Increased expression of phospholipase Dα1 in guard cells decreases water loss with improved seed production under drought in Brassica napus

Pivotal role of heterotrimeric G protein in the crosstalk between sugar signaling and abiotic stress response in plants

Heterotrimeric G-proteins are key modulators of multiple signaling and developmental pathways in plants, in which they act as molecular switches to engage in transmitting various stimuli signals from outside into the cells. Substantial studies have identified G proteins as essential components of the organismal response to abiotic stress, leading to adaptation and survival in plants. Meanwhile, sugars are also well acknowledged key players in stress perception, signaling, and gene expression regulation. Connections between the two significant signaling pathways in stress response are of interest to a general audience in plant biology. In this article, advances unraveling a pivotal role of G proteins in the process of sugar signals outside the cells being translated into the operation of autophagy in cells during stress are reviewed. In addition, we have presented recent findings on G proteins regulating the response to drought, salt, alkali, cold, heat and other abiotic stresses. Perspectives on G-protein research are also provided in the end. Since G protein signaling regulates many agronomic traits, elucidation of detailed mechanism of the related pathways would provide useful insights for the breeding of abiotic stress resistant and high-yield crops.

Overexpression of OsNAR2.1 by OsNAR2.1 promoter increases drought resistance by increasing the expression of OsPLDα1 in rice

BACKGROUND

pOsNAR2.1:OsNAR2.1 expression could significantly increase nitrogen uptake efficiency and grain yield of rice.

RESULT

This study reported the effects of overexpression of OsNAR2.1 by OsNAR2.1 promoter on physiological and agronomic traits associated with drought tolerance. In comparison to the wild-type (WT), the pOsNAR2.1:OsNAR2.1 transgenic lines exhibited a significant improvement in survival rate when subjected to drought stress and then irrigation. Under limited water supply conditions, compared with WT, the photosynthesis and water use efficiency (WUE) of transgenic lines were increased by 39.2% and 28.8%, respectively. Finally, the transgenic lines had 25.5% and 66.4% higher grain yield than the WT under full watering and limited water supply conditions, respectively. Compared with the WT, the agronomic nitrogen use efficiency (NUE) of transgenic lines increased by 25.5% and 66.4% under full watering and limited water supply conditions, and the N recovery efficiency of transgenic lines increased by 29.3% and 50.2%, respectively. The interaction between OsNAR2.1 protein and OsPLDα1 protein was verified by yeast hybrids. After drought treatment, PLDα activity on the plasma membrane of the transgenic line increased 85.0% compared with WT.

CONCLUSION

These results indicated that pOsNAR2.1:OsNAR2.1 expression could improve the drought resistance of rice by increasing nitrogen uptake and regulating the expression of OsPLDα1.

Functional genomics of Brassica napus: Progresses, challenges, and perspectives

Brassica napus, commonly known as rapeseed or canola, is a major oil crop contributing over 13% to the stable supply of edible vegetable oil worldwide. Identification and understanding the gene functions in the B. napus genome is crucial for genomic breeding. A group of genes controlling agronomic traits have been successfully cloned through functional genomics studies in B. napus. In this review, we present an overview of the progress made in the functional genomics of B. napus, including the availability of germplasm resources, omics databases and cloned functional genes. Based on the current progress, we also highlight the main challenges and perspectives in this field. The advances in the functional genomics of B. napus contribute to a better understanding of the genetic basis underlying the complex agronomic traits in B. napus and will expedite the breeding of high quality, high resistance and high yield in B. napus varieties.

DEAD-box RNA helicase 6 regulates drought and abscisic acid stress responses in rapeseed (Brassica napus)

DEAD-box RNA helicase is a major subfamily of RNA helicases with vital roles played in plant growth, development, and plant-environment interactions. RNA helicase 6 in rapeseed (Brassica napus) (BnRH6) is a member of DEAD-box RNA helicase. While previous research has demonstrated the role of BnRH6 in salt stress regulation, the involvement of BnRH6 in drought stress adaptation remains unknown. This report described a function of BnRH6 in drought stress response. BnRH6 was sufficiently induced by osmotic stress. Transgenic Brassica napus and Arabidopsis thaliana (Arabidopsis) overexpressing BnRH6 (OE) showed a drought tolerance phenotype, characterized by improved plant growth, increased survival rates, reduced water loss, leaf chlorosis and oxidative stress. Furthermore, BnRH6 was also induced by exogenous abscisic acid (ABA). BnRH6 overexpression plants exhibited ABA hypersensitivity with lagging seed germination, growth stunt and diminished stomatal opening in the presence of ABA, suggesting the involvement of ABA signal. Assessment of several well-identified drought stress responsive genes such as Calcium-dependent Protein Kinase 14 (BnCDPK14), Enhanced Response to ABA1 (BnERA1) and ABA Insensitive 1 (BnABI1) revealed that their expressions were accordingly changed in BnOE plants, possibly with interplays between BnRH6 and those genes. Our data highlighted the functional role of BnRH6, which plays a positive role in active regulation of drought stress response likely through an ABA-dependent manner in rapeseed plants.

Glycerol-3-Phosphate Acyltransferase GPAT9 Enhanced Seed Oil Accumulation and Eukaryotic Galactolipid Synthesis in Brassica napus

Glycerol-3-phosphate acyltransferase GPAT9 catalyzes the first acylation of glycerol-3-phosphate (G3P), a committed step of glycerolipid synthesis in Arabidopsis. The role of GPAT9 in Brassica napus remains to be elucidated. Here, we identified four orthologs of GPAT9 and found that BnaGPAT9 encoded by BnaC01T0014600WE is a predominant isoform and promotes seed oil accumulation and eukaryotic galactolipid synthesis in Brassica napus. BnaGPAT9 is highly expressed in developing seeds and is localized in the endoplasmic reticulum (ER). Ectopic expression of BnaGPAT9 in E. coli and siliques of Brassica napus enhanced phosphatidic acid (PA) production. Overexpression of BnaGPAT9 enhanced seed oil accumulation resulting from increased 18:2-fatty acid. Lipid profiling in developing seeds showed that overexpression of BnaGPAT9 led to decreased phosphatidylcholine (PC) and a corresponding increase in phosphatidylethanolamine (PE), implying that BnaGPAT9 promotes PC flux to storage triacylglycerol (TAG). Furthermore, overexpression of BnaGPAT9 also enhanced eukaryotic galactolipids including monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), with increased 36:6-MGDG and 36:6-DGDG, and decreased 34:6-MGDG in developing seeds. Collectively, these results suggest that ER-localized BnaGPAT9 promotes PA production, thereby enhancing seed oil accumulation and eukaryotic galactolipid biosynthesis in Brassica napus.

An emerging role of heterotrimeric G-proteins in nodulation and nitrogen sensing

MAIN CONCLUSION

A comprehensive understanding of nitrogen signaling cascades involving heterotrimeric G-proteins and their putative receptors can assist in the production of nitrogen-efficient plants. Plants are immobile in nature, so they must endure abiotic stresses including nutrient stress. Plant development and agricultural productivity are frequently constrained by the restricted availability of nitrogen in the soil. Non-legume plants acquire nitrogen from the soil through root membrane-bound transporters. In depleted soil nitrogen conditions, legumes are naturally conditioned to fix atmospheric nitrogen with the aid of nodulation elicited by nitrogen-fixing bacteria. Moreover, apart from the symbiotic nitrogen fixation process, nitrogen uptake from the soil can also be a significant secondary source to satisfy the nitrogen requirements of legumes. Heterotrimeric G-proteins function as molecular switches to help plant cells relay diverse stimuli emanating from external stress conditions. They are comprised of Gα, Gβ and Gγ subunits, which cooperate with several downstream effectors to regulate multiple plant signaling events. In the present review, we concentrate on signaling mechanisms that regulate plant nitrogen nutrition. Our review highlights the potential of heterotrimeric G-proteins, together with their putative receptors, to assist the legume root nodule symbiosis (RNS) cascade, particularly during calcium spiking and nodulation. Additionally, the functions of heterotrimeric G-proteins in nitrogen acquisition by plant roots as well as in improving nitrogen use efficiency (NUE) have also been discussed. Future research oriented towards heterotrimeric G-proteins through genome editing tools can be a game changer in the enhancement of the nitrogen fixation process. This will foster the precise manipulation and production of plants to ensure global food security in an era of climate change by enhancing crop productivity and minimizing reliance on external inputs.

Interaction between phenylpropane metabolism and oil accumulation in the developing seed of Brassica napus revealed by high temporal-resolution transcriptomes

BACKGROUND

Brassica napus is an important oilseed crop providing high-quality vegetable oils for human consumption and non-food applications. However, the regulation between embryo and seed coat for the synthesis of oil and phenylpropanoid compounds remains largely unclear.

RESULTS

Here, we analyzed the transcriptomes in developing seeds at 2-day intervals from 14 days after flowering (DAF) to 64 DAF. The 26 high-resolution time-course transcriptomes are clearly clustered into five distinct groups from stage I to stage V. A total of 2217 genes including 136 transcription factors, are specifically expressed in the seed and show high temporal specificity by being expressed only at certain stages of seed development. Furthermore, we analyzed the co-expression networks during seed development, which mainly included master regulatory transcription factors, lipid, and phenylpropane metabolism genes. The results show that the phenylpropane pathway is prominent during seed development, and the key enzymes in the phenylpropane metabolic pathway, including TT5, BAN, and the transporter TT19, were directly or indirectly related to many key enzymes and transcription factors involved in oil accumulation. We identified candidate genes that may regulate seed oil content based on the co-expression network analysis combined with correlation analysis of the gene expression with seed oil content and seed coat content.

CONCLUSIONS

Overall, these results reveal the transcriptional regulation between lipid and phenylpropane accumulation during B. napus seed development. The established co-expression networks and predicted key factors provide important resources for future studies to reveal the genetic control of oil accumulation in B. napus seeds.

An intrinsically disordered region-containing protein mitigates the drought-growth trade-off to boost yields

Drought stress poses a serious threat to global agricultural productivity and food security. Plant resistance to drought is typically accompanied by a growth deficit and yield penalty. Herein, we report a previously uncharacterized, dicotyledon-specific gene, Stress and Growth Interconnector (SGI), that promotes growth during drought in the oil crop rapeseed (Brassica napus) and the model plant Arabidopsis (Arabidopsis thaliana). Overexpression of SGI conferred enhanced biomass and yield under water-deficient conditions, whereas corresponding CRISPR SGI mutants exhibited the opposite effects. These attributes were achieved by mediating reactive oxygen species (ROS) homeostasis while maintaining photosynthetic efficiency to increase plant fitness under water-limiting environments. Further spatial-temporal transcriptome profiling revealed dynamic reprogramming of pathways for photosynthesis and stress responses during drought and the subsequent recovery. Mechanistically, SGI represents an intrinsically disordered region-containing protein that interacts with itself, catalase isoforms, dehydrins, and other drought-responsive positive factors, restraining ROS generation. These multifaceted interactions stabilize catalases in response to drought and facilitate their ROS-scavenging activities. Taken altogether, these findings provide insights into currently underexplored mechanisms to circumvent trade-offs between plant growth and stress tolerance that will inform strategies to breed climate-resilient, higher yielding crops for sustainable agriculture.

Functions and interaction of plant lipid signalling under abiotic stresses

Lipids are the primary form of energy storage and a major component of plasma membranes, which form the interface between the cell and the extracellular environment. Several lipids - including phosphoinositide, phosphatidic acid, sphingolipids, lysophospholipids, oxylipins, and free fatty acids - also serve as substrates for the generation of signalling molecules. Abiotic stresses, such as drought and temperature stress, are known to affect plant growth. In addition, abiotic stresses can activate certain lipid-dependent signalling pathways that control the expression of stress-responsive genes and contribute to plant stress adaptation. Many studies have focused either on the enzymatic production and metabolism of lipids, or on the mechanisms of abiotic stress response. However, there is little information regarding the roles of plant lipids in plant responses to abiotic stress. In this review, we describe the metabolism of plant lipids and discuss their involvement in plant responses to abiotic stress. As such, this review provides crucial background for further research on the interactions between plant lipids and abiotic stress.

BnaNTT2 regulates ATP homeostasis in plastid to sustain lipid metabolism and plant growth in Brassica napus

The plastid inner envelope membrane-bond nucleotide triphosphate transporter (NTT) transports cytosolic adenosine triphosphate (ATP) into plastid, which is necessary for the biochemical activities in plastid. We identified a chloroplast-localized BnaC08.NTT2 and obtained the overexpressed lines of BnaC08.NTT2 and CRISPR/Cas9 edited double mutant lines of BnaC08.NTT2 and BnaA08.NTT2 in B. napus. Further studies certified that overexpression (OE) of BnaC08.NTT2 could help transport ATP into chloroplast and exchange adenosine diphosphate (ADP) and this process was inhibited in BnaNTT2 mutants. Additional results showed that the thylakoid was abnormal in a8 c8 double mutants, which also had lower photosynthetic efficiency, leading to retarded plant growth. The BnaC08.NTT2 OE plants had higher photosynthetic efficiency and better growth compared to WT. OE of BnaC08.NTT2 could improve carbon flowing into protein and oil synthesis from glycolysis both in leaves and seeds. Lipid profile analysis showed that the contents of main chloroplast membrane lipids, including monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and phosphatidylglycerol (PG), were significantly reduced in mutants, while there were no differences in OE lines compared to WT. These results suggest that BnaNTT2 is involved in the regulation of ATP/ADP homeostasis in plastid to impact plant growth and seed oil accumulation in B. napus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01322-8.

The phospholipase D gene GhPLDδ confers resistance to Verticillium dahliae and improves tolerance to salt stress

Plant phospholipase D (PLD) and its product phosphatidic acid (PA) function in both abiotic and biotic stress signaling. However, to date, a PLD gene conferring the desired resistance to both biotic and abiotic stresses has not been found in cotton. Here, we isolated and identified a PLD gene GhPLDδ from cotton (Gossypium hirsutum), which functions in Verticillium wilt resistance and salt tolerance. GhPLDδ was highly induced by salicylic acid (SA), methyl jasmonate (MeJA), abscisic acid (ABA), hydrogen peroxide, PEG 6000, NaCl, and Verticillium dahliae in cotton plants. The positive role of GhPLDδ in regulating plant resistance to V. dahliae was confirmed by loss- and gain-of-function analyses. Upon chitin treatment, accumulation of PA, hydrogen peroxide, JA, SA, and the expression of genes involved in MAPK cascades, JA- and SA-related defense responses were positively related to the level of GhPLDδ in plants. The treatment by exogenous PA could activate the expression of genes related to MAPK, SA, and JA signaling pathways. Moreover, GhPLDδ overexpression enhanced salt tolerance in Arabidopsis as demonstrated by the increased germination rate, longer seedling root, higher chlorophyll content, larger fresh weight, lower malondialdehyde content, and fully expand rosette leaves. Additionally, the PA content and the expression of the genes of the MAPK cascades regulated by PA were increased in GhPLDδ-overexpressed Arabidopsis under salt stress. Taken together, these findings suggest that GhPLDδ and PA are involved in regulating plant defense against both V. dahliae infection and salt stress.

Brassica napus BnaNTT1 modulates ATP homeostasis in plastids to sustain metabolism and growth

The plastid-localized nucleotide triphosphate transporter (NTT) transports cytosolic adenosine triphosphate (ATP) into plastid to satisfy the needs of biochemistry activities in plastid. Here, we investigate the key functions of two conserved BnaNTT1 genes, BnaC06.NTT1b and BnaA07.NTT1a, in Brassica napus. Binding assays and metabolic analysis indicate that BnaNTT1 binds ATP/adenosine diphosphate (ADP), transports cytosolic ATP into chloroplast, and exchanges ADP into cytoplasm. Thylakoid structures are abnormal and plant growth is retarded in CRISPR mutants of BnaC06.NTT1b and BnaA07.NTT1a. Both BnaC06.NTT1b and BnaA07.NTT1a play important roles in the regulation of ATP/ADP homeostasis in plastid. Manipulation of BnaC06.NTT1b and BnaA07.NTT1a causes significant changes in glycolysis and membrane lipid composition, suggesting that increased ATP in plastid fuels more seed-oil accumulation. Together, this study implicates the vital role of BnaC06.NTT1b and BnaA07.NTT1a in plant metabolism and growth in B. napus.

Genome-wide investigation of the PLD gene family in alfalfa (Medicago sativa L.): identification, analysis and expression

Background

External environmental factors, such as salt, alkali and drought, severely limit the acreage and yield of alfalfa. The mining of tolerance-related genes in alfalfa and improving the stress resistance of this plant are essential for increasing alfalfa yield. PLD is the main phospholipid hydrolase in plants and plays an important role in plant growth, development, signaling, and resistance to adverse stress. With the availability of whole genome sequences, the annotation and expression of PLDs in alfalfa can now be achieved. At present, few studies have investigated PLDs in alfalfa. Here, we conducted a study of PLDs in alfalfa and identified and analyzed the expression pattern of PLDs under different treatments.

Results

Fifty-nine MsPLDs were identified in alfalfa and classified into six subtypes: MsPLDα, β, γ, δ and ε belong to the C2-PLD subfamily, and MsPLDζ belongs to the PXPH-PLD subfamily. Members of the same PLD subtype have similar physicochemical properties, sequence structure and domains, but their cis-acting elements are different. A qRT-PCR analysis revealed that MsPLDs are expressed in multiple tissues. MsPLDs can respond to alkali, drought, ABA, IAA, and GA3 treatments and particularly to salt stress. Different expression patterns were found for the same gene under different treatments and different genes under the same treatment. Expression of MsPLD05 improved salt tolerance in yeast.

Conclusion

This study represents the first genome-wide characterization of MsPLDs in alfalfa. Most MsPLDs are expressed mainly in mature leaves and respond positively to abiotic stresses and hormonal treatments. This study further expands the resistance gene pool in legume forage grasses and provides a reference for further in-depth study of MsPLDs in alfalfa.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08424-9.

Phospholipase Dδ and H2S increase the production of NADPH oxidase-dependent H2O2 to respond to osmotic stress-induced stomatal closure in Arabidopsis thaliana

Osmotic stress is one of the main stresses that seriously affects the survival of plants, destroying normal cell activities, and potentially leading to plant death. Phospholipase D (PLD), a major lipid hydrolase, hydrolyzes membrane phospholipids to produce phosphatidic acid (PA) and responds to many abiotic stresses. Hydrogen sulfide (H2S) emerges as the third gaseous signaling molecule involved in the complex network of signaling events. Hydrogen peroxide (H2O2) plays a crucial role as a signaling molecule in plant development and growth, and responds to various abiotic and biotic stresses. In this study, the functions and the relationship of PLDδ, H2S, and H2O2 in osmotic stress-induced stomatal closure were explored. By using the seedlings of ecotype (WT), PLDδ-deficient mutant (pldδ), l-cysteine desulfhydrase (LCD)-deficient mutant (lcd), and pldδlcd double mutant, atrbohD, and atrbohF mutant as materials, and the stomatal aperture were analyzed. The relative water loss of pldδ, lcd, and pldδlcd was higher than that of WT. Exogenous PA and NaHS could partially alleviate the leaf wilting and yellowing phenotypes of pldδ, lcd, and pldδlcd under osmotic stress, but the mutants could not be restored to the same phenotype as WT. The fluorescence intensity of H2O2 in guard cells of pldδ, lcd, and pldδlcd was lower than that of WT, indicating that PLDδ and LCD were involved in the production of H2O2 in guard cells. Exogenous application of H2O2 to WT, pldδ, lcd, and pldδlcd significantly induced stomatal closure under osmotic stress. Exogenous NaHS induced stomatal closure of WT, but could not induce stomatal closure of atrbohD and atrbohF under osmotic stress. These results suggest that the accumulation of H2O2 was essential to induce stomatal closure under osmotic stress, and PLDδ and LCD acted upstream of H2O2.

Salt‑responsive transcriptome analysis of canola roots reveals candidate genes involved in the key metabolic pathway in response to salt stress

Salinity is a major constraint on crop growth and productivity, limiting sustainable agriculture in arid regions. Understanding the molecular mechanisms of salt-stress adaptation in canola is important to improve salt tolerance and promote its cultivation in saline lands. In this study, roots of control (no salt) and 200 mM NaCl-stressed canola seedlings were collected for RNA-Seq analysis and qRT-PCR validation. A total of 5385, 4268, and 7105 DEGs at the three time points of salt treatment compared to the control were identified, respectively. Several DEGs enriched in plant signal transduction pathways were highly expressed under salt stress, and these genes play an important role in signaling and scavenging of ROS in response to salt stress. Transcript expression in canola roots differed at different stages of salt stress, with the early-stages (2 h) of salt stress mainly related to oxidative stress response and sugar metabolism, while the late-stages (72 h) of salt stress mainly related to transmembrane movement, amino acid metabolism, glycerol metabolism and structural components of the cell wall. Several families of TFs that may be associated with salt tolerance were identified, including ERF, MYB, NAC, WRKY, and bHLH. These results provide a basis for further studies on the regulatory mechanisms of salt stress adaptation in canola.

The Brassica napus fatty acid exporter FAX1-1 contributes to biological yield, seed oil content, and oil quality

BACKGROUND

In the oilseed crop Brassica napus (rapeseed), various metabolic processes influence seed oil content, oil quality, and biological yield. However, the role of plastid membrane proteins in these traits has not been explored.

RESULTS

Our genome-wide association study (GWAS) of 520 B. napus accessions identified the chloroplast membrane protein-localized FATTY ACID EXPORTER 1-1 (FAX1-1) as a candidate associated with biological yield. Seed transcript levels of BnaFAX1-1 were higher in a cultivar with high seed oil content relative to a low-oil cultivar. BnaFAX1-1 was localized to the plastid envelope. When expressed in Arabidopsis thaliana, BnaFAX1-1 enhanced biological yield (total plant dry matter), seed yield and seed oil content per plant. Likewise, in the field, B. napus BnaFAX1-1 overexpression lines (BnaFAX1-1-OE) displayed significantly enhanced biological yield, seed yield, and seed oil content compared with the wild type. BnaFAX1-1 overexpression also up-regulated gibberellic acid 4 (GA4) biosynthesis, which may contribute to biological yield improvement. Furthermore, oleic acid (C18:1) significantly increased in BnaFAX1-1 overexpression seeds.

CONCLUSION

Our results indicated that the putative fatty acid exporter BnaFAX1-1 may simultaneously improve seed oil content, oil quality and biological yield in B. napus, providing new approaches for future molecular breeding.

Research Advances in Heterotrimeric G-Protein α Subunits and Uncanonical G-Protein Coupled Receptors in Plants

As crucial signal transducers, G-proteins and G-protein-coupled receptors (GPCRs) have attracted increasing attention in the field of signal transduction. Research on G-proteins and GPCRs has mainly focused on animals, while research on plants is relatively rare. The mode of action of G-proteins is quite different from that in animals. The G-protein α (Gα) subunit is the most essential member of the G-protein signal cycle in animals and plants. The G-protein is activated when Gα releases GDP and binds to GTP, and the relationships with the GPCR and the downstream signal are also achieved by Gα coupling. It is important to study the role of Gα in the signaling pathway to explore the regulatory mechanism of G-proteins. The existence of a self-activated Gα in plants makes it unnecessary for the canonical GPCR to activate the G-protein by exchanging GDP with GTP. However, putative GPCRs have been found and proven to play important roles in G-protein signal transduction. The unique mode of action of G-proteins and the function of putative GPCRs in plants suggest that the same definition used in animal research cannot be used to study uncanonical GPCRs in plants. This review focuses on the different functions of the Gα and the mode of action between plants and animals as well as the functions of the uncanonical GPCR. This review employs a new perspective to define uncanonical GPCRs in plants and emphasizes the role of uncanonical GPCRs and Gα subunits in plant stress resistance and agricultural production.

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

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

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.

Leaf transcriptomic response mediated by cold stress in two maize inbred lines with contrasting tolerance levels

Maize (Zea mays L.) is a thermophilic plant and a minor drop in temperature can prolong the maturity period. Plants respond to cold stress through structural and functional modification in cell membranes as well as changes in the photosynthesis and energy metabolism. In order to understand the molecular mechanisms underlying cold tolerance and adaptation, we employed leaf transcriptome sequencing together with leaf microstructure and relative electrical conductivity measurements in two maize inbred lines, having different cold stress tolerance potentials. The leaf physiological and transcriptomic responses of maize seedlings were studied after growing both inbred lines at 5 °C for 0, 12 and 24 h. Differentially expressed genes were enriched in photosynthesis antenna proteins, MAPK signaling pathway, plant hormone signal transduction, circadian rhythm, secondary metabolites related pathways, ribosome, and proteasome. The seedlings of both genotypes employed common stress responsive pathways to respond to cold stress. However, the cold tolerant line B144 protected its photosystem II from photooxidation by upregulating D1 proteins. The sensitive line Q319 was unable to close its stomata. Collectively, B144 exhibited a cold tolerance owing to its ability to mediate changes in stomata opening as well as protecting photosystem. These results increase our understanding on the cold stress tolerance in maize seedlings and propose multiple key regulators of stress responses such as modifications in photosystem II, stomata guard cell opening and closing, changes in secondary metabolite biosynthesis, and circadian rhythm. This study also presents the signal transduction related changes in MAPK and phytohormone signaling pathways in response to cold stress during seedling stage of maize.

Omics: The way forward to enhance abiotic stress tolerance in Brassica napus L

Plant abiotic stresses negative affects growth and development, causing a massive reduction in global agricultural production. Rapeseed (Brassica napus L.) is a major oilseed crop because of its economic value and oilseed production. However, its productivity has been reduced by many environmental adversities. Therefore, it is a prime need to grow rapeseed cultivars, which can withstand numerous abiotic stresses. To understand the various molecular and cellular mechanisms underlying the abiotic stress tolerance and improvement in rapeseed, omics approaches have been extensively employed in recent years. This review summarized the recent advancement in genomics, transcriptomics, proteomics, metabolomics, and their imploration in abiotic stress regulation in rapeseed. Some persisting bottlenecks have been highlighted, demanding proper attention to fully explore the omics tools. Further, the potential prospects of the CRISPR/Cas9 system for genome editing to assist molecular breeding in developing abiotic stress-tolerant rapeseed genotypes have also been explained. In short, the combination of integrated omics, genome editing, and speed breeding can alter rapeseed production worldwide.

Plastid Glycerol-3-phosphate Acyltransferase Enhanced Plant Growth and Prokaryotic Glycerolipid Synthesis in Brassica napus

Plastid-localized glycerol-3-phosphate acyltransferase (ATS1) catalyzes the first-step reaction in glycerolipid assembly through transferring an acyl moiety to glycerol-3-phosphate (G3P) to generate lysophosphatidic acid (LPA), an intermediate in lipid metabolism. The effect of ATS1 overexpression on glycerolipid metabolism and growth remained to be elucidated in plants, particularly oil crop plants. Here, we found that overexpression of BnATS1 from Brassica napus enhanced plant growth and prokaryotic glycerolipid biosynthesis. BnATS1 is localized in chloroplasts and an in vitro assay showed that BnATS1 had acylation activity toward glycerol 3-phosphate to produce LPA. Lipid profiling showed that overexpression of BnATS1 led to increases in multiple glycerolipids including phosphatidylglycerol (PG), monogalactosyldiacylglycerol (MGDG), phosphatidylcholine (PC), and phosphatidylinositol (PI), with increased polyunsaturated fatty acids. Moreover, increased MGDG was attributed to the elevation of 34:6- and 34:5-MGDG, which were derived from the prokaryotic pathway. These results suggest that BnATS1 promotes accumulation of polyunsaturated fatty acids in cellular membranes, thus enhances plant growth under low-temperature conditions in Brassica napus.

Phosphatidic acid: an emerging versatile class of cellular mediators

Lipids function not only as the major structural components of cell membranes, but also as molecular messengers that transduce signals to trigger downstream signaling events in the cell. Phosphatidic acid (PA), the simplest and a minor class of glycerophospholipids, is a key intermediate for the synthesis of membrane and storage lipids, and also plays important roles in mediating diverse cellular and physiological processes in eukaryotes ranging from microbes to mammals and higher plants. PA comprises different molecular species that can act differently, and is found in virtually all organisms, tissues, and organellar membranes, with variations in total content and molecular species composition. The cellular levels of PA are highly dynamic in response to stimuli and multiple enzymatic reactions can mediate its production and degradation. Moreover, its unique physicochemical properties compared with other glycerophospholipids allow PA to influence membrane structure and dynamics, and interact with various proteins. PA has emerged as a class of new lipid mediators modulating various signaling and cellular processes via its versatile effects, such as membrane tethering, conformational changes, and enzymatic activities of target proteins, and vesicular trafficking.

Cytosolic glyceraldehyde-3-phosphate dehydrogenase 2/5/6 increase drought tolerance via stomatal movement and reactive oxygen species scavenging in wheat

Drought is a major threat to wheat growth and crop productivity. However, there has been only limited success in developing drought-hardy cultivars. This lack of progress is due, at least in part, to a lack of understanding of the molecular mechanisms of drought tolerance in wheat. Here, we evaluated the potential role of three cytosolic glyceraldehyde-3-phosphate dehydrogenases (TaGAPC2/5/6) under drought stress in wheat and Arabidopsis. We found that TaGAPC2/5/6 all positively responded to drought stress via reactive oxygen species (ROS) scavenging and stomatal movement. The results of yeast co-transformation and electrophoretic mobility shift assay showed that TaWRKY33 acted as a direct regulator of TaGAPC2/5/6 genes. The dual luciferase reporter assay indicated that TaWRKY33 positively activated the expression of TaGAPC2/5/6. The results of bimolecular fluorescence complementation and yeast two-hybrid system demonstrated that TaGAPC2/5/6 interacted with phospholipase Dδ (PLDδ). We then demonstrated that TaGAPC2/5/6 positively promoted the activity of TaPLDδ in vitro and in vivo. Furthermore, lower PLDδ activity in RNAi wheat could lead to less PA accumulation, causing higher stomatal aperture sizes under drought stress. In summary, our results establish a new positive regulatory mechanism of TaGAPCs which helps wheat fine-tune their drought responses.

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.

Heterogeneous root zone salinity mitigates salt injury to Sorghum bicolor (L.) Moench in a split-root system

The heterogeneous distribution of soil salinity across the rhizosphere can moderate salt injury and improve sorghum growth. However, the essential molecular mechanisms used by sorghum to adapt to such environmental conditions remain uncharacterized. The present study evaluated physiological parameters such as the photosynthetic rate, antioxidative enzyme activities, leaf Na+ and K+ contents, and osmolyte contents and investigated gene expression patterns via RNA sequencing (RNA-seq) analysis under various conditions of nonuniformly distributed salt. Totals of 5691 and 2047 differentially expressed genes (DEGs) in the leaves and roots, respectively, were identified by RNA-seq under nonuniform (NaCl-free and 200 mmol·L-1 NaCl) and uniform (100 mmol·L-1 and 100 mmol·L-1 NaCl) salinity conditions. The expression of genes related to photosynthesis, Na+ compartmentalization, phytohormone metabolism, antioxidative enzymes, and transcription factors (TFs) was enhanced in leaves under nonuniform salinity stress compared with uniform salinity stress. Similarly, the expression of the majority of aquaporins and essential mineral transporters was upregulated in the NaCl-free root side in the nonuniform salinity treatment, whereas abscisic acid (ABA)-related and salt stress-responsive TF transcripts were more abundant in the high-saline root side in the nonuniform salinity treatment. In contrast, the expression of the DEGs identified in the nonuniform salinity treatment remained virtually unaffected and was even downregulated in the uniform salinity treatment. The transcriptome findings might be supportive of the increased photosynthetic rate, reduced Na+ levels, increased antioxidative capability in the leaves and, consequently, the growth recovery of sorghum under nonuniform salinity stress as well as the inhibited sorghum growth under uniform salinity conditions. The increased expression of salt resistance genes activated in response to the nonuniform salinity distribution implied that the cross-talk between the nonsaline and high-saline sides of the roots exposed to nonuniform salt stress is potentially regulated.

Overexpression of WAX INDUCER1/SHINE1 Gene Enhances Wax Accumulation under Osmotic Stress and Oil Synthesis in Brassica napus

WAX INDUCER1/SHINE1 (WIN1) belongs to the AP2/EREBP transcription factor family and plays an important role in wax and cutin accumulation in plants. Here we show that BnWIN1 from Brassica napus (Bn) has dual functions in wax accumulation and oil synthesis. Overexpression (OE) of BnWIN1 led to enhanced wax accumulation and promoted growth without adverse effects on oil synthesis under salt stress conditions. Lipid profiling revealed that BnWIN1-OE plants accumulated more waxes with elevated C29-alkanes, C31-alkanes, C28-alcohol, and C29-alcohol relative to wild type (WT) under salt stress. Moreover, overexpression of BnWIN1 also increased seed oil content under normal growth conditions. BnWIN1 directly bound to the promoter region of genes encoding biotin carboxyl carrier protein 1 (BCCP1), glycerol-3-phosphate acyltransferase 9 (GPAT9), lysophosphatidic acid acyltransferase 5 (LPAT5), and diacylglycerol acyltransferase 2 (DGAT2) involved in the lipid anabolic process. Overexpression of BnWIN1 resulted in upregulated expression of numerous genes involved in de novo fatty acid synthesis, wax accumulation, and oil production. The results suggest that BnWIN1 is a transcriptional activator to regulate the biosynthesis of both extracellular and intracellular lipids.

Genome-Wide Analysis of Phospholipase D Gene Family and Profiling of Phospholipids under Abiotic Stresses in Brassica napus

Oil crop Brassica napus is subjected to environmental stresses such as drought, cold and salt. Phospholipase Ds (PLDs) have vital roles in regulation of plant growth, development and stress tolerance. In this study, 32 BnaPLD genes were identified and classified into six subgroups depending on the conserved protein structures. High similarity in gene and protein structures exists between BnaPLDs and AtPLDs. Gene expression analysis showed that BnaPLDα1s and BnaPLDδs had higher expression than other PLDs. BnaPLDα1 and BnaPLDδ were significantly induced by abiotic stresses including dehydration, NaCl, abscisic acid (ABA) and 4�C. Lipidomic analysis showed that the content of main membrane phospholipids decreased gradually under stresses, except phosphatidylglycerol increased under the treatment of ABA and phosphatidylethanolamine increased under 4�C. Correspondingly, their product of phosphatidic acid increased often with a transient peak at 8 h. The plant height of mutants of PLDα1 was significantly reduced. Agronomic traits such as yield, seed number, silique number and branches were significantly impaired in PLDα1 mutants. These results indicate that there is a large family of PLD genes in B. napus, especially BnaPLDα1s and BnaPLDδs may play important roles in membrane lipids remodeling and maintaining of the growth and stress tolerance of B. napus.

Comparative Transcriptome Analysis of Developing Seeds and Silique Wall Reveals Dynamic Transcription Networks for Effective Oil Production in Brassica napus L

Vegetable oil is an essential constituent of the human diet and renewable raw material for industrial applications. Enhancing oil production by increasing seed oil content in oil crops is the most viable, environmentally friendly, and sustainable approach to meet the continuous demand for the supply of vegetable oil globally. An in-depth understanding of the gene networks involved in oil biosynthesis during seed development is a prerequisite for breeding high-oil-content varieties. Rapeseed (Brassica napus) is one of the most important oil crops cultivated on multiple continents, contributing more than 15% of the world’s edible oil supply. To understand the phasic nature of oil biosynthesis and the dynamic regulation of key pathways for effective oil accumulation in B. napus, comparative transcriptomic profiling was performed with developing seeds and silique wall (SW) tissues of two contrasting inbred lines with ~13% difference in seed oil content. Differentially expressed genes (DEGs) between high- and low-oil content lines were identified across six key developmental stages, and gene enrichment analysis revealed that genes related to photosynthesis, metabolism, carbohydrates, lipids, phytohormones, transporters, and triacylglycerol and fatty acid synthesis tended to be upregulated in the high-oil-content line. Differentially regulated DEG patterns were revealed for the control of metabolite and photosynthate production in SW and oil biosynthesis and accumulation in seeds. Quantitative assays of carbohydrates and hormones during seed development together with gene expression profiling of relevant pathways revealed their fundamental effects on effective oil accumulation. Our results thus provide insights into the molecular basis of high seed oil content (SOC) and a new direction for developing high-SOC rapeseed and other oil crops.

Phosphatidylinositol-hydrolyzing phospholipase C4 modulates rice response to salt and drought

Phosphatidylinositol-specific phospholipase C (PI-PLC) is involved in stress signalling but its signalling function remains largely unknown in crop plants. Here, we report that the PI-PLC4 from rice (Oryza sativa cv), OsPLC4, plays a positive role in osmotic stress response. Two independent knockout mutants, plc4-1 and plc4-2, exhibited decreased seedling growth and survival rate whereas overexpression of OsPLC4 improved survival rate under high salinity and water deficiency, compared with wild type (WT). OsPLC4 hydrolyses PI, phosphatidylinositol 4-phosphate (PI4P), and phosphatidylinositol-4,5-bisphosphate (PIP₂ ) to generate diacylglycerol (DAG) in vitro. Knockout of OsPLC4 attenuated salt-induced increase of phosphatidic acid (PA) whereas overexpression of OsPLC4 decreased the level of PI4P and PIP₂ under salt treatment. Applications of DAG or PA restored the growth defect of plc4-1 to WT but DAG kinase inhibitor 1 blocked the complementary effect of DAG in plc4-1 under salt stress. In addition, the loss of OsPLC4 compromised the increase of inositol triphosphate and free cytoplasmic Ca²⁺ ([Ca²⁺ ]_cyt ) and inhibited the induction of genes involved in Ca²⁺ sensor and osmotic stress response to salt stress. The results indicate that OsPLC4 modulates the activity of two signalling pathways, PA and Ca²⁺ , to affect rice seedling response to osmotic stress.

Shot-Gun Proteomic Analysis on Roots of Arabidopsis pldα1 Mutants Suggesting the Involvement of PLDα1 in Mitochondrial Protein Import, Vesicular Trafficking and Glucosinolate Biosynthesis

Phospholipase Dα1 (PLDα1) belongs to phospholipases, a large phospholipid hydrolyzing protein family. PLDα1 has a substrate preference for phosphatidylcholine leading to enzymatic production of phosphatidic acid, a lipid second messenger with multiple cellular functions. PLDα1 itself is implicated in biotic and abiotic stress responses. Here, we present a shot-gun differential proteomic analysis on roots of two Arabidopsis pldα1 mutants compared to the wild type. Interestingly, PLDα1 deficiency leads to altered abundances of proteins involved in diverse processes related to membrane transport including endocytosis and endoplasmic reticulum-Golgi transport. PLDα1 may be involved in the stability of attachment sites of endoplasmic reticulum to the plasma membrane as suggested by increased abundance of synaptotagmin 1, which was validated by immunoblotting and whole-mount immunolabelling analyses. Moreover, we noticed a robust abundance alterations of proteins involved in mitochondrial import and electron transport chain. Notably, the abundances of numerous proteins implicated in glucosinolate biosynthesis were also affected in pldα1 mutants. Our results suggest a broader biological involvement of PLDα1 than anticipated thus far, especially in the processes such as endomembrane transport, mitochondrial protein import and protein quality control, as well as glucosinolate biosynthesis.

Cucumber Phospholipase D alpha gene overexpression in tobacco enhanced drought stress tolerance by regulating stomatal closure and lipid peroxidation

BACKGROUND

Plant phospholipase D (PLD), which can hydrolyze membrane phospholipids to produce phosphatidic acid (PA), a secondary signaling molecule, has been proposed to function in diverse plant stress responses. Both PLD and PA play key roles in plant growth, development, and cellular processes. PLD was suggested to mediate the regulation of stomatal movements by abscisic acid (ABA) as a response to water deficit. In this research, we characterized the roles of the cucumber phospholipase D alpha gene (CsPLDα, GenBank accession number EF363796) in the growth and tolerance of transgenic tobacco (Nicotiana tabacum) to drought stress.

RESULTS

The CsPLDα overexpression in tobacco lines correlated with the ABA synthesis and metabolism, regulated the rapid stomatal closure in drought stress, and reduced the water loss. The NtNCED1 expression levels in the transgenic lines and wild type (WT) were sharply up-regulated after 16 days of drought stress compared with those before treatment, and the expression level in the transgenic lines was significantly higher than that in the WT. The NtAOG expression level evidently improved after 8 and 16 days compared with that at 0 day of treatment and was significantly lower in the transgenic lines than in the WT. The ABA content in the transgenic lines was significantly higher than that in the WT. The CsPLDα overexpression could increase the osmolyte content and reduce the ion leakage. The proline, soluble sugar, and soluble protein contents significantly increased. By contrast, the electrolytic leakage and malondialdehyde accumulation in leaves significantly decreased. The shoot and root fresh and dry weights of the overexpression lines significantly increased. These results indicated that a significant correlation between CsPLDα overexpression and improved resistance to water deficit.

CONCLUSIONS

The plants with overexpressed CsPLDα exhibited lower water loss, higher leaf relative water content, and heavier fresh and dry matter accumulation than the WT. We proposed that CsPLDα was involved in the ABA-dependent pathway in mediating the stomatal closure and preventing the elevation of intracellular solute potential.

Overexpression of a phospholipase (OsPLDα1) for drought tolerance in upland rice (Oryza sativa L.)

This work aimed to evaluate the drought tolerance of transformed plants of the cultivar BRSMG Curinga that overexpress the rice phospholipase D α1 (OsPLDα1) gene. The productivity of independent transformation event plants of the OsPLDα1 gene was evaluated in an experiment where 19 days of water deficit were applied at the reproductive stage, a very strict growing condition for upland rice. The non-genetically modified cultivar (NGM) under drought treatment reduced productivity by 89% compared with that under irrigated treatment, whereas transformed plants (PLDα1_E2) reduced productivity by only 41%. After the drought treatment, the PLDα1_E2 plants productivity was five times greater than that of the NGM plant. Moreover, no adverse effects on growth and development of the transgenic plants were observed. Seven days after the resumption of irrigation, PLDα1_E2 plants had higher stomatal conductance, greater photosynthetic rate, and transpiration rate than did NGM plants, as well as a higher expression level of the OsPLDα1 gene. A delay in the senescence process was observed in these PLDα1_E2 plants, and this was determined for the recovery of photosynthesis, with greater expression of the Rubisco and lower expression of the SOD. This finding was suggestive of decreased oxidative stress, probably due to gas exchange by the partial closure of the stomata of these transformed plants, which prevented the formation of reactive oxygen species. OsPLDα1 gene overexpression resulted in a reduction in production loss under severe water deficit and revealed a possibility for the development of upland rice cultivars that are more tolerant to extreme drought conditions.

Identification and Characterization of Phospholipase D Genes Putatively Involved in Internal Browning of Pineapple during Postharvest Storage

Phospholipase D (PLD) in plants plays vital roles in growth, development, and stress responses. However, the precise role of PLDs in pineapple remains poorly understood. In this study, 10 putative PLD genes, designated as AcPLD1-AcPLD10, were identified based on the pineapple genome database. The 10 AcPLDs could be clustered into five of the six known PLD families according to sequence characterization. Their deduced amino acid sequences displayed similarities to PLDs from other plant species. Expression analyses of PLD mRNAs from pineapple pulp were performed. The 10 PLDs exhibited differential expression patterns during storage periods of fruits treated with hexaldehyde (a specific PLD inhibitor) which could alleviate internal browning (IB) of pineapple after harvest. Functional subcellular localization signaling assays of two PLD proteins (AcPLD2 and AcPLD9) were performed by fluorescence microscopy. To further detect the potential action mechanism underlying PLD involved in the IB defense response, PLD, hydrogen peroxide (H₂O₂) and H₂O₂ associated with antioxidative enzymes such as superoxide dismutase, catalase, NADPH, and ascorbate peroxidase were quantified by enzyme-linked immunosorbent assay. This report is the first to provide a genome-wide description of the pineapple PLD gene family, and the results should expand knowledge of this family.

Phosphatidic acid binding inhibits RGS1 activity to affect specific signaling pathways in Arabidopsis

Modulation of the active versus inactive forms of the Gα protein is critical for the signaling processes mediated by the heterotrimeric G-protein complex. We have recently established that in Arabidopsis, the regulator of G-protein signaling (RGS1) protein and a lipid-hydrolyzing enzyme, phospholipase Dα1 (PLDα1), both act as GTPase-activity accelerating proteins (GAPs) for the Gα protein to attenuate its activity. RGS1 and PLDα1 interact with each other, and RGS1 inhibits the activity of PLDα1 during regulation of a subset of responses. In this study, we present evidence that this regulation is bidirectional. Phosphatidic acid (PA), a second messenger typically derived from the lipid-hydrolyzing activity of PLDα1, is a molecular target of RGS1. PA binds and inhibits the GAP activity of RGS1. A conserved lysine residue in RGS1 (Lys²⁵⁹ ) is directly involved in RGS1-PA binding. Introduction of this RGS1 protein variant in the rgs1 mutant background makes plants hypersensitive to a subset of abscisic acid-mediated responses. Our data point to the existence of negative feedback loops between these two regulatory proteins that precisely modulate the level of active Gα, consequently generating a highly controlled signal-response output.

Overexpression of Cucumber Phospholipase D alpha Gene (CsPLDα) in Tobacco Enhanced Salinity Stress Tolerance by Regulating Na+-K+ Balance and Lipid Peroxidation

Plant phospholipase D (PLD), which can hydrolyze membrane phospholipids to produce phosphatidic acid (PA), a secondary signaling molecule, has been proposed to function in diverse plant stress responses. In this research, we characterized the roles of the cucumber phospholipase D alpha gene (PLDα, GenBank accession number EF363796) in growth and tolerance to short- and long-term salt stress in transgenic tobacco (Nicotiana tabacum). Fresh and dry weights of roots, PLD activity and content, mitogen activated protein kinase (MAPK) gene expression, Na⁺-K⁺ homeostasis, expression of genes encoding ion exchange, reactive oxygen species (ROS) metabolism and osmotic adjustment substances were investigated in wild type (WT) and CsPLDα-overexpression tobacco lines grown under short- and long-term high salt (250 mM) stress. Under short-term stress (5 h), in both overexpression lines, the PA content, and the expression levels of MAPK and several genes related to ion exchange (NtNHX1, NtNKT1, NtHAK1, NtNHA1, NtVAG1), were promoted by high PLD activity. Meanwhile, the Na⁺/K⁺ ratio decreased. Under long-term stress (16 days), ROS scavenging systems (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase activities) in leaves of transgenic lines were more active than those in WT plants. Meanwhile, the contents of proline, soluble sugar, and soluble protein significantly increased. In contrast, the contents of O₂^•- and H₂O₂, the electrolytic leakage and the accumulation of malondialdehyde in leaves significantly decreased. The root fresh and dry weights of the overexpression lines increased significantly. Na⁺-K⁺ homeostasis had the same trend as under the short-term treatment. These findings suggested that CsPLDα-produced PA can activate the downstream signals' adaptive response to alleviate the damage of salt stress, and the main strategies for adaptation to salt stress are the accumulation of osmoprotective compounds, maintaining Na⁺-K⁺ homeostasis and the scavenging of ROS, which function in the osmotic balancing and structural stabilization of membranes.

Molecular and systems approaches towards drought-tolerant canola crops

1169 I. 1170 II. 1170 III. 1172 IV. 1176 V. 1181 VI. 1182 1183 References 1183 SUMMARY: Modern agriculture is facing multiple challenges including the necessity for a substantial increase in production to meet the needs of a burgeoning human population. Water shortage is a deleterious consequence of both population growth and climate change and is one of the most severe factors limiting global crop productivity. Brassica species, particularly canola varieties, are cultivated worldwide for edible oil, animal feed, and biodiesel, and suffer dramatic yield loss upon drought stress. The recent release of the Brassica napus genome supplies essential genetic information to facilitate identification of drought-related genes and provides new information for agricultural improvement in this species. Here we summarize current knowledge regarding drought responses of canola, including physiological and -omics effects of drought. We further discuss knowledge gained through translational biology based on discoveries in the closely related reference species Arabidopsis thaliana and through genetic strategies such as genome-wide association studies and analysis of natural variation. Knowledge of drought tolerance/resistance responses in canola together with research outcomes arising from new technologies and methodologies will inform novel strategies for improvement of drought tolerance and yield in this and other important crop species.

An Integrated Bioinformatics Analysis Reveals Divergent Evolutionary Pattern of Oil Biosynthesis in High- and Low-Oil Plants

Seed oils provide a renewable source of food, biofuel and industrial raw materials that is important for humans. Although many genes and pathways for acyl-lipid metabolism have been identified, little is known about whether there is a specific mechanism for high-oil content in high-oil plants. Based on the distinct differences in seed oil content between four high-oil dicots (20~50%) and three low-oil grasses (<3%), comparative genome, transcriptome and differential expression analyses were used to investigate this mechanism. Among 4,051 dicot-specific soybean genes identified from 252,443 genes in the seven species, 54 genes were shown to directly participate in acyl-lipid metabolism, and 93 genes were found to be associated with acyl-lipid metabolism. Among the 93 dicot-specific genes, 42 and 27 genes, including CBM20-like SBDs and GPT2, participate in carbohydrate degradation and transport, respectively. 40 genes highly up-regulated during seed oil rapid accumulation period are mainly involved in initial fatty acid synthesis, triacylglyceride assembly and oil-body formation, for example, ACCase, PP, DGAT1, PDAT1, OLEs and STEROs, which were also found to be differentially expressed between high- and low-oil soybean accessions. Phylogenetic analysis revealed distinct differences of oleosin in patterns of gene duplication and loss between high-oil dicots and low-oil grasses. In addition, seed-specific GmGRF5, ABI5 and GmTZF4 were predicted to be candidate regulators in seed oil accumulation. This study facilitates future research on lipid biosynthesis and potential genetic improvement of seed oil content.

Phospholipases as GTPase activity accelerating proteins (GAPs) in plants

GTPase activity accelerating proteins (GAPs) are key regulators of the G-protein signaling cycle. By facilitating effective hydrolysis of the GTP bound on Gα proteins, GAPs control the timing and amplitude of the signaling cycle and ascertain the availability of the inactive heterotrimer for the next round of activation. Until very recently, the studies of GAPs in plants were focused exclusively on the regulator of G-protein signaling (RGS) protein. We now show that phospholipase Dα1 (PLDα1) is also a bona fide GAP in plants and together with the RGS protein controls the level of active Gα protein.

Phloem Proteomics Reveals New Lipid-Binding Proteins with a Putative Role in Lipid-Mediated Signaling

Global climate changes inversely affect our ability to grow the food required for an increasing world population. To combat future crop loss due to abiotic stress, we need to understand the signals responsible for changes in plant development and the resulting adaptations, especially the signaling molecules traveling long-distance through the plant phloem. Using a proteomics approach, we had identified several putative lipid-binding proteins in the phloem exudates. Simultaneously, we identified several complex lipids as well as jasmonates. These findings prompted us to propose that phloem (phospho-) lipids could act as long-distance developmental signals in response to abiotic stress, and that they are released, sensed, and moved by phloem lipid-binding proteins (Benning et al., 2012). Indeed, the proteins we identified include lipases that could release a signaling lipid into the phloem, putative receptor components, and proteins that could mediate lipid-movement. To test this possible protein-based lipid-signaling pathway, three of the proteins, which could potentially act in a relay, are characterized here: (I) a putative GDSL-motif lipase (II) a PIG-P-like protein, with a possible receptor-like function; (III) and PLAFP (phloem lipid-associated family protein), a predicted lipid-binding protein of unknown function. Here we show that all three proteins bind lipids, in particular phosphatidic acid (PtdOH), which is known to participate in intracellular stress signaling. Genes encoding these proteins are expressed in the vasculature, a prerequisite for phloem transport. Cellular localization studies show that the proteins are not retained in the endoplasmic reticulum but surround the cell in a spotted pattern that has been previously observed with receptors and plasmodesmatal proteins. Abiotic signals that induce the production of PtdOH also regulate the expression of GDSL-lipase and PLAFP, albeit in opposite patterns. Our findings suggest that while all three proteins are indeed lipid-binding and act in the vasculature possibly in a function related to long-distance signaling, the three proteins do not act in the same but rather in distinct pathways. It also points toward PLAFP as a prime candidate to investigate long-distance lipid signaling in the plant drought response.

Detection of Mycobacterium tuberculosis and Mycobacterium bovis in Sahiwal cattle from an organized farm using ante-mortem techniques

Aim:

The aim of this study was to investigate the prevalence of bovine tuberculosis (TB) and detection of Mycobacterium bovis in cattle from an organized dairy farm.

Materials and Methods:

A total of 121 animals (93 females and 28 males) of 1 year and above were studied for the prevalence of bovine TB using single intradermal comparative cervical tuberculin (SICCT) test, bovine gamma-interferon (γ-IFN) enzyme immunoassay, and polymerase chain reactions (PCRs).

Results:

Out of total 121 animals, 17 (14.04%) animals were positive reactors to SICCT test while only one (0.82%) animal for γ-IFN assay. By PCR, Mycobacterium TB complex was detected in 19 (15.70%) animals out of which 4 (3.30%) animal were also positive for M. bovis.

Conclusions:

Diagnosis of bovine TB can be done in early stage in live animals with multiple approaches like skin test followed by a molecular technique like PCR which showed promising results.

The role of PLDα1 in providing specificity to signal-response coupling by heterotrimeric G-protein components in Arabidopsis

Heterotrimeric G-proteins comprised of Gα, Gβ and Gγ subunits are important signal transducers in all eukaryotes. In plants, G-proteins affect multiple biotic and abiotic stress responses, as well as many developmental processes, even though their repertoire is significantly limited compared with that in metazoan systems. One canonical and three extra-large Gα, 1 Gβ and 3 Gγ proteins represent the heterotrimeric G-protein complex in Arabidopsis, and a single regulatory protein, RGS1, is one of the few known biochemical regulators of this signaling complex. This quantitative disparity between the number of signaling components and the range of processes they influence is rather intriguing. We now present evidence that the phospholipase Dα1 protein is a key component and modulator of the G-protein complex in affecting a subset of signaling pathways. We also show that the same G-protein subunits and their modulators exhibit distinct physiological and genetic interactions depending on specific signaling and developmental pathways. Such developmental plasticity and interaction specificity likely compensates for the lack of multiplicity of individual subunits, and helps to fine tune the plants' responses to constantly changing environments.

Phospholipase Dε enhances Braasca napus growth and seed production in response to nitrogen availability

Phospholipase D (PLD), which hydrolyses phospholipids to produce phosphatidic acid, has been implicated in plant response to macronutrient availability in Arabidopsis. This study investigated the effect of increased PLDε expression on nitrogen utilization in Brassica napus to explore the application of PLDε manipulation to crop improvement. In addition, changes in membrane lipid species in response to nitrogen availability were determined in the oil seed crop. Multiple PLDε over expression (PLDε-OE) lines displayed enhanced biomass accumulation under nitrogen-deficient and nitrogen-replete conditions. PLDε-OE plants in the field produced more seeds than wild-type plants but have no impact on seed oil content. Compared with wild-type plants, PLDε-OE plants were enhanced in nitrate transporter expression, uptake and reduction, whereas the activity of nitrite reductase was higher under nitrogen-depleted, but not at nitrogen-replete conditions. The level of nitrogen altered membrane glycerolipid metabolism, with greater impacts on young than mature leaves. The data indicate increased expression of PLDε has the potential to improve crop plant growth and production under nitrogen-depleted and nitrogen-replete conditions.

Long-Distance Lipid Signaling and its Role in Plant Development and Stress Response

Lipids are important signaling compounds in plants. They can range from small lipophilic molecules like the dicarboxylic acid Azelaic acid to complex phosphoglycerolipids and regulate plant development as well as the response to biotic and abiotic stress. While their intracellular function is well described, several lipophilic signals are known to be found in the plant phloem and can, thus, also play a role in long-distance signaling. Mostly, they play a role in the pathogen response and systemic acquired resistance. This is particularly true for oxylipins, dehydroabietinal, and azelaic acid. However, several phospholipids have now been described in phloem exudates. Their intracellular function as well as implications and a model for long-distance signaling are discussed in this chapter.

The functions of a cucumber phospholipase D alpha gene (CsPLDα) in growth and tolerance to hyperosmotic stress

Plant phospholipase D (PLD), which can hydrolyze membrane phospholipids to produce phosphatidic acid (PA), a secondary signaling molecule, has been proposed to function in diverse plant stress responses. In this research, a qRT-PCR analysis indicated that the expression of a cucumber phospholipase D alpha gene (CsPLDα) was induced by salt and drought stresses in the roots and leaves. To further study the roles of CsPLDα in regulating plant tolerance to salt, polyethylene glycol (PEG) and abscisic acid (ABA) stresses, transgenic tobacco plants constitutively overexpressing CsPLDα were produced. A qRT-PCR analysis showed that the CsPLDα transcript levels were high in transgenic tobacco lines, whereas no expression was found in wild type (WT) tobacco, indicating that CsPLDα was successfully transferred into the tobacco genome and overexpressed. Under normal conditions for 30 d, seeds of transgenic lines germinated neatly, and the seedlings were robust and bigger than WT plants. When treated with different concentrations of NaCl, PEG and ABA, germination rates and seedling sizes of the transgenic lines were significantly greater than WT. In addition, the germination times for transgenic lines were also remarkably shorter. Further studies indicated that transgenic lines had longer primary roots and more biomass accumulation than WT plants. The water loss in transgenic lines was also much lower than in WT. These findings suggest that the CsPLDα overexpression positively regulates plant tolerance to hyperosmotic stresses, and that CsPLDα is involved in the ABA regulation of stomatal closure and the alleviation of ABA inhibition on seed germination and seedling growth.

Genome-wide analysis of drought induced gene expression changes in flax (Linum usitatissimum)

A robust phenotypic plasticity to ward off adverse environmental conditions determines performance and productivity in crop plants. Flax (linseed), is an important cash crop produced for natural textile fiber (linen) or oilseed with many health promoting products. This crop is prone to drought stress and yield losses in many parts of the world. Despite recent advances in drought research in a number of important crops, related progress in flax is very limited. Since, response of this plant to drought stress has not been addressed at the molecular level; we conducted microarray analysis to capture transcriptome associated with induced drought in flax. This study identified 183 differentially expressed genes (DEGs) associated with diverse cellular, biophysical and metabolic programs in flax. The analysis also revealed especially the altered regulation of cellular and metabolic pathways governing photosynthesis. Additionally, comparative transcriptome analysis identified a plethora of genes that displayed differential regulation both spatially and temporally. These results revealed co-regulated expression of 26 genes in both shoot and root tissues with implications for drought stress response. Furthermore, the data also showed that more genes are upregulated in roots compared to shoots, suggesting that roots may play important and additional roles in response to drought in flax. With prolonged drought treatment, the number of DEGs increased in both tissue types. Differential expression of selected genes was confirmed by qRT-PCR, thus supporting the suggested functional association of these intrinsic genes in maintaining growth and homeostasis in response to imminent drought stress in flax. Together the present study has developed foundational and new transcriptome data sets for drought stress in flax.

Overexpression of a wheat phospholipase D gene, TaPLDα, enhances tolerance to drought and osmotic stress in Arabidopsis thaliana

Phospholipase D (PLD) is crucial for plant responses to stress and signal transduction, however, the regulatory mechanism of PLD in abiotic stress is not completely understood; especially, in crops. In this study, we isolated a gene, TaPLDα, from common wheat (Triticum aestivum L.). Analysis of the amino acid sequence of TaPLDα revealed a highly conserved C2 domain and two characteristic HKD motifs, which is similar to other known PLD family genes. Further characterization revealed that TaPLDα expressed differentially in various organs, such as roots, stems, leaves and spikelets of wheat. After treatment with abscisic acid (ABA), methyl jasmonate, dehydration, polyethylene glycol and NaCl, the expression of TaPLDα was up-regulated in shoots. Subsequently, we generated TaPLDα-overexpressing transgenic Arabidopsis lines under the control of the dexamethasone-inducible 35S promoter. The overexpression of TaPLDα in Arabidopsis resulted in significantly enhanced tolerance to drought, as shown by reduced chlorosis and leaf water loss, higher relative water content and lower relative electrolyte leakage than the wild type. Moreover, the TaPLDα-overexpressing plants exhibited longer roots in response to mannitol treatment. In addition, the seeds of TaPLDα-overexpressing plants showed hypersensitivity to ABA and osmotic stress. Under dehydration, the expression of several stress-related genes, RD29A, RD29B, KIN1 and RAB18, was up-regulated to a higher level in TaPLDα-overexpressing plants than in wild type. Taken together, our results indicated that TaPLDα can enhance tolerance to drought and osmotic stress in Arabidopsis and represents a potential candidate gene to enhance stress tolerance in crops.

Soybean GmMYB73 promotes lipid accumulation in transgenic plants

BACKGROUND

Soybean is one of the most important oil crops. The regulatory genes involved in oil accumulation are largely unclear. We initiated studies to identify genes that regulate this process.

RESULTS

One MYB-type gene GmMYB73 was found to display differential expression in soybean seeds of different developing stages by microarray analysis and was further investigated for its functions in lipid accumulation. GmMYB73 is a small protein with single MYB repeat and has similarity to CPC-like MYB proteins from Arabidopsis. GmMYB73 interacted with GL3 and EGL3, and then suppressed GL2, a negative regulator of oil accumulation. GmMYB73 overexpression enhanced lipid contents in both seeds and leaves of transgenic Arabidopsis plants. Seed length and thousand-seed weight were also promoted. GmMYB73 introduction into the Arabidopsis try cpc double mutant rescued the total lipids, seed size and thousand-seed weight. GmMYB73 also elevated lipid levels in seeds and leaves of transgenic Lotus, and in transgenic hairy roots of soybean plants. GmMYB73 promoted PLDα1 expression, whose promoter can be bound and inhibited by GL2. PLDα1 mutation reduced triacylglycerol levels mildly in seeds but significantly in leaves of Arabidopsis plants.

CONCLUSIONS

GmMYB73 may reduce GL2, and then release GL2-inhibited PLDα1 expression for lipid accumulation. Manipulation of GmMYB73 may potentially improve oil production in legume crop plants.