Molecular Basis of Crops and Fruit Plants in Response to Stress.

This editorial summarizes the main scientific contributions from 11 papers comprising the Special Issue (SI) "Molecular Basis of Crops and Fruit Plants in Response to Stress". Here, we collected papers from different research groups encompassing molecular studies from monocots (ginger, rice, maize) and eudicots (common hazel, cowpea, pepper, soybean, tomato) species submitted to abiotic stresses as heat, cold, salt, drought, and heavy metals or biotic stresses induced by different viruses, such as BPEV, PepGMV, PMMoV, and TEV. These studies explored different aspects of molecular mechanisms involved in plant stress tolerance, establishing comparative analyses among genotypes/cultivars to identify potential molecular markers of stresses that are now available for future application in biotechnological studies. This SI presents a collection of advanced concepts and emerging strategies for readers and researchers aiming to accelerate plant breeding.

Magnesium supplementation alleviates drought damage during vegetative stage of soybean plants.

Our working hypothesis was that magnesium (Mg) supplementation modulates plant performance under low water availability and improves drought tolerance in soybean genotypes. Plants of Bônus 8579, M8808 and TMG1180 genotypes were grown under field conditions and subjected to three water stress treatments (control, moderate and severe stress) and three Mg levels [0.9 (low), 1.3 (adequate) and 1.7 cmolc dm-³ (supplementation)]. After 28 days of drought imposition, the growth parameters, osmotic potential, relative water content, leaf succulence, Mg content and photosynthetic pigments were assessed. In general, drought drastically decreased the growth in all genotypes, and the reductions were intensified from moderate to severe stress. Under adequate Mg supply, TMG1180 was the most drought-tolerant genotype among the soybean plants, but Mg supplementation did not improve its tolerance. Conversely, although the M8808 genotype displayed inexpressive responses to drought under adequate Mg, the Mg-supplemented plants were found to have surprisingly better growth performance under stress compared to Bônus 8579 and TMG1180, irrespective of drought regime. The improved growth of high Mg-treated M8808-stressed plants correlated with low osmotic potential and increased relative water content, as well as shoot Mg accumulation, resulting in increased photosynthetic pigments and culminating in the highest drought tolerance. The results clearly indicate that Mg supplementation is a potential tool for alleviating water stress in M8808 soybean plants. Our findings suggest that the enhanced Mg-induced plant acclimation resulted from increased water content in plant tissues and strategic regulation of Mg content and photosynthetic pigments.

Genome and Transcriptome Analyses of Genes Involved in Ascorbate Biosynthesis in Pepper Indicate Key Genes Related to Fruit Development, Stresses, and Phytohormone Exposures.

Pepper (Capsicum annuum L.) is a vegetable consumed worldwide, primarily used for vitamin C uptake and condiment purposes. Ascorbate (Asc) is a multifunctional metabolite, acting as an antioxidant and enzymatic cofactor involved in multiple cellular processes. Nevertheless, there is no evidence about the contribution of biosynthesis pathways and regulatory mechanisms responsible for Asc reserves in pepper plants. Here, we present a genome- and transcriptome-wide investigation of genes responsible for Asc biosynthesis in pepper during fruit development, stresses, and phytohormone exposures. A total of 21 genes, scattered in ten of twelve pepper chromosomes were annotated. Gene expression analyses of nine transcriptomic experiments supported the primary role of the L-galactose pathway in the Asc-biosynthesizing process, given its constitutive, ubiquitous, and high expression profile observed in all studied conditions. However, genes from alternative pathways generally exhibited low expression or were unexpressed and appeared to play some secondary role under specific stress conditions and phytohormone treatments. Taken together, our findings provide a deeper spatio-temporal understanding of expression levels of genes involved in Asc biosynthesis, and they highlight GGP2, GME1 and 2, and GalLDH members from L-galactose pathway as promising candidates for future wet experimentation, addressing the attainment of increase in ascorbate content of peppers and other crops.

Selection of Soybean and Cowpea Cultivars with Superior Performance under Drought Using Growth and Biochemical Aspects.

Identifying cultivars of leguminous crops exhibiting drought resistance has become crucial in addressing water scarcity issues. This investigative study aimed to select soybean and cowpea cultivars with enhanced potential to grow under water restriction during the vegetative stage. Two parallel trials were conducted using seven soybean (AS3810IPRO, M8644IPRO, TMG1180RR, NS 8338IPRO, BMX81I81IPRO, M8808IPRO, and BÔNUS8579IPRO) and cowpea cultivars (Aracê, Novaera, Pajeú, Pitiúba, Tumucumaque, TVU, and Xique-xique) under four water levels (75, 60, 45, and 30% field capacity-FC) over 21 days. Growth, water content, membrane damage, photosynthetic pigments, organic compounds, and proline levels were analyzed. Drought stress significantly impacted the growth of both crops, particularly at 45 and 30% FC for soybean and 60 and 45% FC for cowpea plants. The BÔNUS8579IPRO and TMG1180RR soybean cultivars demonstrated the highest performance under drought, a response attributed to increased amino acids and proline contents, which likely help to mitigate membrane damage. For cowpea, the superior performance of the drought-stressed Xique-xique cultivar was associated with the maintenance of water content and elevated photosynthetic pigments, which contributed to the preservation of the photosynthetic efficiency and carbohydrate levels. Our findings clearly indicate promising leguminous cultivars that grow under water restriction, serving as viable alternatives for cultivating in water-limited environments.

Soil and foliar Si fertilization alters elemental stoichiometry and increases yield of sugarcane cultivars.

Silicon (Si) fertilization is widely recognized to improve the development of crops, especially in tropical soils and cultivation under dryland management. Herein, our working hypothesis was that Si stoichiometry favors the efficient use of carbon (C), nitrogen (N), and phosphorus (P) in sugarcane plants. Therefore, a field experiment was carried out using a 3 × 3 factorial scheme consisting of three cultivars (RB92579, RB021754 and RB036066) and three forms of Si application (control without Si; sodium silicate spray at 40 mmol L-1 in soil during planting; sodium silicate spray at 40 mmol L-1 on leaves at 75 days after emergence). All Si fertilizations altered the elemental C and P stoichiometry and sugarcane yield, but silicon-induced responses varied depending on sugarcane cultivar and application method. The most prominent impacts were found in the leaf Si-sprayed RB92579 cultivar, with a significant increase of 7.0% (11 Mg ha-1) in stalk yield, 9.0% (12 Mg ha-1) in total recoverable sugar, and 20% (4 Mg ha-1) in sugar yield compared to the Si-without control. In conclusion, our findings clearly show that silicon soil and foliar fertilization alter C:N:P stoichiometry by enhancing the efficiency of carbon and phosphorus utilization, leading to improved sugarcane production and industrial quality.

Macro and Micro-Nutrient Accumulation and Partitioning in Soybean Affected by Water and Nitrogen Supply.

This study aimed to investigate the influence of water availability and nitrogen fertilization on plant growth, nutrient dynamics, and variables related to soybean crop yield. Trials were performed in Teresina, Piauí, Brazil, using randomized blocks in a split-split plot arrangement. The plots corresponded to water regimes (full and deficient), the split plots to N fertilization (0 and 1000 kg ha-1 N-urea), and the split-split plots to harvest times of soybean plants (16, 23, 30, 37, 44, 58, 65, 79 and 86 days after emergence), with three replicates. In general, the accumulation and partitioning of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn) and boron (B) were decreased in plants subjected to water deficit and without N fertilization. Although nitrogen fertilization promoted elevated N accumulation in tissues, it did not result in any significant yield gain, and the highest seed yields were found in plants under full irrigation, regardless of N supplementation. However, deficient irrigation decreased the seed oil content of N-fertilized plants. In conclusion, N fertilization is critical for nutrient homeostasis, and water availability impairs biomass and nutrient accumulation, thereby limiting soybean yield performance.

New insights into molecular targets of salt tolerance in sorghum leaves elicited by ammonium nutrition.

This study investigated the proteome modulation and physiological responses of Sorghum bicolor plants grown in nutrient solutions containing nitrate (NO3-) or ammonium (NH4+) at 5.0 mM, and subjected to salinity with 75 mM NaCl for ten days. Salinity promoted significant reductions in leaf area, root and shoot dry mass of sorghum plants, regardless of nitrogen source; however, higher growth was observed in ammonium-grown plants. The better performance of ammonium-fed stressed plants was associated with low hydrogen peroxide accumulation, and improved CO2 assimilation and K+/Na+ homeostasis under salinity. Proteomic study revealed a nitrogen source-induced differential modulation in proteins related to photosynthesis/carbon metabolism, energy metabolism, response to stress and other cellular processes. Nitrate-fed plants induced thylakoidal electron transport chain proteins and structural and carbon assimilation enzymes, but these mechanisms seemed to be insufficient to mitigate salt damage in photosynthetic performance. In contrast, the greater tolerance to salinity of ammonium-grown plants may have arisen from: i.) de novo synthesis or upregulation of enzymes from photosynthetic/carbon metabolism, which resulted in better CO2 assimilation rates under NaCl-stress; ii.) activation of proteins involved in energy metabolism which made available energy for salt responses, most likely by proton pumps and Na+/H+ antiporters; and iii.) reprogramming of proteins involved in response to stress and other metabolic processes, constituting intricate pathways of salt responses. Overall, our findings not only provide new insights of molecular basis of salt tolerance in sorghum plants induced by ammonium nutrition, but also give new perspectives to develop biotechnological strategies to generate more salt-tolerant crops.

Salt acclimation in sorghum plants by exogenous proline: physiological and biochemical changes and regulation of proline metabolism.

KEY MESSAGE: Mitigation of deleterious effects of salinity promoted by exogenous proline can be partially explained by changes in proline enzymatic metabolism and expression of specific proline-related genes. Proline accumulation is a usual response to salinity. We studied the ability of exogenous proline to mitigate the salt harmful effects in sorghum (Sorghum bicolor) leaves. Ten-day-old plants were cultivated in Hoagland's nutrient solution in either the absence or presence of salinity (NaCl at 75 mM) and sprayed with distilled water or 30 mM proline solution. Salinity deleterious effects were alleviated by exogenous proline 14 days after treatment, with a return in growth and recovery of leaf area and photosynthetic parameters. Part of the salinity response reflected an improvement in ionic homeostasis, provided by reduction in Na+ and Cl- ions and increases in K+ and Ca2+ ions as well as increases of compatible solutes. In addition, the application of proline decreased membrane damage and did not increase relative water content. Proline-treated salt-stressed plants displayed increase in proline content, a response counterbalanced by punctual modulation in proline synthesis (down-regulation of Δ1-pyrroline-5-carboxylate synthetase activity) and degradation (up-regulation of proline dehydrogenase activity) enzymes. These responses were correlated with expression of specific proline-related genes (p5cs1 and prodh). Our findings clearly show that proline treatment results in favorable changes, reducing salt-induced damage and improving salt acclimation in sorghum plants.

Optimized acid hydrolysis of the polysaccharides from the seaweed Solieria filiformis (Kützing) P.W. Gabrielson for bioethanol production / Hidrólise ácida otimizada dos polissacarídeos da macroalga Solieria filiformis (Kützing) P.W. Gabrielson para produção de bioetanol

The seaweeds are bio-resource rich in sulfated and neutral polysaccharides. The tropical seaweed species used in this study (Solieria filiformis), after dried, shows 65.8% (w/w) carbohydrate, 9.6% (w/w) protein, 1.7% (w/w) lipid, 7.0% (w/w) moisture and 15.9% (w/w) ash. The dried seaweed was easily hydrolyzed under mild conditions (0.5 M sulfuric acid, 20 min.), generating fermentable monosaccharides with a maximum hydrolysis efficiency of 63.21%. Galactose and glucose present in the hydrolyzed were simultaneously fermented by Saccharomyces cerevisiae when the yeast was acclimated to galactose and cultivated in broth containing only galactose. The kinetic parameters of the fermentation of the seaweed hydrolyzed were Y(P/S) = 0.48 ± 0.02 g.g−1, PP = 0.27 ± 0.04 g.L−1.h−1, η = 94.1%, representing a 41% increase in bioethanol productivity. Therefore, S. filiformis was a promising renewable resource of polysaccharides easily hydrolyzed, generating a broth rich in fermentable monosaccharides for ethanol production.

As algas marinhas são recursos naturais ricos em polissacarídeos sulfatados e neutros. A espécie de macroalga tropical utilizada neste estudo (Solieria filiformis) apresentou teores de carboidratos de 65,8% (m/m), proteínas de 9,6% (m/m), lipídios de 1,7% (m/m), umidade de 7,0% (m/m) e 15,9 % (m/m) de cinzas. A macroalga seca foi facilmente hidrolisada em condições brandas, na presença de ácido sulfúrico 0,5 M, por 20 min, produzindo monossacarídeos fermentáveis com uma eficiência de hidrólise máxima de 63,21%. A galactose e a glicose presentes no hidrolisado foram fermentadas simultaneamente por Saccharomyces cerevisiae, após aclimatação da levedura cultivada em meio contendo apenas galactose como fonte de carbono. Os parâmetros cinéticos da fermentação do hidrolisado algáceo pela levedura aclimatada a galactose foram Y(P/S) = 0,48 ± 0,02 g.g-1, PP = 0,27 ± 0,04 g.L- 1.h-1, η = 94,1%. Portanto, a macroalga S. filiformis se mostrou um recurso renovável promissor como fonte de polissacarídeos facilmente hidrolisados, gerando um meio nutritivo rico em glucose e galactose para a produção de etanol.

Putative role of glutamine in the activation of CBL/CIPK signalling pathways during salt stress in sorghum.

The salt overly sensitive (SOS) pathway is the only mechanism known for Na+ extrusion in plant cells. SOS pathway activation involves Ca2+-sensing proteins, such as calcineurin B-like (CBL) proteins, and CBL-interacting protein kinases (CIPKs). In this signalling mechanism, a transit increase in cytosolic Ca2+ concentration triggered by Na+ accumulation is perceived by CBL (also known as SOS3). Afterward, SOS3 physically interacts with a CIPK (also known as SOS2), forming the SOS2/SOS3 complex, which can regulate the number downstream targets, controlling ionic homeostasis. For instance, the SOS2/SOS3 complex phosphorylates and activates the SOS1 plasmalemma protein, which is a Na+/H+ antiporter that extrudes Na+ out of the cell. The CBL-CIPK networking system displays specificity, complexity and diversity, constituting a critical response against salt stress and other abiotic stresses. In a study reported in the journal Plant and Cell Physiology, we showed that NH4+ induces the robust activation of transporters for Na+ homeostasis in root cells, especially the SOS1 antiporter and plasma membrane H+-ATPase, differently than does NO3-. Despite some studies having shown that external NH4+ ameliorates salt-induced effects on ionic homeostasis, there is no evidence that NH4+ per se or some product of its assimilation is responsible for these responses. Here, we speculate about the signalling role behind glutamine in CBL-CIPK modulation, which could effectively activate the SOS pathway in NH4+-fed stressed plants.

Exogenous nitric oxide improves salt tolerance during establishment of Jatropha curcas seedlings by ameliorating oxidative damage and toxic ion accumulation.

Jatropha curcas is an oilseed species that is considered an excellent alternative energy source for fossil-based fuels for growing in arid and semiarid regions, where salinity is becoming a stringent problem to crop production. Our working hypothesis was that nitric oxide (NO) priming enhances salt tolerance of J. curcas during early seedling development. Under NaCl stress, seedlings arising from NO-treated seeds showed lower accumulation of Na+ and Cl- than those salinized seedlings only, which was consistent with a better growth for all analyzed time points. Also, although salinity promoted a significant increase in hydrogen peroxide (H2O2) content and membrane damage, the harmful effects were less aggressive in NO-primed seedlings. The lower oxidative damage in NO-primed stressed seedlings was attributed to operation of a powerful antioxidant system, including greater glutathione (GSH) and ascorbate (AsA) contents as well as catalase (CAT) and glutathione reductase (GR) enzyme activities in both endosperm and embryo axis. Priming with NO also was found to rapidly up-regulate the JcCAT1, JcCAT2, JcGR1 and JcGR2 gene expression in embryo axis, suggesting that NO-induced salt responses include functional and transcriptional regulations. Thus, NO almost completely abolished the deleterious salinity effects on reserve mobilization and seedling growth. In conclusion, NO priming improves salt tolerance of J. curcas during seedling establishment by inducing an effective antioxidant system and limiting toxic ion and reactive oxygen species (ROS) accumulation.

Integrative Control Between Proton Pumps and SOS1 Antiporters in Roots is Crucial for Maintaining Low Na+ Accumulation and Salt Tolerance in Ammonium-Supplied Sorghum bicolor.

An effective strategy for re-establishing K+ and Na+ homeostasis is a challenge for the improvement of plant performance in saline soil. Specifically, attempts to understand the mechanisms of Na+ extrusion from plant cells, the control of Na+ loading in the xylem and the partitioning of the accumulated Na+ between different plant organs are ongoing. Our goal was to provide insight into how an external nitrogen source affects Na+ accumulation in Sorghum bicolor under saline conditions. The NH4+ supply improved the salt tolerance of the plant by restricting Na+ accumulation and improving the K+/Na+ homeostasis in shoots, which was consistent with the high activity and expression of Na+/H+ antiporters and proton pumps in the plasma membrane and vacuoles in the roots, resulting in low Na+ loading in the xylem. Conversely, although NO3--grown plants had exclusion and sequestration mechanisms for Na+, these responses were not sufficient to reduce Na+ accumulation. In conclusion, NH4+ acts as an efficient signal to activate co-ordinately responses involved in the regulation of Na+ homeostasis in sorghum plants under salt stress, which leads to salt tolerance.