Crosstalk between phytohormones and secondary metabolites in the drought stress tolerance of crop plants: A review

Metabolic and molecular mechanisms underlying the foliar Zn application induced increase of 2-acetyl-1-pyrroline conferring the 'taro-like' aroma in pumpkin leaves

INTRODUCTION

Fresh pumpkin leaf is popular vegetable for its rich nutrition. The pleasant taro-like odour is important aroma quality of crops, and mostly contributed by 2-acetyl-1-pyrroline in pumpkin. Element Zn can impact metabolite biosynthesis in plants, including aroma formation. However, Zn-induced biochemical responses, especially 2-acetyl-1-pyrroline formation in pumpkin, haven't been elucidated.

METHODS

This study integrated metabolome and transcriptome to explore molecular fluctuations in pumpkin leaves at different time intervals after foliar Zn treatment.

RESULT AND DISCUSSION

We first identified more than one thousand metabolites from pumpkin leaves by integrating different mass spectrometry methods according to the form in which a metabolite exists. Comparative metabolomic analysis revealed there were separately 25 out of 50 and 286 out of 963 metabolites that were respectively identified by gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry, differentially regulated by Zn treatment. Our findings revealed that 50mg/L of Zn significantly enhanced 2-acetyl-1-pyrroline production by more than 38%, which was contributed by increased biosynthesis of its precursors, including ornithine and proline. The following transcriptome analysis discovered 30,574 genes, including 953 novel genes. Zn treatment induced the differential expression of 41.6% of identified genes which were supposed to regulate the downstream metabolite changes in a time-dependent manner. Pathway analysis indicated that alternations in primary metabolism, including carbon metabolism and biosynthesis of amino acids, were vital to the fluctuated aromatic compound generation. Phytohormones and transcription factors may regulate the expression of gene P5CS and proline biosynthesis, which, therefore, affect 2-acetyl-1-pyrroline production. This research reveals molecular mechanisms of 2-acetyl-1-pyrroline formation in pumpkin, which will provide the molecular basis for desired aroma compound production through metabolite engineering.

The roles of plant proteases and protease inhibitors in drought response: a review

Upon exposure to drought, plants undergo complex signal transduction events with concomitant changes in the expression of genes, proteins and metabolites. For example, proteomics studies continue to identify multitudes of drought-responsive proteins with diverse roles in drought adaptation. Among these are protein degradation processes that activate enzymes and signalling peptides, recycle nitrogen sources, and maintain protein turnover and homeostasis under stressful environments. Here, we review the differential expression and functional activities of plant protease and protease inhibitor proteins under drought stress, mainly focusing on comparative studies involving genotypes of contrasting drought phenotypes. We further explore studies of transgenic plants either overexpressing or repressing proteases or their inhibitors under drought conditions and discuss the potential roles of these transgenes in drought response. Overall, the review highlights the integral role of protein degradation during plant survival under water deficits, irrespective of the genotypes' level of drought resilience. However, drought-sensitive genotypes exhibit higher proteolytic activities, while drought-tolerant genotypes tend to protect proteins from degradation by expressing more protease inhibitors. In addition, transgenic plant biology studies implicate proteases and protease inhibitors in various other physiological functions under drought stress. These include the regulation of stomatal closure, maintenance of relative water content, phytohormonal signalling systems including abscisic acid (ABA) signalling, and the induction of ABA-related stress genes, all of which are essential for maintaining cellular homeostasis under water deficits. Therefore, more validation studies are required to explore the various functions of proteases and their inhibitors under water limitation and their contributions towards drought adaptation.

Seed Bio-priming of wheat with a novel bacterial strain to modulate drought stress in Daegu, South Korea

Wheat is one of the major cereal crop grown food worldwide and, therefore, plays has a key role in alleviating the global hunger crisis. The effects of drought stress can reduces crop yields by up to 50% globally. The use of drought-tolerant bacteria for biopriming can improve crop yields by countering the negative effects of drought stress on crop plants. Seed biopriming can reinforce the cellular defense responses to stresses via the stress memory mechanism, that its activates the antioxidant system and induces phytohormone production. In the present study, bacterial strains were isolated from rhizospheric soil taken from around the Artemisia plant at Pohang Beach, located near Daegu, in the South Korea Republic of Korea. Seventy-three isolates were screened for their growth-promoting attributes and biochemical characteristics. Among them, the bacterial strain SH-8 was selected preferred based on its plant growth-promoting bacterial traits, which are as follows: abscisic acid (ABA) concentration = 1.08 ± 0.05 ng/mL, phosphate-solubilizing index = 4.14 ± 0.30, and sucrose production = 0.61 ± 0.13 mg/mL. The novel strain SH-8 demonstrated high tolerance oxidative stress. The antioxidant analysis also showed that SH-8 contained significantly higher levels of catalase (CAT), superoxide dismutase (SOD), and ascorbic peroxidase (APX). The present study also quantified and determined the effects of biopriming wheat (Triticum aestivum) seeds with the novel strain SH-8. SH-8 was highly effective in enhancing the drought tolerance of bioprimed seeds; their drought tolerance and germination potential (GP) were increased by up to 20% and 60%, respectively, compared with those in the control group. The lowest level of impact caused by drought stress and the highest germination potential, seed vigor index (SVI), and germination energy (GE) (90%, 2160, and 80%, respectively), were recorded for seeds bioprimed with with SH-8. These results show that SH-8 enhances drought stress tolerance by up to 20%. Our study suggests that the novel rhizospheric bacterium SH-8 (gene accession number OM535901) is a valuable biostimulant that improves drought stress tolerance in wheat plants and has the potential to be used as a biofertilizer under drought conditions.

GhCDPK60 positively regulates drought stress tolerance in both transgenic Arabidopsis and cotton by regulating proline content and ROS level

Calcium-Dependent Protein Kinases (CDPKs) involved in regulating downstream components of calcium signaling pathways play a role in tolerance to abiotic stresses and seed development in plants. However, functions of only a few cotton CDPKs have been clarified at present. In this study, 80 conserved CDPKs in Gossypium hirsutum L. were identified and characterized, which was divided into four subgroups. Among them, the transcript level of GhCDPK60 was significantly upregulated under drought and several hormone treatments. And we found that the expression levels of several stress-inducible genes down-regulated in GhCDPK60-silence cotton and up-regulated in GhCDPK60-overexpressing Arabidopsis. In addition, physiological analyses demonstrated that GhCDPK60 improved drought stress tolerance by improving the osmotic adjustment ability and reducing the accumulation of reactive oxygen species (ROS) in plants. These findings broaden our understanding of the biological roles of GhCDPK60 and mechanisms underlying drought stress tolerance in cotton.

Identification and differential analysis of noncoding RNAs in response to drought in Phyllostachys aureosulcata f. spectabilis

The role of noncoding RNAs (ncRNAs) in plant resistance to abiotic stresses is increasingly being discovered. Drought stress is one of the most common stresses that affecting plant growth, and high intensity drought has a significant impact on the normal growth of plants. In this study, a high-throughput sequencing was performed on plant tissue samples of Phyllostachys aureosulcata f. spectabilis C. D. Chu et C. S. Chao by drought treatment for 0, 2, 4 and 6 days. The sequencing results were analysed bioinformatically. We detected 336,946 RNAs among all 12 samples, including 192,098 message RNAs (mRNAs), 142,761 long noncoding RNAs (lncRNAs), 1,670 circular RNAs (circRNAs), and 417 microRNAs (miRNAs). We detected 2,419 differentially expressed (DE) ncRNAs, including 213 DE circRNAs, 2,088 DE lncRNAs and 118 DE miRNAs. Then, we used Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) to functionally predict DE ncRNAs. The results showed that most DE ncRNAs are involved in the response to drought stress, mainly in biochemical reactions involved in some metabolites, as well as in organelle activities. In addition, we validated two random circRNAs and demonstrated their circularity. We also found a stable internal reference gene available for Phyllostachys aureosulcata f. spectabilis and validated the accuracy of this experiment by quantitative real-time polymerase chain reaction (qRT-PCR).

Ecological roles of secondary metabolites of Saposhnikovia divaricata in adaptation to drought stress

Saposhnikovia divaricata is a traditional Chinese herb that mainly grows in arid grasslands and strongly adapts to various stresses. Drought is not only a major abiotic stress factor but also a typical feature conducive to producing high-quality medicinal material. The present study investigated by treating S. divaricata plants with polyethylene glycol (PEG-6000). Ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) identified 146 compounds from the roots of S. divaricata, among which seven primary metabolites and 28 secondary metabolites showed significant changes after drought treatment. UV-Vis spectrophotometer detected the activity of antioxidant enzymes and the content of superoxide anion (O2 -.) and malondialdehyde (MDA). The differential primary metabolites revealed that drought promotes glycolysis, reducing primary metabolism and enhancing secondary metabolism. Meanwhile, the differential secondary metabolites showed an increase in the content of compounds upstream of the secondary metabolic pathway, and other glycosides and increased that of the corresponding aglycones. The activities of antioxidant enzymes and the content of O2 -. and MDA shown different changes duing the drought treatment. These observations indicate that drought promotes the biosynthesis and transformation of the secondary metabolites and activity of antioxidant enzymes, improving plant adaptability. The present study also analyzed a few primary and secondary metabolites of S. divaricata under different degrees and durations of drought and speculated on the metabolic pathways in an arid environment. The findings indicate the biological nature, diversity, and complexity of secondary metabolites and the mechanisms of plant adaptation to ecological stress.

Genome-wide association mapping for wheat morphometric seed traits in Iranian landraces and cultivars under rain-fed and well-watered conditions

Seed traits in bread wheat are valuable to breeders and farmers, thus it is important exploring putative QTLs responsible for key traits to be used in breeding programs. GWAS was carried out using 298 bread wheat landraces and cultivars from Iran to uncover the genetic basis of seed characteristics in both rain-fed and well-watered environments. The analyses of linkage disequilibrium (LD) between marker pairs showed that the largest number of significant LDs in landraces (427,017) and cultivars (370,359) was recorded in genome B, and the strongest LD was identified on chromosome 4A (0.318). LD decay was higher in the B and A genomes, compared to the D genome. Mapping by using mrMLM (LOD > 3) and MLM (0.05/m, Bonferroni) led to 246 and 67 marker-trait associations (MTAs) under rain-fed, as well as 257 and 74 MTAs under well-watered conditions, respectively. The study found that 3VmrMLM correctly detected all types of loci and estimated their effects in an unbiased manner, with high power and accuracy and a low false positive rate, which led to the identification of 140 MTAs (LOD > 3) in all environments. Gene ontology revealed that 10 and 10 MTAs were found in protein-coding regions for rain-fed and well-watered conditions, respectively. The findings suggest that landraces studied in Iranian bread wheat germplasm possess valuable alleles, which are responsive to water-limited conditions. MTAs uncovered in this study can be exploited in the genome-mediated development of novel wheat cultivars.

Effects of Salicylic Acid Concentration and Post-Treatment Time on the Direct and Systemic Chemical Defense Responses in Maize (Zea mays L.) Following Exogenous Foliar Application

Salicylic acid (SA) plays a critical role in allergic reactions of plants to pathogens and acquired systemic resistance. Thus far, although some research has been conducted on the direct effects of different concentrations of SA on the chemical defense response of treated plant parts (leaves) after at multiple post-treatments times, few research has reported on the systematic effects of non-treated parts (roots). Therefore, we examined direct and systemic effects of SA concentration and time following foliar application on chemical defense responses in maize variety 5422 with two fully expanded leaves. In the experiments, maize leaves were treated with different SA concentrations of 0.1, 0.5, 1.0, 2.5, 5.0 mM, and then, the presence of defense chemicals and enzymes in treated leaves and non-treated roots was measured at different time points of 3, 12, 24, 48, 72 h following SA foliar application. The results showed that direct and systemic effects of SA treatment to the leaf on chemical defense responses were related to SA concentration and time of measurement after spraying SA. In treated leaves, total phenolics content increased directly by 28.65% at the time point of 12 h following foliar application of 0.5 mM SA. DIMBOA (2,4-dihydroxy-7-methoxy-2H, 1, 4-benzoxazin-3 (4H)-one) content was directly enhanced by 80.56~551.05% after 3~72 h following 0.5~5.0 mM SA treatments. Polyphenol oxidase and superoxide dismutase activities were directly enhanced after 12~72 h following 0.5~5.0 mM SA treatments, whereas peroxidase and catalase activities were increased after 3~24 h following application of 1.0~5.0 mM SA. In non-treated roots, DIMBOA content and polyphenol oxidase activity were enhanced systematically after 3~48 h following 1.0~5.0 mM SA foliar treatments. Superoxide dismutase activities were enhanced after 3~24 h following 0.5~2.5 mM SA applications, but total phenolics content, peroxidase and catalase activity decreased in some particular concentrations or at the different times of measurement in the SA treatment. It can be concluded that SA foliar application at 1.0 and 2.5 mM produces strong chemical defense responses in maize, with the optimal induction time being 24 h following the foliar application.

The bacterial consortia promote plant growth and secondary metabolite accumulation in Astragalus mongholicus under drought stress

Astragalus mongholicus is a widely used Traditional Chinese Medicine. However, cultivated A. mongholicus is often threatened by water shortage at all growth stage, and the content of medicinal compounds of cultivated A. mongholicus is much lower than that of wild plants. To alleviate drought stress on A. mongholicus and improve the accumulation of medicinal components in roots of A. mongholicus, we combined different bacteria with plant growth promotion or abiotic stress resistance characteristics and evaluated the role of bacterial consortium in helping plants tolerate drought stress and improving medicinal component content in roots simultaneously. Through the determination of 429 bacterial strains, it was found that 97 isolates had phosphate solubilizing ability, 63 isolates could release potassium from potash feldspar, 123 isolates could produce IAA, 58 isolates could synthesize ACC deaminase, and 21 isolates could secret siderophore. Eight bacterial consortia were constructed with 25 bacterial isolates with more than three functions or strong growth promoting ability, and six out of eight bacterial consortia significantly improved the root dry weight. However, only consortium 6 could increase the root biomass, astragaloside IV and calycosin-7-glucoside content in roots simultaneously. Under drought challenge, the consortium 6 could still perform these functions. Compared with non-inoculated plants, the root dry weight of consortium inoculated-plants increased by 120.0% and 78.8% under mild and moderate drought stress, the total content of astragaloside IV increased by 183.83% and 164.97% under moderate and severe drought stress, calycosin-7-glucoside content increased by 86.60%, 148.56% and 111.45% under mild, moderate and severe drought stress, respectively. Meanwhile, consortium inoculation resulted in a decrease in MDA level, while soluble protein and proline content and SOD, POD and CAT activities increased. These findings provide novel insights about multiple bacterial combinations to improve drought stress responses and contribute to accumulate more medicinal compounds.

Calcium nanoparticles (Ca-NPs) improve drought stress tolerance in Brassica napus by modulating the photosystem II, nutrient acquisition and antioxidant performance

Foliar-application of nano-particles enhanced the foliar nutrient status and crop growth and yield. It is hypothesized that being second messenger molecule, supplementation of Ca²⁺ via calcium nanoparticles (Ca-NPs) can trigger various signaling pathways of physiological processes which can lead to alleviate the adverse effects of drought stress on the growth of canola (Brassica napus L.). Nano-enabled foliar-application could be an ideal strategy for advancing agricultural productivity. The present study explored the role of calcium nanoparticles (Ca-NPs) in alleviating drought stress in hydroponic Brassica napus (B. napus) plants. The foliar applied Ca-NPs were spherically shaped with an average size of 86 nm. Foliar application of 100 mg L^-1 Ca-NPs enhanced biomass of canola plants and considered as optimal dose. Ca-NPs at 100 mg L^-1 has a greater favorable impact on mesophyll ultrastructure, PSI and PSII efficacy, gas exchange parameters, chlorophyll content, and mineral absorption. The Ca-NPs treatment increased NPQ and Y(NPQ) under drought condition, indicating a higher PSII protective response to stressed conditions with better heat dissipation as a photoprotective component of NPQ. Ca-NPs application also reduced oxidative stress damage as measured by a reduction in reactive oxygen species (ROS) generation in terms of hydrogen peroxide and malondialdehyde (H₂O₂ and MDA). Furthermore, Ca-NPs induced drought tolerance response corresponded to an increased in key antioxidative defense enzymes (SOD, POD, CAT, APX), as well as non-enzymatic components (protease, lipoxygenase, proline, total soluble protein contents, endogenous hormonal biosynthesis), and secondary metabolite expression in B. napus plants. Taken together, the results of this study offer new insights into the physiological and molecular mechanisms by which B. napus responds to Ca-NPs exposure.

A chromosome-scale genome assembly of turmeric provides insights into curcumin biosynthesis and tuber formation mechanism

Curcuma longa, known as the 'golden spice' and 'life spice', is one of the most commonly utilized spices in the world and also has medicinal, cosmetic, dye and flavoring values. Herein, we present the chromosomal-level genome for turmeric to explore the differences between tubers and rhizomes in the regulation of curcumin biosynthesis and the mechanism of tuber formation. We assembled the turmeric genome into 21 pseudochromosomes using Pacbio long reads complemented with Hi-C technologies, which has a total length of 1.11 Gb with scaffold N50 of 50.12 Mb and contains 49,612 protein-coding genes. Genomic evolutionary analysis indicated that turmeric and ginger have shared a recent WGD event. Contraction analysis of gene families showed possible roles for transcription factors, phytohormone signaling, and plant-pathogen interactions associated genes in adaptation to harsh environments. Transcriptomic data from tubers at different developmental stages indicated that candidate genes related to phytohormone signaling and carbohydrate metabolic responses may be associated with the induction of tuber formation. The difference in curcumin content between rhizomes and tubers reflected the remodeling of secondary metabolites under environmental stress, which was associated with plant defense in response to abiotic stresses. Overall, the availability of the C. longa genome provides insight into tuber formation and curcumin biosynthesis in turmeric as well as facilitating the understanding of other Curcuma species.

The antioxidant system response to drought-stressed Diospyros lotus treated with exogenous melatonin

Drought is one of the major abiotic stresses adversely impacting the growth of persimmon, which is a widely cultivated traditional fruit tree in North China. Melatonin is a bio-stimulator involved in mediating plant responses to drought. The role of exogenous melatonin application in the drought tolerance of Diospyros lotus was examined under drought stress with different doses of melatonin (0, 10, 50, and 100 µM). Exogenous melatonin application significantly mitigated the adverse effects of drought stress on chlorophyll fluorescence, lipid peroxidation, reactive oxygen species (ROS) accumulation and nitric oxide (NO) content. The 100-µM melatonin application produced the most beneficial impacts against drought stress. The melatonin-enhanced tolerance could be attributed to improved antioxidant enzymes, reduced drought-induced ROS accumulation, and lipid peroxidation. Melatonin application activated major antioxidant enzymes such as superoxide dismutase, catalase, peroxidase, glutathione reductase, and ascorbate peroxidase. Interestingly, NO concentration was significantly higher in 10 and 50 µM melatonin treatments and lower in 100 µM melatonin treatment compared to the control. Moreover, exogenous melatonin application affected the mRNA transcript levels of several genes involved in ROS metabolism, including DlRBOHA, DlSOD, DlCAT, and DlPOD. Hence, the responses of Diospyros lotus to drought varied with different doses of melatonin. Our results provide a concrete insight into the effects of melatonin with varying doses in alleviating drought as well as a platform for its potential application in the related fields.

Genome-Wide Identification, Characterization, and Expression Analysis of Glutamate Receptor-like Gene (GLR) Family in Sugarcane

The plant glutamate receptor-like gene (GLR) plays a vital role in development, signaling pathways, and in its response to environmental stress. However, the GLR gene family has not been comprehensively and systematically studied in sugarcane. In this work, 43 GLR genes, including 34 in Saccharum spontaneum and 9 in the Saccharum hybrid cultivar R570, were identified and characterized, which could be divided into three clades (clade I, II, and III). They had different evolutionary mechanisms, the former was mainly on the WGD/segmental duplication, while the latter mainly on the proximal duplication. Those sugarcane GLR proteins in the same clade had a similar gene structure and motif distribution. For example, 79% of the sugarcane GLR proteins contained all the motifs, which proved the evolutionary stability of the sugarcane GLR gene family. The diverse cis-acting regulatory elements indicated that the sugarcane GLRs may play a role in the growth and development, or under the phytohormonal, biotic, and abiotic stresses. In addition, GO and KEGG analyses predicted their transmembrane transport function. Based on the transcriptome data, the expression of the clade III genes was significantly higher than that of the clade I and clade II. Furthermore, qRT-PCR analysis demonstrated that the expression of the SsGLRs was induced by salicylic acid (SA) treatment, methyl jasmonic acid (MeJA) treatment, and abscisic acid (ABA) treatment, suggesting their involvement in the hormone synthesis and signaling pathway. Taken together, the present study should provide useful information on comparative genomics to improve our understanding of the GLR genes and facilitate further research on their functions.

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

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

Molecular Aspects of MicroRNAs and Phytohormonal Signaling in Response to Drought Stress: A Review

Phytohormones play an essential role in plant growth and development in response to environmental stresses. However, plant hormones require a complex signaling network combined with other signaling pathways to perform their proper functions. Thus, multiple phytohormonal signaling pathways are a prerequisite for understanding plant defense mechanism against stressful conditions. MicroRNAs (miRNAs) are master regulators of eukaryotic gene expression and are also influenced by a wide range of plant development events by suppressing their target genes. In recent decades, the mechanisms of phytohormone biosynthesis, signaling, pathways of miRNA biosynthesis and regulation were profoundly characterized. Recent findings have shown that miRNAs and plant hormones are integrated with the regulation of environmental stress. miRNAs target several components of phytohormone pathways, and plant hormones also regulate the expression of miRNAs or their target genes inversely. In this article, recent developments related to molecular linkages between miRNAs and phytohormones were reviewed, focusing on drought stress.

Plant Nutrition for Human Health: A Pictorial Review on Plant Bioactive Compounds for Sustainable Agriculture

Is there any relationship between plant nutrition and human health? The overall response to this question is very positive, and a strong relationship between the nutrition of plants and humans has been reported in the literature. The nutritional status of edible plants consumed by humans can have a negative or positive impact on human health. This review was designed to assess the importance of plant bioactive compounds for human health under the umbrella of sustainable agriculture. With respect to the first research question, it was found that plant bioactives (e.g., alkaloids, carotenoids, flavonoids, phenolics, and terpenoids) have a crucial role in human health due to their therapeutic benefits, and their potentiality depends on several factors, including botanical, environmental, and clinical attributes. Plant bioactives could be produced using plant tissue culture tools (as a kind of agro-biotechnological method), especially in cases of underexploited or endangered plants. Bioactive production of plants depends on many factors, especially climate change (heat stress, drought, UV radiation, ozone, and elevated CO2), environmental pollution, and problematic soils (degraded, saline/alkaline, waterlogged, etc.). Under the previously mentioned stresses, in reviewing the literature, a positive or negative association was found depending on the kinds of stress or bioactives and their attributes. The observed correlation between plant bioactives and stress (or growth factors) might explain the importance of these bioactives for human health. Their accumulation in stressed plants can increase their tolerance to stress and their therapeutic roles. The results of this study are in keeping with previous observational studies, which confirmed that the human nutrition might start from edible plants and their bioactive contents, which are consumed by humans. This review is the first report that analyzes this previously observed relationship using pictorial presentation.

Reprogramming of sorghum proteome in response to sugarcane aphid infestation

Sugarcane aphid (SCA; Melanaphis sacchari Zehntner) is a key piercing-sucking pest of sorghum (Sorghum bicolor) that cause significant yield losses. While feeding on host plants, complex signaling networks are invoked from recognition of insect attack to induction of plant defenses. Consequently, these signaling networks lead to the production of insecticidal compounds or limited access of nutrients to insects. Previously, several studies were published on the transcriptomics analysis of sorghum in response to SCA infestation, but no information is available on the physiological changes of sorghum at the proteome level. We used the SCA resistant sorghum genotype SC265 for the global proteomics analysis after 1 and 7 days of SCA infestation using the TMT-plex technique. Peptides matching a total of 4211 proteins were identified and 158 proteins were differentially expressed at day 1 and 7. Overall, proteome profiling of SC265 after SCA infestation at days 1 and 7 revealed the suppression of plant defense-related proteins and upregulation of plant defense and signaling-related proteins, respectively. The plant defense responses based on proteome data were validated using electrical penetration graph (EPG) technique to observe changes in aphid feeding. Feeding behavior analyses revealed that SCA spent significantly longer time in phloem phase on SCA infested plants for day 1 and lesser time in day 7 SCA infested sorghum plants, compared to their respective control plants. Overall, our study provides insights into underlying mechanisms that contribute to sorghum resistance to SCA.

Improving Drought Stress Tolerance in Ramie (Boehmeria nivea L.) Using Molecular Techniques

Ramie is one of the most significant fiber crops and contributes to good quality fiber. Drought stress (DS) is one of the most devastating abiotic factors which is accountable for a substantial loss in crop growth and production and disturbing sustainable crop production. DS impairs growth, plant water relation, and nutrient uptake. Ramie has evolved a series of defense responses to cope with DS. There are numerous genes regulating the drought tolerance (DT) mechanism in ramie. The morphological and physiological mechanism of DT is well-studied; however, modified methods would be more effective. The use of novel genome editing tools like clustered regularly interspaced short palindromic repeats (CRISPR) is being used to edit the recessive genes in crops to modify their function. The transgenic approaches are used to develop several drought-tolerant varieties in ramie, and further identification of tolerant genes is needed for an effective breeding plan. Quantitative trait loci (QTLs) mapping, transcription factors (TFs) and speed breeding are highly studied techniques, and these would lead to the development of drought-resilient ramie cultivars. The use of hormones in enhancing crop growth and development under water scarcity circumstances is critical; however, using different concentrations and testing genotypes in changing environments would be helpful to sort the tolerant genotypes. Since plants use various ways to counter DS, investigating mechanisms of DT in plants will lead to improved DT in ramie. This critical review summarized the recent advancements on DT in ramie using novel molecular techniques. This information would help ramie breeders to conduct research studies and develop drought tolerant ramie cultivars.

Plants' Physio-Biochemical and Phyto-Hormonal Responses to Alleviate the Adverse Effects of Drought Stress: A Comprehensive Review

Water, a necessary component of cell protoplasm, plays an essential role in supporting life on Earth; nevertheless, extreme changes in climatic conditions limit water availability, causing numerous issues, such as the current water-scarce regimes in many regions of the biome. This review aims to collect data from various published studies in the literature to understand and critically analyze plants' morphological, growth, yield, and physio-biochemical responses to drought stress and their potential to modulate and nullify the damaging effects of drought stress via activating natural physiological and biochemical mechanisms. In addition, the review described current breakthroughs in understanding how plant hormones influence drought stress responses and phytohormonal interaction through signaling under water stress regimes. The information for this review was systematically gathered from different global search engines and the scientific literature databases Science Direct, including Google Scholar, Web of Science, related studies, published books, and articles. Drought stress is a significant obstacle to meeting food demand for the world's constantly growing population. Plants cope with stress regimes through changes to cellular osmotic potential, water potential, and activation of natural defense systems in the form of antioxidant enzymes and accumulation of osmolytes including proteins, proline, glycine betaine, phenolic compounds, and soluble sugars. Phytohormones modulate developmental processes and signaling networks, which aid in acclimating plants to biotic and abiotic challenges and, consequently, their survival. Significant progress has been made for jasmonates, salicylic acid, and ethylene in identifying important components and understanding their roles in plant responses to abiotic stress. Other plant hormones, such as abscisic acid, auxin, gibberellic acid, brassinosteroids, and peptide hormones, have been linked to plant defense signaling pathways in various ways.

Silicon- and Boron-Induced Physio-Biochemical Alteration and Organic Acid Regulation Mitigates Aluminum Phytotoxicity in Date Palm Seedlings

The current study aimed to understand the synergistic impacts of silicon (Si; 1.0 mM) and boron (B; 10 µM) application on modulating physio-molecular responses of date palm to mitigate aluminum (Al³⁺; 2.0 mM) toxicity. Results revealed that compared to sole Si and B treatments, a combined application significantly improved plant growth, biomass, and photosynthetic pigments during Al toxicity. Interestingly, Si and B resulted in significantly higher exudation of organic acid (malic acids, citric acids, and acetic acid) in the plant’s rhizosphere. This is also correlated with the reduced accumulation and translocation of Al in roots (60%) and shoots (56%) in Si and B treatments during Al toxicity compared to in sole Al³⁺ treatment. The activation of organic acids by combined Si + B application has significantly regulated the ALMT1, ALMT2 and plasma membrane ATPase; PMMA1 and PMMA3 in roots and shoots. Further, the Si-related transporter Lsi2 gene was upregulated by Si + B application under Al toxicity. This was also validated by the higher uptake and translocation of Si in plants. Al-induced oxidative stress was significantly counteracted by exhibiting lower malondialdehyde and superoxide production in Si + B treatments. Experiencing less oxidative stress was evident from upregulation of CAT and Cyt-Cu/Zn SOD expression; hence, enzymatic activities such as polyphenol oxidase, catalase, peroxidase, and ascorbate peroxidase were significantly activated. In the case of endogenous phytohormones, Si + B application demonstrated the downregulation of the abscisic acid (ABA; NCED1 and NCED6) and salicylic acid (SA; PYL4, PYR1) biosynthesis-related genes. Consequently, we also noticed a lower accumulation of ABA and rising SA levels under Al-stress. The current findings illustrate that the synergistic Si + B application could be an effective strategy for date palm growth and productivity against Al stress and could be further extended in field trails in Al-contaminated fields.

Research Progress in the Field of Microbial Mitigation of Drought Stress in Plants

Plants defend themselves against ecological stresses including drought. Therefore, they adopt various strategies to cope with stress, such as seepage and drought tolerance mechanisms, which allow plant development under drought conditions. There is evidence that microbes play a role in plant drought tolerance. In this study, we presented a review of the literature describing the initiation of drought tolerance mediated by plant inoculation with fungi, bacteria, viruses, and several bacterial elements, as well as the plant transduction pathways identified via archetypal functional or morphological annotations and contemporary "omics" technologies. Overall, microbial associations play a potential role in mediating plant protection responses to drought, which is an important factor for agricultural manufacturing systems that are affected by fluctuating climate.

Heavy metal induced regulation of plant biology: Recent insights

The presence of different forms of heavy metals in the earth crust is very primitive and probably associated with the origin of plant life. However, since the beginning of human civilisation, heavy metal use and its contamination to all living systems on earth have significantly increased due to human anthropogenic activities. Heavy metals are nonbiodegradable, which directly or indirectly impact photosynthesis, antioxidant system, mineral nutrition status, phytohormones and amino acid-derived molecules. Due to the toxic behaviour of some heavy metals, the endogenous status of chemical messengers like phytohormones may get significantly influenced, leading to harmful impacts on plant growth, development and overall yield of the plants. It has been noticed that exogenous application of phytohormones, that is, abscisic acid, salicylic acid, auxins, brassinosteroids, cytokinins, ethylene and gibberellins can positively regulate the heavy metal toxicity in plants through the regulation of the ascorbate-glutathione cycle, nitrogen metabolism, proline metabolisms, transpiration rate, and cell division. Furthermore, it may also restrict the entry of heavy metals into the plant cells, which aids in the recovery of plant growth and productivity. Besides these, some defence molecules also assist the plant in dealing with heavy metal toxicity. Therefore, the present review aims to bridge the knowledge gap in this context and present outstanding discoveries related to plant life supportive processes during stressful conditions including phytohormones and heavy metal crosstalk along with suggestions for future research in this field.

Genome-wide association study identifies SNP markers and putative candidate genes for terpene traits important for Leptocybe invasa resistance in Eucalyptus grandis

Terpenes are an important group of plant specialized metabolites influencing, amongst other functions, defence mechanisms against pests. We used a genome-wide association study to identify single nucleotide polymorphism (SNP) markers and putative candidate genes for terpene traits. We tested 15,387 informative SNP markers derived from genotyping 416 Eucalyptus grandis individuals for association with 3 terpene traits, 1,8-cineole, γ-terpinene, and p-cymene. A multilocus mixed model analysis identified 21 SNP markers for 1,8-cineole on chromosomes 2, 4, 6, 7, 8, 9, 10, and 11, that individually explained 3.0%–8.4% and jointly 42.7% of the phenotypic variation. Association analysis of γ-terpinene found 32 significant SNP markers on chromosomes 1, 2, 4, 5, 6, 9, and 11, explaining 3.4–15.5% and jointly 54.5% of phenotypic variation. For p-cymene, 28 significant SNP markers were identified on chromosomes 1, 2, 3, 5, 6, 7, 10, and 11, explaining 3.4–16.1% of the phenotypic variation and jointly 46.9%. Our results show that variation underlying the 3 terpene traits is influenced by a few minor loci in combination with a few major effect loci, suggesting an oligogenic nature of the traits.

Characterization of Endogenous Levels of Brassinosteroids and Related Genes in Grapevines

Agronomic breeding practices for grapevines (Vitis vinifera L.) include the application of growth regulators in the field. Brassinosteroids (BRs) are a family of sterol-derived plant hormones that regulate several physiological processes and responses to biotic and abiotic stress. In grapevine berries, the production of biologically active BRs, castasterone and 6-deoxocastasterone, has been reported. In this work, key BR genes were identified, and their expression profiles were determined in grapevine. Bioinformatic homology analyses of the Arabidopsis genome found 14 genes associated with biosynthetic, perception and signaling pathways, suggesting a partial conservation of these pathways between the two species. The tissue- and development-specific expression profiles of these genes were determined by qRT-PCR in nine different grapevine tissues. Using UHPLC-MS/MS, 10 different BR compounds were pinpointed and quantified in 20 different tissues, each presenting specific accumulation patterns. Although, in general, the expression profile of the biosynthesis pathway genes of BRs did not directly correlate with the accumulation of metabolites, this could reflect the complexity of the BR biosynthesis pathway and its regulation. The development of this work thus generates a contribution to our knowledge about the presence, and diversity of BRs in grapevines.

Plant Secondary Metabolites Produced in Response to Abiotic Stresses Has Potential Application in Pharmaceutical Product Development

Plant secondary metabolites (PSMs) are vital for human health and constitute the skeletal framework of many pharmaceutical drugs. Indeed, more than 25% of the existing drugs belong to PSMs. One of the continuing challenges for drug discovery and pharmaceutical industries is gaining access to natural products, including medicinal plants. This bottleneck is heightened for endangered species prohibited for large sample collection, even if they show biological hits. While cultivating the pharmaceutically interesting plant species may be a solution, it is not always possible to grow the organism outside its natural habitat. Plants affected by abiotic stress present a potential alternative source for drug discovery. In order to overcome abiotic environmental stressors, plants may mount a defense response by producing a diversity of PSMs to avoid cells and tissue damage. Plants either synthesize new chemicals or increase the concentration (in most instances) of existing chemicals, including the prominent bioactive lead compounds morphine, camptothecin, catharanthine, epicatechin-3-gallate (EGCG), quercetin, resveratrol, and kaempferol. Most PSMs produced under various abiotic stress conditions are plant defense chemicals and are functionally anti-inflammatory and antioxidative. The major PSM groups are terpenoids, followed by alkaloids and phenolic compounds. We have searched the literature on plants affected by abiotic stress (primarily studied in the simulated growth conditions) and their PSMs (including pharmacological activities) from PubMed, Scopus, MEDLINE Ovid, Google Scholar, Databases, and journal websites. We used search keywords: "stress-affected plants," "plant secondary metabolites, "abiotic stress," "climatic influence," "pharmacological activities," "bioactive compounds," "drug discovery," and "medicinal plants" and retrieved published literature between 1973 to 2021. This review provides an overview of variation in bioactive phytochemical production in plants under various abiotic stress and their potential in the biodiscovery of therapeutic drugs. We excluded studies on the effects of biotic stress on PSMs.

Stress-Responsive cis-Regulatory Elements Underline Podophyllotoxin Biosynthesis and Better Performance of Sinopodophyllum hexandrum Under Water Deficit Conditions

Sinopodophyllum hexandrum is an endangered medicinal herb known for its bioactive lignan podophyllotoxin (PTOX), which is used for the preparation of anticancer drugs. In its natural habitat, S. hexandrum is exposed to a multitude of adversities, such as fluctuating temperatures, water deficit, and high UV radiations. Transcriptional regulation of genes, which is regulated by the condition-specific binding of transcriptional factors to precise motifs in the promoter region, underlines responses to an environmental cue. Therefore, analysis of promoter sequences could ascertain the spatio-temporal expression of genes and overall stress responses. Unavailability of genomic information does not permit such analysis in S. hexandrum, especially on regulation of PTOX pathway. Accordingly, this study describes isolation and in silico analysis of 5'-upstream regions of ShPLR (PINORESINOL-LARICIRESINOL REDUCTASE) and ShSLD (SECOISOLARICIRESINOL DEHYDROGENASE), the two key genes of the PTOX biosynthetic pathway. Data showed a range of motifs related to basal transcription, stress-responsive elements, such as those for drought, low temperature, and light, suggesting that the expression of these genes and resulting PTOX accumulation would be affected by, at least, these environmental cues. While the impact of temperature and light on PTOX accumulation is well studied, the effect of water deficit on the physiology of S. hexandrum and PTOX accumulation remains obscure. Given the presence of drought-responsive elements in the promoters of the key genes, the impact of water deficit on growth and development and PTOX accumulation was studied. The results showed decline in relative water content and net photosynthetic rate, and increase in relative electrolyte leakage with stress progression. Plants under stress exhibited a reduction in transpiration rate and chlorophyll content, with a gradual increase in osmoprotectant content. Besides, stressed plants showed an increase in the expression of genes involved in the phenylpropanoid pathway and PTOX biosynthesis, and an increase in PTOX accumulation. Upon re-watering, non-irrigated plants showed a significant improvement in biochemical and physiological parameters. Summarily, our results demonstrated the importance of osmoprotectants during water deficit and the revival capacity of the species from water deficit, wherein PTOX synthesis was also modulated. Moreover, isolated promoter sequences could be employed in genetic transformation to mediate the expression of stress-induced genes in other plant systems.

New approaches to improve crop tolerance to biotic and abiotic stresses

During the last years, a great effort has been dedicated at the development and employment of diverse approaches for achieving more stress-tolerant and climate-flexible crops and sustainable yield increases to meet the food and energy demands of the future. The ongoing climate change is in fact leading to more frequent extreme events with a negative impact on food production, such as increased temperatures, drought, and soil salinization as well as invasive arthropod pests and diseases. In this review, diverse "green strategies" (e.g., chemical priming, root-associated microorganisms), and advanced technologies (e.g., genome editing, high-throughput phenotyping) are described on the basis of the most recent research evidence. Particularly, attention has been focused on the potential use in a context of sustainable and climate-smart agriculture (the so called "next agriculture generation") to improve plant tolerance and resilience to abiotic and biotic stresses. In addition, the gap between the results obtained in controlled experiments and those from application of these technologies in real field conditions (lab to field step) is also discussed.

Transcriptomic Analysis Reveals Regulatory Networks for Osmotic Water Stress and Rewatering Response in the Leaves of Ginkgo biloba

To elucidate the transcriptomic regulation mechanisms that underlie the response of Ginkgo biloba to dehydration and rehydration, we used ginkgo saplings exposed to osmotically driven water stress and subsequent rewatering. When compared with a control group, 137, 1453, 1148, and 679 genes were differentially expressed in ginkgo leaves responding to 2, 6, 12, and 24 h of water deficit, and 796 and 1530 genes were differentially expressed responding to 24 and 48 h of rewatering. Upregulated genes participated in the biosynthesis of abscisic acid, eliminating reactive oxygen species (ROS), and biosynthesis of flavonoids and bilobalide, and downregulated genes were involved in water transport and cell wall enlargement in water stress-treated ginkgo leaves. Under rehydration conditions, the genes associated with water transport and cell wall enlargement were upregulated, and the genes that participated in eliminating ROS and the biosynthesis of flavonoids and bilobalide were downregulated in the leaves of G. biloba. Furthermore, the weighted gene coexpression networks were established and correlated with distinct water stress and rewatering time-point samples. Hub genes that act as key players in the networks were identified. Overall, these results indicate that the gene coexpression networks play essential roles in the transcriptional reconfiguration of ginkgo leaves in response to water stress and rewatering.

Bulk analysis by resequencing and RNA-seq identifies candidate genes for maintaining leaf water content under water deficit in maize

Drought is one of the main abiotic stresses adversely affecting maize growth and grain yield. Identifying drought tolerance-related genes and breeding varieties with enhanced tolerance are effective strategies for minimizing the effects of drought stress. In this study, the leaf relative water content (LRWC) was used for evaluating drought tolerance. QTL-seq analysis of 419 F₂ individuals from a cross between ZhengT22 (the drought-tolerant line with high LRWC) and ZhengA88 (the drought-sensitive line with low LRWC) revealed four LRWC-related QTLs (qLRWC2, qLRWC10a, qLRWC10b, and qLRWC10c) in maize seedlings under water deficit. Of these QTLs, qLRWC2 was located in a 2.03-Mb interval on chromosome 2, whereas qLRWC10a, qLRWC10b, and qLRWC10c were located in 2.85-, 3.99-, and 2.05-Mb intervals, respectively, on chromosome 10, and the 93 genes contained the variation loci locating in the four QTLs regions. To identify the candidate genes within the QTLs, an RNA-seq analysis was performed for the parents exposed to water deficit. Seven genes with effective variation loci showed significant difference in expression either in ZhengA88 or ZhengT22 in response to water deficit. Moreover, among the genes, ZmPrx64, ZmCIPK, HSP90, and ABCG34 have all been shown to be related to water stress in the previous studies. Thus, they are primary considered as the potential candidate genes controlling LRWC under water deficit at the seeding stage of maize in this study. These findings will help clarify the molecular basis of drought tolerance in maize seedlings and may be relevant for future functional analysis and for breeding drought-tolerant maize varieties.

Arbuscular mycorrhizal fungi, a key symbiosis in the development of quality traits in crop production, alone or combined with plant growth-promoting bacteria

Modern agriculture is currently undergoing rapid changes in the face of the continuing growth of world population and many ensuing environmental challenges. Crop quality is becoming as important as crop yield and can be characterised by several parameters. For fruits and vegetables, quality descriptors can concern production cycle (e.g. conventional or organic farming), organoleptic qualities (e.g. sweet taste, sugar content, acidity) and nutritional qualities (e.g. mineral content, vitamins). For other crops, however, the presence of secondary metabolites such as anthocyanins or certain terpenes in the targeted tissues is of interest as well, especially for their human health properties. All plants are constantly interacting with microorganisms. These microorganisms include arbuscular mycorrhizal fungi as well as certain soil bacteria that provide ecosystem services related to plant growth, nutrition and quality parameters. This review is an update of current research on the single and combined (co-inoculation) use of arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria in crop production, with a focus on their positive impacts on crop quality traits (e.g. nutritional value, organoleptic properties). We also highlight the need to dissect mechanisms regulating plant-symbionts and symbiont-symbiont interactions, to develop farming practices and to study a broad range of interactions to optimize the symbiotic potential of root-associated microorganisms.

Targeted Phytohormone Profiling Identifies Potential Regulators of Spikelet Sterility in Rice under Combined Drought and Heat Stress

Rice cultivated under rainfed or semi-irrigated ecosystems is frequently exposed to a combination of drought and heat stress. As a sensitive crop at the reproductive stage, exposure to combined drought and heat stress will have a deleterious effect on yield. In this study, two rice cultivars with contrasting spikelet sterility, AVT2-5315 (low sterility) and AC35027 (high sterility), under combined stress were selected for physiological characterization and phytohormonal profiling at anthesis. Under combined stress, both cultivars did not differ in the physiological parameters such as relative water content, photosynthetic rate, light-adapted chlorophyll fluorescence and biomass, suggesting a similar source activity under stress. However, AVT2-5315 showed better yield due to better pollen and spikelet fertility than AC35027, suggesting its intrinsic tolerance ability under combined stress. Targeted profiling of 15 phytohormones from drought, heat and combined stress-treated flag leaf and spikelet tissues using LC–MS/MS showed increased accumulation of auxins (indole 3-acetic acid and indole 3-butyric acid) in flag leaves and jasmonic acid in spikelets of AVT2-5315, while there was increased accumulation of ethylene in flag leaves and methyl-jasmonate in spikelets of AC35027. Increased accumulation of these hormones correlated with key biosynthetic pathway genes. In the flag leaves, increased accumulation of auxins was correlated with increased transcript levels of YUCCA-like gene 1 (OsYUCCA1) and fish bone (OsFIB), in AVT2-5315 under combined stress. In AC35027, increased ethylene content was correlated with expression of 1-aminocyclopropane-1-carboxylate synthase 1 (OsASC1) and aminocyclopropane-1-carboxylic acid oxidase 2 (OsACO2). Similarly, in spikelets, increased accumulation of jasmonic acid in AVT2-5315 was correlated with expression of allene oxide cyclase (OsAOC) and 12-oxophytodienoic acid reductase 1 (OsOPR1). The mechanism of regulating spikelet sterility by these hormones needs further investigation towards improving rice tolerance to combined stress.

Evaluation of the Morpho-Physiological, Biochemical and Molecular Responses of Contrasting Medicago truncatula Lines under Water Deficit Stress

Medicago truncatula is a forage crop of choice for farmers, and it is a model species for molecular research. The growth and development and subsequent yields are limited by water availability mainly in arid and semi-arid regions. Our study aims to evaluate the morpho-physiological, biochemical and molecular responses to water deficit stress in four lines (TN6.18, JA17, TN1.11 and A10) of M. truncatula. The results showed that the treatment factor explained the majority of the variation for the measured traits. It appeared that the line A10 was the most sensitive and therefore adversely affected by water deficit stress, which reduced its growth and yield parameters, whereas the tolerant line TN6.18 exhibited the highest root biomass production, a significantly higher increase in its total protein and soluble sugar contents, and lower levels of lipid peroxidation with greater cell membrane integrity. The expression analysis of the DREB1B gene using RT-qPCR revealed a tissue-differential expression in the four lines under osmotic stress, with a higher induction rate in roots of TN6.18 and JA17 than in A10 roots, suggesting a key role for DREB1B in water deficit tolerance in M. truncatula.

Dissection of the genetic basis of genotype-by-environment interactions for grain yield and main agronomic traits in Iranian bread wheat landraces and cultivars

Understanding the genetic basis of performance stability is essential to maintain productivity, especially under severe conditions. In the present study, 268 Iranian bread wheat landraces and cultivars were evaluated in four well-watered and two rain-fed conditions for different traits. According to breeding programs, cultivars were in a group with a high mean and stability in terms of GY, GN, and SW traits, while in terms of PH, they had a low mean and high stability. The stability of cultivars and landraces was related to dynamic and static stability, respectively. The highest number of marker pairs and lowest LD decay distance in both cultivars and landraces was observed on the B genome. Population structure differentiated indigenous cultivars and landraces, and the GWAS results for each were almost different despite the commonalities. Chromosomes 1B, 3B, 7B, 2A, and 4A had markers with pleiotropic effects on the stability of different traits. Due to two rain-fed environments, the Gene Ontology (GO) confirmed the accuracy of the results. The identified markers in this study can be helpful in breeding high-performance and stable genotypes and future breeding programs such as fine mapping and cloning.

Metal transporters in organelles and their roles in heavy metal transportation and sequestration mechanisms in plants

Heavy metal toxicity is one of the major concerns for agriculture and health. Accumulation of toxic heavy metals at high concentrations in edible parts of crop plants is the primary cause of disease in humans and cattle. A dramatic increase in industrialization, urbanization, and other high anthropogenic activities has led to the accumulation of heavy metals in agricultural soil, which has consequently disrupted soil conditions and affected crop yield. By now, plants have developed several mechanisms to cope with heavy metal stress. However, not all plants are equally effective in dealing with the toxicity of high heavy metal concentrations. Plants have modified their anatomy, morphophysiology, and molecular networks to survive under changing environmental conditions. Heavy metal sequestration is one of the essential processes evolved by some plants to deal with heavy metals' toxic concentration. Some plants even have the ability to accumulate metals in high quantities in the shoots/organelles without toxic effects. For intercellular and interorganeller metal transport, plants harbor spatially distributed various transporters which mainly help in uptake, translocation, and redistribution of metals. This review discusses different heavy metal transporters in different organelles and their roles in metal sequestration and redistribution to help plants cope with heavy metal stress. A good understanding of the processes at stake helps in developing more tolerant crops without affecting their productivity.

Shedding Light into the Connection between Chemical Components and Biological Effects of Extracts from Epilobium hirsutum: Is It a Potent Source of Bioactive Agents from Natural Treasure?

Epilobium hirsutum is extensively used as a traditional remedy in folk medicine, especially against prostate inflammation. Therefore, we evaluated the chemical profiles and biopharmaceutical potentials of different extracts of E. hirsutum aerial parts and roots. Metabolomic, antioxidant, and enzyme inhibitory profiles were investigated. Human prostate cancer PC3 cells were exposed to the extracts to evaluate antiproliferative effects. Gene expression and bioinformatics analyses were performed to investigate anti-inflammatory mechanisms. Oenothein B and myricetin were prominent compounds in the extracts. In scavenging/reducing assays, the methanol, infusion, and methanol/water extracts exhibited similar activities. We also observed the reduction of PC3 viability occurring following exposure to methanol and methanol/water extracts. According to bioinformatics analysis, myricetin was predicted to interact with COX-2 and TNFα. The interaction between TNFα and oxo-dihydroxy-octadecenoic acid was predicted as well. Intriguingly, the gene expression of COX-2 and TNFα was reduced in PC3 cells after exposure to methanol and methanol/water extracts. These effects were paralleled by the decreased gene expression of IL-8 and NFkB and the inhibition of PGE2 release. Therefore, the present findings suggest the potential use of E. hirsutum for the management of the burden of inflammation and oxidative stress occurring in lower urinary tract diseases, including prostatitis.

Metabolomics and Molecular Approaches Reveal Drought Stress Tolerance in Plants

Metabolic regulation is the key mechanism implicated in plants maintaining cell osmotic potential under drought stress. Understanding drought stress tolerance in plants will have a significant impact on food security in the face of increasingly harsh climatic conditions. Plant primary and secondary metabolites and metabolic genes are key factors in drought tolerance through their involvement in diverse metabolic pathways. Physio-biochemical and molecular strategies involved in plant tolerance mechanisms could be exploited to increase plant survival under drought stress. This review summarizes the most updated findings on primary and secondary metabolites involved in drought stress. We also examine the application of useful metabolic genes and their molecular responses to drought tolerance in plants and discuss possible strategies to help plants to counteract unfavorable drought periods.

NRT1.1 Dual-Affinity Nitrate Transport/Signalling and its Roles in Plant Abiotic Stress Resistance

NRT1.1 is the first nitrate transport protein cloned in plants and has both high- and low-affinity functions. It imports and senses nitrate, which is modulated by the phosphorylation on Thr101 (T101). Structural studies have revealed that the phosphorylation of T101 either induces dimer decoupling or increases structural flexibility within the membrane, thereby switching the NRT1.1 protein from a low- to high-affinity state. Further studies on the adaptive regulation of NRT1.1 in fluctuating nitrate conditions have shown that, at low nitrate concentrations, nitrate binding only at the high-affinity monomer initiates NRT1.1 dimer decoupling and priming of the T101 site for phosphorylation activated by CIPK23, which functions as a high-affinity nitrate transceptor. However, nitrate binding in both monomers retains the unmodified NRT1.1, maintaining the low-affinity mode. This NRT1.1-mediated nitrate signalling and transport may provide a key to improving the efficiency of plant nitrogen use. However, recent studies have revealed that NRT1.1 is extensively involved in plant tolerance of several adverse environmental conditions. In this context, we summarise the recent progress in the molecular mechanisms of NRT1.1 dual-affinity nitrate transport/signalling and focus on its expected and unexpected roles in plant abiotic stress resistance and their regulation processes.

Engineering Climate-Change-Resilient Crops: New Tools and Approaches

Environmental adversities, particularly drought and nutrient limitation, are among the major causes of crop losses worldwide. Due to the rapid increase of the world's population, there is an urgent need to combine knowledge of plant science with innovative applications in agriculture to protect plant growth and thus enhance crop yield. In recent decades, engineering strategies have been successfully developed with the aim to improve growth and stress tolerance in plants. Most strategies applied so far have relied on transgenic approaches and/or chemical treatments. However, to cope with rapid climate change and the need to secure sustainable agriculture and biomass production, innovative approaches need to be developed to effectively meet these challenges and demands. In this review, we summarize recent and advanced strategies that involve the use of plant-related cyanobacterial proteins, macro- and micronutrient management, nutrient-coated nanoparticles, and phytopathogenic organisms, all of which offer promise as protective resources to shield plants from climate challenges and to boost stress tolerance in crops.

Metabolomic Approaches to Studying the Response to Drought Stress in Corn (Zea mays) Cobs

Metabolomics is a technique that allows for the evaluation of the entire extractable chemical profile of a plant, for example, using high-resolution mass spectrometry (HRMS) and can be used to evaluate plant stress responses, such as those due to drought. Metabolomic analysis is dependent upon the efficiency of the extraction protocol. Currently, there are two common extraction procedures widely used in metabolomic experiments, those that extract from plant tissue processed in liquid nitrogen or extraction from lyophilised plant tissues. Here, we evaluated the two using non-targeted metabolomics to show that lyophilisation can stabilise the maize (Zea mays) extractable metabolome, increasing throughput and efficiency of extraction as compared to the more traditional processing in liquid nitrogen. Then, we applied the lyophilisation approach to explore the effect of drought upon the maize metabolome in a non-targeted HRMS metabolomics approach. Metabolomics revealed differences in the mature maize metabolome having undergone three drought conditions imposed at two critical development stages (three-leaf stage and grain-fill stage); moreover, this difference was observed across two tissue types (kernel and inner cob/pith). It was shown that under ideal conditions, the biochemical make-up of the tissue types is different. However, under stress conditions, the stress response dominates the metabolic profile. Drought-related metabolites known from other plant systems have been identified and metabolomics has revealed potential novel drought-stress indicators in our maize system.

Coping with the Challenges of Abiotic Stress in Plants: New Dimensions in the Field Application of Nanoparticles

Abiotic stress in plants is a crucial issue worldwide, especially heavy-metal contaminants, salinity, and drought. These stresses may raise a lot of issues such as the generation of reactive oxygen species, membrane damage, loss of photosynthetic efficiency, etc. that could alter crop growth and developments by affecting biochemical, physiological, and molecular processes, causing a significant loss in productivity. To overcome the impact of these abiotic stressors, many strategies could be considered to support plant growth including the use of nanoparticles (NPs). However, the majority of studies have focused on understanding the toxicity of NPs on aquatic flora and fauna, and relatively less attention has been paid to the topic of the beneficial role of NPs in plants stress response, growth, and development. More scientific attention is required to understand the behavior of NPs on crops under these stress conditions. Therefore, the present work aims to comprehensively review the beneficial roles of NPs in plants under different abiotic stresses, especially heavy metals, salinity, and drought. This review provides deep insights about mechanisms of abiotic stress alleviation in plants under NP application.

Concentrations-dependent effect of exogenous abscisic acid on photosynthesis, growth and phenolic content of Dracocephalum moldavica L. under drought stress

The drought conditions and the application of ABA reduce the photosynthetic activity, and the processes related to the transpiration of Dracocephalum moldavica L. At the same time, the plant increases the production of phenolic compounds and essential oil as a response to stress conditions. In the semi-arid regions, drought stress is the most important environmental limitations for crop production. Abscisic acid (ABA) plays a crucial role in the reactions of plants towards environmental stress such as drought. Field experiments for two consecutive years in 2016 and 2017 were conducted to evaluate the effect of three watering regimes (well-watered, moderate and severe drought) and five exogenous ABA concentrations (0, 5, 10, 20 and 40 μM) on growth, photosynthesis, total phenolic and essential oil content of Dracocephalum moldavica L. Without ABA application, the highest photosynthetic rate (6.1 μmol CO₂ m^-2 s^-1) was obtained under well-watered condition and, moderate and severe drought stress decreased photosynthesis rate by 26.39% and 34.43%, respectively. Some growth parameters such as stem height, leaf area, leaf dry weight and biological yield were also reduced by drought stress. ABA application showed a decreasing trend in photosynthesis rate and mentioned plant growth parameters under all moisture regimes. The highest seed yield (1243.56 kg ha^-1) was obtained under well-watered condition without ABA application. Increasing ABA concentration decreased seed yield in all moisture regimes. The highest total phenolic content (8.9 mg g^-1 FW) and essential oil yield (20.58 kg ha^-1) were obtained from 20 and 5 μM ABA concentration, respectively, under moderate drought stress.

Fullerenol changes metabolite responses differently depending on the iron status of cucumber plants

The unique properties of carbon-based nanomaterials, including fullerenol, have attracted great interest in agricultural and environmental applications. Iron (Fe) is an essential micronutrient for major metabolic processes, for which a shortage causes chlorosis and reduces the yield of many crops cultivated worldwide. In the current study, the metabolic responses of Cucumis sativus (a Strategy I plant) to fullerenol treatments were investigated depending on the Fe status of plants. Cucumber plants were grown hydroponically, either with [+FeII (ferrous) and +FeIII (ferric)] or in Fe-free (-FeII and -FeIII) nutrient solution, with (+F) or without (-F) a fullerenol supply. Iron species-dependent effects were observed in either Fe-fed or Fe-starved plants, with alteration of metabolites involved in the metabolism of carbohydrates, amino acids, organic acids, lipophilic compounds. Metabolic perturbations triggered by fullerenol in the FeIII-treated plants were in the opposite kind from those in the FeII-treated plants. Whereas in the FeIII-fed plants, fullerenol activated the metabolisation of carbohydrates and amino acids, in the FeII-fed plants, fullerenol activated the metabolisation of lipophilic compounds and repressed the metabolisation of carbohydrates and amino acids. In FeIII-deficient plants, fullerenol stimulated the metabolism of C3 carboxylates and lipophilic compounds while repressing the metabolism of amino acids, hexoses and dicarboxylates, while in FeII-deficient plants, activations of the metabolism of amino acids and dicarboxylates and repression of sterol metabolism by fullerenol were observed. The results indicated that the valence state of Fe sources is of importance for re-programming metabolome responses in cucumber to fullerenol either in Fe-sufficient or Fe-deficient conditions. These investigations are significant for understanding fullerenol interactions and risk assessment in plants with different Fe statuses.