The phosphatidylcholine-hydrolysing phospholipase C NPC4 plays a role in response of Arabidopsis roots to salt stress

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.

Comparative metabolomic analysis between tomato and halophyte plants under intercropping conditions

Halophyte-based intercropping appears nowadays as a valuable approach in soil remediation and agriculture. In this work, intercropping between the halophyte Arthrocaulon macrostachyum and tomato (Solanum lycopersicum var. Sargento) was studied in both plant species using comparative mass spectrometry-based metabolomics coupled to metabolic pathway predictions. A significant number of changes in metabolites was observed in the halophyte. In terms of alteration of specific metabolic pathways, intercropping conditions stimulated sugar and starch metabolisms in tomato, whereas in the halophyte, intercropping mainly altered amino acid-related pathways. In addition, arginine and proline metabolism were commonly affected in both tomato and halophyte plants. Moreover, metabolomic changes were associated with physiological alterations in tomato. In this sense, mild oxidative stress was induced in intercropped tomato plants, which, in turn, could trigger signaling events leading to plant adjustment to intercropping conditions. This study represents the first approach toward understanding intercropping interactions at the metabolome level and its effect on plant physiology, opening up prospects for further characterization of this crop cultivation strategy.

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.

Genome-wide characterization of phospholipase D family genes in allotetraploid peanut and its diploid progenitors revealed their crucial roles in growth and abiotic stress responses

Abiotic stresses such as cold, drought and salinity are the key environmental factors that limit the yield and quality of oil crop peanut. Phospholipase Ds (PLDs) are crucial hydrolyzing enzymes involved in lipid mediated signaling and have valuable functions in plant growth, development and stress tolerance. Here, 22, 22 and 46 PLD genes were identified in Arachis duranensis, Arachis ipaensis and Arachis hypogaea, respectively, and divided into α, β, γ, δ, ε, ζ and φ isoforms. Phylogenetic relationships, structural domains and molecular evolution proved the conservation of PLDs between allotetraploid peanut and its diploid progenitors. Almost each A. hypogaea PLD except for AhPLDα6B had a corresponding homolog in A. duranensis and A. ipaensis genomes. The expansion of Arachis PLD gene families were mainly attributed to segmental and tandem duplications under strong purifying selection. Functionally, the most proteins interacting with AhPLDs were crucial components of lipid metabolic pathways, in which ahy-miR3510, ahy-miR3513-3p and ahy-miR3516 might be hub regulators. Furthermore, plenty of cis-regulatory elements involved in plant growth and development, hormones and stress responses were identified. The tissue-specific transcription profiling revealed the broad and unique expression patterns of AhPLDs in various developmental stages. The qRT-PCR analysis indicated that most AhPLDs could be induced by specific or multiple abiotic stresses. Especially, AhPLDα3A, AhPLDα5A, AhPLDβ1A, AhPLDβ2A and AhPLDδ4A were highly up-regulated under all three abiotic stresses, whereas AhPLDα9A was neither expressed in 22 peanut tissues nor induced by any abiotic stresses. This genome-wide study provides a systematic analysis of the Arachis PLD gene families and valuable information for further functional study of candidate AhPLDs in peanut growth and abiotic stress responses.

Association mapping and candidate genes for physiological non-destructive traits: Chlorophyll content, canopy temperature, and specific leaf area under normal and saline conditions in wheat

Wheat plants experience substantial physiological adaptation when exposed to salt stress. Identifying such physiological mechanisms and their genetic control is especially important to improve its salt tolerance. In this study, leaf chlorophyll content (CC), leaf canopy temperature (CT), and specific leaf area (SLA) were scored in a set of 153 (103 having the best genotypic data were used for GWAS analysis) highly diverse wheat genotypes under control and salt stress. On average, CC and SLA decreased under salt stress, while the CT average was higher under salt stress compared to the control. CT was negatively and significantly correlated with CC under both conditions, while no correlation was found between SLA and CC and CT together. High genetic variation and broad-sense-heritability estimates were found among genotypes for all traits. The genome wide association study revealed important QTLs for CC under both conditions (10) and SLA under salt stress (four). These QTLs were located on chromosomes 1B, 2B, 2D, 3A, 3B, 5A, 5B, and 7B. All QTLs detected in this study had major effects with R² extending from 20.20% to 30.90%. The analysis of gene annotation revealed three important candidate genes (TraesCS5A02G355900, TraesCS1B02G479100, and TraesCS2D02G509500). These genes are found to be involved in the response to salt stress in wheat with high expression levels under salt stress compared to control based on mining in data bases.

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.

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.

Genome-wide characterization and expression profiling of the Phospholipase C (PLC) gene family in three orchids of economic importance

Background

Phospholipases hydrolyze glycerophospholipids and generate diverse lipid-derived molecules with secondary messenger activity. Out of these, phospholipase C (PLC) specifically cleaves the phospholipids at ester linkages and yields diacylglycerol (DAG) and phosphorylated head groups. PLCs are classified further as phosphatidylinositol-specific PLCs (PI-PLCs) and non-specific PLCs with biased specificity for phosphatidylcholine (NPC/PC-PLC).

Results

In the present report, we identified and characterized PLC genes in the genomes of three orchids, Phalaenopsis equestris (seven PePLCs), Dendrobium catenatum (eight DcPLCs), and Apostasia shenzhenica (seven AsPLCs). Multiple sequence alignment analysis confirmed the presence of conserved X and Y catalytic domains, calcium/lipid-binding domain (C2 domain) at the C terminal region, and EF-hand at the N-terminal region in PI-PLC proteins and esterase domain in PC-PLC. Systematic phylogenetic analysis established the relationship of the PLC protein sequences and clustered them into two groups (PI-PLC and PC-PLC) along with those of Arabidopsis thaliana and Oryza sativa. Gene architecture studies showed the presence of nine exons in all PI-PLC genes while the number varied from one to five in PC-PLCs. RNA-seq-based spatio-temporal expression profile for PLC genes was generated, which showed that PePC-PLC1, PePC-PLC2A, DcPC-PLC1A, DcPC-PLC1B, DcPC-PLC2, DcPC-PLC1B, and AsPC-PLC1 had significant expression in all reproductive and vegetative tissues. The expression profile is matched to their upstream cis-regulatory promoter elements, which indicates that PLC genes have a role in various growth and development processes and during stress responses.

Conclusions

The present study unwrapped the opportunity for functional characterization of selected PLC genes in planta for plant improvement.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-021-00217-z.

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.

Fight Hard or Die Trying: Current Status of Lipid Signaling during Plant-Pathogen Interaction

Plant diseases pose a substantial threat to food availability, accessibility, and security as they account for economic losses of nearly $300 billion on a global scale. Although various strategies exist to reduce the impact of diseases, they can introduce harmful chemicals to the food chain and have an impact on the environment. Therefore, it is necessary to understand and exploit the plants' immune systems to control the spread of pathogens and enable sustainable agriculture. Recently, growing pieces of evidence suggest a functional myriad of lipids to be involved in providing structural integrity, intracellular and extracellular signal transduction mediators to substantial cross-kingdom cell signaling at the host-pathogen interface. Furthermore, some pathogens recognize or exchange plant lipid-derived signals to identify an appropriate host or development, whereas others activate defense-related gene expression. Typically, the membrane serves as a reservoir of lipids. The set of lipids involved in plant-pathogen interaction includes fatty acids, oxylipins, phospholipids, glycolipids, glycerolipids, sphingolipids, and sterols. Overall, lipid signals influence plant-pathogen interactions at various levels ranging from the communication of virulence factors to the activation and implementation of host plant immune defenses. The current review aims to summarize the progress made in recent years regarding the involvement of lipids in plant-pathogen interaction and their crucial role in signal transduction.

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.

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.

Genome-Wide Investigation of the Phospholipase C Gene Family in Zea mays

Phospholipase C (PLC) is one of the main hydrolytic enzymes in the metabolism of phosphoinositide and plays an important role in a variety of signal transduction processes responding to plant growth, development, and stress. Although the characteristics of many plant PLCs have been studied, PLC genes of maize have not been comprehensively identified. According to the study, five phosphatidylinositol-specific PLC (PI-PLC) and six non-specific PLC (NPC) genes were identified in maize. The PI-PLC and NPC genes of maize are conserved compared with homologous genes in other plants, especially in evolutionary relationship, protein sequences, conserved motifs, and gene structures. Transient expression of ZmPLC-GFP fusion protein in Arabidopsis protoplast cells showed that ZmPLCs are multi-localization. Analyses of transcription levels showed that ZmPLCs were significantly different under various different tissues and abiotic stresses. Association analysis shown that some ZmPLCs significantly associated with agronomic traits in 508 maize inbred lines. These results contribute to study the function of ZmPLCs and to provide good candidate targets for the yield and quality of superior maize cultivars.

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.

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.

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.

Non-specific phospholipases C, NPC2 and NPC6, are required for root growth in Arabidopsis

Mutants in lipid metabolism often show a lethal phenotype during reproduction that prevents investigating a specific role of the lipid during different developmental processes. We focused on two non-specific phospholipases C, NPC2 and NPC6, whose double knock-out causes a gametophyte-lethal phenotype. To investigate the role of NPC2 and NPC6 during vegetative growth, we produced transgenic knock-down mutant lines that circumvent the lethal effect during gametogenesis. Despite no defect observed in leaves, root growth was significantly retarded, with abnormal cellular architecture in root columella cells. Furthermore, the short root phenotype was rescued by exogenous supplementation of phosphocholine, a product of non-specific phospholipase C (NPC) -catalyzed phosphatidylcholine hydrolysis. The expression of phospho-base N-methyltransferase 1 (PMT1), which produces phosphocholine and is required for root growth, was induced in the knock-down mutant lines and was attenuated after phosphocholine supplementation. These results suggest that NPC2 and NPC6 may be involved in root growth by producing phosphocholine via metabolic interaction with a PMT-catalyzed pathway, which highlights a tissue-specific role of NPC enzymes in vegetative growth beyond the gametophyte-lethal phenotype.

Membrane Lipid Remodeling in Response to Salinity

Salinity is one of the most decisive environmental factors threatening the productivity of crop plants. Understanding the mechanisms of plant salt tolerance is critical to be able to maintain or improve crop yield under these adverse environmental conditions. Plant membranes act as biological barriers, protecting the contents of cells and organelles from biotic and abiotic stress, including salt stress. Alterations in membrane lipids in response to salinity have been observed in a number of plant species including both halophytes and glycophytes. Changes in membrane lipids can directly affect the properties of membrane proteins and activity of signaling molecules, adjusting the fluidity and permeability of membranes, and activating signal transduction pathways. In this review, we compile evidence on the salt stress responses of the major membrane lipids from different plant tissues, varieties, and species. The role of membrane lipids as signaling molecules in response to salinity is also discussed. Advances in mass spectrometry (MS)-based techniques have largely expanded our knowledge of salt-induced changes in lipids, however only a handful studies have investigated the underlying mechanisms of membrane lipidome regulation. This review provides a comprehensive overview of the recent works that have been carried out on lipid remodeling of plant membranes under salt treatment. Challenges and future perspectives in understanding the mechanisms of salt-induced changes to lipid metabolisms are proposed.

Seed germination, respiratory processes and phosphatidic acid accumulation in Arabidopsis diacylglycerol kinase knockouts - The effect of brassinosteroid, brassinazole and salinity

Using Arabidopsis thaliana wild type (WT) plants and diacylglycerol kinase knockouts (single mutants - dgk3, dgk1, dgk6; double mutants - dgk3dgk7, dgk5dgk6, dgk1dgk2) we observed that the inhibitor of brassinosteroid (BR) biosynthesis, brassinazole (BRZ), drastically decreased germination of dgk mutants under salt stress, while BRZ co-administration with 24-epibrassinolide (EBL) partially improved germination rates. We also observed a statistically significant decrease in alternative and cytochrome respiratory pathways in response to BRZ treatment under salinity conditions. We showed that production of the lipid second messenger phosphatidic acid (PA) is impaired in dgk mutants in response to EBL treatment and inhibitor of diacylglycerol kinase (DGK) - R59022. This study demonstrates that dgk mutants possess lower germination rates, lower total respiration rates, an alternative respiratory pathway and PA content under optimal and high salinity conditions in response to EBL treatment comparing to WT plants.

Diacylglycerol kinase and associated lipid mediators modulate rice root architecture

Diacylglycerol kinase (DGK) phosphorylates diacylglycerol (DAG) to generate phosphatidic acid (PA), and both DAG and PA are lipid mediators in the cell. Here we show that DGK1 in rice (Oryza sativa) plays important roles in root growth and development. Two independent OsDGK1-knockout (dgk1) lines exhibited a higher density of lateral roots (LRs) and thinner seminal roots (SRs), whereas OsDGK1-overexpressing plants displayed a lower LR density and thicker SRs than wild-type (WT) plants. Overexpression of OsDGK1 led to a decline in the DGK substrate DAG whereas specific PA species decreased in dgk1 roots. Supplementation of DAG to OsDGK1-overexpressing seedlings restored the LR density and SR thickness whereas application of PA to dgk1 seedlings restored the LR density and SR thickness to those of the WT. In addition, treatment of rice seedlings with the DGK inhibitor R59022 increased the level of DAG and decreased PA, which also restored the root phenotype of OsDGK1-overexpressing seedlings close to that of the WT. Together, these results indicate that DGK1 and associated lipid mediators modulate rice root architecture; DAG promotes LR formation and suppresses SR growth whereas PA suppresses LR number and promotes SR thickness.

Isolation and characterization of 1-palmitoyl-2-linoleoyl-sn-glycerol as a hormogonium-inducing factor (HIF) from the coralloid roots of Cycas revoluta (Cycadaceae)

Coralloid roots are specialized tissues of cycads (Cycas revoluta) that are involved in symbioses with nitrogen-fixing Nostoc cyanobacteria. We found that a crude methanolic extract of coralloid roots induced differentiation of the filamentous cell aggregates of Nostoc species into motile hormogonia. Hence, the hormogonium-inducing factor (HIF) was chased using bioassay-based isolation, and the active principle was characterized as a mixture of diacylglycerols (DAGs), mainly composed of 1-palmitoyl-2-linoleoyl-sn-glycerol (1), 1-palmitoyl-2-oleoyl-sn-glycerol (2), 1-stearoyl-2-linolenoyl-sn-glycerol (3), and 1-stearoyl-2-linoleoyl-sn-glycerol (4). Enantioselectively synthesised compound 1 showed a clear HIF activity at 1 nmol (0.6 µg) disc⁻¹ for the filamentous cells, whereas synthesised 2-linoleoyl-3-palmitoyl-sn-glycerol (1′) and 1-palmitoyl-2-linoleoyl-rac-glycerol (1/1′) were less active than 1. Conversely, synthesised 1-linoleoyl-2-palmitoyl-rac-glycerol (8/8′) which is an acyl positional isomer of compound 1 was inactive. In addition, neither 1-monoacylglycerols nor phospholipids structurally related to 1 showed HIF-like activities. As DAGs are protein kinase C (PKC) activators, 12-O-tetradecanoylphorbol-13-acetate (12), urushiol C15:3-Δ^10,13,16 (13), and a skin irritant anacardic acid C15:1-Δ⁸ (14) were also examined for HIF-like activities toward the Nostoc cells. Neither 12 nor 13 showed HIF-like activities, whereas 14 showed an HIF-like activity at 1 nmol/disc. These findings appear to indicate that some DAGs act as hormogonium-inducing signal molecules for filamentous Nostoc cyanobacteria.

24-Epibrassinolide application in plants: An implication for improving drought stress tolerance in plants

Drought stress is one of most dramatic abiotic stresses, reduces crop yield significantly. Application of hormones proved as an effective drought stress ameliorating approach. 24-Epibrassinolide (EBL), an active by-product from brassinolide biosynthesis increases drought stress tolerance in plants significantly. EBL application enhances plant growth and development under drought stress by acting as signalling compound in different physiological processes. This article discussed potential role of 24-epibrassinolide application and drought tolerance in plants. Briefly, EBL sustains or improves plant growth and yield by enhancing carbon assimilation rate, maintaining a balance between ROS and antioxidants and also plays important role in solute accumulation and water relations. Furthermore, we also compared different EBL application methods and concluded that seed priming and foliar application are more productive as compared with root application method. In conclusion, EBL is very impressive phyto-hormone, which can ameliorate drought stress induced detrimental effects in plants.

Lipases associated with plant defense against pathogens

When facing microbe invaders, plants activate genetic and metabolic defense mechanisms and undergo extracellular and intracellular changes to obtain a certain level of host resistance. Dynamic adjustment and adaptation occur in structures containing lipophilic compounds and cellular metabolites. Lipids encompassing fatty acids, fatty acid-based polymers, and fatty acid derivatives are part of the fundamental architecture of cells and tissues and are essential compounds in numerous biological processes. Lipid-associated plant defense responses are mostly facilitated by the activation of lipases (lipid hydrolyzing proteins), which cleave or transform lipid substrates in various subcellular compartments. In this review, several types of plant defense-associated lipases are described, including their molecular aspects, enzymatic actions, cellular functions, and possible functional relevance in plant defense. Defensive roles are discussed considering enzyme properties, lipid metabolism, downstream regulation, and phenotypic traits in loss-of-function mutants.

A pair of nonspecific phospholipases C, NPC2 and NPC6, are involved in gametophyte development and glycerolipid metabolism in Arabidopsis

Phospholipases play crucial roles in plant membrane lipid homeostasis. Nonspecific phospholipase C (NPCs) establish a unique class of phospholipases found only in plants and certain bacteria. Here, we show that two previously uncharacterized NPC isoforms, NPC2 and NPC6, are required for male and female gametophyte development in Arabidopsis. Double mutant plants of npc2-1 npc6-2 could not be retrieved because npc2-1 npc6-2 ovule and pollen development is affected. Genetic complementation, reciprocal crossing and microscope observation of npc2-1/- npc6-2/+ and npc2-1/+ npc6-2/- plants suggest that NPC2 and NPC6 are redundant and are required for normal gametophyte development. Both NPC2 and NPC6 proteins are localized to the plastids. Promoter-GUS assays in transgenic Arabidopsis revealed that NPC2 and NPC6 are preferentially expressed in floral organs rather than in leaves. In vitro enzyme assays showed that NPC2 and NPC6 hydrolyze phosphatidylcholine and phosphatidylethanolamine, but not phosphatidate, being consistent with the reported substrate selectivity of NPCs. The amounts of phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol were increased in buds but not in flowers of npc2-1/- npc6-2/+ and npc2-1/+ npc6-2/- plants, presumably due to reduced phospholipid hydrolysis activity in developing flowers. Our results demonstrate that NPC2 and NPC6 play crucial roles in gametogenesis during flower development.

The Arabidopsis thaliana non-specific phospholipase C2 is involved in the response to Pseudomonas syringae attack

Background and Aims

The non-specific phospholipase C (NPC) is a new member of the plant phospholipase family that reacts to abiotic environmental stresses, such as phosphate deficiency, high salinity, heat and aluminium toxicity, and is involved in root development, silicon distribution and brassinolide signalling. Six NPC genes (NPC1-NPC6) are found in the Arabidopsis genome. The NPC2 isoform has not been experimentally characterized so far.

Methods

The Arabidopsis NPC2 isoform was cloned and heterologously expressed in Escherichia coli. NPC2 enzyme activity was determined using fluorescent phosphatidylcholine as a substrate. Tissue expression and subcellular localization were analysed using GUS- and GFP-tagged NPC2. The expression patterns of NPC2 were analysed via quantitative real-time PCR. Independent homozygous transgenic plant lines overexpressing NPC2 under the control of a 35S promoter were generated, and reactive oxygen species were measured using a luminol-based assay.

Key Results

The heterologously expressed protein possessed phospholipase C activity, being able to hydrolyse phosphatidylcholine to diacylglycerol. NPC2 tagged with GFP was predominantly localized to the Golgi apparatus in Arabidopsis roots. The level of NPC2 transcript is rapidly altered during plant immune responses and correlates with the activation of multiple layers of the plant defence system. Transcription of NPC2 decreased substantially after plant infiltration with Pseudomonas syringae, flagellin peptide flg22 and salicylic acid treatments and expression of the effector molecule AvrRpm1. The decrease in NPC2 transcript levels correlated with a decrease in NPC2 enzyme activity. NPC2-overexpressing mutants showed higher reactive oxygen species production triggered by flg22.

Conclusions

This first experimental characterization of NPC2 provides new insights into the role of the non-specific phospholipase C protein family. The results suggest that NPC2 is involved in the response of Arabidopsis to P. syringae attack.

Phospholipases: An Overview

Phospholipases are lipolytic enzymes that hydrolyze phospholipid substrates at specific ester bonds. Phospholipases are widespread in nature and play very diverse roles from aggression in snake venom to signal transduction, lipid mediator production, and metabolite digestion in humans. Phospholipases vary considerably in structure, function, regulation, and mode of action. Tremendous advances in understanding the structure and function of phospholipases have occurred in the last decades. This introductory chapter is aimed at providing a general framework of the current understanding of phospholipases and a discussion of their mechanisms of action and emerging biological functions.

Structural, expression and evolutionary analysis of the non-specific phospholipase C gene family in Gossypium hirsutum

BACKGROUND

Nonspecific phospholipase C (NPC), which belongs to a phospholipase C subtype, is a class of phospholipases that hydrolyzes the primary membrane phospholipids, such as phosphatidylcholine, to yield sn-1, 2-diacylglycerol and a phosphorylated head-group. NPC plays multiple physiological roles in lipid metabolism and signaling in plants. To fully understand the putative roles of NPC genes in upland cotton, we cloned NPC genes from Gossypium hirsutum and carried out structural, expression and evolutionary analysis.

RESULTS

Eleven NPC genes were cloned from G. hirsutum, which were found on chromosomes scaffold269.1, D03, A07, D07, A08, D11, and scaffold3511_A13. All GhNPCs had typical phosphoesterase domains and have hydrolase activity that acts on ester bonds. GhNPCs were annotated as phospholipase C, which was involved in glycerophospholipid metabolism, ether lipid metabolism, and biosynthesis of secondary metabolites. These GhNPCs showed differential expression patterns in distinct plant tissues and in response to various types of stress (low-phosphate, salt, drought, and abscisic acid). They also had different types and numbers of cis-element. GhNPCs could be classified into four subfamilies. Four pairs of GhNPCs were generated by whole-genome duplication and they underwent purifying selection.

CONCLUSIONS

Our results suggested that GhNPCs are involved in regulating key abiotic stress responses and ABA signaling transduction, and they may have various functional roles for different members under complex abiotic stress conditions. Functional divergence may be the evolutionary driving force for the retention of four pairs of duplicate NPCs. Our analysis provides a solid foundation for the further functional characterization of the GhNPC gene family, and leads to potential applications in the genetic improvement of cotton cultivars.

Identification and characterization of the phosphatidic acid-binding A. thaliana phosphoprotein PLDrp1 that is regulated by PLDα1 in a stress-dependent manner

Phospholipase D (PLD) and its cleavage product phosphatidic acid (PA) are crucial in plant stress-signalling. Although some targets of PLD and PA have been identified, the signalling pathway is still enigmatic. This study demonstrates that the phosphoprotein At5g39570, now called PLD-regulated protein1 (PLDrp1), from Arabidopsis thaliana is directly regulated by PLDα1. The protein PLDrp1 can be divided into two regions with distinct properties. The conserved N-terminal region specifically binds PA, while the repeat-rich C-terminal domain suggests interactions with RNAs. The expression of PLDrp1 depends on PLDα1 and the plant water status. Water stress triggers a pldα1-like phenotype in PLDrp1 mutants and induces the expression of PLDrp1 in pldα1 mutants. The regulation of PLDrp1 by PLDα1 and environmental stressors contributes to the understanding of the complex PLD regulatory network and presents a new member of the PA-signalling chain in plants.

Fatty Acid- and Lipid-Mediated Signaling in Plant Defense

Fatty acids and lipids, which are major and essential constituents of all plant cells, not only provide structural integrity and energy for various metabolic processes but can also function as signal transduction mediators. Lipids and fatty acids can act as both intracellular and extracellular signals. In addition, cyclic and acyclic products generated during fatty acid metabolism can also function as important chemical signals. This review summarizes the biosynthesis of fatty acids and lipids and their involvement in pathogen defense.

Arabidopsis phosphoinositide-specific phospholipase C 4 negatively regulates seedling salt tolerance

Previous physiological and pharmacological studies have suggested that the activity of phosphoinositide-specific phospholipase C (PI-PLC) plays an important role in regulating plant salt stress responses by altering the intracellular Ca²⁺ concentration. However, the individual members of plant PLCs involved in this process need to be identified. Here, the function of AtPLC4 in the salt stress response of Arabidopsis seedlings was analysed. plc4 mutant seedlings showed hyposensitivity to salt stress compared with Col-0 wild-type seedlings, and the salt hyposensitive phenotype could be complemented by the expression of native promoter-controlled AtPLC4. Transgenic seedlings with AtPLC4 overexpression (AtPLC4 OE) exhibited a salt-hypersensitive phenotype, while transgenic seedlings with its inactive mutant expression (AtPLC4m OE) did not exhibit this phenotype. Using aequorin as a Ca²⁺ indicator in plc4 mutant and AtPLC4 OE seedlings, AtPLC4 was shown to positively regulate the salt-induced Ca²⁺ increase. The salt-hypersensitive phenotype of AtPLC4 OE seedlings was partially rescued by EGTA. An analysis of salt-responsive genes revealed that the transcription of RD29B, MYB15 and ZAT10 was inversely regulated in plc4 mutant and AtPLC4 OE seedlings. Our findings suggest that AtPLC4 negatively regulates the salt tolerance of Arabidopsis seedlings, and Ca²⁺ may be involved in regulating this process.

In Vivo Imaging of Diacylglycerol at the Cytoplasmic Leaflet of Plant Membranes

Diacylglycerol (DAG) is an important intermediate in lipid biosynthesis and plays key roles in cell signaling, either as a second messenger itself or as a precursor of phosphatidic acid. Methods to identify distinct DAG pools have proven difficult because biochemical fractionation affects the pools, and concentrations are limiting. Here, we validate the use of a genetically encoded DAG biosensor in living plant cells. The sensor is composed of a fusion between yellow fluorescent protein and the C1a domain of protein kinase C (YFP-C1aPKC) that specifically binds DAG, and was stably expressed in suspension-cultured tobacco BY-2 cells and whole Arabidopsis thaliana plants. Confocal imaging revealed that the majority of the YFP-C1aPKC fluorescence did not locate to membranes but was present in the cytosol and nucleus. Treatment with short-chain DAG or PMA (phorbol-12-myristate-13-acetate), a phorbol ester that binds the C1a domain of PKC, caused the recruitment of the biosensor to the plasma membrane. These results indicate that the biosensor works and that the basal DAG concentration in the cytoplasmic leaflet of membranes (i.e. accessible to the biosensor) is in general too low, and confirms that the known pools in plastids, the endoplasmic reticulum and mitochondria are located at the luminal face of these compartments (i.e. inaccessible to the biosensor). Nevertheless, detailed further analysis of different cells and tissues discovered four novel DAG pools, namely at: (i) the trans-Golgi network; (ii) the cell plate during cytokinesis; (iii) the plasma membrane of root epidermal cells in the transition zone, and (iv) the apex of growing root hairs. The results provide new insights into the spatiotemporal dynamics of DAG in plants and offer a new tool to monitor this in vivo.

Genome-wide identification and characterization of phospholipase C gene family in cotton (Gossypium spp.)

Phospholipase C (PLC) are important regulatory enzymes involved in several lipid and Ca²⁺-dependent signaling pathways. Previous studies have elucidated the versatile roles of PLC genes in growth, development and stress responses of many plants, however, the systematic analyses of PLC genes in the important fiber-producing plant, cotton, are still deficient. In this study, through genome-wide survey, we identified twelve phosphatidylinositol-specific PLC (PI-PLC) and nine non-specific PLC (NPC) genes in the allotetraploid upland cotton Gossypium hirsutum and nine PI-PLC and six NPC genes in two diploid cotton G. arboretum and G.raimondii, respectively. The PI-PLC and NPC genes of G. hirsutum showed close phylogenetic relationship with their homologous genes in the diploid cottons and Arabidopsis. Segmental and tandem duplication contributed greatly to the formation of the gene family. Expression profiling indicated that few of the PLC genes are constitutely expressed, whereas most of the PLC genes are preferentially expressed in specific tissues and abiotic stress conditions. Promoter analyses further implied that the expression of these PLC genes might be regulated by MYB transcription factors and different phytohormones. These results not only suggest an important role of phospholipase C members in cotton plant development and abiotic stress response but also provide good candidate targets for future molecular breeding of superior cotton cultivars.

Effect of 24-epibrassinolide on Brassica napus alternative respiratory pathway, guard cells movements and phospholipid signaling under salt stress

Using Brassica napus roots we observed statistically significant increase in alternative respiratory pathway in response to exogenous 24-epibrassinolide (EBL) under optimal conditions and salinity. Also we observed activation of phospholipid signaling under the same conditions in response to EBL by measuring levels of lipid second messengers - diacylglycerol (DAG) and phosphatidic acid (PA). We found that brassinosteroids cause closure of stomata in isolated leaf disks while inhibitors of alternative oxidase cancelled these effects. This study demonstrates that BRs activate total respiration rate, alternative respiratory pathway, production of PA and DAG, stimulate stomata closure and growth under optimal conditions and salinity. Also, specific inhibitor of brassinosteroids biosynthesis decreased alternative respiratory pathway and production of lipid messengers in rape plants.

Non-specific phospholipase C1 affects silicon distribution and mechanical strength in stem nodes of rice

Silicon, the second abundant element in the crust, is beneficial for plant growth, mechanical strength, and stress responses. Here we show that manipulation of the non-specific phospholipase C1, NPC1, alters silicon content in nodes and husks of rice (Oryza sativa). Silicon content in NPC1-overexpressing (OE) plants was decreased in nodes but increased in husks compared to wild-type, whereas RNAi suppression of NPC1 resulted in the opposite changes to those of NPC1-OE plants. NPC1 from rice hydrolyzed phospholipids and galactolipids to generate diacylglycerol that can be phosphorylated to phosphatidic acid. Phosphatidic acid interacts with Lsi6, a silicon transporter that is expressed at the highest level in nodes. In addition, the node cells of NPC1-OE plants have lower contents of cellulose and hemicellulose, and thinner sclerenchyma and vascular bundle fibre cells than wild-type plants; whereas NPC1-RNAi plants displayed the opposite changes. These data indicate that NPC1 modulates silicon distribution and secondary cell wall deposition in nodes and grains, affecting mechanical strength and seed shattering.

Genome-Wide Analysis and Expression Profiling of the Phospholipase C Gene Family in Soybean (Glycine max)

Phosphatidylinositol-specific phospholipase C (PI-PLC) hydrolyses phosphatidylinositol-4,5-bisphosphate to produce diacylglycerol and inositol 1,4,5-trisphosphate. It plays an important role in plant development and abiotic stress responses. However, systematic analysis and expression profiling of the phospholipase C (PLC) gene family in soybean have not been reported. In this study, 12 putative PLC genes were identified in the soybean genome. Soybean PLCs were found on chromosomes 2, 11, 14 and 18 and encoded 58.8-70.06 kD proteins. Expression pattern analysis by RT-PCR demonstrated that expression of the GmPLCs was induced by PEG, NaCl and saline-alkali treatments in roots and leaves. GmPLC transcripts accumulated specifically in roots after ABA treatment. Furthermore, GmPLC transcripts were analyzed in various tissues. The results showed that GmPLC7 was highly expressed in most tissues, whereas GmPLC12 was expressed in early pods specifically. In addition, subcellular localization analysis was carried out and confirmed that GmPLC10 was localized in the plasma membrane in Nicotiana benthamiana. Our genomic analysis of the soybean PLC family provides an insight into the regulation of abiotic stress responses and development. It also provides a solid foundation for the functional characterization of the soybean PLC gene family.

Identification of Open Stomata1-Interacting Proteins Reveals Interactions with Sucrose Non-fermenting1-Related Protein Kinases2 and with Type 2A Protein Phosphatases That Function in Abscisic Acid Responses

The plant hormone abscisic acid (ABA) controls growth and development and regulates plant water status through an established signaling pathway. In the presence of ABA, pyrabactin resistance/regulatory component of ABA receptor proteins inhibit type 2C protein phosphatases (PP2Cs). This, in turn, enables the activation of Sucrose Nonfermenting1-Related Protein Kinases2 (SnRK2). Open Stomata1 (OST1)/SnRK2.6/SRK2E is a major SnRK2-type protein kinase responsible for mediating ABA responses. Arabidopsis (Arabidopsis thaliana) expressing an epitope-tagged OST1 in the recessive ost1-3 mutant background was used for the copurification and identification of OST1-interacting proteins after osmotic stress and ABA treatments. These analyses, which were confirmed using bimolecular fluorescence complementation and coimmunoprecipitation, unexpectedly revealed homo- and heteromerization of OST1 with SnRK2.2, SnRK2.3, OST1, and SnRK2.8. Furthermore, several OST1-complexed proteins were identified as type 2A protein phosphatase (PP2A) subunits and as proteins involved in lipid and galactolipid metabolism. More detailed analyses suggested an interaction network between ABA-activated SnRK2-type protein kinases and several PP2A-type protein phosphatase regulatory subunits. pp2a double mutants exhibited a reduced sensitivity to ABA during seed germination and stomatal closure and an enhanced ABA sensitivity in root growth regulation. These analyses add PP2A-type protein phosphatases as another class of protein phosphatases to the interaction network of SnRK2-type protein kinases.

Non-specific phospholipase C4 mediates response to aluminum toxicity in Arabidopsis thaliana

Aluminum ions (Al) have been recognized as a major toxic factor for crop production in acidic soils. The first indication of the Al toxicity in plants is the cessation of root growth, but the mechanism of root growth inhibition is largely unknown. Here we examined the impact of Al on the expression, activity, and function of the non-specific phospholipase C4 (NPC4), a plasma membrane-bound isoform of NPC, a member of the plant phospholipase family, in Arabidopsis thaliana. We observed a lower expression of NPC4 using β-glucuronidase assay and a decreased formation of labeled diacylglycerol, product of NPC activity, using fluorescently labeled phosphatidylcholine as a phospholipase substrate in Arabidopsis WT seedlings treated with AlCl3 for 2 h. The effect on in situ NPC activity persisted for longer Al treatment periods (8, 14 h). Interestingly, in seedlings overexpressing NPC4, the Al-mediated NPC-inhibiting effect was alleviated at 14 h. However, in vitro activity and localization of NPC4 were not affected by Al, thus excluding direct inhibition by Al ions or possible translocation of NPC4 as the mechanisms involved in NPC-inhibiting effect. Furthermore, the growth of tobacco pollen tubes rapidly arrested by Al was partially rescued by the overexpression of AtNPC4 while Arabidopsis npc4 knockout lines were found to be more sensitive to Al stress during long-term exposure of Al at low phosphate conditions. Our observations suggest that NPC4 plays a role in both early and long-term responses to Al stress.

Aluminum ions alter the function of non-specific phospholipase C through the changes in plasma membrane physical properties

The first indication of the aluminum (Al) toxicity in plants growing in acidic soils is the cessation of root growth, but the detailed mechanism of Al effect is unknown. Here we examined the impact of Al stress on the activity of non-specific phospholipase C (NPC) in the connection with the processes related to the plasma membrane using fluorescently labeled phosphatidylcholine. We observed a rapid and significant decrease of labeled diacylglycerol (DAG), product of NPC activity, in Arabidopsis seedlings treated with AlCl₃. Interestingly, an application of the membrane fluidizer, benzyl alcohol, restored the level of DAG during Al treatment. Our observations suggest that the activity of NPC is affected by Al-induced changes in plasma membrane physical properties.

Arabidopsis non-specific phospholipase C1: characterization and its involvement in response to heat stress

The Arabidopsis non-specific phospholipase C (NPC) protein family is encoded by the genes NPC1 - NPC6. It has been shown that NPC4 and NPC5 possess phospholipase C activity; NPC3 has lysophosphatidic acid phosphatase activity. NPC3, 4 and 5 play roles in the responses to hormones and abiotic stresses. NPC1, 2 and 6 has not been studied functionally yet. We found that Arabidopsis NPC1 expressed in Escherichia coli possesses phospholipase C activity in vitro. This protein was able to hydrolyse phosphatidylcholine to diacylglycerol. NPC1-green fluorescent protein was localized to secretory pathway compartments in Arabidopsis roots. In the knock out T-DNA insertion line NPC1 (npc1) basal thermotolerance was impaired compared with wild-type (WT); npc1 exhibited significant decreases in survival rate and chlorophyll content at the seventh day after heat stress (HS). Conversely, plants overexpressing NPC1 (NPC1-OE) were more resistant to HS compared with WT. These findings suggest that NPC1 is involved in the plant response to heat.