Overexpression of the phosphatidylinositol synthase gene (ZmPIS) conferring drought stress tolerance by altering membrane lipid composition and increasing ABA synthesis in maize

Multi-Omics Analyses Offer Novel Insights into the Selection of Sugar and Lipid Metabolism During Maize Domestication and Improvement

Over thousands of years of domestication, maize has undergone significant environmental changes. Understanding the genetic and metabolic trace during maize evolution can better contribute to molecular breeding and nutrition quality improvement. This study examines the metabolic profiles and transcriptomes of maize kernels from teosinte, landrace, and maize accessions at 15 days post-pollination. Differentially accumulated metabolites were enriched in sugar and lipid metabolism pathways. The metabolic selection profile exhibited four distinct patterns: continuous increases, constant decrease, initial decline or stability followed by an increase, and initial growth or stability followed by a subsequent decline. Sugars and JA were positive selection while LPCs/LPEs were negative selection during evolution. The expression level of genes related to sugar accumulation was significantly higher in maize, contrasting with enhanced glycolysis and lipid metabolism activity in teosinte. The correlation network highlighted distinct hormonal regulation of sugar and lipid metabolism. We identified 27 candidate genes associated with sugar, lipid, and JA that have undergone strong selection by population genomic regions. The positive selection of the PLD may explain the negative selection of LPCs/LPEs due to substrate competition. These findings enhance our understanding of the evolutionary trajectory of primary metabolism in maize and provide valuable resources for breeding and improvement.

Characterization of Dark Septate Endophytes Under Drought and Rehydration and Their Compensatory Mechanisms in Astragalus membranaceus

Drought is the most significant abiotic stress that impedes agroforestry development. In nature, drought tolerance also depends on the ability to compensate after water restoration. Dark septate endophytes (DSEs) are believed to enhance plant tolerance in drought environments. However, the compensatory mechanisms of DSEs for rehydration after drought stress have not been reported. To assess the drought tolerance and compensatory capacity of DSEs, the following DSEs were investigated in this study using solid-liquid screening and potting tests under different drought gradients, rehydration conditions, and field water-holding capacities: Stagonosporopsis lupini, Microsphaeropsis cytisi, Macrophomina pseudophaseolina, Paraphoma radicina, Alternaria alstroemeriae, Alternaria tellustris, and Papulaspora equi. The results showed that M. pseudophaseolina reached the maximum diameter for plate growth in only 4 d. In a liquid shaker, the biomass of S. lupini peaked after rehydration. The Mantel heatmap indicated that lipid metabolites were significantly expressed in M. pseudophaseolina and S. lupini under drought stress. Correlations between drought tolerance indexes and amino acid metabolites increased dramatically in both DSEs after rehydration. Moreover, in rehydration after drought, the treatments inoculated with M. pseudophaseolina and S. lupini showed significant increases in root weight of 20.36% and 23.82%, respectively, compared with the uninoculated treatment.

Genetic and lipidomic analyses reveal the key role of lipid metabolism for cold tolerance in maize

Lipid remodeling is crucial for cold tolerance in plants. However, the precise alternations of lipidomics during cold responses remain elusive, especially in maize (Zea mays L.). In addition, the key genes responsible for cold tolerance in maize lipid metabolism have not been identified. Here, we integrate lipidomic, transcriptomic, and genetic analysis to determine the profile of lipid remodeling caused by cold stress. We find that the homeostasis of cellular lipid metabolism is essential for maintaining cold tolerance of maize. Also, we detect 210 lipid species belonging to 13 major classes, covering phospholipids, glycerides, glycolipids, and free fatty acids. Various lipid metabolites undergo specific and selective alterations in response to cold stress, especially mono-/di-unsaturated lysophosphatidic acid, lysophosphatidylcholine, phosphatidylcholine, and phosphatidylinositol, as well as polyunsaturated phosphatidic acid, monogalactosyldiacylglycerol, diacylglycerol, and triacylglycerol. In addition, we identify a subset of key enzymes, including ketoacyl-acyl-carrier protein synthase II (KAS II), acyl-carrier protein 2 (ACP2), male sterility33 (Ms33), and stearoyl-acyl-carrier protein desaturase 2 (SAD2) involved in glycerolipid biosynthetic pathways are positive regulators of maize cold tolerance. These results reveal a comprehensive lipidomic profile during the cold response of maize and provide genetic resources for enhancing cold tolerance in crops.

Plant hormones and secondary metabolites under environmental stresses: Enlightening defense molecules

The climatic changes have great threats to sustainable agriculture and require efforts to ensure global food and nutritional security. In this regard, the plant strategic responses, including the induction of plant hormones/plant growth regulators (PGRs), play a substantial role in boosting plant immunity against environmental stress-induced adversities. In addition, secondary metabolites (SMs) have emerged as potential 'stress alleviators' that help plants to adapt against environmental stressors imposing detrimental impacts on plant health and survival. The introduction of SMs in plant biology has shed light on their beneficial effects in mitigating environmental crises. This review explores SMs-mediated plant defense responses and highlights the crosstalk between PGRs and SMs under diverse environmental stressors. In addition, genetic engineering approaches are discussed as a potential revenue to enhance plant hormone-mediated SM production in response to environmental cues. Thus, the present review aims to emphasize the significance of SMs implications with PGRs association and genetic approachability, which could aid in shaping the future strategies that favor agro-ecosystem compatibility under unpredictable environmental conditions.

Drought stress in maize: stress perception to molecular response and strategies for its improvement

Given the future demand for food crops, increasing crop productivity in drought-prone rainfed areas has become essential. Drought-tolerant varieties are warranted to solve this problem in major crops, with drought tolerance as a high-priority trait for future research. Maize is one such crop affected by drought stress, which limits production, resulting in substantial economic losses. It became a more serious issue due to global climate change. The most drought sensitive among all stages of maize is the reproductive stages and the most important for overall maize production. The exact molecular basis of reproductive drought sensitivity remains unclear due to genes' complex regulation of drought stress. Understanding the molecular biology and signaling of the unexplored area of reproductive drought tolerance will provide an opportunity to develop climate-smart drought-tolerant next-generation maize cultivars. In recent decades, significant progress has been made in maize to understand the drought tolerance mechanism. However, improving maize drought tolerance through breeding is ineffective due to the complex nature and multigenic control of drought traits. With the help of advanced breeding techniques, molecular genetics, and a precision genome editing approach like CRISPR-Cas, candidate genes for drought-tolerant maize can be identified and targeted. This review summarizes the effects of drought stress on each growth stage of maize, potential genes, and transcription factors that determine drought tolerance. In addition, we discussed drought stress sensing, its molecular mechanisms, different approaches to developing drought-resistant maize varieties, and how molecular breeding and genome editing will help with the current unpredictable climate change.

QTL mapping for flowering time in a maize-teosinte population under well-watered and water-stressed conditions

Maize grain yield can be greatly reduced when flowering time coincides with drought conditions, which delays silking and consequently increases the anthesis-silking interval. Although the genetic basis of delayed flowering time under water-stressed conditions has been elucidated in maize-maize populations, little is known in this regard about maize-teosinte populations. Here, 16 quantitative trait loci (QTL) for three flowering-time traits, namely days to anthesis, days to silk, and the anthesis-silking interval, were identified in a maize-teosinte introgression population under well-watered and water-stressed conditions; these QTL explained 3.98-32.61% of phenotypic variations. Six of these QTL were considered to be sensitive to drought stress, and the effect of any individual QTL was small, indicating the complex genetic nature of drought resistance in maize. To resolve which genes underlie the six QTL, 11 candidate genes were identified via colocalization analysis of known associations with flowering-time-related drought traits. Among the 11 candidate genes, five were found to be differentially expressed in response to drought stress or under selection during maize domestication, and thus represented the most likely candidates underlying the drought-sensitive QTL. The results lay a foundation for further studies of the genetic mechanisms of drought resistance and provide valuable information for improving drought resistance during maize breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01413-0.

Identification of QTN-by-environment interactions for yield related traits in maize under multiple abiotic stresses

INTRODUCTION

Quantitative trait nucleotide (QTN)-by-environment interactions (QEIs) play an increasingly essential role in the genetic dissection of complex traits in crops as global climate change accelerates. The abiotic stresses, such as drought and heat, are the major constraints on maize yields. Multi-environment joint analysis can improve statistical power in QTN and QEI detection, and further help us to understand the genetic basis and provide implications for maize improvement.

METHODS

In this study, 3VmrMLM was applied to identify QTNs and QEIs for three yield-related traits (grain yield, anthesis date, and anthesis-silking interval) of 300 tropical and subtropical maize inbred lines with 332,641 SNPs under well-watered and drought and heat stresses.

RESULTS

Among the total 321 genes around 76 QTNs and 73 QEIs identified in this study, 34 known genes were reported in previous maize studies to be truly associated with these traits, such as ereb53 (GRMZM2G141638) and thx12 (GRMZM2G016649) associated with drought stress tolerance, and hsftf27 (GRMZM2G025685) and myb60 (GRMZM2G312419) associated with heat stress. In addition, among 127 homologs in Arabidopsis out of 287 unreported genes, 46 and 47 were found to be significantly and differentially expressed under drought vs well-watered treatments, and high vs. normal temperature treatments, respectively. Using functional enrichment analysis, 37 of these differentially expressed genes were involved in various biological processes. Tissue-specific expression and haplotype difference analysis further revealed 24 candidate genes with significantly phenotypic differences across gene haplotypes under different environments, of which the candidate genes GRMZM2G064159, GRMZM2G146192, and GRMZM2G114789 around QEIs may have gene-by-environment interactions for maize yield.

DISCUSSION

All these findings may provide new insights for breeding in maize for yield-related traits adapted to abiotic stresses.

Integrated Analysis of Single-Molecule Real-Time Sequencing and Next-Generation Sequencing Eveals Insights into Drought Tolerance Mechanism of Lolium multiflorum

Lolium multiflorum is widely planted in temperate and subtropical regions globally, and it has high economic value owing to its use as forage grass for a wide variety of livestock and poultry. However, drought seriously restricts its yield and quality. At present, owing to the lack of available genomic resources, many types of basic research cannot be conducted, which severely limits the in-depth functional analysis of genes in L. multiflorum. Therefore, we used single-molecule real-time (SMRT) and next-generation sequencing (NGS) to sequence the complex transcriptome of L. multiflorum under drought. We identified 41,141 DEGs in leaves, 35,559 DEGs in roots, respectively. Moreover, we identified 1243 alternative splicing events under drought. LmPIP5K9 produced two different transcripts with opposite expression patterns, possibly through the phospholipid signaling pathway or the negatively regulated sugar-mediated root growth response to drought stress, respectively. Additionally, 13,079 transcription factors in 90 families were obtained. An in-depth analysis of R2R3-MYB gene family members was performed to preliminarily demonstrate their functions by utilizing subcellular localization and overexpression in yeast. Our data make a significant contribution to the genetics of L. multiflorum, offering a current understanding of plant adaptation to drought stress.

Salvianolic Acid Modulates Physiological Responses and Stress-Related Genes That Affect Osmotic Stress Tolerance in Glycine max and Zea mays

Drought is a serious threat worldwide to soybean and maize production. This study was conducted to discern the impact of salvianolic acid treatment on osmotic-stressed soybean (Glycine max L.) and maize (Zea mays L.) seedlings from the perspective of physiochemical and molecular reactions. Examination of varied salvianolic acid concentrations (0, 0.1, 1, 5, 10, and 25 μM) on soybean and maize seedling growth confirmed that the 0.1 and 1 μM concentrations, respectively, showed an improvement in agronomic traits. Likewise, the investigation ascertained how salvianolic acid application could retrieve osmotic-stressed plants. Soybean and maize seedlings were irrigated with water or 25% PEG for 8 days. The results indicated that salvianolic acid application promoted the survival of the 39-day-old osmotic-stressed soybean and maize plants. The salvianolic acid-treated plants retained high photosynthetic pigments, protein, amino acid, fatty acid, sugar, and antioxidant contents, and demonstrated low hydrogen peroxide and lipid contents under osmotic stress conditions. Gene transcription pattern certified that salvianolic acid application led to an increased expression of GmGOGAT, GmUBC2, ZmpsbA, ZmNAGK, ZmVPP1, and ZmSCE1d genes, and a diminished expression of GmMIPS2, GmSOG1, GmACS, GmCKX, ZmPIS, and ZmNAC48 genes. Together, our results indicate the utility of salvianolic acid to enhance the osmotic endurance of soybean and maize plants.

Enhanced Adaptability to Limited Water Supply Regulated by Diethyl Aminoethyl Hexanoate (DA-6) Associated With Lipidomic Reprogramming in Two White Clover Genotypes

Membrane lipid reprogramming is one of the most important adaptive strategies in plant species under unfavorable environmental circumstances. Therefore, the present experiment was conducted to elucidate the effect of diethyl aminoethyl hexanoate (DA-6), a novel synthetic plant growth regulator, on oxidative damage, photosynthetic performance, changes in lipidomic profile, and unsaturation index of lipids in two white clover (Trifolium repens) cultivars (drought-sensitive "Ladino" and drought-resistant "Riverdel") under PEG-6000-induced water-deficit stress. Results revealed that water-deficit stress significantly enhanced oxidative damage and decreased photosynthetic functions in both cultivars. However, the damage was less in Riverdel. In addition, water-deficit stress significantly decreased the relative content of monogalactocyl-diacylglycerols (MGDG), sulfoquinovosyl-diacylglycerols (SQDG), phosphatidic acisd (PA), phosphatidyl-ethanolamines (PE), phosphatidyl-glycerols (PG), phosphatidyl-serines (PS), ceramides (Cer), hexosylmonoceramides (Hex1Cer), sphingomyelins (SM), and sphingosines (Sph) in both cultivars, but a more pronounced decline was observed in Ladino. Exogenous application of DA-6 significantly increased the relative content of digalactocyl-diacylglycerols (DGDG), monogalactocyl-diacylglycerolsabstra (MGDG), sulfoquinovosyl-diacylglycerols (SQDG), phosphatidic acids (PA), phosphatidyl-ethanolamines (PE), phosphatidyl-glycerols (PG), phosphatidyl-inositols (PI), phosphatidyl-serines (PS), ceramides (Cer), hexosylmonoceramides (Hex1Cer), neutral glycosphingolipids (CerG2GNAc1), and sphingosines (Sph) in the two cultivars under water-deficit stress. DA-6-treated Riverdel exhibited a significantly higher DGDG:MGDG ratio and relative content of sphingomyelins (SM) than untreated plants in response to water deficiency. Furthermore, the DA-6-pretreated plants increased the unsaturation index of phosphatidic acids (PA) and phosphatidylinositols (PI) in Ladino, ceramides (Cer) and hexosylmonoceramides (Hex1Cer) in Riverdel, and sulfoquinovosyl-diacylglycerols (SQDG) in both cultivars under water stress. These results suggested that DA-6 regulated drought resistance in white clover could be associated with increased lipid content and reprogramming, higher DGDG:MGDG ratio, and improved unsaturation index of lipids, contributing to enhanced membrane stability, integrity, fluidity, and downstream signaling transduction.

The Role of Triacylglycerol in the Protection of Cells against Lipotoxicity under Drought in Lolium multiflorum/Festucaarundinacea Introgression Forms

Triacylglycerol is a key lipid compound involved in maintaining homeostasis of both membrane lipids and free fatty acids (FFA) in plant cells under adverse environmental conditions. However, its role in the process of lipid remodeling has not been fully recognized, especially in monocots, including grass species. For our study, two closely related introgression forms of Lolium multiflorum (Italian ryegrass) and Festuca arundinacea (tall fescue), distinct in their level of drought tolerance, were selected as plant models to study rearrangements in plant lipidome under water deficit and further re-watering. The low drought tolerant (LDT) form revealed an elevated level of cellular membrane damage accompanied by an increased content of polyunsaturated FFA and triacylglycerol under water deficit, compared with the high drought tolerant (HDT) form. However, the LDT introgression form demonstrated also the ability to regenerate its membranes after stress cessation. The obtained results clearly indicated that accumulation of triacylglycerol under advanced drought in the LDT form could serve as a cellular protective mechanism against overaccumulation of toxic polyunsaturated FFA and other lipid intermediates. Furthermore, accumulation of triacylglycerol under drought conditions could serve also as storage of substrates required for further regeneration of membranes after stress cessation. The rearrangements in triacylglycerol metabolism were supported by the upregulation of several genes, involved in a biosynthesis of triacylglycerol. With respect to this process, diacylglycerol O-acyltransferase DGAT2 seems to play the most important role in the analyzed grasses.

Mechanisms of Abscisic Acid-Mediated Drought Stress Responses in Plants

Drought is one of the major constraints to rain-fed agricultural production, especially under climate change conditions. Plants evolved an array of adaptive strategies that perceive stress stimuli and respond to these stress signals through specific mechanisms. Abscisic acid (ABA) is a premier signal for plants to respond to drought and plays a critical role in plant growth and development. ABA triggers a variety of physiological processes such as stomatal closure, root system modulation, organizing soil microbial communities, activation of transcriptional and post-transcriptional gene expression, and metabolic alterations. Thus, understanding the mechanisms of ABA-mediated drought responses in plants is critical for ensuring crop yield and global food security. In this review, we highlighted how plants adjust ABA perception, transcriptional levels of ABA- and drought-related genes, and regulation of metabolic pathways to alter drought stress responses at both cellular and the whole plant level. Understanding the synergetic role of drought and ABA will strengthen our knowledge to develop stress-resilient crops through integrated advanced biotechnology approaches. This review will elaborate on ABA-mediated drought responses at genetic, biochemical, and molecular levels in plants, which is critical for advancement in stress biology research.

Genome-wide identification, phylogeny, and expression analysis of the bHLH gene family in tobacco (Nicotiana tabacum)

The basic helix-loop-helix (bHLH) is the second-largest TF family in plants that play important roles in plant growth, development, and stress responses. In this study, a total of 100 bHLHs were identified using Hidden Markov Model profiles in the Nicotiana tabacum genome, clustered into 15 major groups (I-XV) based on their conserved domains and phylogenetic relationships. Group VIII genes were found to be the most abundant, with 27 NtbHLH members. The expansion of NtbHLHs in the genome was due to segmental and tandem duplication. The purifying selection was found to have an important role in the evolution of NtHLHs. Subsequent qRT-PCR validation of five selected genes from transcriptome data revealed that NtbHLH3.1, NtbHLH3.2, NtbHLH24, NtbHLH50, and NtbHLH59.2 have higher expressions at 12 and 24 h in comparison to 0 h (control) of chilling stress. The validated results demonstrated that NtbHLH3.2 and NtbHLH24 genes have 3 and fivefold higher expression at 12 h and 2 and threefold higher expression at 24 h than control plant, shows high sensitivity towards chilling stress. Moreover, the co-expression of positively correlated genes of NtbHLH3.2 and NtbHLH24 confirmed their functional significance in chilling stress response. Therefore, suggesting the importance of NtbHLH3.2 and NtbHLH24 genes in exerting control over the chilling stress responses in tobacco.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01042-x.

Synthesis and regulation of auxin and abscisic acid in maize

Indole-3-acetic acid (IAA), the primary auxin in higher plants, and abscisic acid (ABA) play crucial roles in the ability of maize (Zea mays L.) to acclimatize to various environments by mediating growth, development, defense and nutrient allocation. Although understanding the biochemical reactions for IAA and ABA biosynthesis and signal transduction has progressed, the mechanisms by which auxin and ABA are synthesized and transduced in maize have not been fully elucidated to date. The synthesis and signal transduction pathway of IAA and ABA in maize can be analyzed using an existing model. This article focuses on the research progress toward understanding the synthesis and signaling pathways of IAA and ABA, as well as IAA and ABA regulation of maize growth, providing insight for future development and the significance of IAA and ABA for maize improvement.

Mechanisms and functions of membrane lipid remodeling in plants

Lipid remodeling, defined herein as post-synthetic structural modifications of membrane lipids, play crucial roles in regulating the physicochemical properties of cellular membranes and hence their many functions. Processes affected by lipid remodeling include lipid metabolism, membrane repair, cellular homeostasis, fatty acid trafficking, cellular signaling and stress tolerance. Glycerolipids are the major structural components of cellular membranes and their composition can be adjusted by modifying their head groups, their acyl chain lengths and the number and position of double bonds. This review summarizes recent advances in our understanding of mechanisms of membrane lipid remodeling with emphasis on the lipases and acyltransferases involved in the modification of phosphatidylcholine and monogalactosyldiacylglycerol, the major membrane lipids of extraplastidic and photosynthetic membranes, respectively. We also discuss the role of triacylglycerol metabolism in membrane acyl chain remodeling. Finally, we discuss emerging data concerning the functional roles of glycerolipid remodeling in plant stress responses. Illustrating the molecular basis of lipid remodeling may lead to novel strategies for crop improvement and other biotechnological applications such as bioenergy production.

Importance of inositols and their derivatives in cowpea under root dehydration: An omics perspective

This work presents a robust analysis of the inositols (INSs) and raffinose family oligosaccharides (RFOs) pathways, using genomic and transcriptomic tools in cowpea under root dehydration. Nineteen (~70%) of the 26 scrutinized enzymes presented transcriptional up-regulation in at least one treatment time. The transcriptional orchestration allowed categorization of the analyzed enzymes as time-independent (those showing the same regulation throughout the assay) and time-dependent (those showing different transcriptional regulation over time). It is suggested that up-regulated time-independent enzymes (INSs: myo-inositol oxygenase, inositol-tetrakisphosphate 1-kinase 3, phosphatidylinositol 4-phosphate 5-kinase 4-like, 1-phosphatidylinositol-3-phosphate 5-kinase, phosphoinositide phospholipase C, and non-specific phospholipase C; RFOs: α-galactosidase, invertase, and raffinose synthase) actively participate in the reorganization of cowpea molecular physiology under the applied stress. In turn, time-dependent enzymes, especially those up-regulated in some of the treatment times (INSs: inositol-pentakisphosphate 2-kinase, phosphatidylinositol 4-kinase, phosphatidylinositol synthase, multiple inositol polyphosphate phosphatase 1, methylmalonate-semialdehyde dehydrogenase, triosephosphate isomerase, myo-inositol-3-phosphate synthase, phosphatidylinositol 3,4,5-trisphosphate 3-phosphatase and protein-tyrosine-phosphatase, and phosphatidylinositol 3-kinase; RFOs: galactinol synthase) seem to participate in fine-tuning of the molecular physiology, helping the cowpea plants to acclimatize under dehydration stress. Not all loci encoding the studied enzymes were expressed during the assay; most of the expressed ones exhibited a variable transcriptional profile in the different treatment times. Genes of the INSs and RFOs pathways showed high orthology with analyzed Phaseoleae members, suggesting a relevant role within this legume group. Regarding the promoter regions of INSs and RFOs genes, some bona fide cis-regulatory elements were identified in association with seven transcription factor families (AP2-EFR, Dof-type, MADS-box, bZIP, CPP, ZF-HD, and GATA-type). Members of INSs and RFOs pathways potentially participate in other processes regulated by these proteins in cowpea.

Membrane dynamics during individual and combined abiotic stresses in plants and tools to study the same

The plasma membrane (PM) is possibly the most diverse biological membrane of plant cells; it separates and guards the cell against its external environment. It has an extremely complex structure comprising a mosaic of lipids and proteins. The PM lipids are responsible for maintaining fluidity, permeability and integrity of the membrane and also influence the functioning of membrane proteins. However, the PM is the primary target of environmental stress, which affects its composition, conformation and properties, thereby disturbing the cellular homeostasis. Maintenance of integrity and fluidity of the PM is a prerequisite for ensuring the survival of plants during adverse environmental conditions. The ability of plants to remodel membrane lipid and protein composition plays a crucial role in adaptation towards varying abiotic environmental cues, including high or low temperature, drought, salinity and heavy metals stress. The dynamic changes in lipid composition affect the functioning of membrane transporters and ultimately regulate the physical properties of the membrane. Plant membrane-transport systems play a significant role in stress adaptation by cooperating with the membrane lipidome to maintain the membrane integrity under stressful conditions. The present review provides a holistic view of stress responses and adaptations in plants, especially the changes in the lipidome and proteome of PM under individual or combined abiotic stresses, which cause alterations in the activity of membrane transporters and modifies the fluidity of the PM. The tools to study the varying lipidome and proteome of the PM are also discussed.

Ascophyllum nodosum Biostimulant Improves the Growth of Zea mays Grown Under Phosphorus Impoverished Conditions

Phosphorous is one of the major limiting factors determining plant growth. Current agricultural practices mainly rely on the use of chemical fertilizers posing threat to the ecosystem. In this study, the application of an Ascophyllum nodosum extract (ANE) in phosphorous (P)-limited conditions improved the fresh and dry weight of shoots and roots of Zea mays. ANE-treated Z. mays grown under P-limited conditions showed a higher P content than the control. ANE activated simultaneous responses, at multiple levels, in Z. mays grown under P-limited conditions as seen from the regulation of gene expression at the whole-plant level to specific biochemical responses on a subcellular level. ANE-supplemented Z. mays grown under P-limited conditions also showed reduced electrolyte leakage and lipid peroxidation by an improved membrane stability. ANE treatment reduced P-limitation-induced oxidative damage in Z. mays by reducing H2O2 andO 2 - accumulation. Furthermore, ANE also induced the accumulation of the total contents of soluble sugars, amino acids, phenolics, and flavonoids. Gene expression analysis suggested that ANE differentially modulated the expression of P-starvation responsive genes involved in metabolic, signal transduction, and developmental pathways in Z. mays. ANE also modulated the expression of genes involved in sugar, lipid, and secondary metabolism. Thus, this study illustrated the role of ANE in improving the productivity of Z. mays, an important crop, in P-limited conditions. Furthermore, it sets the framework to increase agricultural productivity in nutrient deficient soils using a sustainable, eco-friendly strategy.

Galactolipid and Phospholipid Profile and Proteome Alterations in Soybean Leaves at the Onset of Salt Stress

Salinity is a major environmental factor that constrains soybean yield and grain quality. Given our past observations using the salt-sensitive soybean (Glycine max [L.] Merr.) accession C08 on its early responses to salinity and salt-induced transcriptomic modifications, the aim of this study was to assess the lipid profile changes in this cultivar before and after short-term salt stress, and to explore the adaptive mechanisms underpinning lipid homeostasis. To this end, lipid profiling and proteomic analyses were performed on the leaves of soybean seedlings subjected to salt treatment for 0, 0.5, 1, and 2 h. Our results revealed that short-term salt stress caused dynamic lipid alterations resulting in recycling for both galactolipids and phospholipids. A comprehensive understanding of membrane lipid adaption following salt treatment was achieved by combining time-dependent lipidomic and proteomic data. Proteins involved in phosphoinositide synthesis and turnover were upregulated at the onset of salt treatment. Salinity-induced lipid recycling was shown to enhance jasmonic acid and phosphatidylinositol biosyntheses. Our study demonstrated that salt stress resulted in a remodeling of membrane lipid composition and an alteration in membrane lipids associated with lipid signaling and metabolism in C08 leaves.

Molecular study of drought response in the Mediterranean conifer Pinus pinaster Ait.: Differential transcriptomic profiling reveals constitutive water deficit-independent drought tolerance mechanisms

Adaptation of long-living forest trees to respond to environmental changes is essential to secure their performance under adverse conditions. Water deficit is one of the most significant stress factors determining tree growth and survival. Maritime pine (Pinus pinaster Ait.), the main source of softwood in southwestern Europe, is subjected to recurrent drought periods which, according to climate change predictions for the years to come, will progressively increase in the Mediterranean region. The mechanisms regulating pine adaptive responses to environment are still largely unknown. The aim of this work was to go a step further in understanding the molecular mechanisms underlying maritime pine response to water stress and drought tolerance at the whole plant level. A global transcriptomic profiling of roots, stems, and needles was conducted to analyze the performance of siblings showing contrasted responses to water deficit from an ad hoc designed full-sib family. Although P. pinaster is considered a recalcitrant species for vegetative propagation in adult phase, the analysis was conducted using vegetatively propagated trees exposed to two treatments: well-watered and moderate water stress. The comparative analyses led us to identify organ-specific genes, constitutively expressed as well as differentially expressed when comparing control versus water stress conditions, in drought-sensitive and drought-tolerant genotypes. Different response strategies can point out, with tolerant individuals being pre-adapted for coping with drought by constitutively expressing stress-related genes that are detected only in latter stages on sensitive individuals subjected to drought.

Volatilome-Genome-Wide Association Study on Wholemeal Maize Flour

Odor and aroma, resulting from the perception of volatiles by the olfactory receptors, are important in consumer food acceptance. To develop more efficient molecular breeding tools to improve the odor/aroma on maize (Zea mays L.), a staple food crop, increasing the knowledge on the genetic basis of maize volatilome is needed. In this work, we conducted a genome-wide association study on a unique germplasm collection to identify genomic regions controlling maize wholemeal flour's volatilome. We identified 64 regions on the maize genome and candidate genes controlling the levels of 15 volatiles, mainly aldehydes. As an example, the Zm00001d033623 gene was within a region associated with 2-octenal (E) and 2-nonenal (E), two byproducts of linoleic acid oxidation. This gene codes for linoleate 9S-lipoxygenase, an enzyme responsible for oxidizing linoleic acid. This knowledge can now support the development of molecular tools to increase the selection efficacy/efficiency of these volatiles within maize breeding programs.

Transcription factors as molecular switches to regulate drought adaptation in maize

Here, we reviewed major transcription factors of maize that confer drought stress tolerance, and their target genes and involved signaling pathway. Transcription factors in maize can be promising candidates for improving comprehensive resistance of multiple environmental stimuli. Adverse environmental stress is the main influencing factor affecting plant growth and reproduction, which poses tremendous threats to sustainable agriculture development and crops productivity worldwide. Among various abiotic stress factors, drought is the most vital adversity with the characteristics of frequent occurrences, long duration, and globality. Maize (Zea mays L.) is a major source of food supply for human being and livestock and recently for biofuel. Maize is the crop that is highly susceptible to drought stress. Drought stress tolerance in plants is quite complex, and it is not ideal to improve crop drought tolerance through a single resistant gene. Transcription factors participate in the regulation of plant growth and development, morphogenesis, and various environmental stress responses via regulating the expression level of their target stress-responsive genes independently or cross talk with other transcription factors, thereby the comprehensive resistance of multiple stresses in crops is improved. This review aims to summarize the major drought-tolerant transcription factors in maize and their regulatory network. With the continuous identification of maize transcription factors, more will be demonstrated to confer drought tolerance either in maize or other crops. It is expected that the transcription factors will greatly enrich the functional gene resources and will be a benefit to drought-tolerant maize cultivars breeding.

Comprehensive and quantitative profiling of lipid molecular species by LC-ESI-MS/MS of four native species from semiarid Patagonian Monte

The maintenance of lipid and fatty acids unsaturated composition has been described as one of the mechanisms associated to drought tolerance, but research about the lipid profile in native plants of semiarid environment is still limited. The primary objective was to study whether lipid profiles correlates with drought resistance strategies (tolerant or avoidant) of two life forms (shrubs and grasses). The lipid classes and molecular species of green leaves of Larrea divaricata and Lycium chilense shrubs and Pappostipa speciosa and Poa ligularis grasses were determined using LC-ESI-MS/MS. The soil water content was very low during spring and leaf relative water content was between 47 and 74% in the four species. Lipid profiling was different between both life forms. The prevalent compounds were digalactosyldiacylglycerol (DGDG), monogalactosyldiacylglycerol (MGDG) and phosphatidic acid (PA). The lipid signature shows that L. divaricata adjust its lipid composition to tolerate drought, increasing the content of: a) total lipids and total phospholipids, b) structural phospholipids (36:4 and 36:2-PC, phosphatidylcholine; 36:4-PE, phosphatidylethanolamine), c) chloroplast and mitochondria lipids (32:1 and 32:0-PG, phosphatidylglycerol; 34:3, 36:6 and 36:3-DGDG), d) signaling lipids (34:3, 34:2 and 36:5-PA and PI, phosphatidylinositol), and e) polyunsaturated fatty acids (PUFAs, 18:3 and 18:2) and long chain polyunsaturated fatty acids (LC-PUFAs, in 40:2 and 42:2-PS, phosphatidylserine). This membrane lipid composition contributes to membrane stabilization as metabolic-functional strategy for drought tolerance in the Patagonian Monte. In addition, the 18:3 present in lipids of both grasses could be incorporated to lamb fed based on pastures and result healthy for human dietary.

A novel sweetpotato bZIP transcription factor gene, IbbZIP1, is involved in salt and drought tolerance in transgenic Arabidopsis

The overexpression of IbbZIP1 leads to a significant upregulation of abiotic-related genes, suggesting that IbbZIP1 gene confers salt and drought tolerance in transgenic Arabidopsis. Basic region/leucine zipper motif (bZIP) transcription factors regulate flower development, seed maturation, pathogen defense, and stress signaling in plants. Here, we cloned a novel bZIP transcription factor gene, named IbbZIP1, from sweetpotato [Ipomoea batatas (L.) Lam.] line HVB-3. The full length of IbbZIP1 exhibited transactivation activity in yeast. The expression of IbbZIP1 in sweetpotato was strongly induced by NaCl, PEG6000, and abscisic acid (ABA). Its overexpression in Arabidopsis significantly enhanced salt and drought tolerance. Under salt and drought stresses, the transgenic Arabidopsis plants showed significant upregulation of the genes involved in ABA and proline biosynthesis and reactive oxygen species scavenging system, significant increase of ABA and proline contents and superoxide dismutase activity and significant decrease of H₂O₂ content. These results demonstrate that the IbbZIP1 gene confers salt and drought tolerance in transgenic Arabidopsis. This study provides a novel bZIP gene for improving the tolerance of sweetpotato and other plants to abiotic stresses.

Induced Expression of Xerophyta viscosa XvSap1 Gene Enhances Drought Tolerance in Transgenic Sweet Potato

Drought stress often leads to reduced yields and is a perilous delimiter for expanded cultivation and increased productivity of sweet potato. Cell wall stabilization proteins have been identified to play a pivotal role in mechanical stabilization during desiccation stress mitigation in plants. They are involved in numerous cellular processes that modify cell wall properties to tolerate the mechanical stress during dehydration. This provides a plausible approach to engineer crops for enhanced stable yields under adverse climatic conditions. In this study, we genetically engineered sweet potato cv. Jewel with XvSap1 gene encoding a protein related to cell wall stabilization, isolated from the resurrection plant Xerophyta viscosa, under stress-inducible XvPSap1 promoter via Agrobacterium-mediated transformation. Detection of the transgene by PCR, Southern blot, and quantitative real-time PCR (qRT-PCR) analyses revealed the integration of XvSap1 in the three independent events. Phenotypic evaluation of shoot length, number of leaves, and yield revealed that the transgenic plants grew better than the wild-type plants under drought stress. Assessment of biochemical indices during drought stress showed higher levels of chlorophyll, free proline, and relative water content and decreased lipid peroxidation in transgenic plants than in wild types. Our findings demonstrate that XvSap1 enhances drought tolerance in transgenic sweet potato without causing deleterious phenotypic and yield changes. The transgenic drought-tolerant sweet potato lines provide a valuable resource as a drought-tolerant crop on arid lands of the world.

Maize Sep15-like functions in endoplasmic reticulum and reactive oxygen species homeostasis to promote salt and osmotic stress resistance

In animals, the Sep15 protein participates in disease resistance, growth, and development, but the function of its plant homologues remains unclear. Here, the function of maize Sep15 was analysed by characterization of two independent Sep15-like loss-of-function mutants. In the absence of ZmSep15-like, seedling tolerance to both water and salinity stress was compromised. The mutants experienced a heightened level of endoplasmic reticulum stress, and over-accumulated reactive oxygen species, resulting in leaf necrosis. Characterization of Arabidopsis thaliana atsep15 mutant as well as like with ectopic expression of ZmSep15-like indicated that ZmSep15-like contributed to tolerance of both osmotic and salinity stress. ZmSep15-like interacted physically with UDP-glucose: glycoprotein glucosyltransferase1 (UGGT1). When the interaction was disrupted, the response to both osmotic and salinity stresses was impaired in maize or Arabidopsis. Co-expressing ZmUGGT1 and ZmUGGT2 enhanced the tolerance of A. thaliana to both stressors, indicating a functional interaction between them. Together, the data indicated that plants Sep15-like proteins promote osmotic and salinity stress resistance by influencing endoplasmic reticulum stress response and reactive oxygen species level.

Differentially expressed ZmASR genes associated with chilling tolerance in maize (Zea mays) varieties

The ABA-stress-ripening (ASR) gene is an abiotic stress-response gene that is widely present in higher plants. The expression of ASR was recently shown to effectively improve plant tolerance to several abiotic stresses. However, the role of ASR during chilling stress in maize (Zea mays L.) is unclear. In this study, we tested two maize varieties under chilling treatment. Our results showed that Jinyu 5 (JY5), a chilling-sensitive variety, had lower maximum PSII efficiency (Fv/Fm) and higher lipid peroxidation levels than Jidan 198 (JD198) under chilling conditions. At the same time, the enzymes superoxide dismutase (SOD) and peroxidase (POD) were more active in JD198 than in JY5 under chilling conditions. In addition, exogenous ABA spray pretreatments enhanced the chilling tolerance of maize, showing results such as increased Fv/Fm ratios, and SOD and POD activity; significantly reduced lipid peroxidation levels and increased expression of ZmASR1 in both JD198 and JY5 under chilling conditions. Moreover, when the ZmASR1 expression levels in the two maize varieties were compared, the chilling-sensitive line JY5 had significantly lower expression in both the leaves and roots than JD198 under chilling stress, indicating that the expression of ZmASR1 is a chilling response option in plants. Furthermore, we overexpressed ZmASR1 in JY5; this resulted in enhanced maize chilling tolerance, which reduced the decreases in Fv/Fm and the malondialdehyde content and enhanced SOD and POD activity. Overall, these results suggest that ZmASR1 expression plays a protective role against chilling stress in plants.

The Genome Sequence of the Wild Tomato Solanum pimpinellifolium Provides Insights Into Salinity Tolerance

Solanum pimpinellifolium, a wild relative of cultivated tomato, offers a wealth of breeding potential for desirable traits such as tolerance to abiotic and biotic stresses. Here, we report the genome assembly and annotation of S. pimpinellifolium 'LA0480.' Moreover, we present phenotypic data from one field experiment that demonstrate a greater salinity tolerance for fruit- and yield-related traits in S. pimpinellifolium compared with cultivated tomato. The 'LA0480' genome assembly size (811 Mb) and the number of annotated genes (25,970) are within the range observed for other sequenced tomato species. We developed and utilized the Dragon Eukaryotic Analyses Platform (DEAP) to functionally annotate the 'LA0480' protein-coding genes. Additionally, we used DEAP to compare protein function between S. pimpinellifolium and cultivated tomato. Our data suggest enrichment in genes involved in biotic and abiotic stress responses. To understand the genomic basis for these differences in S. pimpinellifolium and S. lycopersicum, we analyzed 15 genes that have previously been shown to mediate salinity tolerance in plants. We show that S. pimpinellifolium has a higher copy number of the inositol-3-phosphate synthase and phosphatase genes, which are both key enzymes in the production of inositol and its derivatives. Moreover, our analysis indicates that changes occurring in the inositol phosphate pathway may contribute to the observed higher salinity tolerance in 'LA0480.' Altogether, our work provides essential resources to understand and unlock the genetic and breeding potential of S. pimpinellifolium, and to discover the genomic basis underlying its environmental robustness.

Overproduction of Bioactive Algal Chrysolaminarin by the Critical Carbon Flux Regulator Phosphoglucomutase

Chrysolaminarin, the primary polysaccharide reservoir in some marine algae, has attracted much attention due to its broad health properties. However, its biosynthetic pathway and regulation mechanisms have rarely been reported which hinders the improvement of production efficiency. Therefore, this study aims to identify key metabolic nodes in the chrysolaminarin biosynthetic pathway. A phosphoglucomutase (PGM) in the model microalga Phaeodactylum tricornutum, revealing its critical role in chrysolaminarin biosynthesis is identified. PGM overexpression significantly elevates chrysolaminarin content by 2.54-fold and reaches 25.6% of cell dry weight; while algal growth and photosynthesis are not impaired. Besides, PGM overexpression up- and down-regulates the expression of chrysolaminarin and lipid biosynthetic genes, respectively. Microscopic analysis of aniline blue stained cells reveals that overproduced chrysolaminarin localized predominantly in vacuoles. Lipidomic analyses reveal that PGM overexpression significantly reduces the lipid content. The findings reveal the critical role of PGM in regulating the carbon flux between carbohydrate and lipid biosynthesis in microalgae, and provide a promising candidate for high efficiency production of chrysolaminarin.

ZmNF-YB16 Overexpression Improves Drought Resistance and Yield by Enhancing Photosynthesis and the Antioxidant Capacity of Maize Plants

ZmNF-YB16 is a basic NF-YB superfamily member and a member of a transcription factor complex composed of NF-YA, NF-YB, and NF-YC in maize. ZmNF-YB16 was transformed into the inbred maize line B104 to produce homozygous overexpression lines. ZmNF-YB16 overexpression improves dehydration and drought stress resistance in maize plants during vegetative and reproductive stages by maintaining higher photosynthesis and increases the maize grain yield under normal and drought stress conditions. Based on the examination of differentially expressed genes between the wild-type (WT) and transgenic lines by quantitative real time PCR (qRT-PCR), ZmNF-YB16 overexpression increased the expression of genes encoding antioxidant enzymes, the antioxidant synthase, and molecular chaperones associated with the endoplasmic reticulum (ER) stress response, and improved protection mechanism for photosynthesis system II. Plants that overexpression ZmNF-YB16 showed a higher rate of photosynthesis and antioxidant enzyme activity, better membrane stability and lower electrolyte leakage under control and drought stress conditions. These results suggested that ZmNF-YB16 played an important role in drought resistance in maize by regulating the expression of a number of genes involved in photosynthesis, the cellular antioxidant capacity and the ER stress response.

The phosphatidylinositol synthase gene (GhPIS) contributes to longer, stronger, and finer fibers in cotton

Cotton fibers are the most important natural raw material used in textile industries world-wide. Fiber length, strength, and fineness are the three major traits which determine the quality and economic value of cotton. It is known that exogenous application of phosphatidylinositols (PtdIns), important structural phospholipids, can promote cotton fiber elongation. Here, we sought to increase the in planta production of PtdIns to improve fiber traits. Transgenic cotton plants were generated in which the expression of a cotton phosphatidylinositol synthase gene (i.e., GhPIS) was controlled by the fiber-specific SCFP promoter element, resulting in the specific up-regulation of GhPIS during cotton fiber development. We demonstrate that PtdIns content was significantly enhanced in transgenic cotton fibers and the elevated level of PtdIns stimulated the expression of genes involved in PtdIns phosphorylation as well as promoting lignin/lignin-like phenolic biosynthesis. Fiber length, strength and fineness were also improved in the transgenic plants as compared to the wild-type cotton, with no loss in overall fiber yield. Our data indicate that fiber-specific up-regulation of PtdIns synthesis is a promising strategy for cotton fiber quality improvement.

Heat and Drought Stresses in Crops and Approaches for Their Mitigation

Drought and heat are major abiotic stresses that reduce crop productivity and weaken global food security, especially given the current and growing impacts of climate change and increases in the occurrence and severity of both stress factors. Plants have developed dynamic responses at the morphological, physiological and biochemical levels allowing them to escape and/or adapt to unfavorable environmental conditions. Nevertheless, even the mildest heat and drought stress negatively affects crop yield. Further, several independent studies have shown that increased temperature and drought can reduce crop yields by as much as 50%. Response to stress is complex and involves several factors including signaling, transcription factors, hormones, and secondary metabolites. The reproductive phase of development, leading to the grain production is shown to be more sensitive to heat stress in several crops. Advances coming from biotechnology including progress in genomics and information technology may mitigate the detrimental effects of heat and drought through the use of agronomic management practices and the development of crop varieties with increased productivity under stress. This review presents recent progress in key areas relevant to plant drought and heat tolerance. Furthermore, an overview and implications of physiological, biochemical and genetic aspects in the context of heat and drought are presented. Potential strategies to improve crop productivity are discussed.

Heat and Drought Stresses in Crops and Approaches for Their Mitigation

Drought and heat are major abiotic stresses that reduce crop productivity and weaken global food security, especially given the current and growing impacts of climate change and increases in the occurrence and severity of both stress factors. Plants have developed dynamic responses at the morphological, physiological and biochemical levels allowing them to escape and/or adapt to unfavorable environmental conditions. Nevertheless, even the mildest heat and drought stress negatively affects crop yield. Further, several independent studies have shown that increased temperature and drought can reduce crop yields by as much as 50%. Response to stress is complex and involves several factors including signaling, transcription factors, hormones, and secondary metabolites. The reproductive phase of development, leading to the grain production is shown to be more sensitive to heat stress in several crops. Advances coming from biotechnology including progress in genomics and information technology may mitigate the detrimental effects of heat and drought through the use of agronomic management practices and the development of crop varieties with increased productivity under stress. This review presents recent progress in key areas relevant to plant drought and heat tolerance. Furthermore, an overview and implications of physiological, biochemical and genetic aspects in the context of heat and drought are presented. Potential strategies to improve crop productivity are discussed.

Genomewide identification of genes involved in the potato response to drought indicates functional evolutionary conservation with Arabidopsis plants

Potato is one of the four most important food crop plants worldwide and is strongly affected by drought. The following two pairs of potato cultivars, which are related in ancestry but show different drought tolerances, were chosen for comparative gene expression studies: Gwiazda/Oberon and Tajfun/Owacja. Comparative RNA-seq analyses of gene expression differences in the transcriptomes obtained from drought-tolerant versus drought-sensitive plants during water shortage conditions were performed. The 23 top-ranking genes were selected, 22 of which are described here as novel potato drought-responsive genes. Moreover, all but one of the potato genes selected have homologues in the Arabidopsis genome. Of the seven tested A. thaliana mutants with altered expression of the selected homologous genes, compared to the wild-type Arabidopsis plants, six showed an improved tolerance to drought. These genes encode carbohydrate transporter, mitogen-activated protein kinase kinase kinase 15 (MAPKKK15), serine carboxypeptidase-like 19 protein (SCPL19), armadillo/beta-catenin-like repeat-containing protein, high-affinity nitrate transporter 2.7 and nonspecific lipid transfer protein type 2 (nsLPT). The evolutionary conservation of the functions of the selected genes in the plant response to drought confirms the importance of these identified potato genes in the ability of plants to cope with water shortage conditions. Knowledge regarding these gene functions can be used to generate potato cultivars that are resistant to unfavourable conditions. The approach used in this work and the obtained results allowed for the identification of new players in the plant response to drought.

Molecular cloning and characterization of PtrZPT2-1, a ZPT2 family gene encoding a Cys2/His2-type zinc finger protein from trifoliate orange (Poncirus trifoliata (L.) Raf.) that enhances plant tolerance to multiple abiotic stresses

In plants, most Cys2/His2 (C2H2) zinc finger proteins with two zinc finger domains (ZPT2) are involved in abiotic stress responses. In this study, a ZPT2 family gene PtrZPT2-1 was cloned from trifoliate orange (Poncirus trifoliata (L.) Raf.). PtrZPT2-1 is composed of 245 amino acids, has a putative molecular weight of 25.99kDa and an isoelectric point of 8.41. PtrZPT2-1 contained two C2H2 zinc finger domains, one nuclear localization signal (B-box), one transcription repression domain (DLN-box), and one protein-protein interaction domain (L-box). PtrZPT2-1 was localized to the nucleus. The PtrZPT2-1 expression was strongly induced by cold, drought, salt and ABA stresses. Overexpression of PtrZPT2-1 increased the survival rates, and the ABA, soluble sugar and proline levels but decreased the ion leakage, the malondialdehyde (MDA) content and reduced the H2O2 accumulation in the transgenic tobacco after cold, drought or salt treatments. Furthermore, the expression levels of 15 abiotic stress-related genes were significantly increased in the transgenic tobacco overexpressing PtrZPT2-1 after cold, drought or salt stress treatments. Our results indicated that overexpression of PtrZPT2-1 in the transgenic tobacco could improve the cold, drought and salt resistance of the plants by increasing the levels of osmotic regulatory solutes and decreasing the accumulation of H2O2.

Phosphoinositide signaling in plant development

The membranes of eukaryotic cells create hydrophobic barriers that control substance and information exchange between the inside and outside of cells and between cellular compartments. Besides their roles as membrane building blocks, some membrane lipids, such as phosphoinositides (PIs), also exert regulatory effects. Indeed, emerging evidence indicates that PIs play crucial roles in controlling polarity and growth in plants. Here, I highlight the key roles of PIs as important regulatory membrane lipids in plant development and function.

Occurrence of plastidial triacylglycerol synthesis and the potential regulatory role of AGPAT in the model diatom Phaeodactylum tricornutum

BACKGROUND

Microalgae have emerged as a potential feedstock for biofuels and bioactive components. However, lack of microalgal strains with promising triacylglycerol (TAG) content and desirable fatty acid composition have hindered its commercial feasibility. Attempts on lipid overproduction by metabolic engineering remain largely challenging in microalgae.

RESULTS

In this study, a microalgal 1-acyl-sn-glycerol-3-phosphate acyltransferase designated AGPAT1 was identified in the model diatom Phaeodactylum tricornutum. AGPAT1 contained four conserved acyltransferase motifs I-IV. Subcellular localization prediction and thereafter immuno-electron microscopy revealed the localization of AGPAT1 to plastid membranes. AGPAT1 overexpression significantly altered the primary metabolism, with increased total lipid content but decreased content of total carbohydrates and soluble proteins. Intriguingly, AGPAT1 overexpression coordinated the expression of other key genes such as DGAT2 and GPAT involved in TAG synthesis, and consequently increased TAG content by 1.81-fold with a significant increase in polyunsaturated fatty acids, particularly EPA and DHA. Moreover, besides increased lipid droplets in the cytosol, ultrastructural observation showed a number of TAG-rich plastoglobuli formed in plastids.

CONCLUSION

The results suggested that AGPAT1 overexpression could elevate TAG biosynthesis and, moreover, revealed the occurrence of plastidial TAG synthesis in the diatom. Overall, our data provide a new insight into microalgal lipid metabolism and candidate target for metabolic engineering.

Water Deficit Affects Primary Metabolism Differently in Two Lolium multiflorum/Festuca arundinacea Introgression Forms with a Distinct Capacity for Photosynthesis and Membrane Regeneration

Understanding how plants respond to drought at different levels of cell metabolism is an important aspect of research on the mechanisms involved in stress tolerance. Furthermore, a dissection of drought tolerance into its crucial components by the use of plant introgression forms facilitates to analyze this trait more deeply. The important components of plant drought tolerance are the capacity for photosynthesis under drought conditions, and the ability of cellular membrane regeneration after stress cessation. Two closely related introgression forms of Lolium multiflorum/Festuca arundinacea, differing in the level of photosynthetic capacity during stress, and in the ability to regenerate their cellular membranes after stress cessation, were used as forage grass models in a primary metabolome profiling and in an evaluation of chloroplast 1,6-bisphosphate aldolase accumulation level and activity, during 11 days of water deficit, followed by 10 days of rehydration. It was revealed here that the introgression form, characterized by the ability to regenerate membranes after rehydration, contained higher amounts of proline, melibiose, galactaric acid, myo-inositol and myo-inositol-1-phosphate involved in osmoprotection and stress signaling under drought. Moreover, during the rehydration period, this form also maintained elevated accumulation levels of most the primary metabolites, analyzed here. The other introgression form, characterized by the higher capacity for photosynthesis, revealed a higher accumulation level and activity of chloroplast aldolase under drought conditions, and higher accumulation levels of most photosynthetic products during control and drought periods. The potential impact of the observed metabolic alterations on cellular membrane recovery after stress cessation, and on a photosynthetic capacity under drought conditions in grasses, are discussed.

A New Insight of Salt Stress Signaling in Plant

Many studies have been conducted to understand plant stress responses to salinity because irrigation-dependent salt accumulation compromises crop productivity and also to understand the mechanism through which some plants thrive under saline conditions. As mechanistic understanding has increased during the last decades, discovery-oriented approaches have begun to identify genetic determinants of salt tolerance. In addition to osmolytes, osmoprotectants, radical detoxification, ion transport systems, and changes in hormone levels and hormone-guided communications, the Salt Overly Sensitive (SOS) pathway has emerged to be a major defense mechanism. However, the mechanism by which the components of the SOS pathway are integrated to ultimately orchestrate plant-wide tolerance to salinity stress remains unclear. A higher-level control mechanism has recently emerged as a result of recognizing the involvement of GIGANTEA (GI), a protein involved in maintaining the plant circadian clock and control switch in flowering. The loss of GI function confers high tolerance to salt stress via its interaction with the components of the SOS pathway. The mechanism underlying this observation indicates the association between GI and the SOS pathway and thus, given the key influence of the circadian clock and the pathway on photoperiodic flowering, the association between GI and SOS can regulate growth and stress tolerance. In this review, we will analyze the components of the SOS pathways, with emphasis on the integration of components recognized as hallmarks of a halophytic lifestyle.

AtMYB12 regulates flavonoids accumulation and abiotic stress tolerance in transgenic Arabidopsis thaliana

In plants, transcriptional regulation is the most important tool for modulating flavonoid biosynthesis. The AtMYB12 gene from Arabidopsis thaliana has been shown to regulate the expression of key enzyme genes involved in flavonoid biosynthesis, leading to the increased accumulation of flavonoids. In this study, the codon-optimized AtMYB12 gene was chemically synthesized. Subcellular localization analysis in onion epidermal cells indicated that AtMYB12 was localized to the nucleus. Its overexpression significantly increased accumulation of flavonoids and enhanced salt and drought tolerance in transgenic Arabidopsis plants. Real-time quantitative PCR (qRT-PCR) analysis showed that overexpression of AtMYB12 resulted in the up-regulation of genes involved in flavonoid biosynthesis, abscisic acid (ABA) biosynthesis, proline biosynthesis, stress responses and ROS scavenging under salt and drought stresses. Further analyses under salt and drought stresses showed significant increases of ABA, proline content, superoxide dismutase (SOD) and peroxidase (POD) activities, as well as significant reduction of H2O2 and malonaldehyde (MDA) content. The results demonstrate the explicit role of AtMYB12 in conferring salt and drought tolerance by increasing the levels of flavonoids and ABA in transgenic Arabidopsis. The AtMYB12 gene has the potential to be used to enhance tolerance to abiotic stresses in plants.

Glycerolipidome responses to freezing- and chilling-induced injuries: examples in Arabidopsis and rice

BACKGROUND

Glycerolipids are the principal constituent of cellular membranes; remodelling of glycerolipids plays important roles in temperature adaptation in plants. Temperate plants can endure freezing stress, but even chilling at above-zero temperatures can induce death in tropical species. However, little is known about the differences in glycerolipid response to low temperatures between chilling-sensitive and freezing-tolerant plants. Using ESI-MS/MS-based lipidomic analysis, we compared the glycerolipidome of chilling (4 and 10 °C)-treated rice with that of freezing (-6 and -12 °C)-treated Arabidopsis, both immediately after these low-temperature treatments and after a subsequent recovery culture period.

RESULTS

Arabidopsis is a 16:3 plant that harbours both eukaryotic and prokaryotic-type lipid synthesis pathways, while rice is an 18:3 plant that harbours only the eukaryotic lipid synthesis pathway. Arabidopsis contains higher levels of galactolipids than rice and has a higher double bond index (DBI). Arabidopsis contains lower levels of high melting point phosphatidylglycerol (PG) molecules and has a lower average acyl chain length (ACL). Marked phospholipid degradation occurred during the recovery culture period of non-lethal chilling treated rice, but did not occur in non-lethal freezing treated Arabidopsis. Glycerolipids with larger head groups were synthesized more in Arabidopsis than in rice at sub-lethal low-temperatures. Levels of phosphatidic acid (PA) and phosphatidylinositol (PI) rose in both plants after low-temperature treatment. The DBI and ACL of total lipids did not change during low-temperature treatment.

CONCLUSIONS

A higher DBI and a lower ACL could make the membranes of Arabidopsis more fluid at low temperatures. The ability to synthesize glycerolipids containing a larger head group may correlate with low-temperature tolerance. The low-temperature-induced increase of PA may play a dual role in plant responses to low temperatures: as a lipid signal that initiates tolerance responses, and as a structural molecule that, on extensive in large accumulation, could damage the integrity of membranes. Changes in ACL and DBI are responses of plants to long-term low temperature.

A novel Cys2/His2 zinc finger protein gene from sweetpotato, IbZFP1, is involved in salt and drought tolerance in transgenic Arabidopsis

IbZFP1, encoding a Cys 2/His 2 zinc finger protein gene from sweetpotato, enhances salt and drought tolerance in transgenic Arabidopsis by regulating ABA signaling pathway, proline biosynthesis, stress responses and ROS scavenging. In plants, Cys2/His2 zinc finger proteins play important roles in regulating the growth and development or responses to abiotic stresses. In this study, a novel Cys2/His2 zinc finger protein gene, named IbZFP1, was isolated from drought-tolerant sweetpotato [Ipomoea batatas (L.) Lam.] line Xu55-2. Subcellular localization analysis in onion epidermal cells indicated that IbZFP1 was localized to the nucleus. Expression analysis in yeast showed that the full length of IbZFP1 exhibited transcriptional activation. Expression of IbZFP1 was induced by NaCl, polyethylene glycol and abscisic acid (ABA). Overexpression of IbZFP1 significantly enhanced salt and drought tolerance in transgenic Arabidopsis plants. Real-time quantitative PCR (qRT-PCR) analysis showed that overexpression of IbZFP1 up-regulated the genes involved in ABA signaling pathway, proline biosynthesis, stress responses, and ROS scavenging under salt and drought stresses. Meanwhile, Western blot and enzymatic analyses showed that the activities of 9-cis-epoxycarotenoid dioxygenase, pyrroline-5-carboxylate synthase, superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase were also increased. Further component analyses indicated that the significant increase of ABA, proline, soluble sugar and total chlorophyll content and the significant reduction of H2O2 and malonaldehyde content were observed under salt and drought stresses. In addition, the rates of electrolyte leakage and water loss were reduced in transgenic plants. The overall results demonstrate the explicit role of IbZFP1 in conferring salt and drought tolerance in transgenic Arabidopsis plants. The IbZFP1 gene has the potential to be used to enhance the tolerance to abiotic stresses in plants.

A myo-inositol-1-phosphate synthase gene, IbMIPS1, enhances salt and drought tolerance and stem nematode resistance in transgenic sweet potato

Myo-inositol-1-phosphate synthase (MIPS) is a key rate limiting enzyme in myo-inositol biosynthesis. The MIPS gene has been shown to improve tolerance to abiotic stresses in several plant species. However, its role in resistance to biotic stresses has not been reported. In this study, we found that expression of the sweet potato IbMIPS1 gene was induced by NaCl, polyethylene glycol (PEG), abscisic acid (ABA) and stem nematodes. Its overexpression significantly enhanced stem nematode resistance as well as salt and drought tolerance in transgenic sweet potato under field conditions. Transcriptome and real-time quantitative PCR analyses showed that overexpression of IbMIPS1 up-regulated the genes involved in inositol biosynthesis, phosphatidylinositol (PI) and ABA signalling pathways, stress responses, photosynthesis and ROS-scavenging system under salt, drought and stem nematode stresses. Inositol, inositol-1,4,5-trisphosphate (IP3 ), phosphatidic acid (PA), Ca(2+) , ABA, K(+) , proline and trehalose content was significantly increased, whereas malonaldehyde (MDA), Na(+) and H2 O2 content was significantly decreased in the transgenic plants under salt and drought stresses. After stem nematode infection, the significant increase of inositol, IP3 , PA, Ca(2+) , ABA, callose and lignin content and significant reduction of MDA content were found, and a rapid increase of H2 O2 levels was observed, peaked at 1 to 2 days and thereafter declined in the transgenic plants. This study indicates that the IbMIPS1 gene has the potential to be used to improve the resistance to biotic and abiotic stresses in plants.

Genotypic Variation in Growth and Physiological Response to Drought Stress and Re-Watering Reveals the Critical Role of Recovery in Drought Adaptation in Maize Seedlings

Non-irrigated crops in temperate climates and irrigated crops in arid climates are subjected to continuous cycles of water stress and re-watering. Thus, fast and efficient recovery from water stress may be among the key determinants of plant drought adaptation. The present study was designed to comparatively analyze the roles of drought resistance and drought recovery in drought adaptation and to investigate the physiological basis of genotypic variation in drought adaptation in maize (Zea mays) seedlings. As the seedlings behavior in growth associate with yield under drought, it could partly reflect the potential of drought adaptability. Growth and physiological responses to progressive drought stress and recovery were observed in seedlings of 10 maize lines. The results showed that drought adaptability is closely related to drought recovery (r = 0.714(**)), but not to drought resistance (r = 0.332). Drought induced decreases in leaf water content, water potential, osmotic potential, gas exchange parameters, chlorophyll content, Fv/Fm and nitrogen content, and increased H2O2 accumulation and lipid peroxidation. After recovery, most of these physiological parameters rapidly returned to normal levels. The physiological responses varied between lines. Further correlation analysis indicated that the physiological bases of drought resistance and drought recovery are definitely different, and that maintaining higher chlorophyll content (r = 0.874(***)) and Fv/Fm (r = 0.626(*)) under drought stress contributes to drought recovery. Our results suggest that both drought resistance and recovery are key determinants of plant drought adaptation, and that drought recovery may play a more important role than previously thought. In addition, leaf water potential, chlorophyll content and Fv/Fm could be used as efficient reference indicators in the selection of drought-adaptive genotypes.

Identification of a 467 bp Promoter of Maize Phosphatidylinositol Synthase Gene (ZmPIS) Which Confers High-Level Gene Expression and Salinity or Osmotic Stress Inducibility in Transgenic Tobacco

Salinity and drought often affect plant growth and crop yields. Cloning and identification of salinity and drought stress inducible promoters is of great significance for their use in the genetic improvement of crop resistance. Previous studies showed that phosphatidylinositol synthase is involved in plant salinity and drought stress responses but its promoter has not been characterized by far. In the study, the promoter (pZmPIS, 1834 bp upstream region of the translation initiation site) was isolated from maize genome. To functionally validate the promoter, eight 5' deletion fragments of pZmPIS in different lengths were fused to GUS to produce pZmPIS::GUS constructs and transformed into tobacco, namely PZ1-PZ8. The transcription activity and expression pattern obviously changed when the promoter was truncated. Previous studies have demonstrated that NaCl and PEG treatments are usually used to simulate salinity and drought treatments. The results showed that PZ1-PZ7 can respond well upon NaCl and PEG treatments, while PZ8 not. PZ7 (467 bp) displayed the highest transcription activity in all tissues of transgenic tobacco amongst 5' deleted promoter fragments, which corresponds to about 20 and 50% of CaMV35S under normal and NaCl or PEG treatment, respectively. This implied that PZ7 is the core region of pZmPIS which confers high-level gene expression and NaCl or PEG inducible nature. The 113 bp segment between PZ7 and PZ8 (-467 to -355 bp) was considered as the key sequence for ZmPIS responding to NaCl or PEG treatment. GUS transient assay in tobacco leaves showed that this segment was sufficient for the NaCl or PEG stress response. Bioinformatic analysis revealed that the 113 bp sequence may contain new elements that are crucial for ZmPIS response to NaCl or PEG stress. These results promote our understanding on transcriptional regulation mechanism of ZmPIS and the characterized PZ7 promoter fragment would be an ideal candidate for the overexpression of drought and salinity responsive gene to improve crop resistance.

Remodeling of Leaf Cellular Glycerolipid Composition under Drought and Re-hydration Conditions in Grasses from the Lolium-Festuca Complex

Drought tolerant plant genotypes are able to maintain stability and integrity of cellular membranes in unfavorable conditions, and to regenerate damaged membranes after stress cessation. The profiling of cellular glycerolipids during drought stress performed on model species such as Arabidopsis thaliana does not fully cover the picture of lipidome in monocots, including grasses. Herein, two closely related introgression genotypes of Lolium multiflorum (Italian ryegrass) × Festuca arundinacea (tall fescue) were used as a model for other grass species to describe lipid rearrangements during drought and re-hydration. The genotypes differed in their level of photosynthetic capacity during drought, and in their capacity for membrane regeneration after stress cessation. A total of 120 lipids, comprising the classes of monogalactosyldiacyloglycerol, digalactosyldiacyloglycerol, sulfoquinovosyldiacylglycerol, phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, diacylglicerol, and triacylglicerol, were analyzed. The results clearly showed that water deficit had a significant impact on lipid metabolism in studied forage grasses. It was revealed that structural and metabolic lipid species changed their abundance during drought and re-watering periods and some crucial genotype-dependent differences were also observed. The introgression genotype characterized by an ability to regenerate membranes after re-hydration demonstrated a higher accumulation level of most chloroplast and numerous extra-chloroplast membrane lipid species at the beginning of drought. Furthermore, this genotype also revealed a significant reduction in the accumulation of most chloroplast lipids after re-hydration, compared with the other introgression genotype without the capacity for membrane regeneration. The potential influence of observed lipidomic alterations on a cellular membrane stability and photosynthetic capacity, are discussed. HIGHLIGHTS A higher drought tolerance of grasses could be associated with an earlier lipidome response to a stress signal and with a membrane regeneration after stress cessation accompanied by a turnover of chloroplast lipids.

Aboveground Whitefly Infestation Modulates Transcriptional Levels of Anthocyanin Biosynthesis and Jasmonic Acid Signaling-Related Genes and Augments the Cope with Drought Stress of Maize

Up to now, the potential underlying molecular mechanisms by which maize (Zea mays L.) plants elicit defense responses by infestation with a phloem feeding insect whitefly [Bemisia tabaci (Genn.)] have been barely elucidated against (a)biotic stresses. To fill this gap of current knowledge maize plants were infested with whitefly and these plants were subsequently assessed the levels of water loss. To understand the mode of action, plant hormone contents and the stress-related mRNA expression were evaluated. Whitefly-infested maize plants did not display any significant phenotypic differences in above-ground tissues (infested site) compared with controls. By contrast, root (systemic tissue) biomass was increased by 2-fold by whitefly infestation. The levels of endogenous indole-3-acetic acid (IAA), jasmonic acid (JA), and hydrogen peroxide (H₂O₂) were significantly higher in whitefly-infested plants. The biosynthetic or signaling-related genes for JA and anthocyanins were highly up-regulated. Additionally, we found that healthier plants were obtained in whitefly-infested plants under drought conditions. The weight of whitefly-infested plants was approximately 20% higher than that of control plants at 14 d of drought treatment. The drought tolerance-related genes, ZmbZIP72, ZmSNAC1, and ZmABA1, were highly expressed in the whitefly-infected plants. Collectively, our results suggest that IAA/JA-derived maize physiological changes and correlation of H₂O₂ production and water loss are modulated by above-ground whitefly infestation in maize plants.

Global Reprogramming of Transcription in Chinese Fir (Cunninghamia lanceolata) during Progressive Drought Stress and after Rewatering

Chinese fir (Cunninghamia lanceolata), an evergreen conifer, is the most commonly grown afforestation species in southeast China due to its rapid growth and good wood qualities. To gain a better understanding of the drought-signalling pathway and the molecular metabolic reactions involved in the drought response, we performed a genome-wide transcription analysis using RNA sequence data. In this study, Chinese fir plantlets were subjected to progressively prolonged drought stress, up to 15 d, followed by rewatering under controlled environmental conditions. Based on observed morphological changes, plantlets experienced mild, moderate, or severe water stress before rehydration. Transcriptome analysis of plantlets, representing control and mild, moderate, and severe drought-stress treatments, and the rewatered plantlets, identified several thousand genes whose expression was altered in response to drought stress. Many genes whose expression was tightly coupled to the levels of drought stress were identified, suggesting involvement in Chinese fir drought adaptation responses. These genes were associated with transcription factors, signal transport, stress kinases, phytohormone signalling, and defence/stress response. The present study provides the most comprehensive transcriptome resource and the first dynamic transcriptome profiles of Chinese fir under drought stress. The drought-responsive genes identified in this study could provide further information for understanding the mechanisms of drought tolerance in Chinese fir.