Phytohormones and their metabolic engineering for abiotic stress tolerance in crop plants

Plant lectins: Classical molecules with emerging roles in stress tolerance

Biotic and abiotic stresses impose adverse effects on plant's development, growth, and production. For the past many years, researchers are trying to understand the stress induced responses in plants and decipher strategies to produce stress tolerant crops. It has been demonstrated that molecular networks encompassing an array of genes and functional proteins play a key role in generating responses to combat different stresses. Newly, there has been a resurgence of interest to explore the role of lectins in modulating various biological responses in plants. Lectins are naturally occurring proteins that form reversible linkages with their respective glycoconjugates. To date, several plant lectins have been recognized and functionally characterized. However, their involvement in stress tolerance is yet to be comprehensively analyzed in greater detail. The availability of biological resources, modern experimental tools, and assay systems has provided a fresh impetus for plant lectin research. Against this backdrop, the present review provides background information on plant lectins and recent knowledge on their crosstalks with other regulatory mechanisms, which play a remarkable role in plant stress amelioration. It also highlights their versatile role and suggests that adding more information to this under-explored area will usher in a new era of crop improvement.

Nitric oxide mitigates vanadium toxicity in soybean (Glycine max L.) by modulating reactive oxygen species (ROS) and antioxidant system

Vanadium (V) induced hazardous effects posturing a serious concern on crop production as well as food security. However, the nitric oxide (NO)-mediated alleviation of V-induced oxidative stress in soybean seedlings is still unknown. Therefore, this research was designed to explore the effects of exogenous NO to mitigate the V-induced phytotoxicity in soybean plants. Our upshots disclosed that NO supplementation considerably improved the plant biomass, growth, and photosynthetic attributes by regulating the carbohydrates, and plants biochemical composition, which further improved the guard cells, and stomatal aperture of soybean leaves. Additionally, NO regulated the plant hormones, and phenolic profile which restricted the V contents absorption (65.6%), and translocation (57.9%) by maintaining the nutrient acquisition. Furthermore, it detoxified the excessive V contents, and upsurged the antioxidants defense mechanism to lower the MDA, and scavenge ROS production. The molecular analysis further verified the NO-based regulation of lipid, sugar production, and degradation as well as detoxification mechanism in the soybean seedlings. Exclusively, we elaborated very first time the behind mechanism of V-induced oxidative stress alleviation by exogenous NO, hence illustrating the NO supplementation role as a stress alleviating agent for soybean grown in V contaminated areas to elevate the crop development and production.

White clover from the exclusion zone of the Chernobyl NPP: Morphological, biochemical, and genetic characteristics

A comprehensive study of the biological effects of chronic radiation exposure (8 μGy/h) in populations of white clover (Trifolium repens L.) from the Chernobyl exclusion zone was carried out. White clover is one of the most important pasture legumes, having many agricultural applications. Studies at two reference and three radioactively contaminated plots showed no stable morphological effects in white clover at this level of radiation exposure. Increased activities of catalase and peroxidases were found in some impacted plots. Auxin concentration was enhanced in the radioactively contaminated plots. Genes involved in the maintenance of water homeostasis and photosynthetic processes (TIP1 and CAB1) were upregulated at radioactively contaminated plots.

Nitrogen supply alleviates cold stress by increasing photosynthesis and nitrogen assimilation in maize seedlings

Cold stress inhibits the early growth of maize, leading to reduced productivity. Nitrogen (N) is an essential nutrient that stimulates maize growth and productivity, but the relationship between N availability and cold tolerance is poorly characterized. Therefore, we studied the acclimation of maize under combined cold stress and N treatments. Exposure to cold stress caused a decline in growth and N assimilation, but increased abscisic acid (ABA) and carbohydrate accumulation. The application of different N concentrations from the priming stage to the recovery period resulted in the following observations: (i) high N supply alleviated cold stress-dependent growth inhibition, as shown by increased biomass, chlorophyll and Rubisco content and PSII efficiency; (ii) cold stress-induced ABA accumulation was repressed under high N, presumably due to enhanced stomatal conductance; (iii) the mitigating effects of high N on cold stress could be due to the increased activities of N assimilation enzymes and improved redox homeostasis. After cold stress, the ability of maize seedlings to recover increased under high N treatment, indicating the potential role of high N in the cold stress tolerance of maize seedlings.

Deciphering the melatonin-mediated response and signalling in the regulation of heavy metal stress in plants

MAIN CONCLUSION

Melatonin has a protective effect against heavy metal stress in plants by immobilizing HM in cell walls and sequestering them in root cell vacuoles, reducing HM's translocation from roots to shoots. It enhances osmolyte production, increases antioxidant enzyme activity, and improves photosynthesis, thereby improving cellular functions. Understanding the melatonin-mediated response and signalling can sustain crop production in heavy metal-stressed soils. Melatonin is a pleiotropic signal molecule that plays a critical role in plant growth and stress tolerance, particularly against heavy metals in soil. Heavy metals (HMs) are ubiquitously found in the soil-water environment and readily taken up by plants, thereby disrupting mineral nutrient homeostasis, osmotic balance, oxidative stress, and altered primary and secondary metabolism. Plants combat HM stress through inbuilt defensive mechanisms, such as metal exclusion, restricted foliar translocation, metal sequestration and compartmentalization, chelation, and scavenging of free radicals by antioxidant enzymes. Melatonin has a protective effect against the damaging effects of HM stress in plants. It achieves this by immobilizing HM in cell walls and sequestering them in root cell vacuoles, reducing HM's translocation from roots to shoots. This mechanism improves the uptake of macronutrients and micronutrients in plants. Additionally, melatonin enhances osmolyte production, improving the plant's water relations, and increasing the activity of antioxidant enzymes to limit lipid peroxidation and reactive oxygen species (ROS) levels. Melatonin also decreases chlorophyll degradation while increasing its synthesis, and enhances RuBisCO activity for better photosynthesis. All these functions contribute to improving the cellular functions of plants exposed to HM stress. This review aims to gain better insight into the melatonin-mediated response and signalling under HM stress in plants, which may be useful in sustaining crop production in heavy metal-stressed soils.

Detrimental effects of Cd and temperature on rice and functions of microbial community in paddy soils

Heavy metal (HM) contamination and high environmental temperature (HT) are caused by anthropogenic activities that negatively impact soil microbial communities and agricultural productivity. Although HM contaminations have deleterious effects on microbes and plants; there are hardly any reports on the combined effects of HM and HT. Here, we reported that HT coupled with cadmium (Cd) accumulation in soil and irrigated water could seriously affect crop growth and productivity, alternatively influencing the microbial community and nutrient cycles of paddy soils in rice fields. We analyzed different mechanisms of plants and microflora in the rhizospheric region, such as plant rhizospheric nitrification, endophytes colonization, nutrient uptake, and physiology of temperature-sensitive (IR64) and temperature-resistant Huanghuazhan (HZ) rice cultivars against different Cd levels (2, 5 and 10 mg kg^-1) with rice plants grown under 25 °C and 40 °C temperatures. Consequently, an increment in Cd accumulation was observed with rising temperature leading to enhanced expression of OsNTRs. In contrast, a greater decline in the microbial community was detected in IR64 cultivar than HZ. Similarly, ammonium oxidation, root-IAA, shoot-ABA production, and 16S rRNA gene abundance in the rhizosphere and endosphere were significantly influenced by HT and Cd levels, resulting in a significant decrease in the colonization of endophytes and the surface area of roots, leading to a decreased N uptake from the soil. Overall, the outcomes of this study unveiled the novel effects of Cd, temperature, and their combined effect on rice growth and functions of the microbial community. These results provide effective strategies to overcome Cd-phytotoxicity on the health of endophytes and rhizospheric bacteria in Cd-contaminated soil by using temperature-tolerant rice cultivars.

Growth, antioxidant system, and phytohormonal status of barley cultivars contrasting in cadmium tolerance

Cadmium leads to disturbance of plant growth, and the manifestation of toxicity can vary greatly in different genotypes within one species. In this work we studied the effect of Cd on growth, antioxidant enzyme activity, and phytohormonal status of four barley cultivars (cvs. Simfoniya, Mestnyj, Ca 220702, Malva). According to the earlier study on seedlings, these cultivars were contrast in tolerance to Cd: Simfoniya and Mestnyj are Cd-tolerant and Ca 220702 and Malva are Cd-sensitive. The results presented showed that barley plants accumulated more Cd in straw than in grain. Tolerant cultivars accumulated significantly less Cd in grain than sensitive ones. The leaf area appeared to be a growth parameter susceptible to Cd treatment. The significant differences in leaf area values depended on Cd contamination and were not associated with cultivars' tolerance. Tolerance of cultivars was contingent on the activity of the antioxidant defense system. Indeed, activity of enzymes decreased in sensitive cultivars Ca 220702 and Malva under Cd stress. In contrast, in tolerant cultivars, increased activity of guaiacol peroxidase was revealed. The concentrations of abscisic acid and salicylic acid mostly increased as a result of Cd treatment, while the concentrations of auxins and trans-zeatin either decreased or did not change. The results obtained indicate that antioxidant enzymes and phytohormones play an important role in the response of barley plants to elevated concentrations of cadmium; however, these parameters are not able to explain the differentiation of barley cultivars in terms of tolerance to cadmium at the seedling stage. Therefore, barley intraspecific polymorphism for cadmium resistance is determined by the interplay of antioxidant enzymes, phytohormones, and other factors that require further elucidation.

Unclasping potentials of genomics and gene editing in chickpea to fight climate change and global hunger threat

Genomics and genome editing promise enormous opportunities for crop improvement and elementary research. Precise modification in the specific targeted location of a genome has profited over the unplanned insertional events which are generally accomplished employing unadventurous means of genetic modifications. The advent of new genome editing procedures viz; zinc finger nucleases (ZFNs), homing endonucleases, transcription activator like effector nucleases (TALENs), Base Editors (BEs), and Primer Editors (PEs) enable molecular scientists to modulate gene expressions or create novel genes with high precision and efficiency. However, all these techniques are exorbitant and tedious since their prerequisites are difficult processes that necessitate protein engineering. Contrary to first generation genome modifying methods, CRISPR/Cas9 is simple to construct, and clones can hypothetically target several locations in the genome with different guide RNAs. Following the model of the application in crop with the help of the CRISPR/Cas9 module, various customized Cas9 cassettes have been cast off to advance mark discrimination and diminish random cuts. The present study discusses the progression in genome editing apparatuses, and their applications in chickpea crop development, scientific limitations, and future perspectives for biofortifying cytokinin dehydrogenase, nitrate reductase, superoxide dismutase to induce drought resistance, heat tolerance and higher yield in chickpea to encounter global climate change, hunger and nutritional threats.

The hot science in rice research: How rice plants cope with heat stress

Global climate change has great impacts on plant growth and development, reducing crop productivity worldwide. Rice (Oryza sativa L.), one of the world's most important food crops, is susceptible to high-temperature stress from seedling stage to reproductive stage. In this review, we summarize recent advances in understanding the molecular mechanisms underlying heat stress responses in rice, including heat sensing and signalling, transcriptional regulation, transcript processing, protein translation, and post-translational regulation. We also highlight the irreversible effects of high temperature on reproduction and grain quality in rice. Finally, we discuss challenges and opportunities for future research on heat stress responses in rice.

ASLncR: a novel computational tool for prediction of abiotic stress-responsive long non-coding RNAs in plants

Abiotic stresses are detrimental to plant growth and development and have a major negative impact on crop yields. A growing body of evidence indicates that a large number of long non-coding RNAs (lncRNAs) are key to many abiotic stress responses. Thus, identifying abiotic stress-responsive lncRNAs is essential in crop breeding programs in order to develop crop cultivars resistant to abiotic stresses. In this study, we have developed the first machine learning-based computational model for predicting abiotic stress-responsive lncRNAs. The lncRNA sequences which were responsive and non-responsive to abiotic stresses served as the two classes of the dataset for binary classification using the machine learning algorithms. The training dataset was created using 263 stress-responsive and 263 non-stress-responsive sequences, whereas the independent test set consists of 101 sequences from both classes. As the machine learning model can adopt only the numeric data, the Kmer features ranging from sizes 1 to 6 were utilized to represent lncRNAs in numeric form. To select important features, four different feature selection strategies were utilized. Among the seven learning algorithms, the support vector machine (SVM) achieved the highest cross-validation accuracy with the selected feature sets. The observed 5-fold cross-validation accuracy, AU-ROC, and AU-PRC were found to be 68.84, 72.78, and 75.86%, respectively. Furthermore, the robustness of the developed model (SVM with the selected feature) was evaluated using an independent test dataset, where the overall accuracy, AU-ROC, and AU-PRC were found to be 76.23, 87.71, and 88.49%, respectively. The developed computational approach was also implemented in an online prediction tool ASLncR accessible at https://iasri-sg.icar.gov.in/aslncr/ . The proposed computational model and the developed prediction tool are believed to supplement the existing effort for the identification of abiotic stress-responsive lncRNAs in plants.

Genetic Diversity in Natural Populations of Rhodiola Species of Different Adaptation Strategies

Representatives of the Crassulaceae family's genus Rhodiola are succulents, making them distinctive in a changing environment. One of the most significant tools for analyzing plant resources, including numerous genetic processes in wild populations, is the analysis of molecular genetic polymorphism. This work aimed to look at the polymorphisms of allelic variations of the superoxide dismutase (SOD) and auxin response factor (ARF) gene families, as well as the genetic diversity of five Rhodiola species, using the retrotransposons-based fingerprinting approach. The multi-locus exon-primed intron-crossing (EPIC-PCR) profiling approach was used to examine allelic variations in the SOD and ARF gene families. We implemented the inter-primer binding site (iPBS) PCR amplification technique for genome profiling, which demonstrated a significant level of polymorphism in the Rhodiola samples studied. Natural populations of Rhodiola species have a great capacity for adaptation to unfavorable environmental influences. The genetic variety of wild populations of Rhodiola species leads to their improved tolerance of opposing environmental circumstances and species evolutionary divergence based on the diversity of reproductive systems.

Season, storage and extraction method impact on the phytochemical profile of Terminalia ivorensis

BACKGROUND

Terminalia ivorensis (TI) is used in West African ethnomedicine for the treatment of conditions including ulcers, malaria and wounds. Despite its widespread use, the phytochemical profile of TI remains largely undetermined. This research investigated the effects of extraction method, season, and storage conditions on the phytochemical composition of TI to contribute towards understanding the potential benefits.

METHODS

TI bark was collected in September 2014, September 2018 and February 2018 during the rainy or dry seasons in Eastern Region, Ghana. Samples were extracted sequentially with organic solvents (petroleum ether, chloroform, ethyl acetate and ethanol) or using water (traditional). Metabolites were identified by liquid chromatography-mass spectrometry/mass spectrometry and compared statistically by ANOVA.

RESULTS

A total of 82 different phytochemicals were identified across all samples. A greater yield of the major phytochemicals (44%, p < 0.05) was obtained by water as compared with organic extraction. There was also a higher concentration of metabolites present in cold (63%, p < 0.05) compared with hot water extraction. A significantly (p < 0.05) higher number of phytochemicals were identified from TI collected in the dry (85%) compared to the rainy season (69%). TI bark stored for four years retained 84% of the major phytochemicals.

CONCLUSION

This work provides important information on composition and how this is modified by growing conditions, storage and method of extraction informing progress on the development of TI as a prophylactic formulation or medicine.

Silicon-Induced Morphological, Biochemical and Molecular Regulation in Phoenix dactylifera L. under Low-Temperature Stress

Climate changes abruptly affect optimum growth temperatures, leading to a negative influence on plant physiology and productivity. The present study aimed to investigate the extent of low-temperature stress effects on date palm growth and physiological indicators under the exogenous application of silicon (Si). Date palm seedlings were treated with Si (1.0 mM) and exposed to different temperature regimes (5, 15, and 30 °C). It was observed that the application of Si markedly improved fresh and dry biomass, photosynthetic pigments (chlorophyll and carotenoids), plant morphology, and relative water content by ameliorating low-temperature-induced oxidative stress. Low-temperature stress (5 and 15 °C), led to a substantial upregulation of ABA-signaling-related genes (NCED-1 and PyL-4) in non Si treated plants, while Si treated plants revealed an antagonistic trend. However, jasmonic acid and salicylic acid accumulation were markedly elevated in Si treated plants under stress conditions (5 and 15 °C) in comparison with non Si treated plants. Interestingly, the upregulation of low temperature stress related plant plasma membrane ATPase (PPMA3 and PPMA4) and short-chain dehydrogenases/reductases (SDR), responsible for cellular physiology, stomatal conductance and nutrient translocation under silicon applications, was observed in Si plants under stress conditions in comparison with non Si treated plants. Furthermore, a significant expression of LSi-2 was detected in Si plants under stress, leading to the significant accumulation of Si in roots and shoots. In contrast, non Si plants demonstrated a low expression of LSi-2 under stress conditions, and thereby, reduced level of Si accumulation were observed. Less accumulation of oxidative stress was evident from the expression of superoxide dismutase (SOD) and catalase (CAT). Additionally, Si plants revealed a significant exudation of organic acids (succinic acid and citric acid) and nutrient accumulation (K and Mg) in roots and shoots. Furthermore, the application of Si led to substantial upregulation of the low temperature stress related soybean cold regulated gene (SRC-2) and ICE-1 (inducer of CBF expression 1), involved in the expression of CBF/DREB (C-repeat binding factor/dehydration responsive element binding factor) gene family under stress conditions in comparison with non Si plants. The current research findings are crucial for exploring the impact on morpho-physio-biochemical attributes of date palms under low temperature and Si supplementation, which may provide an efficient strategy for growing plants in low-temperature fields.

Genome-wide characterization, chromosome localization, and expression profile analysis of poplar non-specific lipid transfer proteins

Plant non-specific lipid transfer proteins (nsLTPs) are small and have a broad biological function involved in reproductive development and abiotic stress resistance. Although a small part of plant nsLTPs have been identified, these proteins have not been characterized in poplar at the genomic level. A genome-wide characterization and expression identification of poplar nsLTP members were performed in this study. A total of 42 poplar nsLTP genes were identified from the poplar genome. A comprehensive analysis of poplar nsLTPs was conducted by a phylogenetic tree, duplication events, gene structures, and conserved motifs. The cis-elements of poplar nsLTPs were predicted to respond to light, hormone, and abiotic stress. Many transcription factors (TFs) were identified to interact with poplar nsLTP cis-elements. The tested poplar nsLTPs were expressed in leaves, stems, and roots, but their expression levels differed among tested tissues. Most poplar nsLTP expression levels were changed by abiotic stress, implying that poplar nsLTP may be involved in abiotic stress resistance. Network analysis showed that poplar nsLTPs are putative genes involved in fatty acid (FA) metabolism. This research provides sight into the further study to explain the regulatory mechanism of the poplar nsLTPs.

Iron-based nanomaterials reduce cadmium toxicity in rice (Oryza sativa L.) by modulating phytohormones, phytochelatin, cadmium transport genes and iron plaque formation

Rice is known to accumulate cadmium (Cd) in its grains, causing a severe threat to billions of people worldwide. The possible phytotoxicity and mechanism of 50-200 mg/L hydroxyapatite NPs (nHA), iron oxide NPs (nFe2O3) or nano zero valent iron (nZVI) co-exposed with Cd (100 μM) in rice seedlings were investigated. Three types of nanoparticles significantly reduced the bioaccumulation of Cd in rice shoots by 16-63%, with nZVI showing the greatest effect, followed by nHA and nFe2O3. A decrease in Cd content in the roots was observed only in the nZVI treatment, with values ranging from 8 to 19%. Correspondingly, nZVI showed the best results in promoting plant growth, increasing rice plant height, shoot and root biomass by 13%, 29% and 42%. In vitro studies showed that nZVI reduced the content of Cd in the solution by 20-52% through adsorption, which might have contributed to the immobilization of Cd in root. Importantly, the nZVI treatment resulted in 267% more iron plaques on the root surface, which acted as a barrier to hinder the entry of Cd. Moreover, all three nanoparticles significantly reduced the oxidative stress induced by Cd by regulating phytohormones, phytochelatin, inorganic homeostasis and the expression of genes associated with Cd uptake and transport. Overall, this study elucidates for the first time the multiple complementing mechanisms for some nanoparticles to reduce Cd uptake and transport in rice and provides theoretical basis for applying nanoparticles for reducing Cd accumulation in edible plants.

Salicylic acid had the potential to enhance tolerance in horticultural crops against abiotic stress

Horticultural crops are greatly disturbed by severe abiotic stress conditions. This is considered one of the major threats to the healthy lives of the human population. Salicylic acid (SA) is famous as one of the multifunctional phytohormones that are widely found in plants. It is also an important bio-stimulator involved in the regulation of growth and the developmental stages of horticultural crops. The productivity of horticultural crops has been improved with the supplemental use of even small amounts of SA. It has good capability to reduce oxidative injuries that occur from the over-production of reactive oxygen species (ROS), potentially elevated photosynthesis, chlorophyll pigments, and stomatal regulation. Physiological and biochemical processes have revealed that SA enhances signaling molecules, enzymatic and non-enzymatic antioxidants, osmolytes, and secondary metabolites activities within the cell compartments of plants. Numerous genomic approaches have also explored that SA regulates transcriptions profiling, transcriptional apprehensions, genomic expression, and metabolism of stress-related genes. Many plant biologists have been working on SA and its functioning in plants; however, its involvement in the enhancement of tolerance against abiotic stress in horticultural crops is still unidentified and needs more attention. Therefore, the current review is focused on a detailed exploration of SA in physiological and biochemical processes in horticultural crops subjected to abiotic stress. The current information is comprehensive and aims to be more supportive of the development of higher-yielding germplasm against abiotic stress.

Starch and Sucrose Metabolism and Plant Hormone Signaling Pathways Play Crucial Roles in Aquilegia Salt Stress Adaption

Salt stress is one of the main abiotic stresses that strongly affects plant growth. Clarifying the molecular regulatory mechanism in ornamental plants under salt stress is of great significance for the ecological development of saline soil areas. Aquilegia vulgaris is a perennial with a high ornamental and commercial value. To narrow down the key responsive pathways and regulatory genes, we analyzed the transcriptome of A. vulgaris under a 200 mM NaCl treatment. A total of 5600 differentially expressed genes were identified. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis pointed out that starch and sucrose metabolism and plant hormone signal transduction were significantly improved. The above pathways played crucial roles when A. vulgaris was coping with salt stress, and their protein-protein interactions (PPIs) were predicted. This research provides new insights into the molecular regulatory mechanism, which could be the theoretical basis for screening candidate genes in Aquilegia.

Recent progress and perspectives on physiological and molecular mechanisms underlying cold tolerance of tea plants

Tea is one of the most consumed and widely planted beverage plant worldwide, which contains many important economic, healthy, and cultural values. Low temperature inflicts serious damage to tea yields and quality. To cope with cold stress, tea plants have evolved a cascade of physiological and molecular mechanisms to rescue the metabolic disorders in plant cells caused by the cold stress; this includes physiological, biochemical changes and molecular regulation of genes and associated pathways. Understanding the physiological and molecular mechanisms underlying how tea plants perceive and respond to cold stress is of great significance to breed new varieties with improved quality and stress resistance. In this review, we summarized the putative cold signal sensors and molecular regulation of the CBF cascade pathway in cold acclimation. We also broadly reviewed the functions and potential regulation networks of 128 cold-responsive gene families of tea plants reported in the literature, including those particularly regulated by light, phytohormone, and glycometabolism. We discussed exogenous treatments, including ABA, MeJA, melatonin, GABA, spermidine and airborne nerolidol that have been reported as effective ways to improve cold resistance in tea plants. We also present perspectives and possible challenges for functional genomic studies on cold tolerance of tea plants in the future.

Cytogenetic and Biochemical Responses of Wheat Seeds to Proton Irradiation at the Bragg Peak

The present study aimed to evaluate the morphological, cytogenetic and biochemical changes in wheat seedlings as affected by seed exposure to a proton beam at the Bragg peak. The average energy of the proton beam was of 171 MeV at the entrance into the irradiator room while at the point of sample irradiation the beam energy was of 150 MeV, with the average value of the Linear Energy Transfer of 0.539 keV/μm and the dose rate of 0.55 Gy/min, the radiation doses being of the order of tens of Gy. Cytogenetic investigation has revealed the remarkable diminution of the mitotic index as linear dose-response curve as well as the spectacular linear increase of the aberration index. Analyzing some biometric parameters, it was found that neither dry matter nor water content of wheat seedlings was influenced by proton beam exposure. Studying the biochemical parameters related to the antioxidant defense system, we found that the irradiation caused the slight increasing tendency of peroxidase activity as well as the decreasing trend in the activity of superoxidedismutase in the seedlings grown from the irradiated seeds. The level of malonedialdehyde (MDA) and total polyphenols showed an increasing tendency in all seedling variants corresponding to irradiated seeds, compared to the control. We conclude that the irradiation clearly induced dose-response curves at the level of cytogenetic parameters together with relatively slight variation tendency of some biochemical parameters related to the antioxidant defense system while imperceptible changes could be noticed in the biometric parameters.

Insights on Phytohormonal Crosstalk in Plant Response to Nitrogen Stress: A Focus on Plant Root Growth and Development

Nitrogen (N) is a vital mineral component that can restrict the growth and development of plants if supplied inappropriately. In order to benefit their growth and development, plants have complex physiological and structural responses to changes in their nitrogen supply. As higher plants have multiple organs with varying functions and nutritional requirements, they coordinate their responses at the whole-plant level based on local and long-distance signaling pathways. It has been suggested that phytohormones are signaling substances in such pathways. The nitrogen signaling pathway is closely associated with phytohormones such as auxin (AUX), abscisic acid (ABA), cytokinins (CKs), ethylene (ETH), brassinosteroid (BR), strigolactones (SLs), jasmonic acid (JA), and salicylic acid (SA). Recent research has shed light on how nitrogen and phytohormones interact to modulate physiology and morphology. This review provides a summary of the research on how phytohormone signaling affects root system architecture (RSA) in response to nitrogen availability. Overall, this review contributes to identifying recent developments in the interaction between phytohormones and N, as well as serving as a foundation for further study.

Strigolactones modulate stem length and diameter of cherry rootstocks through interaction with other hormone signaling pathways

Stem growth and development has considerable effects on plant architecture and yield performance. Strigolactones (SLs) modulate shoot branching and root architecture in plants. However, the molecular mechanisms underlying SLs regulate cherry rootstocks stem growth and development remain unclear. Our studies showed that the synthetic SL analog rac-GR24 and the biosynthetic inhibitor TIS108 affected stem length and diameter, aboveground weight, and chlorophyll content. The stem length of cherry rootstocks following TIS108 treatment reached a maximum value of 6.97 cm, which was much higher than that following rac-GR24 treatments at 30 days after treatment. Stem paraffin section showed that SLs affected cell size. A total of 1936, 743, and 1656 differentially expressed genes (DEGs) were observed in stems treated with 10 μM rac-GR24, 0.1 μM rac-GR24, and 10 μM TIS108, respectively. RNA-seq results highlighted several DEGs, including CKX, LOG, YUCCA, AUX, and EXP, which play vital roles in stem growth and development. UPLC-3Q-MS analysis revealed that SL analogs and inhibitors affected the levels of several hormones in the stems. The endogenous GA₃ content of stems increased significantly with 0.1 μM rac-GR24 or 10 μM TIS108 treatment, which is consistent with changes in the stem length following the same treatments. This study demonstrated that SLs affected stem growth of cherry rootstocks by changing other endogenous hormone levels. These results provide a solid theoretical basis for using SLs to modulate plant height and achieve sweet cherry dwarfing and high-density cultivation.

Instigating prevalent abiotic stress resilience in crop by exogenous application of phytohormones and nutrient

In recent times, the demand for food and feed for the ever-increasing population has achieved unparalleled importance, which cannot afford crop yield loss. Now-a-days, the unpleasant situation of abiotic stress triggers crop improvement by affecting the different metabolic pathways of yield and quality advances worldwide. Abiotic stress like drought, salinity, cold, heat, flood, etc. in plants diverts the energy required for growth to prevent the plant from shock and maintain regular homeostasis. Hence, the plant yield is drastically reduced as the energy is utilized for overcoming the stress in plants. The application of phytohormones like the classical auxins, cytokinins, ethylene, and gibberellins, as well as more recent members including brassinosteroids, jasmonic acids, etc., along with both macro and micronutrients, have enhanced significant attention in creating key benefits such as reduction of ionic toxicity, improving oxidative stress, maintaining water-related balance, and gaseous exchange modification during abiotic stress conditions. Majority of phytohormones maintain homeostasis inside the cell by detoxifying the ROS and enhancing the antioxidant enzyme activities which can enhance tolerance in plants. At the molecular level, phytohormones activate stress signaling pathways or genes regulated by abscisic acid (ABA), salicylic acid (SA), Jasmonic acid (JA), and ethylene. The various stresses primarily cause nutrient deficiency and reduce the nutrient uptake of plants. The application of plant nutrients like N, K, Ca, and Mg are also involved in ROS scavenging activities through elevating antioxidants properties and finally decreasing cell membrane leakage and increasing the photosynthetic ability by resynthesizing the chlorophyll pigment. This present review highlighted the alteration of metabolic activities caused by abiotic stress in various crops, the changes of vital functions through the application of exogenous phytohormones and nutrition, as well as their interaction.

Plant Hormonomics: A Key Tool for Deep Physiological Phenotyping to Improve Crop Productivity

Agriculture is particularly vulnerable to climate change. To cope with the risks posed by climate-related stressors to agricultural production, global population growth, and changes in food preferences, it is imperative to develop new climate-smart crop varieties with increased yield and environmental resilience. Molecular genetics and genomic analyses have revealed that allelic variations in genes involved in phytohormone-mediated growth regulation have greatly improved productivity in major crops. Plant science has remarkably advanced our understanding of the molecular basis of various phytohormone-mediated events in plant life. These findings provide essential information for improving the productivity of crops growing in changing climates. In this review, we highlight the recent advances in plant hormonomics (multiple phytohormone profiling) and discuss its application to crop improvement. We present plant hormonomics as a key tool for deep physiological phenotyping, focusing on representative plant growth regulators associated with the improvement of crop productivity. Specifically, we review advanced methodologies in plant hormonomics, highlighting mass spectrometry- and nanosensor-based plant hormone profiling techniques. We also discuss the applications of plant hormonomics in crop improvement through breeding and agricultural management practices.

Plant hormone cytokinin at the crossroads of stress priming and control of photosynthesis

To cope with biotic and abiotic stress conditions, land plants have evolved several levels of protection, including delicate defense mechanisms to respond to changes in the environment. The benefits of inducible defense responses can be further augmented by defense priming, which allows plants to respond to a mild stimulus faster and more robustly than plants in the naïve (non-primed) state. Priming provides a low-cost protection of agriculturally important plants in a relatively safe and effective manner. Many different organic and inorganic compounds have been successfully tested to induce resistance in plants. Among the plethora of commonly used physicochemical techniques, priming by plant growth regulators (phytohormones and their derivatives) appears to be a viable approach with a wide range of applications. While several classes of plant hormones have been exploited in agriculture with promising results, much less attention has been paid to cytokinin, a major plant hormone involved in many biological processes including the regulation of photosynthesis. Cytokinins have been long known to be involved in the regulation of chlorophyll metabolism, among other functions, and are responsible for delaying the onset of senescence. A comprehensive overview of the possible mechanisms of the cytokinin-primed defense or stress-related responses, especially those related to photosynthesis, should provide better insight into some of the less understood aspects of this important group of plant growth regulators.

Phytohormones regulate the abiotic stress: An overview of physiological, biochemical, and molecular responses in horticultural crops

Recent changing patterns of global climate have turned out to be a severe hazard to the horticulture crops production. A wide range of biotic and abiotic stresses often affect plants due to their sessile nature. Horticultural crop losses are mainly caused by abiotic factors such as drought, salt, heat, cold, floods, and ultraviolet radiation. For coping up with these adversities, well-developed mechanisms have been evolved in plants, which play a role in perceiving stress signals and enabling optimal growth responses. Interestingly, the use of phytohormones for suppressing the impact of abiotic stress has gained much attention in recent decades. For circumvention of stress at various levels, including physiological, molecular, as well as biochemical, a sophisticated mechanism is reported to be provided by the phytohormones, thus labeling these phytohormones a significant role in plant growth and development. Phytohormones can improves tolerance against abiotic stresses by increasing seed germination, seedling growth, leaf photosynthesis, root growth, and antioxidant enzymes and reducing the accumulation of reactive oxygen species, malonaldehyde, and electrolyte leakage. Recent discoveries highlight the significant role of a variety of phytohormones including melatonin (MEL), Gamma-aminobutyric acid (GABA), jasmonic acid (JA), salicylic acid (SA), brassinosteroids (BRs), and strigolactones (SLs) in abiotic stress tolerance enhancement of horticultural plants. Thus, current review is aimed to summarize the developmental concepts regarding role of phytohormones in abiotic-stress mitigation, mainly in horticultural crops, along with the description of recent studies which identified the role of different phytohormones in stressed environments. Hence, such a review will help in paving the path for sustainable agriculture growth via involvement of phytohormones in enhancement of abiotic stress tolerance of horticultural crops.

Analysis of metabolic and transcription levels provides insights into the interactions of plant hormones and crosstalk with MAPKs in the early signaling response of cherry tomato fruit induced by the yeast cell wall

Yeast cell walls (YCW) are promising bio-based elicitors for controlling post-harvest fruit decay. In this study, 1% YCW induction increased the resistance of cherry tomato fruits, reducing disease incidence by 66%. This study aimed to explore the interaction of hormones and crosstalk with MAPKs (mitogen-activated protein kinases) in the early response of resistance regulation in cherry tomato fruits treated with YCW and U0126. We analyzed the temporal changes in hormone content, the expression of critical genes involved in phytohormone biosynthesis, and signal transduction in cherry tomato fruits response to the induction. Results revealed that jasmonic acid (JA) and brassinosteroids (BR) significantly regulated early resistance response in fruit induced by 1% YCW. The salicylic acid (SA) pathway is inhibited by the activation of the JA pathway. JA and SA signaling pathway crosstalk with the MAPK3 pathway. BR plays an essential role in the regulation of fruit resistance. The BR pathway may function independently when JA/SA and MAPK3 pathways are inhibited.

Modifications of Phytohormone Metabolism Aimed at Stimulation of Plant Growth, Improving Their Productivity and Tolerance to Abiotic and Biotic Stress Factors

Due to the growing human population, the increase in crop yield is an important challenge for modern agriculture. As abiotic and biotic stresses cause severe losses in agriculture, it is also crucial to obtain varieties that are more tolerant to these factors. In the past, traditional breeding methods were used to obtain new varieties displaying demanded traits. Nowadays, genetic engineering is another available tool. An important direction of the research on genetically modified plants concerns the modification of phytohormone metabolism. This review summarizes the state-of-the-art research concerning the modulation of phytohormone content aimed at the stimulation of plant growth and the improvement of stress tolerance. It aims to provide a useful basis for developing new strategies for crop yield improvement by genetic engineering of phytohormone metabolism.

Comparative transcriptome profiling of resistant and susceptible foxtail millet responses to Sclerospora graminicola infection

BACKGROUND

Downy mildew of foxtail millet, which is caused by the biotrophic oomycete Sclerospora graminicola (Sacc.) Schroeter, is one of the most disruptive diseases. The foxtail millet-S. graminicola interaction is largely unexplored. Transcriptome sequencing technology can help to reveal the interaction mechanism between foxtail millet and its pathogens.

RESULTS

Transmission electron microscopy observations of leaves infected with S. graminicola showed that the structures of organelles in the host cells gradually became deformed and damaged, or even disappeared from the 3- to 7-leaf stages. However, organelles in the leaves of resistant variety were rarely damaged. Moreover, the activities of seven cell wall degrading enzymes in resistant and susceptible varieties were also quite different after pathogen induction and most of enzymes activities were significantly higher in the susceptible variety JG21 than in the resistant variety G1 at all stages. Subsequently, we compared the transcriptional profiles between the G1 and JG21 in response to S. graminicola infection at 3-, 5-, and 7-leaf stages using RNA-Seq technology. A total of 473 and 1433 differentially expressed genes (DEGs) were identified in the resistant and susceptible varieties, respectively. The pathway analysis of the DEGs showed that the highly enriched categories were related to glutathione metabolism, plant hormone signalling, phenylalanine metabolism, and cutin, suberin and wax biosynthesis. Some defence-related genes were also revealed in the DEGs, including leucine-rich protein kinase, Ser/Thr protein kinase, peroxidase, cell wall degrading enzymes, laccases and auxin response genes. Our results also confirmed the linkage of transcriptomic data with qRT-PCR data. In particular, LRR protein kinase encoded by Seita.8G131800, Ser/Thr protein kinase encoded by Seita.2G024900 and Seita. 2G024800, which have played an essential resistant role during the infection by S. graminicola.

CONCLUSIONS

Transcriptome sequencing revealed that host resistance to S. graminicola was likely due to the activation of defence-related genes, such as leucine-rich protein kinase and Ser/Thr protein kinase. Our study identified pathways and genes that contribute to the understanding of the interaction between foxtail millet and S. graminicola at the transcriptomic level. The results will help us better understand the resistance mechanism of foxtail millet against S. graminicola.

Specific roles of strigolactones in plant physiology and remediation of heavy metals from contaminated soil

Strigolactones (SLs) have been implicated in various developmental processes of the plant, including the response against several abiotic stresses. It is well known as a class of endogenous phytohormones that regulates shoot branching, secondary growth and root morphology. This hormone facilitates plants in responding to nitrogen and phosphorus starvation by shaping the above and below ground structural design. SLs actively participate within regulatory networks of plant stress adaptation that are governed by phytohormones. Heavy metals (HMs) in soil are considered a serious environmental problem that causes various harmful effects on plants. SLs along with other plant hormones imply the role in plant architecture is far from being fully understood. Strategy to remove/remediation of HMs from the soil with the help of SLs has not been defined yet. Therefore, the present review aims to comprehensively provide an overview of SLs role in fine-tuning plant architectures, relation with other plant hormones under abiotic stress, and remediation of HMs contaminated soil using SLs.

The transcription factor VaMYC2 from Chinese wild Vitis amurensis enhances cold tolerance of grape (V. vinifera) by up-regulating VaCBF1 and VaP5CS

Cultivated grapes, one of the most important fruit crops in the world, are sensitive to low temperature. Since Chinese wild grape Vitis amurensis is highly tolerant to cold, it is imperative to study and utilize its cold-tolerance genes for molecular breeding. Here, a VaMYC2 gene from V. amurensis was cloned, and its function was investigated by expressing VaMYC2 in the cold-sensitive V. vinifera cultivar 'Thompson Seedless'. The expression of VaMYC2 could be induced by cold stress, methyl jasmonate and ethylene treatment, but was inhibited by abscisic acid in leaves of V. amurensis. When transgenic grape lines expressing VaMYC2 were subjected to cold stress (-1 °C) for 41 h, the transgenic lines showed less freezing injury and lower electrolyte leakage and malondialdehyde content, but higher contents of soluble sugars, soluble proteins and proline, and antioxidant enzyme activities compared with wild-type. Moreover, the expression of some cold-tolerance related genes increased in transgenic lines. Besides, the interactions of VaMYC2 with VaJAZ1 and VaJAZ7B were confirmed by yeast two-hybrid and bimolecular fluorescence complementation assays. Yeast one-hybrid and dual luciferase assays showed that VaMYC2 can bind to the promoters of VaCBF1 and VaP5CS and activate their expressions. In conclusion, expression of VaMYC2 in V. vinifera enhances cold tolerance of transgenic grapes which is attributed to enhanced accumulation of osmotic regulatory substances, cell membrane stability, antioxidant enzyme activity, and expression of cold tolerance-related genes. Also, VaMYC2 interacts with VaJAZ1 and VaJAZ7, and activates the expression of VaCBF1 and VaP5CS to mediate cold tolerance in grapes.

Transcriptomic and physiological analyses unravel the effect and mechanism of halosulfuron-methyl on the symbiosis between rhizobium and soybean

Halosulfuron-methyl (HSM) is a new and highly effective sulfonylurea herbicide widely used in weed control, but its residue in the environment poses a potential risk to soybean. Soybean-rhizobium symbiotic nitrogen fixation is crucial for sustainable agricultural development and ecological environment health. However, the impact of HSM on the symbiosis between soybean and rhizobium is unclear. In this study, the effects of HSM on the soybean-rhizobium symbiotic process and nitrogen fixation were investigated by means of transcriptomic and physiological analyses. Treatment with a concentration of HSM less than 0.5 mg L^-1 had no effect on rhizobium growth, but significantly reduced nodules number, the biomass of soybean nodules, and nitrogenase activity in root nodules (P < 0.05). Transcriptomic analysis showed that differentially expressed genes (DEGs) involved in NH₄⁺ assimilation were significantly downregulated (P < 0.05). In addition, the activities of NH₄⁺ assimilation enzymes were markedly reduced. This result was further confirmed by the accumulation of NH₄⁺ in root nodules, indicating that the inhibition of nitrogen fixation by HSM may be caused by excessive NH₄⁺ accumulation in root nodules. Furthermore, DEGs involved in flavonoid synthesis, phytohormone biosynthesis, and phytohormone signaling transduction were significantly downregulated (P < 0.05), which was consistent with the decrease in flavonoid and phytohormone contents determined in this study. These results suggested that HSM may inhibit soybean nodulation by inhibiting flavonoid synthesis in soybean roots, disrupting the balance of plant endogenous hormones in roots during symbiosis, and blocking the transmission of hormone signals during the symbiosis. Our findings provide new insights into the effects of HSM on the legume-rhizobium nodule symbiotic process.

Protein l-isoAspartyl Methyltransferase (PIMT) and antioxidants in plants

All life forms, including plants, accumulate reactive oxygen species (ROS) as a byproduct of metabolism; however, environmental stresses, including abiotic stresses and pathogen attacks, cause enhanced accumulation of ROS in plants. The increased accumulation of ROS often causes oxidative damage to cells. Organisms are able to maintain levels of ROS below permissible limits by several mechanisms, including efficient antioxidant systems. In addition to antioxidant systems, recent studies suggest that protein l-isoaspartyl methyltransferase (PIMT), a highly conserved protein repair enzyme across evolutionary diverse organisms, plays a critical role in maintaining ROS homeostasis by repairing isoaspartyl-mediated damage to antioxidants in plants. Under stress conditions, antioxidant proteins undergo spontaneous isoaspartyl (isoAsp) modification which is often detrimental to protein structure and function. This reduces the catalytic action of antioxidants and disturbs the ROS homeostasis of cells. This chapter focuses on PIMT and its interaction with antioxidants in plants, where PIMT constitutes a secondary level of protection by shielding a primary level of antioxidants from dysfunction and permitting them to guard during unfavorable situations.

Arabidopsis thaliana Accessions from the Chernobyl Exclusion Zone Show Decreased Sensitivity to Additional Acute Irradiation

Chronic ionising radiation exposure is a main consequence of radioactive pollution of the environment. The development of functional genomics approaches coupled with morphological and physiological studies allows new insights into plant adaptation to life under chronic irradiation. Using morphological, reproductive, physiological, and transcriptomic experiments, we evaluated the way in which Arabidopsis thaliana natural accessions from the Chernobyl exclusion zone recover from chronic low-dose and acute high-dose γ-irradiation of seeds. Plants from radioactively contaminated areas were characterized by lower germination efficiency, suppressed growth, decreased chlorophyll fluorescence, and phytohormonal changes. The transcriptomes of plants chronically exposed to low-dose radiation indicated the repression of mobile genetic elements and deregulation of genes related to abiotic stress tolerance. Furthermore, these chronically irradiated natural accessions showed higher tolerance to acute 150 Gy γ-irradiation of seeds, according to transcriptome and phytohormonal profiles. Overall, the lower sensitivity of the accessions from radioactively contaminated areas to acute high-dose irradiation may come at the cost of their growth performance under normal conditions.

The Barley Heavy Metal Associated Isoprenylated Plant Protein HvFP1 Is Involved in a Crosstalk between the Leaf Development and Abscisic Acid-Related Drought Stress Responses

The heavy metal associated isoprenylated plant proteins (HIPPs) are characterized by at least one heavy metal associated (HMA) domain and a C-terminal isoprenylation motif. Hordeum vulgare farnesylated protein 1 (HvFP1), a barley HIPP, is upregulated during drought stress, in response to abscisic acid (ABA) and during leaf senescence. To investigate the role of HvFP1, two independent gain-of-function lines were generated. In a physiological level, the overexpression of HvFP1 results in the delay of normal leaf senescence, but not in the delay of rapid, drought-induced leaf senescence. In addition, the overexpression of HvFP1 suppresses the induction of the ABA-related genes during drought and senescence, e.g., HvNCED, HvS40, HvDhn1. Even though HvFP1 is induced during drought, senescence and the ABA treatment, its overexpression suppresses the ABA regulated genes. This indicates that HvFP1 is acting in a negative feedback loop connected to the ABA signaling. The genome-wide transcriptomic analysis via RNA sequencing revealed that the gain-of-function of HvFP1 positively alters the expression of the genes related to leaf development, photomorphogenesis, photosynthesis and chlorophyll biosynthesis. Interestingly, many of those genes encode proteins with zinc binding domains, implying that HvFP1 may act as zinc supplier via its HMA domain. The results show that HvFP1 is involved in a crosstalk between stress responses and growth control pathways.

Molecular and Physiological Mechanisms to Mitigate Abiotic Stress Conditions in Plants

Agriculture production faces many abiotic stresses, mainly drought, salinity, low and high temperature. These abiotic stresses inhibit plants' genetic potential, which is the cause of huge reduction in crop productivity, decrease potent yields for important crop plants by more than 50% and imbalance agriculture's sustainability. They lead to changes in the physio-morphological, molecular, and biochemical nature of the plants and change plants' regular metabolism, which makes them a leading cause of losses in crop productivity. These changes in plant systems also help to mitigate abiotic stress conditions. To initiate the signal during stress conditions, sensor molecules of the plant perceive the stress signal from the outside and commence a signaling cascade to send a message and stimulate nuclear transcription factors to provoke specific gene expression. To mitigate the abiotic stress, plants contain several methods of avoidance, adaption, and acclimation. In addition to these, to manage stress conditions, plants possess several tolerance mechanisms which involve ion transporters, osmoprotectants, proteins, and other factors associated with transcriptional control, and signaling cascades are stimulated to offset abiotic stress-associated biochemical and molecular changes. Plant growth and survival depends on the ability to respond to the stress stimulus, produce the signal, and start suitable biochemical and physiological changes. Various important factors, such as the biochemical, physiological, and molecular mechanisms of plants, including the use of microbiomes and nanotechnology to combat abiotic stresses, are highlighted in this article.

Comprehensive Phytohormone Profiling of Kohlrabi during In Vitro Growth and Regeneration: The Interplay with Cytokinin and Sucrose

The establishment of an efficient protocol for in vitro growth and regeneration of kohlrabi (Brassica oleracea var. gongylodes) allowed us to closely examine the phytohormone profiles of kohlrabi seedlings at four growth stages (T1-T4), additionally including the effects of cytokinins (CKs)-trans-zeatin (transZ) and thidiazuron (TDZ)-and high sucrose concentrations (6% and 9%). Resulting phytohormone profiles showed complex time-course patterns. At the T2 stage of control kohlrabi plantlets (with two emerged true leaves), levels of endogenous CK free bases and gibberellin GA₂₀ increased, while increases in jasmonic acid (JA), JA-isoleucine (JA-Ile), indole-3-acetic acid (IAA) and indole-3-acetamide (IAM) peaked later, at T3. At the same time, the content of most of the analyzed IAA metabolites decreased. Supplementing growth media with CK induced de novo formation of shoots, while both CK and sucrose treatments caused important changes in most of the phytohormone groups at each developmental stage, compared to control. Principal component analysis (PCA) showed that sucrose treatment, especially at 9%, had a stronger effect on the content of endogenous hormones than CK treatments. Correlation analysis showed that the dynamic balance between the levels of certain bioactive phytohormone forms and some of their metabolites could be lost or reversed at particular growth stages and under certain CK or sucrose treatments, with correlation values changing between strongly positive and strongly negative. Our results indicate that the kohlrabi phytohormonome is a highly dynamic system that changes greatly along the developmental time scale and also during de novo shoot formation, depending on exogenous factors such as the presence of growth regulators and different sucrose concentrations in the growth media, and that it interacts intensively with these factors to facilitate certain responses.

NAC Transcription Factor GmNAC12 Improved Drought Stress Tolerance in Soybean

NAC transcription factors (TFs) could regulate drought stresses in plants; however, the function of NAC TFs in soybeans remains unclear. To unravel NAC TF function, we established that GmNAC12, a NAC TF from soybean (Glycine max), was involved in the manipulation of stress tolerance. The expression of GmNAC12 was significantly upregulated more than 10-fold under drought stress and more than threefold under abscisic acid (ABA) and ethylene (ETH) treatment. In order to determine the function of GmNAC12 under drought stress conditions, we generated GmNAC12 overexpression and knockout lines. The present findings showed that under drought stress, the survival rate of GmNAC12 overexpression lines increased by more than 57% compared with wild-type plants, while the survival rate of GmNAC12 knockout lines decreased by at least 46%. Furthermore, a subcellular localisation analysis showed that the GmNAC12 protein is concentrated in the nucleus of the tobacco cell. In addition, we used a yeast two-hybrid assay to identify 185 proteins that interact with GmNAC12. Gene ontology (GO) and KEGG analysis showed that GmNAC12 interaction proteins are related to chitin, chlorophyll, ubiquitin–protein transferase, and peroxidase activity. Hence, we have inferred that GmNAC12, as a key gene, could positively regulate soybean tolerance to drought stress.

Effect of three water-regimes on morpho-physiological, biochemical and yield responses of local and foreign olive cultivars under field conditions

BACKGROUND

Drought stress is among the most serious threats jeopardizing the economic yield of crop plants in Iran. In particular, in response to withholding irrigation, the reduction in performance and quality of a precious plant such as the olive tree is remarkable. Therefore, the selection of cultivars that are resistant or tolerant to drought has been recognized as one of the most effective long-term strategies for sustainably alleviating the adverse effects of this stress. In this view, our study evaluated the response of 8 olive cultivars including 4 elite native cultivars (Zard Aliabad, Roughani, Dezful, and Shengeh) and 4 foreign cultivars (Manzanilla, Sevillana, Konservolia, and Mission) to water shortage in the Dallaho Olive Research station of Sarpole-Zahab in Kermanshah province in 2020. Olive trees underwent 3 levels of irrigation treatment including 100% full irrigation (control), 75%, and 50% deficit irrigation.

RESULTS

Based on the results, 50% deficit irrigation decreased both growth and pomological traits, but determined the highest dry matter percentage. As the severity of drought stress increased, with an accumulation of sodium and malondialdehyde, an incremental increase in osmolytes was observed, as well as an enhancement of the activity of antioxidant enzymes (peroxidase and catalase). In contrast, full irrigation led to an increase in photosynthetic pigments, calcium, and potassium. Dezful and Konservolia cultivars revealed a significantly higher growth rate, correlated in the former to higher levels of chlorophyll, compatible compounds, total phenolic content, relative water content, potassium to sodium ratio, catalase, and peroxidase activities compared with other cultivars. Konservolia showed the best yield parameters under 75% and 100% irrigation regimes, correlated to higher chlorophyll, potassium, and total phenolic content (in particular at 75% ET).

CONCLUSIONS

Generally, the selection of more resilient or tolerant cultivars to sustain water scarcity stress is a widely operative solution to extend rainfed orchards in semi-arid environments. Our study showed that Dezful and Konservolia had the best adaptive mechanisms to cope with the detrimental effects of drought stress.

Novel Approaches for Sustainable Horticultural Crop Production: Advances and Prospects

Reduction of plant growth, yield and quality due to diverse environmental constrains along with climate change significantly limit the sustainable production of horticultural crops. In this review, we highlight the prospective impacts that are positive challenges for the application of beneficial microbial endophytes, nanomaterials (NMs), exogenous phytohormones strigolactones (SLs) and new breeding techniques (CRISPR), as well as controlled environment horticulture (CEH) using artificial light in sustainable production of horticultural crops. The benefits of such applications are often evaluated by measuring their impact on the metabolic, morphological and biochemical parameters of a variety of cultures, which typically results in higher yields with efficient use of resources when applied in greenhouse or field conditions. Endophytic microbes that promote plant growth play a key role in the adapting of plants to habitat, thereby improving their yield and prolonging their protection from biotic and abiotic stresses. Focusing on quality control, we considered the effects of the applications of microbial endophytes, a novel class of phytohormones SLs, as well as NMs and CEH using artificial light on horticultural commodities. In addition, the genomic editing of plants using CRISPR, including its role in modulating gene expression/transcription factors in improving crop production and tolerance, was also reviewed.

Perspectives and potential applications of endophytic microorganisms in cultivation of medicinal and aromatic plants

Ensuring food and nutritional security, it is crucial to use chemicals in agriculture to boost yields and protect the crops against biotic and abiotic perturbations. Conversely, excessive use of chemicals has led to many deleterious effects on the environment like pollution of soil, water, and air; loss of soil fertility; and development of pest resistance, and is now posing serious threats to biodiversity. Therefore, farming systems need to be upgraded towards the use of biological agents to retain agricultural and environmental sustainability. Plants exhibit a huge and varied niche for endophytic microorganisms inside the planta, resulting in a closer association between them. Endophytic microorganisms play pivotal roles in plant physiological and morphological characteristics, including growth promotion, survival, and fitness. Their mechanism of action includes both direct and indirect, such as mineral phosphate solubilization, fixating nitrogen, synthesis of auxins, production of siderophore, and various phytohormones. Medicinal and aromatic plants (MAPs) hold a crucial position worldwide for their valued essential oils and several phytopharmaceutically important bioactive compounds since ancient times; conversely, owing to the high demand for natural products, commercial cultivation of MAPs is on the upswing. Furthermore, the vulnerability to various pests and diseases enforces noteworthy production restraints that affect both crop yield and quality. Efforts have been made towards enhancing yields of plant crude drugs by improving crop varieties, cell cultures, transgenic plants, etc., but these are highly cost-demanding and time-consuming measures. Thus, it is essential to evolve efficient, eco-friendly, cost-effective simpler approaches for improvement in the yield and health of the plants. Harnessing endophytic microorganisms as biostimulants can be an effective and alternative step. This review summarizes the concept of endophytes, their multidimensional interaction inside the host plant, and the salient benefits associated with endophytic microorganisms in MAPs.

Rhizobium inoculation and exogenous melatonin synergistically increased thermotolerance by improving antioxidant defense, photosynthetic efficiency, and nitro-oxidative homeostasis in Medicago truncatula

Global warming negatively affects plant growth due to the detrimental effects of high temperature-induced heat stress. Rhizobium inoculation (RI) and exogenous melatonin (MT) have shown a positive role in resisting abiotic stress. However, their synergistic effect on avoiding heat-induced damages in Medicago truncatula has not been studied yet. Hence, the objective of the present study was to evaluate the impact of these amendments (RI and MT) to ameliorate the heat damages in Medicago truncatula. The study was comprised of two factors: (1) heat-induced stress: (i) optimum temperature (26 ± 1°C): (23 ± 1°C) (day: night), (ii) moderate heat (35 ± 1°C): (28 ± 1°C), and (iii) severe heat (41 ± 1°C): (35 ± 1°C) for 72 h, and (2) amendments: (i) no RI + no MT (NRI + NMT), (ii) Rhizobium inoculation (RI), (iii) 60 μM melatonin (MT), and (iii) RI + MT. Results showed that the combined application of RI and MT was better than their individual applications, as it prevented heat-induced membrane damages by declining the hydrogen peroxide (34.22% and 29.78%), superoxide anion radical (29.49% and 26.71%), malondialdehyde contents (26.43% and 21.96%), and lipoxygenase activity (44.75% and 25.51%) at both heat stress levels as compared to NRI + NMT. Moreover, RI + MT treated plants showed higher antioxidative and methylglyoxal detoxification enzymes (Gly I and Gly II) activities under heat stress. While, NRI + NMT treated plants showed a higher level of methylglyoxal contents (47.99% and 46.71%) under both levels of heat stress. Relative to NRI + NMT plants, RI + MT pretreated plants exhibited improved heat tolerance as indicated by higher chlorophyll (37.42% and 43.52%), carotenoid contents (32.41% and 47.08%), and photosynthetic rate (42.62% and 64.63%), under moderate and severe heat stress, respectively. Furthermore, RI + MT pretreated plants had considerably higher indole-3 acetic acid and abscisic acid concentrations under moderate (54.02% and 53.92%) and severe (68.36% and 64.61%) heat stress conditions. Similarly, plant dry biomass, NPK uptake, nitric oxide, and nitrate reductase activity were high in RI + MT treated plants, under both levels of stress. Therefore, this study advocates the positive synergistic effect of RI and MT pretreatment against moderate and severe heat-induced stress and for possible maintenance of plant growth under changing scenarios of global warming.

Plant hormones and neurotransmitter interactions mediate antioxidant defenses under induced oxidative stress in plants

Due to global climate change, abiotic stresses are affecting plant growth, productivity, and the quality of cultivated crops. Stressful conditions disrupt physiological activities and suppress defensive mechanisms, resulting in stress-sensitive plants. Consequently, plants implement various endogenous strategies, including plant hormone biosynthesis (e.g., abscisic acid, jasmonic acid, salicylic acid, brassinosteroids, indole-3-acetic acid, cytokinins, ethylene, gibberellic acid, and strigolactones) to withstand stress conditions. Combined or single abiotic stress disrupts the normal transportation of solutes, causes electron leakage, and triggers reactive oxygen species (ROS) production, creating oxidative stress in plants. Several enzymatic and non-enzymatic defense systems marshal a plant's antioxidant defenses. While stress responses and the protective role of the antioxidant defense system have been well-documented in recent investigations, the interrelationships among plant hormones, plant neurotransmitters (NTs, such as serotonin, melatonin, dopamine, acetylcholine, and γ-aminobutyric acid), and antioxidant defenses are not well explained. Thus, this review discusses recent advances in plant hormones, transgenic and metabolic developments, and the potential interaction of plant hormones with NTs in plant stress response and tolerance mechanisms. Furthermore, we discuss current challenges and future directions (transgenic breeding and genome editing) for metabolic improvement in plants using modern molecular tools. The interaction of plant hormones and NTs involved in regulating antioxidant defense systems, molecular hormone networks, and abiotic-induced oxidative stress tolerance in plants are also discussed.

Worldwide Selection Footprints for Drought and Heat in Bread Wheat (Triticum aestivum L.)

Genome–environment Associations (GEA) or Environmental Genome-Wide Association scans (EnvGWAS) have been poorly applied for studying the genomics of adaptive traits in bread wheat landraces (Triticum aestivum L.). We analyzed 990 landraces and seven climatic variables (mean temperature, maximum temperature, precipitation, precipitation seasonality, heat index of mean temperature, heat index of maximum temperature, and drought index) in GEA using the FarmCPU approach with GAPIT. Historical temperature and precipitation values were obtained as monthly averages from 1970 to 2000. Based on 26,064 high-quality SNP loci, landraces were classified into ten subpopulations exhibiting high genetic differentiation. The GEA identified 59 SNPs and nearly 89 protein-encoding genes involved in the response processes to abiotic stress. Genes related to biosynthesis and signaling are mainly mediated by auxins, abscisic acid (ABA), ethylene (ET), salicylic acid (SA), and jasmonates (JA), which are known to operate together in modulation responses to heat stress and drought in plants. In addition, we identified some proteins associated with the response and tolerance to stress by high temperatures, water deficit, and cell wall functions. The results provide candidate regions for selection aimed to improve drought and heat tolerance in bread wheat and provide insights into the genetic mechanisms involved in adaptation to extreme environments.

Effects of Phloem-Feeding Pest, Dalbulus maidis on Morphological Expression of Drought-Tolerant Traits in Maize

Drought is amongst the most important stressors affecting maize production globally. Existing strategies to offset drought impacts are centered around the rapid development of drought-tolerant cultivars through plant breeding. However, under both current conditions and projected climate changes, additional stressors such as insect pests will co-occur. To determine the impact of combined insect and drought stress on drought tolerance in maize, we assessed the effects of Dalbulus maidis, drought, and both stresses combined in drought-tolerant maize hybrids. We measured several maize morphological growth traits (i.e., plant height, stem diameter, shoot weight, root weight, root length, and root-to-shoot ratio) at the end of a 28-day period of pulse-stress and no-stress control exposure. We found that seedling growth declined when both stressors co-occurred. Nevertheless, drought-tolerant maize hybrids remained strongly tolerant to drought regardless of D. maidis infestation. While our results showed that drought tolerance is maintained in drought-tolerant maize seedlings, future studies should address any effects on maize yield. Our study highlights the importance of testing the combined effects of drought and insect stressors to better predict insect–plant interactions in the context of plant breeding for drought-tolerant traits in a changing climate.

Stress-Tolerant Endophytic Isolate Priestia aryabhattai BPR-9 Modulates Physio-Biochemical Mechanisms in Wheat (Triticum aestivum L.) for Enhanced Salt Tolerance

In efforts to improve plant productivity and enhance defense mechanisms against biotic and abiotic stresses, endophytic bacteria have been used as an alternative to chemical fertilizers and pesticides. In the current study, 25 endophytic microbes recovered from plant organs of Triticum aestivum L. (wheat) were assessed for biotic (phyto-fungal pathogens) and abiotic (salinity, drought, and heavy metal) stress tolerance. Among the recovered isolates, BPR-9 tolerated maximum salinity (18% NaCl), drought (15% PEG-6000), and heavy metals (µg mL-1): Cd (1200), Cr (1000), Cu (1000), Pb (800), and Hg (30). Based on phenotypic and biochemical characteristics, as well as 16S rDNA gene sequencing, endophytic isolate BPR-9 was recognized as Priestia aryabhattai (accession no. OM743254.1). This isolate was revealed as a powerful multi-stress-tolerant crop growth promoter after extensive in-vitro testing for plant growth-promoting attributes, nutrient (phosphate, P; potassium, K; and zinc, Zn) solubilization efficiency, extracellular enzyme (protease, cellulase, amylase, lipase, and pectinase) synthesis, and potential for antagonistic activity against important fungal pathogens viz. Alternaria solani, Rhizoctonia solani, Fusarium oxysporum, and Ustilaginoidea virens. At elevated salt levels, increases were noted in indole-3-acetic acid; siderophores; P, K, and Zn-solubilization; ACC deaminase; and ammonia synthesized by Priestia aryabhattai. Additionally, under in-vitro plant bioassays, wheat seedlings inoculated with P. aryabhattai experienced superior growth compared to non-inoculated seedlings in high salinity (0-15% NaCl) environment. Under NaCl stress, germination rate, plant length, vigor indices, and leaf pigments of wheat seedlings significantly increased following P. aryabhattai inoculation. Furthermore, at 2%-NaCl, B. aryabhattai greatly and significantly (p ≤ 0.05) decreased relative leaf water content, membrane damage, and electrolyte leakage compared with the non-inoculated control. Catalase, superoxide dismutase, and peroxidase activity increased by 29, 32, and 21%, respectively, in wheat seedlings exposed to 2% NaCl and inoculated with the bacteria. The present findings demonstrate that endophytic P. aryabhattai strains might be used in the future as a multi-stress reducer and crop growth promoter in agronomically important crops including cereals.

Using the Maize Nested Association Mapping (NAM) Population to Partition Arbuscular Mycorrhizal Effects on Drought Stress Tolerance into Hormonal and Hydraulic Components

In this study, a first experiment was conducted with the objective of determining how drought stress alters the radial water flow and physiology in the whole maize nested association mapping (NAM) population and to find out which contrasting maize lines should be tested in a second experiment for their responses to drought in combination with an arbuscular mycorrhizal (AM) fungus. Emphasis was placed on determining the role of plant aquaporins and phytohormones in the responses of these contrasting maize lines to cope with drought stress. Results showed that both plant aquaporins and hormones are altered by the AM symbiosis and are highly involved in the physiological responses of maize plants to drought stress. The regulation by the AM symbiosis of aquaporins involved in water transport across cell membranes alters radial water transport in host plants. Hormones such as IAA, SA, ABA and jasmonates must be involved in this process either by regulating the own plant-AM fungus interaction and the activity of aquaporins, or by inducing posttranscriptional changes in these aquaporins, which in turns alter their water transport capacity. An intricate relationship between root hydraulic conductivity, aquaporins and phytohormones has been observed, revealing a complex network controlling water transport in maize roots.

Significance of Arbuscular Mycorrhizal Fungi in Mitigating Abiotic Environmental Stress in Medicinal and Aromatic Plants: A Review

Medicinal and aromatic plants (MAPs) have been used worldwide for thousands of years and play a critical role in traditional medicines, cosmetics, and food industries. In recent years, the cultivation of MAPs has become of great interest worldwide due to the increased demand for natural products, in particular essential oils (EOs). Climate change has exacerbated the effects of abiotic stresses on the growth, productivity, and quality of MAPs. Hence, there is a need for eco-friendly agricultural strategies to enhance plant growth and productivity. Among the adaptive strategies used by MAPs to cope with the adverse effects of abiotic stresses including water stress, salinity, pollution, etc., their association with beneficial microorganisms such as arbuscular mycorrhizal fungi (AMF) can improve MAPs' tolerance to these stresses. The current review (1) summarizes the effect of major abiotic stresses on MAPs' growth and yield, and the composition of EOs distilled from MAP species; (2) reports the mechanisms through which AMF root colonization can trigger the response of MAPs to abiotic stresses at morphological, physiological, and molecular levels; (3) discusses the contribution and synergistic effects of AMF and other amendments (e.g., plant growth-promoting bacteria, organic or inorganic amendments) on MAPs' growth and yield, and the composition of distilled EOs in stressed environments. In conclusion, several perspectives are suggested to promote future investigations.

Gamma ray-induced tissue responses and improved secondary metabolites accumulation in Catharanthus roseus

The present study investigated the impact of gamma ray irradiation on callus biomass growth and the yield of vincristine and vinblastine of in vitro grown tissues of Catharanthus roseus. The biochemical alteration underlying the synthesis of secondary metabolites has also been studied and a comparison of yield was prepared. The embryogenic tissues were exposed to 20, 40, 60, 80, and 100 Gy gamma ray doses and the callus biomass fresh weight, the embryogenesis (the embryo numbers, germination, plant regeneration), the alteration of protein, proline, and sugar attributes at different morphogenetic stages were monitored. The callus biomass growth was maximum (1.65 g) in 20 Gy exposed tissues and was less in 100 Gy treatment (0.33 g). The gamma-irradiated embryogenic tissues differentiated into embryos but the embryogenesis % and somatic embryo number per culture reduced with increasing doses. It was least in 80 Gy where very low numbers of embryos were formed (3.45 and 3.30 mean torpedo and cotyledonary embryo numbers per callus mass, respectively) which later germinated into plantlets. Protein, proline, sugar, and different antioxidant enzymes, i.e., superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) activities, were investigated as the tissues were exposed to gamma ray elicitation/signaling, evoking cellular stress. Increased 80 Gy gamma dose inhibited a 42.73% decrease in protein accumulation at initiation stages of embryogenic tissue. Soluble sugar level also declined gradually being least in 80 Gy treated tissues (14.51 mg gm^-1 FW) compared to control (20.2 mg gm^-1 FW). Proline content, however, increased with increasing gamma doses, maximum at 80 Gy (8.28 mg gm^-1 FW). The SOD, APX, and CAT activity increased linearly with enhanced level of gamma doses and maximum, i.e., 3.91 EU min^-1 mg^-1, 1.71 EU min^-1 mg^-1, and 4.89 EU min^-1 mg^-1, protein activity was noted for SOD, APX, and CAT, respectively, at 80 Gy gamma rays treated tissues. The quantification of vinblastine and vincristine in gamma ray elicitated tissues was made by using high-pressure thin layer chromatography (HPTLC). Somatic embryo-regenerated plant's leaves had the maximum yield of vinblastine (15.13 µgm gm^-1 DW) at 40 Gy irradiation dose compared to control (13.30 µgm gm^-1 DW)-the increased yield % is 13.75. The stem is also rich source producing 11.98 µgm gm^-1 DW of vinblastine. Among the various developmental stages of embryos, vinblastine content was highest in germinating stage of embryos (10.14 µgm gm^-1 DW) compared to other three, i.e., initiation, proliferation, and maturation embryo stages. Similarly, highest accumulation of vincristine (6.32 µg gm^-1 DW) was noted at low gamma irradiation dose (20 Gy) in leaf tissues. The present study indicates that the synthesis of vinblastine and vincristine was growth- and development-specific and the lower 20-40 Gy gamma levels were more effective in enriching alkaloids while higher doses declined yield. KEY POINTS: • Vinblastine and vincristine yield was quantified in in vitro grown tissues and leaves of embryo regenerated Catharanthus roseus after gamma ray treatment. • The accumulation of vinblastine and vincristine was maximum in regenerated leaves; low doses were more efficient in improving yield. • Gamma ray irradiation impacted biochemical profiles, caused cellular stress, and perhaps responsible for improved alkaloid yield.

Effects of the Rhizosphere Fungus Cunninghamella bertholletiae on the Solanum lycopersicum Response to Diverse Abiotic Stresses

This study examined the efficiency of fungal strain (Cunninghamella bertholletiae) isolated from the rhizosphere of Solanum lycopersicum to reduce symptoms of salinity, drought and heavy metal stresses in tomato plants. In vitro evaluation of C. bertholletiae demonstrated its ability to produce indole-3-Acetic Acid (IAA), ammonia and tolerate varied abiotic stresses on solid media. Tomato plants at 33 days’ old, inoculated with or without C. bertholletiae, were treated with 1.5% sodium chloride, 25% polyethylene glycol, 3 mM cadmium and 3 mM lead for 10 days, and the impact of C. bertholletiae on plant performance was investigated. Inoculation with C. bertholletiae enhanced plant biomass and growth attributes in stressed plants. In addition, C. bertholletiae modulated the physiochemical apparatus of stressed plants by raising chlorophyll, carotenoid, glucose, fructose, and sucrose contents, and reducing hydrogen peroxide, protein, lipid metabolism, amino acid, antioxidant activities, and abscisic acid. Gene expression analysis showed enhanced expression of SlCDF3 and SlICS genes and reduced expression of SlACCase, SlAOS, SlGRAS6, SlRBOHD, SlRING1, SlTAF1, and SlZH13 genes following C. bertholletiae application. In conclusion, our study supports the potential of C. bertholletiae as a biofertilizer to reduce plant damage, improve crop endurance and remediation under stress conditions.

VaMYB44 transcription factor from Chinese wild Vitis amurensis negatively regulates cold tolerance in transgenic Arabidopsis thaliana and V. vinifera

Heterologous expression of VaMYB44 gene in Arabidopsis and V. vinifera cv. 'Thompson Seedless' increases cold sensitivity, which is mediated by the interaction of VaMYC2 and VaTIFY5A with VaMYB44 MYB transcription factors play critical roles in plant stress response. However, the function of MYB44 under low temperature stress is largely unknown in grapes. Here, we isolated a VaMYB44 gene from Chinese wild Vitis amurensis acc. 'Shuangyou' (cold-resistant). The VaMYB44 is expressed in various organs and has lower expression levels in stems and young leaves. Exposure of the cold-sensitive V. vinifera cv. 'Thompson Seedless' and cold-resistant 'Shuangyou' grapevines to cold stress (-1 °C) resulted in differential expression of MYB44 in leaves with the former reaching 14 folds of the latter after 3 h of cold stress. Moreover, the expression of VaMYB44 was induced by exogenous ethylene, abscisic acid, and methyl jasmonate in the leaves of 'Shuangyou'. Notably, the subcellular localization assay identified VaMYB44 in the nucleus. Interestingly, heterologous expression of VaMYB44 in Arabidopsis and 'Thompson Seedless' grape increased freezing-induced damage compared to their wild-type counterparts. Accordingly, the transgenic lines had higher malondialdehyde content and electrolyte permeability, and lower activities of superoxide dismutase, peroxidase, and catalase. Moreover, the expression levels of some cold resistance-related genes decreased in transgenic lines. Protein interaction assays identified VaMYC2 and VaTIFY5A as VaMYB44 interacting proteins, and VaMYC2 could bind to the VaMYB44 promoter and promote its transcription. In conclusion, the study reveals VaMYB44 as the negative regulator of cold tolerance in transgenic Arabidopsis and transgenic grapes, and VaMYC2 and VaTIFY5A are involved in the cold sensitivity of plants by interacting with VaMYB44.