Phospholipid-based signaling in plants

Exploring the connections between ER-based lipid metabolism and plasma membrane nanodomain signaling

Recent advancements in our understanding of cell membrane dynamics have shed light on the importance of plasma membrane (PM) nanodomains in plant cell signaling. Nevertheless, many aspects of membrane nanodomains, including their regulatory mechanisms and biological functions, remain enigmatic. To address this knowledge gap, our review article proposes a novel perspective wherein signaling pathways target endoplasmic reticulum (ER)-based lipid metabolism to exert control over the formation and function of membrane nanodomains. Subsequently, these nanodomains reciprocate by influencing the localization and activity of signaling molecules at the PM. We place a specific emphasis on ER-based enzymatic reactions, given the ER's central role in membrane lipid biosynthesis and its capacity to directly impact PM lipid composition, particularly with regard to saturation levels - an essential determinant of nanodomain properties. The interplay among cell signaling, glycerolipid metabolism, and PM nanodomain may create feedforward/feedback loops that fine-tune cellular responses to developmental and environmental cues.

A clade of receptor-like cytoplasmic kinases and 14-3-3 proteins coordinate inositol hexaphosphate accumulation

Inositol hexaphosphate (InsP6) is the major storage form of phosphorus in seeds. Reducing seed InsP6 content is a breeding objective in agriculture, as InsP6 negatively impacts animal nutrition and the environment. Nevertheless, how InsP6 accumulation is regulated remains largely unknown. Here, we identify a clade of receptor-like cytoplasmic kinases (RLCKs), named Inositol Polyphosphate-related Cytoplasmic Kinases 1-6 (IPCK1-IPCK6), deeply involved in InsP6 accumulation. The InsP6 concentration is dramatically reduced in seeds of ipck quadruple (T-4m/C-4m) and quintuple (C-5m) mutants, accompanied with the obviously increase of phosphate (Pi) concentration. The plasma membrane-localized IPCKs recruit IPK1 involved in InsP6 synthesis, and facilitate its binding and activity via phosphorylation of GRF 14-3-3 proteins. IPCKs also recruit IPK2s and PI-PLCs required for InsP4/InsP5 and InsP3 biosynthesis respectively, to form a potential IPCK-GRF-PLC-IPK2-IPK1 complex. Our findings therefore uncover a regulatory mechanism of InsP6 accumulation governed by IPCKs, shedding light on the mechanisms of InsP biosynthesis in eukaryotes.

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

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

PINOID-centered genetic interactions mediate auxin action in cotyledon formation

Auxin plays a key role in plant growth and development through auxin local synthesis, polar transport, and auxin signaling. Many previous reports on Arabidopsis have found that various types of auxin-related genes are involved in the development of the cotyledon, including the number, symmetry, and morphology of the cotyledon. However, the molecular mechanism by which auxin is involved in cotyledon formation remains to be elucidated. PID, which encodes a serine/threonine kinase localized to the plasma membrane, has been found to phosphorylate the PIN1 protein and regulate its polar distribution in the cell. The loss of function of pid resulted in an abnormal number of cotyledons and defects in inflorescence. It was interesting that the pid mutant interacted synergistically with various types of mutant to generate the severe developmental defect without cotyledon. PID and these genes were indicated to be strongly correlated with cotyledon formation. In this review, PID-centered genetic interactions, related gene functions, and corresponding possible pathways are discussed, providing a perspective that PID and its co-regulators control cotyledon formation through multiple pathways.

Arabidopsis thaliana phosphoinositide-specific phospholipase C 2 is required for Botrytis cinerea proliferation

Phospholipase C (PLC) plays a key role in lipid signaling during plant development and stress responses. PLC activation is one of the earliest responses during pathogen perception. Arabidopsis thaliana contains seven PLC encoding genes (AtPLC1 to AtPLC7) and two pseudogenes (AtPLC8 and AtPLC9), being AtPLC2 the most abundant isoform with constitutive expression in all plant organs. PLC has been linked to plant defense signaling, in particular to the production of reactive oxygen species (ROS). Previously, we demonstrated that AtPLC2 is involved in ROS production via the NADPH oxidase isoforms RBOHD activation during stomata plant immunity. Here we studied the role of AtPLC2 on plant resistance against the necrotrophic fungus Botrytis cinerea, a broad host-range and serious agricultural pathogen. We show that the AtPLC2-silenced (amiR PLC2) or null mutant (plc2-1) plants developed smaller B. cinerea lesions. Moreover, plc2-1 showed less ROS production and an intensified SA-dependent signaling upon infection, indicating that B. cinerea uses AtPLC2-triggered responses for a successful proliferation. Therefore, AtPLC2 is a susceptibility (S) gene that facilitates B. cinerea infection and proliferation.

Advances and opportunities in unraveling cold-tolerance mechanisms in the world's primary staple food crops

Temperatures below or above optimal growth conditions are among the major stressors affecting productivity, end-use quality, and distribution of key staple crops including rice (Oryza sativa), wheat (Triticum aestivum), and maize (Zea mays L.). Among temperature stresses, cold stress induces cellular changes that cause oxidative stress and slowdown metabolism, limit growth, and ultimately reduce crop productivity. Perception of cold stress by plant cells leads to the activation of cold-responsive transcription factors and downstream genes, which ultimately impart cold tolerance. The response triggered in crops to cold stress includes gene expression/suppression, the accumulation of sugars upon chilling, and signaling molecules, among others. Much of the information on the effects of cold stress on perception, signal transduction, gene expression, and plant metabolism are available in the model plant Arabidopsis but somewhat lacking in major crops. Hence, a complete understanding of the molecular mechanisms by which staple crops respond to cold stress remain largely unknown. Here, we make an effort to elaborate on the molecular mechanisms employed in response to low-temperature stress. We summarize the effects of cold stress on the growth and development of these crops, the mechanism of cold perception, and the role of various sensors and transducers in cold signaling. We discuss the progress in cold tolerance research at the genome, transcriptome, proteome, and metabolome levels and highlight how these findings provide opportunities for designing cold-tolerant crops for the future.

The wide world of non-mammalian phospholipase D enzymes

Phospholipase D (PLD) hydrolyses phosphatidylcholine (PtdCho) to produce free choline and the critically important lipid signaling molecule phosphatidic acid (PtdOH). Since the initial discovery of PLD activities in plants and bacteria, PLDs have been identified in a diverse range of organisms spanning the taxa. While widespread interest in these proteins grew following the discovery of mammalian isoforms, research into the PLDs of non-mammalian organisms has revealed a fascinating array of functions ranging from roles in microbial pathogenesis, to the stress responses of plants and the developmental patterning of flies. Furthermore, studies in non-mammalian model systems have aided our understanding of the entire PLD superfamily, with translational relevance to human biology and health. Increasingly, the promise for utilization of non-mammalian PLDs in biotechnology is also being recognized, with widespread potential applications ranging from roles in lipid synthesis, to their exploitation for agricultural and pharmaceutical applications.

Underpinning beneficial maize response to application of minimally processed homogenates of red and brown seaweeds

Sap from the fresh seaweed Kappaphycus alvarezii (KA) has been reported to improve crop growth, quality, and stress alleviation. However, limited studies are reported for the minimally processed aqueous homogenates (MPHs) derived from dry seaweeds. The present investigation was envisaged to characterize the MPHs from the red seaweed KA and a brown seaweed Sargassum wightii (SW) and also assess the effect of foliar application on maize (Zea mays) crop performance when applied alone or in proportions ranging from 0% to 100%. Two doses (0.35% and 0.7%) were compared with control. Both the MPHs contained several compounds like retronecine, tyrosyl-glycine, hexyl 2-furoate, 1-phosphatidyl-1D-myo-inositol, 12-(2,3-dihydroxycyclopentyl)-2-dodecanone, and trihomomethionine and many others that have known bioactivity for enhancing plant growth and providing stress tolerance. Both doses of MPHs enhanced crop growth and yield; however, the best response was in general observed at a lower dose. The MPH of SW at 100% gave the highest seed yield at a lower dose, which was also on par with that obtained under a lower dose of 100% KA. Other combinations, 80:20 and 40:60 KA : SW, were also found to give comparable yields. The highest dose of 100% MPH of SW was found on par with control, a phenomenon that was investigated in detail with respect to metabolites and antioxidant profile in leaves as well as membrane modeling. Higher ROS and certain sugar and organic acids were observed in 100% MPH of SW at a higher dose, although none of the antioxidant enzymes were significantly affected, nor was there any change in membrane characteristics of the leaf with respect to control as well as lower dose. Improvements in the seed yield were attributed to improved photosynthate production on account of higher dry matter accumulation in the MPH-treated plants, which may also be attributed to the presence of bioactive compounds in the biostimulants. In the future, it is imperative to direct scientific investigations towards the quantification and identification of the most effective concentrations of these compounds within MPHs to optimize plant responses. The study indicated the beneficial use of the MPHs towards increasing crop production by employing optimum dose as foliar spray to crops.

PLC1 mediated Cycloastragenol-induced stomatal movement by regulating the production of NO in Arabidopsis thaliana

BACKGROUND

Astragalus grows mainly in drought areas. Cycloastragenol (CAG) is a tetracyclic triterpenoid allelochemical extracted from traditional Chinese medicine Astragalus root. Phospholipase C (PLC) and Gα-submit of the heterotrimeric G-protein (GPA1) are involved in many biotic or abiotic stresses. Nitric oxide (NO) is a crucial gas signal molecule in plants.

RESULTS

In this study, using the seedlings of Arabidopsis thaliana (A. thaliana), the results showed that low concentrations of CAG induced stomatal closure, and high concentrations inhibited stomatal closure. 30 µmol·L-1 CAG significantly increased the relative expression levels of PLC1 and GPA1 and the activities of PLC and GTP hydrolysis. The stomatal aperture of plc1, gpa1, and plc1/gpa1 was higher than that of WT under CAG treatment. CAG increased the fluorescence intensity of NO in guard cells. Exogenous application of c-PTIO to WT significantly induced stomatal aperture under CAG treatment. CAG significantly increased the relative expression levels of NIA1 and NOA1. Mutants of noa1, nia1, and nia2 showed that NO production was mainly from NOA1 and NIA1 by CAG treatment. The fluorescence intensity of NO in guard cells of plc1, gpa1, and plc1/gpa1 was lower than WT, indicating that PLC1 and GPA1 were involved in the NO production in guard cells. There was no significant difference in the gene expression of PLC1 in WT, nia1, and noa1 under CAG treatment. The gene expression levels of NIA1 and NOA1 in plc1, gpa1, and plc1/gpa1 were significantly lower than WT, indicating that PLC1 and GPA1 were positively regulating NO production by regulating the expression of NIA1 and NOA1 under CAG treatment.

CONCLUSIONS

These results suggested that the NO accumulation was essential to induce stomatal closure under CAG treatment, and GPA1 and PLC1 acted upstream of NO.

Combined transcriptome and metabolome analysis reveal that the white and yellow mango pulp colors are associated with carotenoid and flavonoid accumulation, and phytohormone signaling

Mango (Mangifera indica L.) is a widely appreciated tropical fruit for its rich color and nutrition. However, knowledge on the molecular basis of color variation is limited. Here, we studied HY3 (yellowish-white pulp) and YX4 (yellow pulp), reaped with 24 h gap from the standard harvesting time. The carotenoids and total flavonoids increased with the advance of harvest time (YX4 > HY34). Transcriptome sequencing showed that higher expressions of the core carotenoid biosynthesis genes and flavonoid biosynthesis genes are correlated to their respective contents. The endogenous indole-3-acetic acid and jasmonic acid contents decreased but abscisic acid and ethylene contents increased with an increase in harvesting time (YX4 > HY34). Similar trends were observed for the corresponding genes. Our results indicate that the color differences are related to carotenoid and flavonoid contents, which in turn are influenced by phytohormone accumulation and signaling.

Drought and heat stress mediated activation of lipid signaling in plants: a critical review

Lipids are a principal component of plasma membrane, acting as a protective barrier between the cell and its surroundings. Abiotic stresses such as drought and temperature induce various lipid-dependent signaling responses, and the membrane lipids respond differently to environmental challenges. Recent studies have revealed that lipids serve as signal mediators forreducing stress responses in plant cells and activating defense systems. Signaling lipids, such as phosphatidic acid, phosphoinositides, sphingolipids, lysophospholipids, oxylipins, and N-acylethanolamines, are generated in response to stress. Membrane lipids are essential for maintaining the lamellar stack of chloroplasts and stabilizing chloroplast membranes under stress. However, the effects of lipid signaling targets in plants are not fully understood. This review focuses on the synthesis of various signaling lipids and their roles in abiotic stress tolerance responses, providing an essential perspective for further investigation into the interactions between plant lipids and abiotic stress.

Phosphoproteomics analysis of the effect of target of rapamycin kinase inhibition on Cucumis sativus in response to Podosphaera xanthii

Target of rapamycin (TOR) kinase is a conserved sensor of cell growth in yeasts, plants, and mammals. Despite the extensive research on the TOR complex in various biological processes, large-scale phosphoproteomics analysis of TOR phosphorylation events upon environmental stress are scarce. Powdery mildew caused by Podosphaera xanthii poses a major threat to the quality and yield of cucumber (Cucumis sativus L.). Previous studies concluded that TOR participated in abiotic and biotic stress responses. Hence, studying the underlying mechanism of TOR-P. xanthii infection is particularly important. In this study, we performed a quantitative phosphoproteomics studies of Cucumis against P. xanthii attack under AZD-8055 (TOR inhibitor) pretreatment. A total of 3384 phosphopeptides were identified from the 1699 phosphoproteins. The Motif-X analysis showed high sensitivity and specificity of serine sites under AZD-8055-treatment or P. xanthii stress, and TOR exhibited a unique preference for proline at +1 position and glycine at -1 position to enhance the phosphorylation response to P. xanthii. The functional analysis suggested that the unique responses were attributed to proteins related to plant hormone signaling, mitogen-activated protein kinase cascade signaling, phosphatidylinositol signaling system, and circadian rhythm; and calcium signaling- and defense response-related proteins. Our results provided rich resources for understanding the molecular mechanism of how the TOR kinase controlled plant growth and stress adaptation.

Recent Advances in Life History Transition with Nematode-Trapping Fungus Arthrobotrys oligospora and Its Application in Sustainable Agriculture

Parasitic nematodes cause great annual loss in the agricultural industry globally. Arthrobotrys oligospora is the most prevalent and common nematode-trapping fungus (NTF) in the environment and the candidate for the control of plant- and animal-parasitic nematodes. A. oligospora is also the first recognized and intensively studied NTF species. This review highlights the recent research advances of A. oligospora as a model to study the biological signals of the switch from saprophytism to predation and their sophisticated mechanisms for interacting with their invertebrate hosts, which is of vital importance for improving the engineering of this species as an effective biocontrol fungus. The application of A. oligospora in industry and agriculture, especially as biological control agents for sustainable purposes, was summarized, and we discussed the increasing role of A. oligospora in studying its sexual morph and genetic transformation in complementing biological control research.

The Arabidopsis thaliana trehalose-6-phosphate phosphatase gene AtTPPI regulates primary root growth and lateral root elongation

Roots are the main organs through which plants absorb water and nutrients. As the key phytohormone involved in root growth, auxin functions in plant environmental responses by modulating auxin synthesis, distribution and polar transport. The Arabidopsis thaliana trehalose-6-phosphate phosphatase gene AtTPPI can improve root architecture, and tppi1 mutants have significantly shortened primary roots. However, the mechanism underlying the short roots of the tppi1 mutant and the upstream signaling pathway and downstream genes regulated by AtTPPI are unclear. Here, we demonstrated that the AtTPPI gene could promote auxin accumulation in AtTPPI-overexpressing plants. By comparing the transcriptomic data of tppi1 and wild-type roots, we found several upregulations of auxin-related genes, including GH3.3, GH3.9 and GH3.12, may play an important role in the AtTPPI gene-mediated auxin transport signaling pathway, ultimately leading to changes in auxin content and primary root length. Moreover, increased AtTPPI expression can regulate primary root growth and lateral root elongation under different concentration of nitrate conditions. Overall, constitutive expression of AtTPPI increased auxin contents and improved lateral root elongation, constituting a new method for improving the nitrogen utilization efficiency of plants.

Dendrobium Multi-Omics Reveal Lipid Remodeling in Response to Freezing

Freezing damage is a common phenomenon responsible for reduced yields of economic crops. Regulation of lipid metabolism plays an important role in plant growth and adaptation during freezing. We previously carried out transcriptome and untargeted metabolome analyses to determine the regulation of flavonol and anthocyanin biosynthesis during freezing treatment (FT) and post-freezing recovery (FR) in Dendrobium catenatum. However, changes in lipid levels are hard to confirm by untargeted metabolomics analysis alone. Regulation of lipid metabolism in response to freezing is largely unknown in Dendrobium. In this study, a multi-omics strategy was used to offer a better means of studying metabolic flow during FT and FR. To this end, 6976 proteins were identified by the 4D_label-free proteome, including 5343 quantified proteins. For each of the two conditions, we enriched differentially accumulated proteins (DAPs) into 15 gene ontology (GO) terms, including primary metabolism, lipid metabolism, and photosynthesis processes. We also identified 7 lipid categories and 3672 lipid species using lipidome assays. We found significant remodeling occurring in the phospholipid category during FT and FR. We also found that most sphingolipids were significantly upregulated. An integrated multi-omics analysis revealed significant changes in the expression levels of 141 mRNAs and encoding proteins under both FT and FR conditions. During FT, phospholipase A (PLA) and phospholipase D (PLD) were associated with phospholipid editing and galactolipid remodeling. These results provide valuable new insights into how the freezing tolerance of D. catenatum might be improved by genetic engineering.

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.

Identification and expression analysis of phospholipase C family genes between different male fertility accessions in pepper

Phospholipase C (PLC) is one of the major lipid-hydrolyzing enzymes, involved in lipid-mediating signal pathway. PLCs have been found to play a significant role in the growth and development of plants. In this study, the genome-wide identification and characteristic analysis of CaPLC family genes in pepper were conducted and the expression of two CaPLC genes were investigated. The results showed that a total of 11 CaPLC family genes were systematically identified, which were distributed on five chromosomes and divided into two groups based on their evolutionary relevance. Some cis-elements responding to different hormones and stresses were screened in the promoters of CaPLC genes. Quantitative real-time PCR indicated that the expression of CaPIPLC1 and CaPIPLC5 in flowers were dozens of times higher than in other tissues. In addition, with the development of flower buds, the relative expressions of CaPIPLC1 and CaPIPLC5 gradually increased in fertile materials R1 and F₁. However, no expression of CaPIPLC1 and CaPIPLC5 were detected at all developmental stages of cytoplasmic male sterile lines (CMS) compared with fertile accessions. The study revealed the number and characteristics of the CaPLC family genes, which supplied a basic and systematic understanding of CaPLC family. In addition, these findings provided new insights into the role of CaPLC genes in pollen development and fertility restoration in pepper.

Dynamic DNA methylation changes reveal tissue-specific gene expression in sugarcane

DNA methylation is an important mechanism for the dynamic regulation of gene expression and silencing of transposons during plant developmental processes. Here, we analyzed genome-wide methylation patterns in sugarcane (Saccharum officinarum) leaves, roots, rinds, and piths at single-base resolution. DNA methylation patterns were similar among the different sugarcane tissues, whereas DNA methylation levels differed. We also found that DNA methylation in different genic regions or sequence contexts plays different roles in gene expression. Differences in methylation among tissues resulted in many differentially methylated regions (DMRs) between tissues, particularly CHH DMRs. Genes overlapping with DMRs tended to be differentially expressed (DEGs) between tissues, and these DMR-associated DEGs were enriched in biological pathways related to tissue function, such as photosynthesis, sucrose synthesis, stress response, transport, and metabolism. Moreover, we observed many DNA methylation valleys (DMVs), which always overlapped with transcription factors (TFs) and sucrose-related genes, such as WRKY, bZIP, WOX, SPS, and FBPase. Collectively, these findings provide significant insights into the complicated interplay between DNA methylation and gene expression and shed light on the epigenetic regulation of sucrose-related genes in sugarcane.

Series-temporal transcriptome profiling of cotton reveals the response mechanism of phosphatidylinositol signaling system in the early stage of drought stress

Plants are sessile organisms suffering severe environmental conditions. Drought stress is one of the major environmental issues that affect plant growth and productivity. Although complex regulatory gene networks of plants under drought stress have been analyzed extensively, the response mechanism in the early stage of drought stress is still rarely mentioned. Here, we performed transcriptome analyses on cotton samples treated for a short time (10 min, 30 min, 60 min, 180 min) using 10% PEG, which is used to simulate drought stress. The analysis of differently expressed genes (DEGs) showed that the number of DEGs in roots was obviously more than that in stems and leaves at the four time points and maintained >2000 FDEGs (DEGs appearing for the first time) from 10 min, indicating that root tissues of plants respond to drought stress quickly and continuously strongly. Gene ontology (GO) analysis showed that DEGs in roots were mainly enriched in protein modification and microtubule-based process. DEGs were found significantly enriched in phosphatidylinositol signaling system at 10 min through Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, implying the great importance of phosphatidylinositol signal in the early stage of drought stress. What was more, two co-expression modules, which were significantly positively correlated with drought stress, were found by Weighted Gene Co-expression Network Analysis (WGCNA). From one of the co-expression modules, we identified a hub-gene Gohir.A07G058200, which is annotated as "phosphatidylinositol 3- and 4-kinase" in phosphatidylinositol signaling system, and found this gene may interact with auxin-responsive protein. This result suggested that Gohir.A07G058200 may be involved in the crosstalk of phosphatidylinositol signal and auxin signal in the early stage of drought stress. In summary, through transcriptome sequencing, we found that phosphatidylinositol signaling system is an important signal transduction pathway in early stage in response to drought stress, and it may interact with auxin signal transduction through phosphatidylinositol 3- and 4-kinase.

Protein polarization: Spatiotemporal precisions in cell division and differentiation

Specification of cell polarity is vital to normal cell growth, morphogenesis, and function. As other eukaryotes, plants generate cellular polarity that is coordinated with tissue polarity and organ axes. In development, new cell types are generated by stem-cell division and differentiation, a process often involving proteins that are polarized to cortical domains at the plasma membrane. In the past decade, pioneering work using the model plant Arabidopsis identified multiple proteins that are polarized in dividing cells to instruct divisional behaviors and/or specify cell fates. In this review, we use these polarized cell-division regulators as example to summarize key mechanisms underlying protein polarization in plant cells. Recent progress underscores that self-organizing amplification processes are commonly involved in establishing cell polarity, and cellular polarity is influenced by both tissue-level and local mechanochemical cues. In addition, protein polarization during asymmetric cell division shows a distinct feature of temporal control in the stomatal lineage. We further discuss possible coordination between protein polarization and the progression of cell cycle in this developmental context.

Cytidinediphosphate diacylglycerol synthase—Mediated phosphatidic acid metabolism is crucial for early embryonic development of Arabidopsis

Embryonic development is a key developmental event in plant sexual reproduction; however, regulatory networks of plant early embryonic development, particularly the effects and functional mechanisms of phospholipid molecules are still unknown due to the limitation of sample collection and analysis. We innovatively applied the microspore-derived in vitro embryogenesis of Brassica napus and revealed the dynamics of phospholipid molecules, especially phosphatidic acid (PA, an important second messenger that plays an important role in plant growth, development, and stress responses), at different embryonic developmental stages by using a lipidomics approach. Further analysis of Arabidopsis mutants deficiency of CDS1 and CDS2 (cytidinediphosphate diacylglycerol synthase, key protein in PA metabolism) revealed the delayed embryonic development from the proembryo stage, indicating the crucial effect of CDS and PA metabolism in early embryonic development. Decreased auxin level and disturbed polar localization of auxin efflux carrier PIN1 implicate that CDS-mediated PA metabolism may regulate early embryogenesis through modulating auxin transport and distribution. These results demonstrate the dynamics and importance of phospholipid molecules during embryo development, and provide informative clues to elucidate the regulatory network of embryogenesis.

As an important stage of plant life cycle, embryogenesis initiates with fertilization and terminates with embryo maturation, and plays important roles for seed development. In Arabidopsis, embryogenesis can be divided into three general phases during which distinct developmental and physiological events occur: proembryo stage that starts with asymmetric division of zygote, the transition from globular to heart stage, and late embryogenesis which is marked by organ expansion and maturation. Genetics studies have identified the genes and network that play important regulatory roles in embryogenesis, however, effects and functional mechanisms of phospholipids molecules, the major building blocks of cell membranes and signal transduction cascades in mammals and plants, in embryogenesis remain unknown. To overcome the limitation of sample collection, we innovatively applied the microspore-derived in vitro embryogenesis of Brassica napus and revealed the dynamics of phospholipid molecules, especially phosphatidic acid (PA) at different embryonic developmental stages by using a lipidomics approach. Further genetics analysis revealed the crucial effect of CDS (cytidinediphosphate diacylglycerol synthase, key protein in PA metabolism)—mediated PA metabolism in early embryonic development through modulating auxin transport and distribution, demonstrating the dynamics and importance of phospholipid molecules during embryo development.

Regulatory Mechanism of Trap Formation in the Nematode-Trapping Fungi

Nematode-trapping (NT) fungi play a significant role in the biological control of plant- parasitic nematodes. NT fungi, as a predator, can differentiate into specialized structures called “traps” to capture, kill, and consume nematodes at a nutrient-deprived condition. Therefore, trap formation is also an important indicator that NT fungi transition from a saprophytic to a predacious lifestyle. With the development of gene knockout and multiple omics such as genomics, transcriptomics, and metabolomics, increasing studies have tried to investigate the regulation mechanism of trap formation in NT fungi. This review summarizes the potential regulatory mechanism of trap formation in NT fungi based on the latest findings in this field. Signaling pathways have been confirmed to play an especially vital role in trap formation based on phenotypes of various mutants and multi-omics analysis, and the involvement of small molecule compounds, woronin body, peroxisome, autophagy, and pH-sensing receptors in the formation of traps are also discussed. In addition, we also highlight the research focus for elucidating the mechanism underlying trap formation of NT fungi in the future.

Molecular Insights into Freezing Stress in Peach Based on Multi-Omics and Biotechnology: An Overview

In nature or field conditions, plants are frequently exposed to diverse environmental stressors. Among abiotic stresses, the low temperature of freezing conditions is a critical factor that influences plants, including horticultural crops, decreasing their growth, development, and eventually quality and productivity. Fortunately, plants have developed a mechanism to improve the tolerance to freezing during exposure to a range of low temperatures. In this present review, current findings on freezing stress physiology and genetics in peach (Prunus persica) were refined with an emphasis on adaptive mechanisms for cold acclimation, deacclimation, and reacclimation. In addition, advancements using multi-omics and genetic engineering approaches unravel the molecular physiological mechanisms, including hormonal regulations and their general perceptions of freezing tolerance in peach were comprehensively described. This review might pave the way for future research to the horticulturalists and research scientists to overcome the challenges of freezing temperature and improvement of crop management in these conditions.

Myco-Synergism Boosts Herbivory-Induced Maize Defense by Triggering Antioxidants and Phytohormone Signaling

BACKGROUND

Biocontrol strategies are the best possible and eco-friendly solution to develop resistance against O furnacalis and improve the maize yield. However, the knowledge about underlying molecular mechanisms, metabolic shifts, and hormonal signaling is limited.

METHODS

Here, we used an axenic and a consortium of entomopathogenic Beauveria bassiana OFDH1-5 and a pathogen-antagonistic Trichoderma asperellum GDFS1009 in maize and observed that consortium applications resulted in higher chlorophyll contents and antioxidants activities [superoxide dismutase (SOD), peroxidase (POD), proline, protease, and polyphenol oxidase (PPO)] with a decrease in O. furnacalis survival. We performed a comprehensive transcriptome and an untargeted metabolome profiling for the first time at a vegetative stage in fungal inoculated maize leaves at 0-, 12-, 24-, 48-, and 72-h post insect infestation.

RESULTS

The consortium of B. bassiana and T. asperellum leads to 80-95% of O. furnacalis mortality. A total of 13,156 differentially expressed genes were used for weighted gene coexpression network analysis. We identified the six significant modules containing thirteen candidate genes [protein kinase (GRMZM2G025459), acyl-CoA dehydrogenase (GRMZM5G864319), thioredoxin gene (GRMZM2G091481), glutathione S-transferase (GRMZM2G116273), patatin-like phospholipase gene (GRMZM2G154523), cytochrome P450 (GRMZM2G139874), protease inhibitor (GRMZM2G004466), (AC233926.1_FG002), chitinase (GRMZM2G453805), defensin (GRMZM2G392863), peroxidase (GRMZM2G144153), GDSL- like lipase (AC212068.4_FG005), and Beta-glucosidase (GRMZM2G031660)], which are not previously reported that are highly correlated with Jasmonic acid - Ethylene (JA-ET) signaling pathway and antioxidants. We detected a total of 130 negative and 491 positive metabolomic features using a ultrahigh-performance liquid chromatography ion trap time-of-flight mass spectrometry (UHPLC-QTOF-MS). Intramodular significance and real time-quantitative polymerase chain reaction (RT-qPCR) expressions showed that these genes are the true candidate genes. Consortium treated maize had higher jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) levels.

CONCLUSION

Our results provide insights into the genetics, biochemicals, and metabolic diversity and are useful for future biocontrol strategies against ACB attacks.

Genome-wide in silico identification of phospholipase D (PLD) gene family from Corchorus capsularis and Corchorus olitorius: reveals their responses to plant stress

Background

Plant grows in nature facing various types of abiotic stresses for their normal growth and development. During abiotic stress, plants evolve different types of mechanisms to survive in a hostile environment. Phospholipase D (PLD) plays important role in the regulation of diverse cellular processes including stress responses in plants. Member of PLD genes are well studied in different model plants; however, their functions in the jute are not clear yet.

Result

In the present study, a total of 12 and 11 PLD genes were identified in the genome of C. capsularis and C. olitorius, respectively. The presence of the two conserved HKD motifs in PLD genes except for CoPLDδ-2 in jute suggests their strong lipase activity. Twenty different motifs were found in the identified PLD genes, and PLD-β1, PLD-γ1, and all members of PLD-δ1 of both jute species contained the highest number of motifs. Phylogenetic analysis showed the close evolutionary relationship among the five groups of jute PLD proteins along with the PLD proteins from Arabidopsis. Tissue-specific expression pattern of PLDα1-2, PLD-α2, PLDβ1, PLDγ1, and PLDδ1 of two jute species suggested their involvement in plant growth and development. However, the expression pattern of PLDα1-2, PLDα1-3, PLD-α4, PLDδ1, and PLDδ3 indicated their association during waterlogging stress. In addition, PLD-α2, PLDβ1, and PLDδ2 seemed to be involved in drought stress as well as salinity stress.

Conclusion

This genome-wide identification of jute PLD genes from C. capsularis and C. olitorius will help to further functional characterization of the PLD genes for developing stress-tolerant jute variety.

Auxin transport in developing protophloem: A case study in canalization

Spatiotemporal cues orchestrate the development of organs and cellular differentiation in multicellular organisms. For instance, in the root apical meristem an auxin gradient patterns the transition from stem cell maintenance to transit amplification and eventual differentiation. Among the proximal tissues generated by this growth apex, the early, so-called protophloem, is the first tissue to differentiate. This observation has been linked to increased auxin activity in the developing protophloem sieve element cell files as compared to the neighboring tissues. Here we review recent progress in the characterization of the unique mechanism by which auxin canalizes its activity in the developing protophloem and fine-tunes its own transport to guide proper timing of protophloem sieve element differentiation.

Identification of key genes and molecular mechanisms associated with temperature stress in lentil

Extreme temperature is one of the serious threats to crop production in present and future scenarios of global climate changes. Lentil (Lens culinaris) is an important crop, and there is a serious lack of genetic information regarding environmental and temperature stresses responses. This study is the first report of evaluation of key genes and molecular mechanisms related to temperature stresses in lentil using the RNA sequencing technique. De novo transcriptome assembly created 44,673 contigs and differential gene expression analysis revealed 7494 differentially expressed genes between the temperature stresses and control group. Basic annotation of generated transcriptome assembly in our study led to the identification of 2765 novel transcripts that have not been identified yet in lentil genome draft v1.2. In addition, several unigenes involved in mechanisms of temperature sensing, calcium and hormone signaling and DNA-binding transcription factor activity were identified. Also, common mechanisms in response to temperature stresses, including the proline biosynthesis, the photosynthetic light reactions balancing, chaperone activity and circadian rhythms, are determined by the hub genes through the protein-protein interaction networks analysis. Deciphering the mechanisms of extreme temperature tolerance would be a new way for developing crops with enhanced plasticity against climate change. In general, this study has identified set of mechanisms and various genes related to cold and heat stresses which will be useful in better understanding of the lentil's reaction to temperature stresses.

Phospholipase C (AoPLC2) regulates mycelial development, trap morphogenesis, and pathogenicity of the nematode-trapping fungus Arthrobotrys oligospora

AIMS

Phospholipase C (PLC) is a hydrolase involved in signal transduction in eukaryotic cells. This study aimed to understand the function of PLC in the nematode-trapping fungus Arthrobotrys oligospora.

METHODS AND RESULTS

Orthologous PLC (AoPLC2) of A. oligospora was functionally analysed using gene disruption and multi-phenotypic analysis. Disrupting Aoplc2 caused a deformation of partial hyphal cells (about 10%) and conidia (about 50%), decreased the number of nuclei in both conidia and hyphal cells, and increased the accumulation of lipid droplets. Meanwhile, the sporulation-related genes fluG and abaA were downregulated in ΔAoplc2 mutants than in the wild-type strain. Moreover, ΔAoplc2 mutants were more sensitive to osmotic stressors. Importantly, the number of traps, electron-dense bodies in traps, and nematicidal activity of ΔAoplc2 mutants were reduced, and the shape of the traps was deformed. In addition, AoPLC2 was involved in the biosynthesis of secondary metabolites in A. oligospora.

CONCLUSIONS

AoPLC2 plays an important role in the development of hyphae, spores, and cell nuclei, responses to stress, formation of traps, and predation of nematodes in A. oligospora.

SIGNIFICANCE AND IMPACT OF STUDY

This study reveals the various functions of phospholipase C and elucidates the regulation of trap morphogenesis in nematode-trapping fungi.

Lipid Signaling Modulates the Response to Fumonisin Contamination and Its Source, Fusarium verticillioides, in Maize

Fumonisin-contaminated maize (Zea mays L.) products are a major health concern because of their toxic effects in humans and animals. Breeding maize for increased mycotoxin resistance is one of the key sustainable strategies for mitigating the effects of fumonisin contamination. Recent studies suggest a link between fumonisin accumulation and plant lipid and oxylipin profiles. However, the data collected so far do not reveal a cause-and-effect relationship. In this study, to decipher the multifactorial nature of mycotoxin resistance and plant-pathogen interaction mechanisms, we examined the oxylipin and complex lipid profiles of two maize hybrids (H21 and H22, the latter showing significantly lower FBs content) grown in the open field in two locations over 3years. Untargeted ultra-high performance liquid chromatography coupled with quadrupole-time-of-flight (UHPLC-Q-TOF), together with chemometrics analysis, successfully distinguished between the two hybrids as having low- and high-level fumonisin contamination. Considering that H21 and H22 were exposed to the same environmental factors, the higher activation of lipid signaling systems in H22 suggests that other routes are enabled in the less susceptible hybrids to limit fumonisin B (FB) accumulation. Our results highlighted the crucial role played by oxylipin and sphingolipid signaling in modulating the complex maize response to F. verticillioides infection. Overall, our results returned a global view on the changes in lipid metabolites related to fumonisin accumulation under open field conditions, and revealed a strong activation of the lipid signaling cascade in maize in the presence of FB₁.

Lipidomic metabolism associated with acetic acid priming-induced salt tolerance in Carex rigescens

Acetic acid priming may mitigate salt stress to plants by modulating lipid metabolism. Carex rigescens is a stress-tolerant turfgrass species with a widespread distribution in north China. The objective of this study was to figure out whether modification of lipid profiles, including the contents, compositions and saturation levels of leaf lipids, may contribute to acetic acid modulated salt tolerance in C. rigescens. Plants of C. rigescens were primed with or without acetic acid (30 mM) and subsequently exposed to salt stress (300 mM NaCl) for 15 days. Salt stress affected the physiological performance of C. rigescens, while acetic acid-primed plants showed significantly lower malondialdehyde content, proline content, and electrolyte leakage than non-primed plants under salt stress. Acetic acid priming enhanced the contents of phospholipids and glycolipids involved in membrane stabilization and stress signaling (phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, digalactosyl diacylglycerol, monogalactosyl diacylglycerol, and sulfoquinovosyldiacylglycerol), reduced the content of toxic lipid intermediates (free fatty acids) during subsequent exposure to salt stress. Furthermore, expression levels of genes involved in lipid metabolism such as CK and PLDα changed due to acetic acid priming. These results demonstrated that acetic acid priming could enhance salt tolerance of C. rigescens by regulating lipid metabolism. The lipids could be used as biomarkers to select for salt-tolerant grass germplasm.

In Vitro Growth Conditions Boost Plant Lipid Remodelling and Influence Their Composition

Acyl-lipids are vital components for all life functions of plants. They are widely studied using often in vitro conditions to determine inter alia the impact of genetic modifications and the description of biochemical and physiological functions of enzymes responsible for acyl-lipid metabolism. What is currently lacking is knowledge of if these results also hold in real environments-in in vivo conditions. Our study focused on the comparative analysis of both in vitro and in vivo growth conditions and their impact on the acyl-lipid metabolism of Camelina sativa leaves. The results indicate that in vitro conditions significantly decreased the lipid contents and influenced their composition. In in vitro conditions, galactolipid and trienoic acid (16:3 and 18:3) contents significantly declined, indicating the impairment of the prokaryotic pathway. Discrepancies also exist in the case of acyl-CoA:lysophospholipid acyltransferases (LPLATs). Their activity increased about 2-7 times in in vitro conditions compared to in vivo. In vitro conditions also substantially changed LPLATs' preferences towards acyl-CoA. Additionally, the acyl editing process was three times more efficient in in vitro leaves. The provided evidence suggests that the results of acyl-lipid research from in vitro conditions may not completely reflect and be directly applicable in real growth environments.

Cloning and Functional Identification of Phosphoethanolamine Methyltransferase in Soybean (Glycine max)

Phosphoethanolamine methyltransferase (PEAMT), a kind of S-adenosylmethionine-dependent methyltransferases, plays an essential role in many biological processes of plants, such as cell metabolism, stress response, and signal transduction. It is the key rate-limiting enzyme that catalyzes the three-step methylation of ethanolamine-phosphate (P-EA) to phosphocholine (P-Cho). To understand the unique function of PEAMT in soybean (Glycine max) lipid synthesis, we cloned two phosphoethanolamine methyltransferase genes GmPEAMT1 and GmPEAMT2, and performed functional identification. Both GmPEAMT1 and GmPEAMT2 contain two methyltransferase domains. GmPEAMT1 has the closest relationship with MtPEAMT2, and GmPEAMT2 has the closest relationship with CcPEAMT. GmPEAMT1 and GmPEAMT2 are located in the nucleus and endoplasmic reticulum. There are many light response elements and plant hormone response elements in the promoters of GmPEAMT1 and GmPEAMT2, indicating that they may be involved in plant stress response. The yeast cho2 opi3 mutant, co-expressing Arabidopsis thaliana phospholipid methyltransferase (PLMT) and GmPEAMT1 or GmPEAMT2, can restore normal growth, indicating that GmPEAMTs can catalyze the methylation of phosphoethanolamine to phosphate monomethylethanolamine. The heterologous expression of GmPEAMT1 and GmPEAMT2 can partially restore the short root phenotype of the Arabidopsis thaliana peamt1 mutant, suggesting GmPEAMTs have similar but different functions to AtPEAMT1.

NCP2/RHD4/SAC7, SAC6 and SAC8 phosphoinositide phosphatases are required for PtdIns4P and PtdIns(4,5)P2 homeostasis and Arabidopsis development

Phosphoinositides play important roles in plant growth and development. Several SAC domain phosphoinositide phosphatases have been reported to be important for plant development. Here, we show functional analysis of SUPPRESSOR OF ACTIN 6 (SAC6) to SAC8 in Arabidopsis, a subfamily of phosphoinositide phosphatases containing SAC-domain and two transmembrane motifs. We isolated an Arabidopsis mutant ncp2 that lacked cotyledons in seedling and embryo in pid, a background defective in auxin signaling and transport. NCP2 encodes RHD4/SAC7 phosphoinositide phosphatase. SAC6, SAC7 and SAC8 exhibit overlapping and specific expression patterns in seedling and embryo. The sac6 sac7 embryos either fail to develop into seeds, or have three or four cotyledons. The embryo development of sac7 sac8 and sac6 sac7 sac8 mutants is significantly delayed or lethal, and the seedlings are arrested at early stages. Auxin maxima are decreased in double and triple sac mutants. The contents of PtdIns4P and PtdIns(4,5)P2 in sac6 sac7 and sac7 sac8 mutants are dramatically increased. Protein trafficking of the plasma membrane (PM)-localized protein PIN1 and PIN2 from trans-Golgi network/early endosome back to PM is delayed in sac7 sac8 mutants. These results indicate that SAC6-SAC8 are essential for maintaining homeostasis of PtdIns4P and PtdIns(4,5)P2, and auxin-mediated development in Arabidopsis.

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.

Enhancer-mediated reporter gene expression in Arabidopsis thaliana: a forward genetic screen

Gene expression is controlled and regulated by interactions between cis-regulatory DNA elements (CREs) and regulatory proteins. Enhancers are one of the most important classes of CREs in eukaryotes. Eukaryotic genes, especially those related to development or responses to environmental cues, are often regulated by multiple enhancers in different tissues and/or at different developmental stages. Remarkably, little is known about the molecular mechanisms by which enhancers regulate gene expression in plants. We identified a distal enhancer, CREβ, which regulates the expression of AtDGK7, which encodes a diacylglycerol kinase in Arabidopsis. We developed a transgenic line containing the luciferase reporter gene (LUC) driven by CREβ fused with a minimal cauliflower mosaic virus (CaMV) 35S promoter. The CREβ enhancer was shown to play a role in the response to osmotic pressure of the LUC reporter gene. A forward genetic screen pipeline based on the transgenic line was established to generate mutations associated with altered expression of the LUC reporter gene. We identified a suite of mutants with variable LUC expression levels as well as different segregation patterns of the mutations in populations. We demonstrate that this pipeline will allow us to identify trans-regulatory factors associated with CREβ function as well as those acting in the regulation of the endogenous AtDGK7 gene.

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.

Attracted to membranes: lipid-binding domains in plants

Membranes are essential for cells and organelles to function. As membranes are impermeable to most polar and charged molecules, they provide electrochemical energy to transport molecules across and create compartmentalized microenvironments for specific enzymatic and cellular processes. Membranes are also responsible for guided transport of cargoes between organelles and during endo- and exocytosis. In addition, membranes play key roles in cell signaling by hosting receptors and signal transducers and as substrates and products of lipid second messengers. Anionic lipids and their specific interaction with target proteins play an essential role in these processes, which are facilitated by specific lipid-binding domains. Protein crystallography, lipid-binding studies, subcellular localization analyses, and computer modeling have greatly advanced our knowledge over the years of how these domains achieve precision binding and what their function is in signaling and membrane trafficking, as well as in plant development and stress acclimation.

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

In plants, defense-associated signal transduction involves key membrane-related processes, such as phospholipid-based signaling and membrane trafficking. Coordination of these processes occurs in the lipid bilayer of plasma membrane (PM) and luminal/extracellular membranes. Deciphering the spatiotemporal organization of phospholipids and lipid-protein interactions provides crucial information on the mechanisms that link phospholipid-based signaling and membrane trafficking in plant immunity. In this review, we summarize recent advances in our understanding of these connections, including deployment of key enzymes and molecules in phospholipid pathways, and roles of lipid diversity in membrane trafficking. We highlight the mechanisms that mediate feedback between phospholipid-based signaling and membrane trafficking to regulate plant immunity, including their novel roles in balancing endocytosis and exocytosis.

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.

Cellular requirements for PIN polar cargo clustering in Arabidopsis thaliana

Cell and tissue polarization is fundamental for plant growth and morphogenesis. The polar, cellular localization of Arabidopsis PIN-FORMED (PIN) proteins is crucial for their function in directional auxin transport. The clustering of PIN polar cargoes within the plasma membrane has been proposed to be important for the maintenance of their polar distribution. However, the more detailed features of PIN clusters and the cellular requirements of cargo clustering remain unclear. Here, we characterized PIN clusters in detail by means of multiple advanced microscopy and quantification methods, such as 3D quantitative imaging or freeze-fracture replica labeling. The size and aggregation types of PIN clusters were determined by electron microscopy at the nanometer level at different polar domains and at different developmental stages, revealing a strong preference for clustering at the polar domains. Pharmacological and genetic studies revealed that PIN clusters depend on phosphoinositol pathways, cytoskeletal structures and specific cell-wall components as well as connections between the cell wall and the plasma membrane. This study identifies the role of different cellular processes and structures in polar cargo clustering and provides initial mechanistic insight into the maintenance of polarity in plants and other systems.

Recent advances in bio-chemical, molecular and physiological aspects of membrane lipid derivatives in plant pathology

Plant pathogens pose a significant threat to the food industry and food security accounting for 10-40% crop losses annually on a global scale. Economic losses from plant diseases are estimated at $300B for major food crops and are associated with reduced food availability and accessibility and also high food costs. Although strategies exist to reduce the impact of diseases in plants, many of these introduce harmful chemicals to our food chain. Therefore, it is important to understand and utilize plants' immune systems to control plant pathogens to enable more sustainable agriculture. Lipids are core components of cell membranes and as such are part of the first line of defense against pathogen attack. Recent developments in omics technologies have advanced our understanding of how plant membrane lipid biosynthesis, remodelling and/or signalling modulate plant responses to infection. Currently, there is limited information available in the scientific literature concerning lipid signalling targets and their biochemical and physiological consequences in response to plant pathogens. This review focusses on the functions of membrane lipid derivatives and their involvement in plant responses to pathogens as biotic stressors. We describe major plant defense systems including systemic-acquired resistance, basal resistance, hypersensitivity and the gene-for-gene concept in this context.

Autophagy-mediated compartmental cytoplasmic deletion is essential for tobacco pollen germination and male fertility

In plants, macroautophagy/autophagy has mainly been associated with stress-related processes but how it impacts normal physiological and developmental processes remains largely unexplored. Pollen germination is the critical first step toward fertilization in flowering plants. It is metabolically demanding and relies on high levels of cytoplasmic reorganization activities to support a dramatic morphological transformation that underlies the development of a pollen tube as the conduit to deliver sperm for fertilization. The role of autophagy in this process remains unclear. Here we provide evidence that pollen germination is accompanied by elevated autophagic activity and successful pollen tube emergence depends on autophagy-mediated cytoplasmic deletion. Genetic and cytological experiments demonstrate that inhibition of autophagy prevents pollen germination while induces the persistence of a layer of undegraded cytoplasm at the germination aperture. Together, these results unveil a novel compartmentalized autophagy. Furthermore, high-throughput comparative lipidomic analyses show that suppressed autophagy-induced inhibition of pollen germination is accompanied by altered profiles of stored and signaling lipids. Proteomic analyses reveal that autophagy likely exert its role in pollen germination via downstream mitochondria-related pathways. These findings reveal a critical role for autophagy in initiating pollen germination and provide evidences for compartmental cytoplasmic deletion being crucial for male fertility. Abbreviations: 3-MA: 3-methyladenine; ATG: autophagy-related gene; Cer: ceramide; CL: cardiolipin; Con A: concanamycin A; DAG: diradylglycerol; GO: gene ontology; HAG: hour after germination; LC-MS: liquid chromatography-mass spectrometry; MAG: min after germination; MDC: monodansylcadaverine; PE: phosphatidylethanolamine; PI: phosphatidylinositol; PLD: phospholipase D; PtdIns3K: phosphatidylinositol 3-kinase; RT-qPCR: quantitative real-time reverse transcription PCR; TAG: triradylglycerol; TEM: transmission electron microscopy; TMT: tandem mass tagging.

Metabolomic adjustments in the orchid mycorrhizal fungus Tulasnella calospora during symbiosis with Serapias vomeracea

All orchids rely on mycorrhizal fungi for organic carbon, at least during early development. In fact, orchid seed germination leads to the formation of a protocorm, a heterotrophic postembryonic structure colonized by intracellular fungal coils, thought to be the site of nutrient transfer. The molecular mechanisms underlying mycorrhizal interactions and metabolic changes induced by this symbiosis in both partners remain mostly unknown. We studied plant-fungus interactions in the mycorrhizal association between the Mediterranean orchid Serapias vomeracea and the basidiomycete Tulasnella calospora using nontargeted metabolomics. Plant and fungal metabolomes obtained from symbiotic structures were compared with those obtained under asymbiotic conditions. Symbiosis induced substantial metabolomic alterations in both partners. In particular, structural and signaling lipid compounds increased markedly in the external fungal mycelium growing near the symbiotic protocorms, whereas chito-oligosaccharides were identified uniquely in symbiotic protocorms. This work represents the first description of metabolic changes occurring in orchid mycorrhiza. These results - combined with previous transcriptomic data - provide novel insights on the mechanisms underlying the orchid mycorrhizal association and open intriguing questions on the role of fungal lipids in this symbiosis.

Root Adaptation via Common Genetic Factors Conditioning Tolerance to Multiple Stresses for Crops Cultivated on Acidic Tropical Soils

Crop tolerance to multiple abiotic stresses has long been pursued as a Holy Grail in plant breeding efforts that target crop adaptation to tropical soils. On tropical, acidic soils, aluminum (Al) toxicity, low phosphorus (P) availability and drought stress are the major limitations to yield stability. Molecular breeding based on a small suite of pleiotropic genes, particularly those with moderate to major phenotypic effects, could help circumvent the need for complex breeding designs and large population sizes aimed at selecting transgressive progeny accumulating favorable alleles controlling polygenic traits. The underlying question is twofold: do common tolerance mechanisms to Al toxicity, P deficiency and drought exist? And if they do, will they be useful in a plant breeding program that targets stress-prone environments. The selective environments in tropical regions are such that multiple, co-existing regulatory networks may drive the fixation of either distinctly different or a smaller number of pleiotropic abiotic stress tolerance genes. Recent studies suggest that genes contributing to crop adaptation to acidic soils, such as the major Arabidopsis Al tolerance protein, AtALMT1, which encodes an aluminum-activated root malate transporter, may influence both Al tolerance and P acquisition via changes in root system morphology and architecture. However, trans-acting elements such as transcription factors (TFs) may be the best option for pleiotropic control of multiple abiotic stress genes, due to their small and often multiple binding sequences in the genome. One such example is the C2H2-type zinc finger, AtSTOP1, which is a transcriptional regulator of a number of Arabidopsis Al tolerance genes, including AtMATE and AtALMT1, and has been shown to activate AtALMT1, not only in response to Al but also low soil P. The large WRKY family of transcription factors are also known to affect a broad spectrum of phenotypes, some of which are related to acidic soil abiotic stress responses. Hence, we focus here on signaling proteins such as TFs and protein kinases to identify, from the literature, evidence for unifying regulatory networks controlling Al tolerance, P efficiency and, also possibly drought tolerance. Particular emphasis will be given to modification of root system morphology and architecture, which could be an important physiological "hub" leading to crop adaptation to multiple soil-based abiotic stress factors.

The value of asymmetry: how polarity proteins determine plant growth and morphology

Cell polarity is indispensable for forming complex multicellular organisms. Proteins that polarize at specific plasma membrane domains can either serve as scaffolds for effectors or coordinate intercellular communication and transport. Here, I give an overview of polarity protein complexes and their fundamental importance for plant development, and summarize novel mechanistic insights into their molecular networks. Examples are presented for proteins that polarize at specific plasma membrane domains to orient cell division planes, alter cell fate progression, control transport, direct cell growth, read global polarity axes, or integrate external stimuli into plant growth. The recent advances in characterizing protein polarity during plant development enable a better understanding of coordinated plant growth and open up intriguing paths that could provide a means to modulate plant morphology and adaptability in the future.

Lipid kinases PIP5K7 and PIP5K9 are required for polyamine-triggered K+ efflux in Arabidopsis roots

Polyamines, such as putrescine, spermidine and spermine (Spm), are low-molecular-weight polycationic molecules present in all living organisms. Despite their implication in plant cellular processes, little is known about their molecular mode of action. Here, we demonstrate that polyamines trigger a rapid increase in the regulatory membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP₂ ), and that this increase is required for polyamine effects on K⁺ efflux in Arabidopsis roots. Using in vivo ³² P_i -labelling of Arabidopsis seedlings, low physiological (μm) concentrations of Spm were found to promote a rapid PIP₂ increase in roots that was time- and dose-dependent. Confocal imaging of a genetically encoded PIP₂ biosensor revealed that this increase was triggered at the plasma membrane. Differential ³² P_i -labelling suggested that the increase in PIP₂ was generated through activation of phosphatidylinositol 4-phosphate 5-kinase (PIP5K) activity rather than inhibition of a phospholipase C or PIP₂ 5-phosphatase activity. Systematic analysis of transfer DNA insertion mutants identified PIP5K7 and PIP5K9 as the main candidates involved in the Spm-induced PIP₂ response. Using non-invasive microelectrode ion flux estimation, we discovered that the Spm-triggered K⁺ efflux response was strongly reduced in pip5k7 pip5k9 seedlings. Together, our results provide biochemical and genetic evidence for a physiological role of PIP₂ in polyamine-mediated signalling controlling K⁺ flux in plants.

Multiple basic amino acid residues contribute to phosphatidic acid-mediated inhibition of rice potassium channel OsAKT2

Anionic phospholipid phosphatidic acid (PA) behaves as an important second messenger involved in many cellular processes, such as development, cytoskeletal dynamics, vesicle trafficking, and stress response. Recently, it was reported that PA can directly bind with the rice Shaker K⁺ channel OsAKT2 to inhibit its channel activity. Two adjacent arginine residues (R644 and R645) in ANK domain were identified as a PA-binding site essential to the PA-mediated inhibition of OsAKT2. However, there may be still other PA-binding sites unidentified in OsAKT2. Here, using a PA biosensor (PAleon), we found that the exogenous PA treatment significantly increased the PA level at the plasma membrane of Xenopus oocytes which were used to express OsAKT2 for electrophysiological assays. As reported previously, exogenous PA markedly inhibited OsAKT2 K⁺ currents. Replacement of two adjacent basic residues (R190 and K191) in the S4 voltage sensor by glycine completely abolished the time-dependent K⁺ currents of OsAKT2, but this variant was insensitive to PA treatment. In addition, we also identified other two adjacent arginines (R755 and R756) located in the cytosolic domain as a PA-binding site, which were also essential to the PA-mediated inhibition of OsAKT2. These results provide a more comprehensive understanding of the PA-K⁺ channel interaction mechanism. Combining the findings here with the previous study, we propose that multiple basic residues (R190/K191, R644/R645, and R755/R756) in different domains of OsAKT2 contribute to PA-mediated regulation of OsAKT2.

Signalling Pinpointed to the Tip: The Complex Regulatory Network That Allows Pollen Tube Growth

Plants display a complex life cycle, alternating between haploid and diploid generations. During fertilisation, the haploid sperm cells are delivered to the female gametophyte by pollen tubes, specialised structures elongating by tip growth, which is based on an equilibrium between cell wall-reinforcing processes and turgor-driven expansion. One important factor of this equilibrium is the rate of pectin secretion mediated and regulated by factors including the exocyst complex and small G proteins. Critically important are also non-proteinaceous molecules comprising protons, calcium ions, reactive oxygen species (ROS), and signalling lipids. Among the latter, phosphatidylinositol 4,5-bisphosphate and the kinases involved in its formation have been assigned important functions. The negatively charged headgroup of this lipid serves as an interaction point at the apical plasma membrane for partners such as the exocyst complex, thereby polarising the cell and its secretion processes. Another important signalling lipid is phosphatidic acid (PA), that can either be formed by the combination of phospholipases C and diacylglycerol kinases or by phospholipases D. It further fine-tunes pollen tube growth, for example by regulating ROS formation. How the individual signalling cues are intertwined or how external guidance cues are integrated to facilitate directional growth remain open questions.

Phospholipid Signaling Is a Component of the Salicylic Acid Response in Plant Cell Suspension Cultures

Salicylic acid (SA) is an important signaling molecule involved in plant defense. While many proteins play essential roles in SA signaling, increasing evidence shows that responses to SA appear to involve and require lipid signals. The phospholipid-generated signal transduction involves a family of enzymes that catalyze the hydrolysis or phosphorylation of phospholipids in membranes to generate signaling molecules, which are important in the plant cellular response. In this review, we focus first, the role of SA as a mitigator in biotic/abiotic stress. Later, we describe the experimental evidence supporting the phospholipid–SA connection in plant cells, emphasizing the roles of the secondary lipid messengers (phosphatidylinositol 4,5-bisphosphate (PIP₂) and phosphatidic acid (PA)) and related enzymes (phospholipase D (PLD) and phospholipase C (PLC)). By placing these recent finding in context of phospholipids and SA in plant cells, we highlight the role of phospholipids as modulators in the early steps of SA triggered transduction in plant cells.