heterologously expressed the TaPI-PLC1-2B gene in rice and studied the transcriptional differences in transgenic and wide-type rice plants in the presence and absence of drought and salt stress. Our results showed that 2130 and 1759 genes expressed differentially in the TaPI-PLC1-2B overexpression rice line under salt and drought stress, respectively. Gene ontology enrichment results showed that differentially expressed genes (DEGs) were significantly enriched in cellular process, metabolic process, stimulus-response, cell, organelle, catalytic activity, and other functional processes under salt and drought stress. In addition, the Kyoto Encyclopedia of Genes and Genomes pathway analysis showed DEG enrichment in plant-pathogen interaction, phosphoinositol, plant hormones, and other signaling pathways under the two stress treatments. Furthermore, the chromosomal localization of salt and drought stress-responsive DEGs showed a clear distribution pattern on specific rice chromosomes. For instance, the greatest number of drought stress-responsive genes mapped to rice chromosomes 1 and 6. The current analysis has built the basis for future explorations to decipher the TaPI-PLC1-2B-mediated plant stress response mechanism in the relatively challenging wheat system.

Nonspecific phospholipase C3 of radish has phospholipase D activity towards glycosylinositol phosphoceramide

Glycosylinositol phosphoceramide (GIPC) is a major sphingolipid in the plasma membranes of plants. Previously, we found an enzyme activity that produces phytoceramide 1-phosphate (PC1P) by hydrolysis of the D position of GIPC in cabbage and named this activity as GIPC-phospholipase D (PLD). Here, we purified GIPC-PLD by sequential chromatography from radish roots. Peptide mass fingerprinting analysis revealed that the potential candidate for GIPC-PLD protein was nonspecific phospholipase C3 (NPC3), which has not been characterized as a PLD. The recombinant NPC3 protein obtained by heterologous expression system in Escherichia coli produced PC1P from GIPC and showed essentially the same enzymatic properties as those we characterized as GIPC-PLD in cabbage, radish and Arabidopsis thaliana. From these results, we conclude that NPC3 is one of the enzymes that degrade GIPC.

Advances in Plant Lipid Metabolism Responses to Phosphate Scarcity

Low phosphate (Pi) availability in soils severely limits crop growth and production. Plants have evolved to have numerous physiological and molecular adaptive mechanisms to cope with Pi starvation. The release of Pi from membrane phospholipids is considered to improve plant phosphorus (P) utilization efficiency in response to Pi starvation and accompanies membrane lipid remodeling. In this review, we summarize recent discoveries related to this topic and the molecular basis of membrane phospholipid alteration and triacylglycerol metabolism in response to Pi depletion in plants at different subcellular levels. These findings will help to further elucidate the molecular mechanisms underlying plant adaptation to Pi starvation and thus help to develop crop cultivars with high P utilization efficiency.

The Examination of the Role of Rice Lysophosphatidic Acid Acyltransferase 2 in Response to Salt and Drought Stresses

Phosphatidic acid (PA) is an important signal molecule in various biological processes including osmotic stress. Lysophosphatidic acid acyltransferase (LPAT) acylates the sn-2 position of the glycerol backbone of lysophosphatidic acid (LPA) to produce PA. The role of LPAT2 and its PA in osmotic stress response remains elusive in plants. Here we showed that LPAT2-derived PA is important for salt and drought stress tolerance in rice. Rice LPAT2 was localized to the endoplasmic reticulum (ER) to catalyze the PA synthesis. The LPAT2 transcript was induced by osmotic stress such as high salinity and water deficit. To reveal its role in osmotic stress response, an LPAT2 knockdown mutant, designated lpat2, was isolated from rice, which contained a reduced PA level relative to wild type (WT) plants under salt stress and water deficit. The lpat2 mutant was more susceptible to osmotic stress and less sensitive to abscisic acid (ABA) than that of WT, which was recovered by either PA supplementation or genetic LPAT2 complementation. Moreover, suppressed LPAT2 also led to a large number of differentially expressed genes (DEGs) involved in diverse processes, particularly, in ABA response, kinase signaling, and ion homeostasis in response to salt stress. Together, LPAT2-produced PA plays a positive role in osmotic tolerance through mediating ABA response, which leads to transcriptional alteration of genes related to ABA response, protein kinase signaling, and ion homeostasis.

Agrobacterium-mediated cassava transformation for the Asian elite variety KU50

Cassava genetic transformation has mostly been reported for African cassava varieties, but not for Asian varieties. This is the first report of cassava transformation in Asian elite varieties using friable embryogenic calli. Agrobacterium-mediated cassava transformation via friable embryogenic calli (FEC) has enabled the robust production of transgenic cassava. So far, mostly the model cassava variety 60444 and African varieties have been transformed because of their good production and regeneration from embryogenic tissues. It is important to develop transformation methods for elite Asian cassava varieties to meet the changing needs in one of the world's major cassava production areas. However, a suitable transformation method for the Asian elite variety Kasetsart 50 (KU50) has not been developed. Here, we report a transformation method for KU50, the cultivar with the highest planting area in Thailand and Vietnam. In cassava transformation, the preparation of FEC as the target tissue for transgene integration is a key step. FEC induction from KU50 was improved by using media with reduced nutrients and excess vitamin B1, and somatic embryo and plant regeneration optimized by manipulation of naphthalene acetic acid (NAA), and benzylamino purine (BAP). The transformation efficiency for KU50 was 22%, approximately half that of 60444 at 45%. Transcriptome analysis indicated that the expression of genes related to cell-wall loosening was upregulated in FEC from KU50 compared with 60444, indicating that cell-wall production and assembly were disproportionate in the Asian variety. The transformation system for KU50 reported here will contribute to the molecular breeding of cassava plants for Asian farmers using transgenic and genome-editing technologies.

The functions of phospholipases and their hydrolysis products in plant growth, development and stress responses

Cell membranes are the initial site of stimulus perception from environment and phospholipids are the basic and important components of cell membranes. Phospholipases hydrolyze membrane lipids to generate various cellular mediators. These phospholipase-derived products, such as diacylglycerol, phosphatidic acid, inositol phosphates, lysophopsholipids, and free fatty acids, act as second messengers, playing vital roles in signal transduction during plant growth, development, and stress responses. This review focuses on the structure, substrate specificities, reaction requirements, and acting mechanism of several phospholipase families. It will discuss their functional significance in plant growth, development, and stress responses. In addition, it will highlight some critical knowledge gaps in the action mechanism, metabolic and signaling roles of these phospholipases and their products in the context of plant growth, development and stress responses.

Jasmonate-Dependent Response of the Flower Abscission Zone Cells to Drought in Yellow Lupine

Lipid membranes, as primary places of the perception of environmental stimuli, are a source of various oxygenated polyunsaturated fatty acids-oxylipins-functioning as modulators of many signal transduction pathways, e.g., phytohormonal. Among exogenous factors acting on plant cells, special attention is given to drought, especially in highly sensitive crop species, such as yellow lupine. Here, we used this species to analyze the contribution of lipid-related enzymes and lipid-derived plant hormones in drought-evoked events taking place in a specialized group of cells-the flower abscission zone (AZ)-which is responsible for organ detachment from the plant body. We revealed that water deficits in the soil causes lipid peroxidation in these cells and the upregulation of phospholipase D, lipoxygenase, and, concomitantly, jasmonic acid (JA) strongly accumulates in AZ tissue. Furthermore, we followed key steps in JA conjugation and signaling under stressful conditions by monitoring the level and tissue localization of enzyme providing JA derivatives (JASMONATE RESISTANT1) and the JA receptor (CORONATINE INSENSITIVE1). Collectively, drought-triggered AZ activation during the process of flower abscission is closely associated with the lipid modifications, leading to the formation of JA, its conjugation, and induction of signaling pathways.

Comparison of TLC, HPLC, and direct-infusion ESI-MS methods for the identification and quantification of diacylglycerol molecular species

Diacylglycerols (DAGs) are anabolic precursors to membrane lipid and storage triacylglycerol biosynthesis, metabolic intermediates of lipid catabolism, and potent cellular signaling molecules. The different DAG molecular species that accumulate over development or in different tissues reflect the changing aspects of cellular lipid metabolism. Consequently, an accurate determination of DAG molecular species in biological samples is essential to understand various metabolic processes and their diagnostic relevance. However, quantification of DAG molecular species in various biological samples represents a challenging task because of their low abundance, hydrophobicity, and instability. This chapter describes the most common chromatographic (TLC and HPLC) and mass spectrometry (MS) methods used to analyze DAG molecular species. In addition, we directly compared the three methods using DAG obtained by phospholipase C hydrolysis of phosphatidylcholine purified from a Nicotiana benthamiana leaf extract. We conclude that each method identified similar major molecular species, however, the exact levels of those varied mainly due to sensitivity of the technique, differences in sample preparation, and processing. This chapter provides three different methods to analyze DAG molecular species, and the discussion of the benefits and challenges of each technique will aid in choosing the right method for your analysis.

Characterization of the Glehnia littoralis Non-specific Phospholipase C Gene GlNPC3 and Its Involvement in the Salt Stress Response

Glehnia littoralis is a medicinal halophyte that inhabits sandy beaches and has high ecological and commercial value. However, the molecular mechanism of salt adaptation in G. littoralis remains largely unknown. Here, we cloned and identified a non-specific phospholipase C gene (GlNPC3) from G. littoralis, which conferred lipid-mediated signaling during the salt stress response. The expression of GlNPC3 was induced continuously by salt treatment. Overexpression of GlNPC3 in Arabidopsis thaliana increased salt tolerance compared to wild-type (WT) plants. GlNPC3-overexpressing plants had longer roots and higher fresh and dry masses under the salt treatment. The GlNPC3 expression pattern revealed that the gene was expressed in most G. littoralis tissues, particularly in roots. The subcellular localization of GlNPC3 was mainly at the plasma membrane, and partially at the tonoplast. GlNPC3 hydrolyzed common membrane phospholipids, such as phosphotidylserine (PS), phosphoethanolamine (PE), and phosphocholine (PC). In vitro enzymatic assay showed salt-induced total non-specific phospholipase C (NPC) activation in A. thaliana GlNPC3-overexpressing plants. Plant lipid profiling showed a significant change in the membrane-lipid composition of A. thaliana GlNPC3-overexpressing plants compared to WT after the salt treatment. Furthermore, downregulation of GlNPC3 expression by virus-induced gene silencing in G. littoralis reduced the expression levels of some stress-related genes, such as SnRK2, P5SC5, TPC1, and SOS1. Together, these results indicated that GlNPC3 and GlNPC3-mediated membrane lipid change played a positive role in the response of G. littoralis to a saline environment.

Emerging role of phospholipase C mediated lipid signaling in abiotic stress tolerance and development in plants

Environmental stimuli are primarily perceived at the plasma membrane. Stimuli perception leads to membrane disintegration and generation of molecules which trigger lipid signaling. In plants, lipid signaling regulates important biological functions however, the molecular mechanism involved is unclear. Phospholipases C (PLCs) are important lipid-modifying enzymes in eukaryotes. In animals, PLCs by hydrolyzing phospholipids, such as phosphatidylinositol-4,5-bisphosphate [PI(4,5)P₂] generate diacylglycerol (DAG) and inositol- 1,4,5-trisphosphate (IP₃). However, in plants their phosphorylated variants i.e., phosphatidic acid (PA) and inositol hexakisphosphate (IP₆) are proposed to mediate lipid signaling. Specific substrate preferences divide PLCs into phosphatidylinositol-PLC (PI-PLC) and non-specific PLCs (NPC). PLC activity is regulated by various cellular factors including, calcium (Ca²⁺) concentration, phospholipid substrate, and post-translational modifications. Both PI-PLCs and NPCs are implicated in plants' response to stresses and development. Emerging evidences show that PLCs regulate structural and developmental features, like stomata movement, microtubule organization, membrane remodelling and root development under abiotic stresses. Thus, crucial insights are provided into PLC mediated regulatory mechanism of abiotic stress responses in plants. In this review, we describe the structure and regulation of plant PLCs. In addition, cellular and physiological roles of PLCs in abiotic stresses, phosphorus deficiency, aluminium toxicity, pollen tube growth, and root development are discussed.

Phospholipids in Salt Stress Response

High salinity threatens crop production by harming plants and interfering with their development. Plant cells respond to salt stress in various ways, all of which involve multiple components such as proteins, peptides, lipids, sugars, and phytohormones. Phospholipids, important components of bio-membranes, are small amphoteric molecular compounds. These have attracted significant attention in recent years due to the regulatory effect they have on cellular activity. Over the past few decades, genetic and biochemical analyses have partly revealed that phospholipids regulate salt stress response by participating in salt stress signal transduction. In this review, we summarize the generation and metabolism of phospholipid phosphatidic acid (PA), phosphoinositides (PIs), phosphatidylserine (PS), phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), as well as the regulatory role each phospholipid plays in the salt stress response. We also discuss the possible regulatory role based on how they act during other cellular activities.

Rice Non-Specific Phospholipase C6 Is Involved in Mesocotyl Elongation

Mesocotyl elongation of rice is crucial for seedlings pushing out of deep soil. The underlying mechanisms of phospholipid signaling in mesocotyl growth of rice are elusive. Here we report that the rice non-specific phospholipase C6 (OsNPC6) is involved in mesocotyl elongation. Our results indicated that all five OsNPCs (OsNPC1, OsNPC2, OsNPC3, OsNPC4 and OsNPC6) hydrolyzed the substrate phosphatidylcholine to phosphocholine (PCho), and all of them showed plasma membrane localization. Overexpression (OE) of OsNPC6 produced plants with shorter mesocotyls compared to those of Nipponbare and npc6 mutants. Although the mesocotyl growth of npc6 mutants was not much affected without gibberellic acid (GA)3, it was obviously elongated by treatment with GA. Upon GA3 treatment, SLENDER RICE1 (SLR1), the DELLA protein of GA signaling, was drastically increased in OE plants; by contrast, the level of SLR1 was found decreased in npc6 mutants. The GA-enhanced mesocotyl elongation and the GA-impaired SLR1 level in npc6 mutants were attenuated by the supplementation of PCho. Further analysis indicated that the GA-induced expression of phospho-base N-methyltransferase 1 in npc6 mutants was significantly weakened by the addition of PCho. In summary, our results suggest that OsNPC6 is involved in mesocotyl development via modulation of PCho in rice.

Phospholipase Dα6 and phosphatidic acid regulate gibberellin signaling in rice

Phospholipase D (PLD) hydrolyzes membrane lipids to produce phosphatidic acid (PA), a lipid mediator involved in various cellular and physiological processes. Here, we show that PLDα6 and PA regulate the distribution of GIBBERELLIN (GA)-INSENSITIVE DWARF1 (GID1), a soluble gibberellin receptor in rice. PLDα6-knockout (KO) plants display less sensitivity to GA than WT, and PA restores the mutant to a normal GA response. PA binds to GID1, as documented by liposome binding, fat immunoblotting, and surface plasmon resonance. Arginines 79 and 82 of GID1 are two key amino acid residues required for PA binding and also for GID1's nuclear localization. The loss of PLDα6 impedes GA-induced nuclear localization of GID1. In addition, PLDα6-KO plants attenuated GA-induced degradation of the DELLA protein SLENDER RICE1 (SLR1). These data suggest that PLDα6 and PA positively mediate GA signaling in rice via PA binding to GID1 and promotion of its nuclear translocation.

Synaptotagmins at the endoplasmic reticulum-plasma membrane contact sites maintain diacylglycerol homeostasis during abiotic stress

Endoplasmic reticulum-plasma membrane contact sites (ER-PM CS) play fundamental roles in all eukaryotic cells. Arabidopsis thaliana mutants lacking the ER-PM protein tether synaptotagmin1 (SYT1) exhibit decreased PM integrity under multiple abiotic stresses, such as freezing, high salt, osmotic stress, and mechanical damage. Here, we show that, together with SYT1, the stress-induced SYT3 is an ER-PM tether that also functions in maintaining PM integrity. The ER-PM CS localization of SYT1 and SYT3 is dependent on PM phosphatidylinositol-4-phosphate and is regulated by abiotic stress. Lipidomic analysis revealed that cold stress increased the accumulation of diacylglycerol at the PM in a syt1/3 double mutant relative to wild-type while the levels of most glycerolipid species remain unchanged. In addition, the SYT1-green fluorescent protein fusion preferentially binds diacylglycerol in vivo with little affinity for polar glycerolipids. Our work uncovers a SYT-dependent mechanism of stress adaptation counteracting the detrimental accumulation of diacylglycerol at the PM produced during episodes of abiotic stress.

Plant phospholipase D: novel structure, regulatory mechanism, and multifaceted functions with biotechnological application

Phospholipases D (PLDs) are important membrane lipid-modifying enzymes in eukaryotes. Phosphatidic acid, the product of PLD activity, is a vital signaling molecule. PLD-mediated lipid signaling has been the subject of extensive research leading to discovery of its crystal structure. PLDs are involved in the pathophysiology of several human diseases, therefore, viewed as promising targets for drug design. The availability of a eukaryotic PLD crystal structure will encourage PLD targeted drug designing. PLDs have been implicated in plants response to biotic and abiotic stresses. However, the molecular mechanism of response is not clear. Recently, several novel findings have shown that PLD mediated modulation of structural and developmental processes, such as: stomata movement, root growth and microtubule organization are crucial for plants adaptation to environmental stresses. Involvement of PLDs in regulating membrane remodeling, auxin mediated alteration of root system architecture and nutrient uptake to combat nitrogen and phosphorus deficiencies and magnesium toxicity is established. PLDs via vesicle trafficking modulate cytoskeleton and exocytosis to regulate self-incompatibility (SI) signaling in flowering plants, thereby contributes to plants hybrid vigor and diversity. In addition, the important role of PLDs has been recognized in biotechnologically important functions, including oil/TAG synthesis and maintenance of seed quality. In this review, we describe the crystal structure of a plant PLD and discuss the molecular mechanism of catalysis and activity regulation. Further, the role of PLDs in regulating plant development under biotic and abiotic stresses, nitrogen and phosphorus deficiency, magnesium ion toxicity, SI signaling and pollen tube growth and in important biotechnological applications has been discussed.

Phosphoinositide-specific phospholipase C gene involved in heat and drought tolerance in wheat (Triticum aestivum L.)

BACKGROUND

Phosphoinositide-specific phospholipase C proteins mediate environmental stress responses in many plants. However, the potential of PI-PLC genes involved with abiotic stress tolerance in wheat remains un-explored.

OBJECTIVE

To study TaPLC1 genetic relation with wheat drought and heat resistance.

METHODS

The seedlings were treated with PI-PLC inhibitor U73122 at the single leaf stage. The seedlings were treated with drought and heat stress at the two leaf stage, and some physiological indexes and the expression profile of TaPLC1 gene were determined. And the TaPLC1 overexpression vector was transferred to Arabidopsis and selected to T3 generation for drought and heat stress treatment.

RESULTS

After 4 h of drought and heat stress, the SOD activity, MDA and soluble sugar content of the two cultivars with inhibitor were higher than those without inhibitor, the chlorophyll content decreased. CS seedlings showed significant wilting phenomenon, and TAM107 showed slight wilting. After the elimination of drought and heat stress, all seedling wilting gradually recovered, while the leaf tips of the two varieties treated with inhibitors began to wilt and turn yellow, which was more significant 5 days after the drought and heat stress, while the degree of spring wilting and yellow in CS was earlier than that in TAM107. The expression patterns of TaPLC1 gene were different in the two cultivars, but the expression levels reached the maximum at 30 min of heat stress. The change of TaPLC1 expression in TAM107 without inhibitor treatment was significantly greater than that in CS. The expression level of TaPLC1 in the two cultivars under stress was significantly different between the two cultivars treated with inhibitor and untreated, and was lower than that of the normal plants under normal conditions. These results indicated that inhibition of TaPLC1 gene expression could enhance the sensitivity of seedlings to stress. In Arabidopsis, the root lengths of transgenic and wild-type seedlings were shortened after drought stress treatment, but the root lengths of transgenic plants decreased slightly. And the expression of TaPLC1 gene was significantly increased after drought and heat stress. This indicated that overexpression of TaPLC1 improved drought resistance of Arabidopsis.

CONCLUSIONS

The results of this study suggest that TaPLC1 may be involved in the regulation mechanism of drought and heat stress in wheat.

Acylation of non-specific phospholipase C4 determines its function in plant response to phosphate deficiency

Non-specific phospholipase C (NPC) is involved in plant growth, development and stress responses. To elucidate the mechanism by which NPCs mediate cellular functions, here we show that NPC4 is S-acylated at the C terminus and that acylation determines its plasma membrane (PM) association and function. The acylation of NPC4 was detected using NPC4 isolated from Arabidopsis and reconstituted in vitro. The C-terminal Cys-533 was identified as the S-acylation residue, and the mutation of Cys-533 to Ala-533 in NPC4 (NPC4^C533A ) led to the loss of S-acylation and membrane association of NPC4. The knockout of NPC4 impeded the phosphate deficiency-induced decrease of the phosphosphingolipid glycosyl inositol phosphoryl ceramide (GIPC), but introducing NPC4^C533A to npc4-1 failed to complement this defect, thereby supporting the hypothesis that the non-acylated NPC4^C533A fails to hydrolyze GIPC during phosphate deprivation. Moreover, NPC4^C533A failed to complement the primary root growth in npc4-1 under stress. In addition, NPC4 in Brassica napus was S-acylated and mutation of the S-acylating cysteine residue of BnaC01.NPC4 led to the loss of S-acylation and its membrane association. Together, our results reveal that S-acylation of NPC4 in the C terminus is conserved and required for its membrane association, phosphosphingolipid hydrolysis and function in plant stress responses.

Nonspecific phospholipase C4 hydrolyzes phosphosphingolipids and sustains plant root growth during phosphate deficiency

Phosphate is a vital macronutrient for plant growth, and its availability in soil is critical for agricultural sustainability and productivity. A substantial amount of cellular phosphate is used to synthesize phospholipids for cell membranes. Here, we identify a key enzyme, nonspecific phospholipase C4 (NPC4) that is involved in phosphosphingolipid hydrolysis and remodeling in Arabidopsis during phosphate starvation. The level of glycosylinositolphosphorylceramide (GIPC), the most abundant sphingolipid in Arabidopsis thaliana, decreased upon phosphate starvation. NPC4 was highly induced by phosphate deficiency, and NPC4 knockouts in Arabidopsis decreased the loss of GIPC and impeded root growth during phosphate starvation. Enzymatic analysis showed that NPC4 hydrolyzed GIPC and displayed a higher activity toward GIPC as a substrate than toward the common glycerophospholipid phosphatidylcholine. NPC4 was associated with the plasma membrane lipid rafts in which GIPC is highly enriched. These results indicate that NPC4 uses GIPC as a substrate in planta and the NPC4-mediated sphingolipid remodeling plays a positive role in root growth in Arabidopsis response to phosphate deficiency.

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.

Plant Acyl-CoA-Binding Proteins-Their Lipid and Protein Interactors in Abiotic and Biotic Stresses

Plants are constantly exposed to environmental stresses during their growth and development. Owing to their immobility, plants possess stress-sensing abilities and adaptive responses to cope with the abiotic and biotic stresses caused by extreme temperatures, drought, flooding, salinity, heavy metals and pathogens. Acyl-CoA-binding proteins (ACBPs), a family of conserved proteins among prokaryotes and eukaryotes, bind to a variety of acyl-CoA esters with different affinities and play a role in the transport and maintenance of subcellular acyl-CoA pools. In plants, studies have revealed ACBP functions in development and stress responses through their interactions with lipids and protein partners. This review summarises the roles of plant ACBPs and their lipid and protein interactors in abiotic and biotic stress responses.

Genomic-Wide Analysis of the PLC Family and Detection of GmPI-PLC7 Responses to Drought and Salt Stresses in Soybean

Phospholipase C (PLC) performs significant functions in a variety of biological processes, including plant growth and development. The PLC family of enzymes principally catalyze the hydrolysis of phospholipids in organisms. This exhaustive exploration of soybean GmPLC members using genome databases resulted in the identification of 15 phosphatidylinositol-specific PLC (GmPI-PLC) and 9 phosphatidylcholine-hydrolyzing PLC (GmNPC) genes. Chromosomal location analysis indicated that GmPLC genes mapped to 10 of the 20 soybean chromosomes. Phylogenetic relationship analysis revealed that GmPLC genes distributed into two groups in soybean, the PI-PLC and NPC groups. The expression patterns and tissue expression analysis showed that GmPLCs were differentially expressed in response to abiotic stresses. GmPI-PLC7 was selected to further explore the role of PLC in soybean response to drought and salt stresses by a series of experiments. Compared with the transgenic empty vector (EV) control lines, over-expression of GmPI-PLC7 (OE) conferred higher drought and salt tolerance in soybean, while the GmPI-PLC7-RNAi (RNAi) lines exhibited the opposite phenotypes. Plant tissue staining and physiological parameters observed from drought- and salt-stressed plants showed that stress increased the contents of chlorophyll, oxygen free radical (O2 -), hydrogen peroxide (H2O2) and NADH oxidase (NOX) to amounts higher than those observed in non-stressed plants. This study provides new insights in the functional analysis of GmPLC genes in response to abiotic stresses.

Arabidopsis NRT1.2 interacts with the PHOSPHOLIPASE Dα1 (PLDα1) to positively regulate seed germination and seedling development in response to ABA treatment

NRT1.2 has been characterized as a low-affinity nitrate transporter and an abscisic acid (ABA) transporter in Arabidopsis. In this study, we demonstrate that NRT1.2 positively regulated the ABA response during germination and seedling development. The transgenic Arabidopsis NRT1.2-over-expressionors showed increased sensitivity to ABA during these processes. qRT-PCR assays indicated that NRT1.2 over-production in 7-days-old seedlings up-regulated the expression of ABA-responsive genes: ABI1, ABI2, ABI3, ABI4, ABI5, RAB18, RD29A, and RD29B and PHOSPHOLIPASE Dα1 (PLDα1). The expression of these genes was suppressed in the nrt1.2 mutant in comparison with the wild type following ABA treatment. Importantly, bimolecular fluorescence complementation assays indicated that NRT1.2 interacts with PLDα1 at the plasma membrane. Their interaction was further confirmed by using yeast two hybrid (Y2H) experiments with the mating-based split ubiquitin system (MbSUS). Moreover, genetic assays indicated that PLDα1 acts epistatically on NRT1.2 to affect ABA signaling. Taken together, our results provide detailed mechanisms of NRT1.2 in ABA-mediated seed germination and seedling development.

Expression and evolution of the phospholipase C gene family in Brachypodium distachyon

BACKGROUND

Phospholipase C (PLC) is an enzyme that hydrolyzes phospholipids and plays an important role in plant growth and development. The Brachypodium distachyon is a model plant of Gramineae, but the research on PLC gene family of Brachypodium has not been reported.

OBJECTIVE

This study was performed to identify the PLC family gene in Brachypodium and to determine the expression profiles of PLCs under the abiotic stress.

METHODS

Complete genome sequences and transcriptomes of Brachypodium were downloaded from the PLAZA. The hidden Markov model-based profile of the conserved PLC domain was submitted as a query to identify all potential PLC domain sequences with HMMER software. Expression profiles of BdPLCs were obtained based on the qRT-PCR analysis.

RESULTS

There were 8 PLC genes in Brachypodium (BdPI-PLCs 1-4 and BdNPCs 1-4). All members of BdPI-PLC had three conserved domains of X, Y, and C2, and no EF-hand was found. All BdNPCs contained a phosphatase domain. BdPI-PLC genes were distributed on Chr1, Chr2 and Chr4, with different types and numbers of cis-regulatory elements in their respective gene promoters. Phylogenetic analysis showed that the genetic relationship between Brachypodium and rice was closer than Arabidopsis. The expression patterns of BdPI-PLC gene under abiotic stresses (drought, low temperature, high temperature and salt stress) were up-regulated, indicated their important roles in response to low temperature, high temperature, drought and salt stresses.

CONCLUSIONS

This study provides comprehensive information for the study of Brachypodium PLC gene family and lays a foundation for further research on the molecular mechanism of Brachypodium stress adaptation.

Regulation of ABA-Non-Activated SNF1-Related Protein Kinase 2 Signaling Pathways by Phosphatidic Acid

Phosphatidic acid (PA) is involved in the regulation of plant growth and development, as well as responses to various environmental stimuli. Several PA targets in plant cells were identified, including two SNF1-related protein kinases 2 (SnRK2s), SnRK2.10 and SnRK2.4, which are not activated by abscisic acid (ABA). Here, we investigated the effects of PA on various elements of ABA-non-activated SnRK2 signaling. PA 16:0/18:1 was found to modulate the SnRK2 structure and the phosphorylation of some SnRK2 targets. Conversely, phosphorylation by the ABA-non-activated SnRK2s, of one of such targets, dehydrin Early Responsive to Dehydration 14 (ERD14), affects its interaction with PA and subcellular localization. Moreover, PA 16:0/18:1 modulates the activity and/or localization of negative regulators of the ABA-non-activated SnRK2s, not only of the ABA insensitive 1 (ABI1) phosphatase, which was identified earlier, but also of another protein phosphatase 2C, PP2CA. The activity of both phosphatases was inhibited by about 50% in the presence of 50 μM PA. PA 16:0/18:1 also impacts the phosphorylation and subcellular localization of SnRK2-interacting calcium sensor, known to inhibit SnRK2 activity in a calcium-dependent manner. Thus, PA was found to regulate ABA-non-activated SnRK2 signaling at several levels: the activity, phosphorylation status and/or localization of SnRK2 cellular partners.

Genome-Wide Identification and Expression Profile Analysis of the Phospholipase C Gene Family in Wheat (Triticum aestivum L.)

Phospholipid-hydrolyzing enzymes include members of the phospholipase C (PLC) family that play important roles in regulating plant growth and responding to stress. In the present study, a systematic in silico analysis of the wheat PLC gene family revealed a total of 26 wheat PLC genes (TaPLCs). Phylogenetic and sequence alignment analyses divided the wheat PLC genes into 2 subfamilies, TaPI-PLC (containing the typical X, Y, and C2 domains) and TaNPC (containing a phosphatase domain). TaPLC expression patterns differed among tissues, organs, and under abiotic stress conditions. The transcript levels of 8 TaPLC genes were validated through qPCR analyses. Most of the TaPLC genes were sensitive to salt stress and were up-regulated rapidly, and some were sensitive to low temperatures and drought. Overexpression of TaPI-PLC1-2B significantly improved resistance to salt and drought stress in Arabidopsis, and the primary root of P1-OE was significantly longer than that of the wild type under stress conditions. Our results not only provide comprehensive information for understanding the PLC gene family in wheat, but can also provide a solid foundation for functional characterization of the wheat PLC gene family.

Non-specific phospholipase C (NPC): an emerging class of phospholipase C in plant growth and development

Non-specific phospholipase C (NPC) is a novel class of phospholipase C found only in bacteria and higher plants. NPC hydrolyzes major phospholipid classes such as phosphatidylcholine (PC) and phosphatidylethanolamine (PE) to produce diacylglycerol (DAG) and a corresponding phosphate-containing polar head group. Originally known as a toxin in certain bacteria to invade the host cell, this class of phospholipase has been well-investigated in bacteriology. Since the first discovery of eukaryotic NPC in Arabidopsis in 2005, this emerging class of phospholipase has received greater attention in plant biology in elucidating the biochemical characteristics and physiological function in the context of plant growth regulation and stress response. Particularly in the last few years, there has been significant progress made in understanding the fundamental character of 6 NPC isoforms in Arabidopsis, as well as novel function in other plant models. Now that research with plant NPC is entering into a new phase, this review aims to summarize recent progress in plant NPC along with some future perspectives.

Patatin-Related Phospholipase pPLAIIIγ Involved in Osmotic and Salt Tolerance in Arabidopsis

Patatin-related phospholipases (pPLAs) are acyl-hydrolyzing enzymes implicated in various processes, including lipid metabolism, signal transduction, plant growth and stress responses, but the function for many specific pPLAs in plants remains unknown. Here we determine the effect of patatin-related phospholipase A pPLAIIIγ on Arabidopsis response to abiotic stress. Knockout of pPLAIIIγ rendered plants more sensitive whereas overexpression of pPLAIIIγ enhanced plant tolerance to NaCl and drought in seed germination and seedling growth. The pPLAIIIγ-knockout and overexpressing seedlings displayed a lower and higher level of lysolipids and free fatty acids than that of wild-type plants in response to NaCl stress, respectively. These results indicate that pPLAIIIγ acts a positive regulator of salt and osmatic stress tolerance in Arabidopsis.

Nonspecific phospholipase C6 increases seed oil production in oilseed Brassicaceae plants

Plant oils are valuable commodities for food, feed, renewable industrial feedstocks and biofuels. To increase vegetable oil production, here we show that the nonspecific phospholipase C6 (NPC6) promotes seed oil production in the Brassicaceae seed oil species Arabidopsis, Camelina and oilseed rape. Overexpression of NPC6 increased seed oil content, seed weight and oil yield both in Arabidopsis and Camelina, whereas knockout of NPC6 decreased seed oil content and seed size. NPC6 is associated with the chloroplasts and microsomal membranes, and hydrolyzes phosphatidylcholine and galactolipids to produce diacylglycerol. Knockout and overexpression of NPC6 decreased and increased, respectively, the flux of fatty acids from phospholipids and galactolipids into triacylglycerol production. Candidate-gene association study in oilseed rape indicates that only BnNPC6.C01 of the four homeologues NPC6s is associated with seed oil content and yield. Haplotypic analysis indicates that the BnNPC6.C01 favorable haplotype can increase both seed oil content and seed yield. These results indicate that NPC6 promotes membrane glycerolipid turnover to accumulate TAG production in oil seeds and that NPC6 has a great application potential for oil yield improvement.

A Plant-Specific N-terminal Extension Reveals Evolutionary Functional Divergence within Translocator Proteins

Conserved translocator proteins (TSPOs) mediate cell stress responses possibly in a cell-type-specific manner. This work reports on the molecular function of plant TSPO and their possible evolutionary divergence. Arabidopsis thaliana TSPO (AtTSPO) is stress induced and has a conserved polybasic, plant-specific N-terminal extension. AtTSPO reduces water loss by depleting aquaporin PIP2;7 in the plasma membrane. Herein, AtTSPO was found to bind phosphoinositides in vitro, but only full-length AtTSPO or chimeric mouse TSPO with an AtTSPO N-terminus bound PI(4,5)P₂in vitro and modified PIP2;7 levels in vivo. Expression of AtTSPO but not its N-terminally truncated variant enhanced phospholipase C activity and depleted PI(4,5)P₂ from the plasma membrane and its enrichment in Golgi membranes. Deletion or point mutations within the AtTSPO N-terminus affected PI(4,5)P₂ binding and almost prevented AtTSPO-PIP2;7 interaction in vivo. The findings imply functional divergence of plant TSPOs from bacterial and animal counterparts via evolutionary acquisition of the phospholipid-interacting N-terminus.

Genome wide characterization of phospholipase A & C families and pattern of lysolipids and diacylglycerol changes under abiotic stresses in Brassica napus L

Plant phospholipase A (PLA) and C (PLC) families are least explored in terms of structure, diversity and their roles in membrane lipid remodeling under stress conditions. In this study, we performed gene family analysis, determined gene expression in different tissues and monitored transcriptional regulation of patatin-related PLA family and PLC family in oil crop Brassica napus under dehydration, salt, abscisic acid and cold stress. The identified 29 BnapPLA genes and 40 BnaPLC genes shared high similarities with Arabidopsis pPLAs and PLCs, respectively. This study highlighted the expression pattern of BnapPLAs and BnaPLCs in different tissues and their expression in response to abiotic stresses in Brassica napus. The results revealed that several members of BnapPLA3, PI-PLC1/2 and NPC1 were actively regulated by abiotic stresses. Lipid changes at different time points under stress conditions were also measured. Lipid profiling revealed that the level of lysophospholipids and diacylglycerol (DAG) showed a varied pattern of changes under different abiotic stress treatments. The change of lipids correlated with the transcriptional regulation of a few specific members of pPLA and PLC families. Our study suggested that A and C-type phospholipases in Brassica napus may have diverse physiological and regulatory roles in abiotic stress response and tolerance.