RNAseq Analysis Reveals Altered Expression of Key Ion Transporters Causing Differential Uptake of Selective Ions in Canola (Brassica napus L.) Grown under NaCl Stress

The efficiency of chlorophyll fluorescence as a selection criterion for salinity and climate aridity tolerance in barley genotypes

Introduction

In the Near East and North Africa (NENA) region, crop production is being affected by various abiotic factors, including freshwater scarcity, climate, and soil salinity. As a result, farmers in this region are in search of salt-tolerant crops that can thrive in these harsh environments, using poor-quality groundwater. The main staple food crop for most of the countries in this region, Tunisia included, is barley.

Methods

The present study was designed to investigate the sensitivity and tolerance of six distinct barley genotypes to aridity and salinity stresses in five different natural field environments by measuring their photosynthetic activity.

Results and discussion

The results revealed that tolerant genotypes were significantly less affected by these stress factors than sensitive genotypes. The genotypes that were more susceptible to salinity and aridity stress exhibited a significant decline in their photosynthetic activity. Additionally, the fluorescence yields in growth phases J, I, and P declined significantly in the order of humid environment (BEJ), semi-arid site (KAI), and arid environment (MED) and became more significant when salt stress was added through the use of saline water for irrigation. The stress adversely affected the quantum yield of primary photochemistry (φP0), the quantum yield of electron transport (φE0), and the efficiency by trapped excitation (ψ0) in the vulnerable barley genotypes. Moreover, the performance index (PI) of the photosystem II (PSII) was found to be the most distinguishing parameter among the genotypes tested. The PI of sensitive genotypes was adversely affected by aridity and salinity. The PI of ICARDA20 and Konouz decreased by approximately 18% and 33%, respectively, when irrigated with non-saline water. The reduction was even greater, reaching 39%, for both genotypes when irrigated with saline water. However, tolerant genotypes Souihli and Batini 100/1B were less impacted by these stress factors.The fluorescence study provided insights into the photosynthetic apparatus of barley genotypes under stress. It enabled reliable salinity tolerance screening. Furthermore, the study confirmed that the chlorophyll a fluorescence induction curve had an inflection point (step K) even before the onset of visible signs of stress, indicating physiological disturbances, making chlorophyll fluorescence an effective tool for identifying salinity tolerance in barley.

Transcriptomic analysis reveals candidate genes associated with salinity stress tolerance during the early vegetative stage in fababean genotype, Hassawi-2

Abiotic stresses are a significant constraint to plant production globally. Identifying stress-related genes can aid in the development of stress-tolerant elite genotypes and facilitate trait and crop manipulation. The primary aim of this study was to conduct whole transcriptome analyses of the salt-tolerant faba bean genotype, Hassawi-2, under different durations of salt stress (6 h, 12 h, 24 h, 48 h, and 72 h) at the early vegetative stage, to better understand the molecular basis of salt tolerance. After de novo assembly, a total of 140,308 unigenes were obtained. The up-regulated differentially expressed genes (DEGs) were 2380, 2863, 3057, 3484, and 4820 at 6 h, 12 h, 24 h, 48 h, and 72 h of salt stress, respectively. Meanwhile, 1974, 3436, 2371, 3502, and 5958 genes were downregulated at 6 h, 12 h, 24 h, 48 h, and 72 h of salt stress, respectively. These DEGs encoded various regulatory and functional proteins, including kinases, plant hormone proteins, transcriptional factors (TFs) basic helix-loop-helix (bHLH), Myeloblastosis (MYB), and (WRKY), heat shock proteins (HSPs), late embryogenesis abundant (LEA) proteins, dehydrin, antioxidant enzymes, and aquaporin proteins. This suggests that the faba bean genome possesses an abundance of salinity resistance genes, which trigger different adaptive mechanisms under salt stress. Some selected DEGs validated the RNA sequencing results, thus confirming similar gene expression levels. This study represents the first transcriptome analysis of faba bean leaves subjected to salinity stress offering valuable insights into the mechanisms governing salt tolerance in faba bean during the vegetative stage. This comprehensive investigation enhances our understanding of precise gene regulatory mechanisms and holds promise for the development of novel salt-tolerant faba bean salt-tolerant cultivars.

Photosynthesis and Salt Exclusion Are Key Physiological Processes Contributing to Salt Tolerance of Canola (Brassica napus L.): Evidence from Physiology and Transcriptome Analysis

Plant salt tolerance is controlled by various physiological processes such as water and ion homeostasis, photosynthesis, and cellular redox balance, which are in turn controlled by gene expression. In the present study, plants of six canola cultivars (DGL, Dunkled, Faisal Canola, Cyclone, Legend, and Oscar) were evaluated for salt tolerance by subjecting them to 0 or 200 mM NaCl stress. Based on growth, cultivars DGL, Dunkled, and Faisal Canola were ranked as salt tolerant, while cultivars Cyclone, Legend, and Oscar were ranked as salt-sensitive ones. Differential salt tolerance in these canola cultivars was found to be associated with a relatively lower accumulation of Na⁺ and greater accumulation of K⁺ in the leaves, lower oxidative damage (MDA), and better antioxidative defense system (Superoxide dismutase, SOD; peroxidase, POD, and catalase, CAT). Cultivar Oscar was the poorest to discriminate Na⁺ and K⁺ uptake and accumulation in leaves and had poor antioxidant potential to scavenge ROS. Salt stress did not affect the structural stability of photosystem-II (PSII) till three weeks, thereafter it caused a significant decrease. Salt stress increased the performance index (PI_ABS) by increasing the density of active reaction centers in Oscar. Salt stress decreased the antenna size thereby lowering the absorption and trapping energy flux, and maintaining the electron transport with an increase in heat dissipation. This may represent a potential mechanism to cope with salt stress. Transcriptome analysis of salt-sensitive cultivar Oscar further revealed that salt stress down-regulated DEGs related to hormonal signal transduction pathways, photosynthesis, and transcription factors, while DEGs related to the biosynthesis of amino acid and ion transport were up-regulated. In conclusion, salt tolerance in canola cultivars was associated with ion exclusion and maintenance of photosynthesis. Salt stress sensitivity in cultivar Oscar was mainly associated with poor control of ion homeostasis which caused oxidative stress and reduced photosynthetic efficiency.

Comparative genetic, biochemical and physiological analysis of sodium and chlorine in wheat

Plant with a great diversity shows several responses towards the biotic and abiotic stresses. Among these abiotic stresses, salinity is the main damaging factor as it reduces the yield of wheat plant with moderate salt tolerance. For its survival, plant undergoes through some genetic, biochemical and physiological changes to tackle the stress. This review mainly describes the conditions where various ions present in the soil, especially sodium and chlorine, enter into the plant and the genes or proteins involved with survival mechanism against the damage in plants. Salt stress causes alteration in enzymatic activity and Photosynthesis, oxidative stress, damage of cellular structure and components and ionic imbalance. Ion toxicity stress occur due to accumulation of excessive sodium ion and chloride ion. Transcriptional factors TaPIMP, TaSRG and TaMYBsdu 1 play key role in gene expression mechanism to overcome the stress. High affinity potassium transporter gene family is responsible for salt tolerance in wheat plant. HKT1;4 and HKT1;5 genes are responsible for Na exclusion in Triticum monococcum. Forty QTLs were found with the marker assisted selection in bread wheat for salinity tolerance and some morphological traits, 5 QTLs were related to sodium ion exclusion. In bread wheat, salt stress tolerance mechanism is mainly an exclusion of Na⁺ ions but also include K⁺ ion concentration. The salinity tolerant germplasm MW#293 provides an opportunity for the development of future salinity tolerant bread wheat.

Transcriptomic and Metabolomic Analyses Reveal the Differential Regulatory Mechanisms of Compound Material on the Responses of Brassica campestris to Saline and Alkaline Stresses

Oilseed rape not only has the function of improve saline and alkaline soils, but also alleviate the local feed shortage. However, medium- and high-degree soil salinization and alkalinization always inhibit the growth of oilseed rape. Studies have shown that compound material can improve the tolerance to saline and alkaline stress of crops, but the difference in the regulation mechanism of compound material on oilseed rape in saline and alkaline soils is not clear. This study explored the difference through determining the leaf ion contents, physiological indexes, transcriptomics, and metabolomics of oilseed rape in salinized soil (NaCl 8 g kg^-1) and alkalinized soil (Na₂CO₃ 8 g kg^-1) at full flowering stage, respectively after the application of compound material. The results showed that in salinized and alkalinized soil, the compound material upregulated the genes related to the regulation of potassium ion transport, and changed the amino acid metabolic pathway, which reduced the contents of Na⁺, malondialdehyde (MDA), and relative conductivity (REC) in leaves, and increased the contents of K⁺ and Mg²⁺ and the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). However, there were differences in the regulation mechanism of compound material in salinized and alkalinized soil. In salinized soil, the compound material improved the tolerance of oilseed rape to saline stress by upregulating transcription factors mannose-1-phosphate guanylyltransferase (GPMM) and Glutamine--fructose-6-phosphate transaminase (GFPT) and downregulating phosphomannomutase (PMM) to change nucleotide metabolism pathway and lipid metabolism pathway. In alkalized soil, the compound material improved the tolerance of oilseed rape to alkaline stress by upregulating transcription factors Phenylalanine ammonia lyase (PAL) to change the biosynthesis pathway of other secondary metabolites. Therefore, the compound material can improve the tolerance of oilseed rape to saline and alkaline stress by regulating the genetic adaptability and apparent plasticity, but the mechanisms were different. This study provides a practical method for the ecological environment restoration and the development of animal husbandry.

Potassium signaling in plant abiotic responses: Crosstalk with calcium and reactive oxygen species/reactive nitrogen species

Potassium ion (K⁺) has been regarded as an essential signaling in plant growth and development. K⁺ transporters and channels at transcription and protein levels have been made great progress. K⁺ can enhance plant abiotic stress resistance. Meanwhile, it is now clear that calcium (Ca²⁺), reactive oxygen species (ROS), and reactive nitrogen species (RNS) act as signaling molecules in plants. They regulate plant growth and development and mediate K⁺ transport. However, the interaction of K⁺ with these signaling molecules remains unclear. K⁺ may crosstalk with Ca²⁺ and ROS/RNS in abiotic stress responses in plants. Also, there are interactions among K⁺, Ca²⁺, and ROS/RNS signaling pathways in plant growth, development, and abiotic stress responses. They regulate ion homeostasis, antioxidant system, and stress resistance-related gene expression in plants. Future work needs to focus on the deeper understanding of molecular mechanism of crosstalk among K⁺, Ca²⁺, and ROS/RNS under abiotic stress.

Rapid Response Indicators for Predicting Changes in Soil Properties Due to Solarization or Biosolarization on an Intensive Horticultural Crop in Semiarid Regions

Agriculture practices developed since the middle of the last century have led to the degradation of different resources and made it necessary to promote agricultural models that are less aggressive towards nature. Sustainable agricultural growth requires a more efficient use of land. An experimental model was designed with four treatments in the Campo de Cartagena area (SE Spain): biosolarization with manure (BSM), biosolarization with brassicas (BB), solarization (S), and a pilot test (PT). The general objective was to determine by means of rapid response indicators the changes occurring in soil properties as a consequence of the implementation of these solarization or biosolarization practices and their influence on the quality and yield of a lettuce crop. The results show that there was no significant response in the physical and biological properties of the soil. Physicochemical properties such as pHw, and electrical conductivity (ECe), as well as chemicals such as total nitrogen (TN) and the content of some macro and micronutrients, can be considered as rapid response indicators. The highest yields (Yc) and highest commercial quality (Mc) of lettuce were obtained in the BB and BSM treatments (Yc > 23,000 kg ha−1; Mc > 413 g). These treatments resulted in biological NO3− sequestration and, in the case of BB, salt immobilization (ECe: 6 dS m−1). According to these results, BSM and BB can be recommended for sustainable agriculture and even as valid methods for the recovery of soils affected by salts and NO3−. Our results should increase the feasibility of these techniques in semiarid areas.

Adaptation Strategies to Improve the Resistance of Oilseed Crops to Heat Stress Under a Changing Climate: An Overview

Temperature is one of the decisive environmental factors that is projected to increase by 1. 5°C over the next two decades due to climate change that may affect various agronomic characteristics, such as biomass production, phenology and physiology, and yield-contributing traits in oilseed crops. Oilseed crops such as soybean, sunflower, canola, peanut, cottonseed, coconut, palm oil, sesame, safflower, olive etc., are widely grown. Specific importance is the vulnerability of oil synthesis in these crops against the rise in climatic temperature, threatening the stability of yield and quality. The natural defense system in these crops cannot withstand the harmful impacts of heat stress, thus causing a considerable loss in seed and oil yield. Therefore, a proper understanding of underlying mechanisms of genotype-environment interactions that could affect oil synthesis pathways is a prime requirement in developing stable cultivars. Heat stress tolerance is a complex quantitative trait controlled by many genes and is challenging to study and characterize. However, heat tolerance studies to date have pointed to several sophisticated mechanisms to deal with the stress of high temperatures, including hormonal signaling pathways for sensing heat stimuli and acquiring tolerance to heat stress, maintaining membrane integrity, production of heat shock proteins (HSPs), removal of reactive oxygen species (ROS), assembly of antioxidants, accumulation of compatible solutes, modified gene expression to enable changes, intelligent agricultural technologies, and several other agronomic techniques for thriving and surviving. Manipulation of multiple genes responsible for thermo-tolerance and exploring their high expressions greatly impacts their potential application using CRISPR/Cas genome editing and OMICS technology. This review highlights the latest outcomes on the response and tolerance to heat stress at the cellular, organelle, and whole plant levels describing numerous approaches applied to enhance thermos-tolerance in oilseed crops. We are attempting to critically analyze the scattered existing approaches to temperature tolerance used in oilseeds as a whole, work toward extending studies into the field, and provide researchers and related parties with useful information to streamline their breeding programs so that they can seek new avenues and develop guidelines that will greatly enhance ongoing efforts to establish heat stress tolerance in oilseeds.

Foliar Application of Potassium Mitigates Salinity Stress Conditions in Spinach (Spinacia oleracea L.) through Reducing NaCl Toxicity and Enhancing the Activity of Antioxidant Enzymes

Agronomic biofortification is the purposeful utilization of mineral fertilizers to increase the concentration of desired minerals in edible plant parts for enhancing their dietary intake. It is becoming crucial to enhance the dietary intake of K for addressing hidden hunger and related health issues such as cardiac diseases and hypertension. This study was designed to enhance the potassium concentration in edible parts of spinach through its foliar application under saline environment. The salinity levels of electrical conductivity (EC) = 4, 6, and 8 dS m−1 were applied using sodium chloride (NaCl) along with control. The levels of K for foliar sprays were 5 and 10 mM, along with control. The present experiment was performed under two factorial arrangements in a completely randomized design (CRD). After 60 days of sowing, the crop was harvested. Data regarding growth, ionic, physiological, and biochemical parameters, i.e., shoot dry weight, relative water content, electrolyte leakage, total chlorophyll content, tissue sodium (Na) and K concentration, activities of superoxide dismutase (SOD), and catalase (CAT) were recorded and those were found to be significantly (p ≤ 0.05) affected by foliar application of K on spinach under saline conditions. The highest growth, physiological and biochemical responses of spinach were observed in response to foliar-applied K at 10 mM. It is concluded that agronomic bio-fortification by foliar use of K can be a useful strategy to increase tissue K intakes and minimize Na toxicity in the vegetables studied under saline conditions.

Seed priming with proline improved photosystem II efficiency and growth of wheat (Triticum aestivum L.)

BACKGROUND

Proline can promote growth of plants by increasing photosynthetic activity under both non-stress and abiotic stress conditions. However, its role in non-stressed conditions is least studied. An experiment was conducted to assess as to whether increase in growth of wheat due to seed priming with proline under non-stress condition was associated with proline-induced changes in photosystem II (PSII) activity. Seeds of four wheat varieties (S-24, Sehar-06, Galaxy-13, and Pasban-90) were primed with different concentrations of proline (0, 5, 15 and 25 mM) for 12 h and allowed to grow under normal conditions. Biomass accumulation and photosynthetic performance, being two most sensitive features/indicators of plant growth, were selected to monitor proline modulated changes.

RESULTS

Seed priming with proline increased the fresh and dry weights of shoots and roots, and plant height of all four wheat varieties. Maximum increase in growth attributes was observed in all four wheat varieties at 15 mM proline. Maximum growth improvement due to proline was found in var. Galaxy-13, whereas the reverse was true for S-24. Moreover, proline treatment changed the Fo, Fm, Fv/Fo, PI_ABS, PI_Tot in wheat varieties indicating changes in PSII activity. Proline induced changes in energy fluxes for absorption, trapping, electron transport and heat dissipation per reaction center indicated that var. Galaxy-13 had better ability to process absorbed light energy through photosynthetic machinery. Moreover, lesser PSII efficiency in var. S-24 was due to lower energy flux for electron transport and greater energy flux for heat dissipation. This was further supported by the fact that var. S-24 had disturbance at acceptor side of PSI as reflected by reduction in ΔV_IP, probability and energy flux for electron transport at the PSI end electron acceptors.

CONCLUSION

Seed priming with proline improved the growth of wheat varieties, which depends on type of variety and concentration of proline applied. Seed priming with proline significantly changed the PSII activity in wheat varieties, however, its translation in growth improvement depends on potential of processing of absorbed light energy by electron acceptors of electron transport chain, particularly those present at PSI end.

Identification of novel source of salt tolerance in local bread wheat germplasm using morpho-physiological and biochemical attributes

Salt tolerant wheat cultivars may be used as genetic resource for wheat breeding to ensure yield stability in future. The study was aimed to select salt tolerant cultivar(s) to identify novel source of salt tolerance in local wheat germplasm. Initially, 40 local wheat cultivars were screened at 150 mM NaCl stress at seedling stage. Selected salt-tolerant (three; S-24, LU-26S and Pasban-90) and salt-sensitive (four; MH-97, Kohistan-97, Inqilab-91 and Iqbal-2000) wheat cultivars were further evaluated using growth, yield, biochemical and physiological attributes. Growth and yield of selected cultivars were reduced under salt stress due to decline in plant water status, limited uptake of macronutrients (N, P and K), reduced K⁺/Na⁺ ratio, photosynthetic pigments and quantum yield of PSII. Wheat plants tried to acclimate salt stress by osmotic adjustment (accumulation of total soluble sugars, proline and free amino acids). Degree of salinity tolerance in cvs. S-24 and LU-26S found to be associated with maintenance of K⁺/Na⁺ ratio, osmo-protectant and photosynthetic activity and can be used as donor for salt tolerance in wheat breeding program at least in Pakistan. These cultivars can be further characterized using molecular techniques to identify QTLs/genes for salt exclusion, osmo-protectant and photosynthetic activity for molecular breeding.