Under saline conditions, plants consistently maintain cytosolic Na+ concentrations between 10 and 30 mM, sequestering excess Na+ to the vacuole. We demonstrate that this cytosolic Na+ homeostasis is regulated by inward Na+-permeable channels and outward Na+:H+ antiporters at both the plasma membrane and tonoplast. Sodium's interplay with K+ transport adds complexity and selective transport is crucial to avoid conflicting ion fluxes. Our models predict that Na+:H+ antiport regulation at the plasma membrane significantly impacts cytosolic Na+ levels, while channel and antiport regulation are equally important at the tonoplast. The energetic implications of these transport mechanisms are discussed. In contrast to the cytosol, chloroplast Na+ concentrations vary significantly between species and increase with soil salinity, raising questions as to how C4 and CAM plants acquire pyruvate under saline conditions. However, modelling transport activity at the chloroplast membrane requires far more knowledge of the associated transport systems and the chloroplastic Na+ content.

Climate change induces many abiotic stresses, including soil salinity, significantly challenging global agriculture. Salinity stress tolerance (SST) is a complex trait, both physiologically and genetically, and is conferred at various levels of plant functional organization. As both the sustainability and profitability of agricultural production systems are critically dependent on SST, plant breeders are trying to design and develop salinity-smart crop plants capable of thriving under high salinity conditions. The accessibility of extreme-quality reference genomes for cultivated crops, naturally salinity-smart plants, and crop wild relatives has fast-tracked the discovery of key genes and quantitative trait loci (QTLs), marker development, genotyping assays and molecular breeding products with improved SST. Employing fast-forward breeding tools, namely genomic selection (GS), haplotype-based breeding (HBB), artificial intelligence (AI) and high-throughput phenotyping (HTP), has shown influence not only for fast-tracking genetic gains but also for reducing the time and cost of developing commercial cultivars with enhanced SST and yield stability. This review discusses the advancement and prospects of various genomics-assisted breeding (GAB) tools, including genome sequencing, QTL mapping, GWAS, GS, HBB, pan-genomics, single-cell/tissue genomics and phenotyping, epigenomics and transgenomics, to exploit the genetic landscape for improving SST. Additionally, we explore the integration of HTP and AI, which demonstrates how these innovative approaches can optimize breeding efficiency and guide large-scale breeding efforts for designing salinity-smart crops to ensure sustainable agriculture and global food security. The collective adoption of these tools suggests bridging the gap between research and field application to deliver stress-smart varieties designed for saline-affected regions worldwide.

Analysis of salinity tolerance processes in wheat has focused on salt exclusion from shoots while root phenotypes have received limited attention. Here, we consider the varying phenotypic response of four bread wheat varieties that differ in their type and degree of salt tolerance and assess their molecular responses to salinity and changes in root cell wall lignification. These varieties were Westonia introgressed with Nax1 and Nax2 root sodium transporters (HKT1;4-A and HKT1;5-A) that reduce Na+ accumulation in leaves, as well as the 'tissue tolerant' Portuguese landrace Mocho de Espiga Branca that has a mutation in the homologous gene HKT1;5-D and has high Na+ concentration in leaves. These three varieties were compared with the relatively more salt-sensitive cultivar Gladius. Through the use of root histochemical analysis, ion concentrations, as well as differential proteomics and targeted metabolomics, we provide an integrated view of the wheat root response to salinity. We show different metabolic re-arrangements in energy conversion, primary metabolic machinery and phenylpropanoid pathway leading to monolignol production in a genotype and genotype by treatment-dependent manner that alters the extent and localisation of root lignification which correlated with an improved capacity of wheat roots to cope better under salinity stress.

Both drought and soil salinity are common occurrences in arid climates, and many of the plant responses and adaptations are in common. In this chapter we discuss whether breeding plants for drought tolerance will benefit their growth and yield in saline soil, and whether breeding plants for salt tolerance will provide a benefit in dry soil with low salinity. We summarise the knowledge of traits and QTLs that are useful for breeding, and finish with some relevant case studies with different crops.

Gene editing boosts the yields of sorghum, rice and millet grown in alkaline soils.

Abiotic stresses such as drought and heat continue to impact crop production in a warming world. This review distinguishes seven inherent capacities that enable plants to respond to abiotic stresses and continue growing, although at a reduced rate, to achieve a productive yield. These are the capacities to selectively take up essential resources, store them and supply them to different plant parts, generate the energy required for cellular functions, conduct repairs to maintain plant tissues, communicate between plant parts, manage existing structural assets in the face of changed circumstances, and shape-shift through development to be efficient in different environments. By illustration, we show how all seven plant capacities are important for reproductive success of major crop species during drought, salinity, temperature extremes, flooding, and nutrient stress. Confusion about the term 'oxidative stress' is explained. This allows us to focus on the strategies that enhance plant adaptation by identifying key responses that can be targets for plant breeding.

Wheat production in many countries is threatened by climate change and rising sea levels causing increases in salt-water intrusion in low-lying coastal areas. Large areas of the coastal zone of Bangladesh remain fallow during the dry season primarily due to salinity. It is estimated that 0.86 million hectares of land currently under fallow in the dry season would be suitable for wheat production using varieties with enhanced salt tolerance. This study investigated the impact of salt tolerance Nax genes (Na+ exclusion) on the grain yield of bread wheat grown on saline soils in southern Bangladesh. Nax1 and Nax2 genes were separately crossed into two Bangladeshi bread wheat varieties, BARI Gom 25 and BARI Gom 26, through conventional crossing with marker-assisted selection. The key outcome was strong evidence that both Nax genes have the capacity to lower leaf Na+ concentration in locally adapted bread wheat and consequently deliver improved yields in challenging field environments in southern Bangladesh with moderate to high salinity. The genetic backgrounds of the adapted varieties played a significant role in the expression of these genes. There was a differential response in the phenotypic expression of Nax genes to reduce leaf Na+ levels between the two local varieties selected as recurrent parents and the resultant variation in yield. The average reduction in leaf Na+ concentrations from the third backcrossed lines in the BARI Gom 25 background was about twice that of lines in the BARI Gom 26 background. These same lines typically yielded between 10% and 20% higher than BARI Gom 25 on moderate to high salinity sites, whereas the backcrossed lines in the BARI Gom 26 background yielded similarly to their recurrent parent at these same sites. The contrast in the differential phenotypic expression of the Nax genes evident in the two recurrent parents represented in this study highlights the importance of crossing salt tolerance Nax genes into a range of locally adapted high-yielding genetic backgrounds to identify the greatest potential for improvement in salt tolerance.

Crop yields must increase to meet the demands of a growing world population. Soil salinization is increasing due to the impacts of climate change, reducing the area of arable land for crop production. Plant root systems are plastic, and their architecture can be modulated to (1) acquire nutrients and water for growth, and (2) respond to hostile soil environments. Saline soils inhibit primary root growth and alter root system architecture (RSA) of crop plants. In this review, we explore how crop root systems respond and adapt to salinity, focusing predominately on the staple cereal crops wheat, maize, rice, and barley, that all play a major role in global food security. Cereal crops are classified as glycophytes (salt-sensitive) however salt-tolerance can differ both between species and within a species. In the past, due to the inherent difficulties associated with visualising and measuring root traits, crop breeding strategies have tended to focus on optimising shoot traits. High-resolution phenotyping techniques now make it possible to visualise and measure root traits in soil systems. A steep, deep and cheap root ideotype has been proposed for water and nitrogen capture. Changes in RSA can be an adaptive strategy to avoid saline soils whilst optimising nutrient and water acquisition. In this review we propose a new model for designing crops with a salt-tolerant root ideotype. The proposed root ideotype would exhibit root plasticity to adapt to saline soils, root anatomical changes to conserve energy and restrict sodium (Na+) uptake, and transport mechanisms to reduce the amount of Na+ transported to leaves. In the future, combining high-resolution root phenotyping with advances in crop genetics will allow us to uncover root traits in complex crop species such as wheat, that can be incorporated into crop breeding programs for yield stability in saline soils.

The impact of salinity on wheat plants is often studied by analysis of shoot responses, even though the main mechanism of tolerance is shoot Na+ exclusion. Wheat roots directly experience rising NaCl concentrations and show more physiological responses in root tips than in mature roots and altered responses with time; but the molecular reason for these differential responses is unclear. We have found that there is a distinct difference between the proteome responses of wheat root tip and mature root tissues to salinity. Translation and protein synthesis related proteins showed a significant decrease in abundance, most of the glycolytic enzymes and selected TCA cycle enzymes and ATP synthase subunits were significantly decreased in abundance under salt stress in root tips only. The root tip response in wheat indicates the protein synthesis capacity and energy production were impaired under salt stress which correlated with the anatomical response of root growth decrease and its respiratory rate. Wheat root responses are direct and rapid effects of the soil salinity in this species, therefore shoot responses such as reduction in shoot growth and photosynthetic capacity need to be considered in light of these effects on root metabolism. Significance: Salinity is a critical environmental factor limiting crop production throughout the world. Wheat (Triticum aestivum) is the most significant cereal crop for human nutrition and both its growth and yield is negatively impacted by salinity. Salinity stress is known to impose osmotic stress in plants during the initial phase of exposure and ion toxicity in the later stages of development. Roots are the first plant organ to perceive the salt. However, intensive breading approaches to develop salt tolerant crops have mainly focussed on exclusion of salt from above ground tissues, and only achieved limited success to date. Wheat roots physiologically respond to salinity by overall reduction in the length of seminal mots. The stunting of the wheat root system is considered to be a result of higher sensitivity of root tips to salinity. However, the metabolic changes that underpin selective root tip sensitivity is largely unknown. Here, we carried out non-targeted profiling of mature root versus root tip proteomes under control and salt stress conditions. We found distinct changes in abundance of proteins involved in carbon and energy metabolism and protein metabolism in mature roots and root tips in response to salt stress. We further investigated the impact of these changes on metabolic machinery in the wheat root proteome using a targeted MS approach. We found evidence that protein synthesis and energy production machinery becomes limiting in mot tips, while the same processes in mature root remains less affected by salt stress. Our proteomic data explain the impairment of root growth and physiological characteristics as well as improve the understanding of wheat root responses under salinity which is an essential first step for further investigation of molecular traits underpinning root characteristics to improve salt tolerance of wheat.

The existence of salinity stress can be traced well before the domestication of crops, but the documentation and mitigation of this menace started only 100 years ago. Due to the unavailability of appropriate equipment and lack of sophisticated techniques, the salinity appraisal of soils and crop injury at early times was done visually. Initially, the major focus of scientists was on reclamation and management of salt-affected soils to render them fit for agriculture. Later, they strived to assess the degree of salt tolerance of different plant species using growth and morphological traits as well as some fundamental physiological criteria, most importantly ion uptake, and accumulation. In the early 20th century, the idea of developing salt tolerant crops, as an alternative to soil reclamation was realized, and the terms “biological fix” or in general “biological approach” were coined. This triggered plant breeders to initiate breeding programs aimed at developing salt tolerant crop cultivars. Although conventional selection and breeding has several limitations, mainly its slowness, it has yielded many salt tolerant lines and cultivars of different crops. To speed up the crop breeding programs, a genetic engineering approach referred to as “transgenic approach” was introduced during the late 20th century. Plant biotechnologists have produced large numbers of transgenic lines of different crops however their use in developing salt tolerant cultivars is not remarkable. Furthermore, genetically modified (GM) crops are prohibited in many countries because of putative health risks and biosafety concerns. More recently, for precise editing of genomes of organisms, new molecular tools have been developed. For example, CRISPR-Cas9 is being used to precisely edit genes involved in abiotic stress tolerance, including salt tolerance. Its success in terms of developing cultivars tolerant to multiple stresses including salt stress is expected.

Soil salinity affects sugarcane (Saccharum officinale L.) production in arid and semiarid climates, severely reducing productivity. This study aimed to identify differentially regulated proteins in two cultivars that differ markedly in tolerance of saline soil. Plants were grown for 30 days and then subjected to treatments of 0 and 160 mM NaCl for 15 days. The tolerant cultivar showed a 3-fold upregulation of lipid metabolising enzymes, GDSL-motif lipases, which are associated with defence to abiotic stress, and which were not upregulated in the sensitive cultivar. Lipoxygenase was 2-fold upregulated in the tolerant cultivar but not in the sensitive cultivar, as were Type III chlorophyll a/b binding proteins. Other differences were that in the sensitive cultivar, the key enzyme of C4 photosynthesis, phosphoenolpyruvate carboxylase was downregulated, along with other chloroplast enzymes. Na+ concentrations had not reached toxic concentrations in either cultivar by this time of exposure to salt, so these changes would be in response to the osmotic effect of the soil salinity, and likely be in common with plants undergoing drought stress.

Summary The impact of salinity on wheat plants is often studied by analysis of shoot responses, even though the main mechanism of tolerance is shoot Na + exclusion. There is a need to understand the molecular responses of root tissues that directly experience rising NaCl concentrations. We have combined analysis of root growth, ion content and respiration with proteome responses in wheat root tip and mature root tissues under saline conditions. We find significant changes in translation and protein synthesis, energy metabolism and amino acid metabolism in a root tissue specific manner. Translation and protein synthesis related proteins showed significant decreases in abundance only in root tips, as did most of the glycolytic enzymes and selected TCA cycle enzymes and ATP synthase subunits. This selective root tip proteome response indicates protein synthesis capacity and energy production were impaired under salt stress, correlating with the anatomical response of roots and reduced root tip respiration rate. Wheat roots respond directly to soil salinity, therefore shoot responses such as reduction in shoot growth and photosynthetic capacity need to be considered in light of these effects.

Approximately 1 billion ha of the global land surface is currently salt-affected, representing about 7% of the earth's land surface. Whereas most of it results from natural geochemical processes, an estimated 30% of irrigated lands globally are salt-affected through secondary human-induced salinization. Application of lower quality, alternative irrigation water is further threatening expansion of the areal extent of soil salinity, in addition to climate change causing increases of salt-water intrusion in coastal areas and increasing crop water requirements. The reduced availability of freshwater resources for irrigation, the continued reduction of the world's cultivated agricultural area by land degradation and urbanization, in conjunction with a growing world population further complicates the problem seeking sustainable solutions. This scoping review prioritizes critical knowledge gaps and makes recommendations for 10 priorities in soil salinity research toward a sustainable and productive agricultural system for a food-secure future world. We also include basin-specific case studies that illustrate progress of the world's major irrigated areas in addressing impacts of soil salinization. By identifying research priorities, we seek to accelerate enhanced research funding to bring new knowledge and innovative solutions toward mitigation of soil salinity impacts. We further want to inspire the science community to develop new directions in salinity research.

Dissemination of new knowledge is arguably the most critical component of the academic activity. In this context, scientific publishing is a pinnacle of any research work. Although the scientific content has always been the primary measure of a paper’s impact, by itself it may not always be sufficient for maximum impact. Good scientific writing and ability to meet priority characteristics of the target journal are essential, and inability to meet appropriate standards may jeopardise the chances for dissemination of results. This paper analyses the key features necessary for successfully publishing scientific research manuscripts. Conclusions are validated by a survey of 22 international scientific journals in agriculture and plant biology whose editors-in-chief have provided current data on key features related to manuscript acceptance or rejection. The top priorities for manuscript rejection by scientific journals in agriculture and plant biology are: (1) lack of sufficient novelty; (2) flaws in methods or data interpretation; (3) inadequate data analyses; and (4) poor critical scientific thinking. The inability to meet these requirements may result in rejection of even the best set of data. Recommendations are made for critical thinking and integration of good scientific writing with quality research. These recommendations will improve the quality of manuscripts submitted for publication to scientific journals and hence improve their likelihood of acceptance.

Plant roots must exclude almost all of the Na+ and Cl- in saline soil while taking up water, otherwise these ions would build up to high concentrations in leaves. Plants evaporate c. 50 times more water than they retain, so 98% exclusion would result in shoot NaCl concentrations equal to that of the external medium. Taking up just 2% of the NaCl allows a plant to osmotically adjust the Na+ and Cl- in vacuoles, while organic solutes provide the balancing osmotic pressure in the cytoplasm. We quantify the costs of this exclusion by roots, the regulation of Na+ and Cl- transport through the plant, and the costs of osmotic adjustment with organic solutes in roots.

Summary Agriculture is expanding into regions that are affected by salinity. This review considers the energetic costs of salinity tolerance in crop plants and provides a framework for a quantitative assessment of costs. Different sources of energy, and modifications of root system architecture that would maximize water vs ion uptake are addressed. Energy requirements for transport of salt (NaCl) to leaf vacuoles for osmotic adjustment could be small if there are no substantial leaks back across plasma membrane and tonoplast in root and leaf. The coupling ratio of the H + ‐ ATP ase also is a critical component. One proposed leak, that of Na + influx across the plasma membrane through certain aquaporin channels, might be coupled to water flow, thus conserving energy. For the tonoplast, control of two types of cation channels is required for energy efficiency. Transporters controlling the Na + and Cl − concentrations in mitochondria and chloroplasts are largely unknown and could be a major energy cost. The complexity of the system will require a sophisticated modelling approach to identify critical transporters, apoplastic barriers and root structures. This modelling approach will inform experimentation and allow a quantitative assessment of the energy costs of NaCl tolerance to guide breeding and engineering of molecular components.

Sugarcane is an important crop in tropical regions of the world, often being exposed to environments with high salinity, but little is known of genetic variation in salt tolerance. The aim of this work was to compare the performance of two genetically diverse cultivars of sugarcane under different concentrations of salinity (0, 40, 80 and 160 mM NaCl) over a period of 30 days. SP 81-3250 was more salt-tolerant and maintained its rate of biomass production, photosynthesis and leaf area up to 160 mM NaCl, whereas IAC 87-3396 was sensitive to 80 mM NaCl. SP 81-3250 maintained very low concentrations of Na+ in both leaves and roots with increasing time and salinity, whereas in IAC 87-3396 the Na+ concentrations were 2-5 times higher. SP 81-3250 had a greater accumulation of proline, and lower lipid peroxidation, whereas glycine betaine and sucrose concentrations were similar in the two cultivars. This suggests that the tolerance of SP 81-3250 to high salinity was due to its ability to exclude Na+ while taking up water from the soil, and that measurements of Na+ concentration in leaves could be used to select salt-tolerant genotypes for saline areas.

The wheat gene pool has a tremendous amount of genetic diversity for salinity tolerance. During the last few decades, several wheat genetic stocks have been developed showing all three types of tolerance mechanisms, i.e., tissue tolerance, osmotic tolerance and ion (Na+) exclusion. However, delivery of improved crop varieties adapted to saline conditions has been lagging behind due to several reasons including the huge knowledge gap in understanding genetic basis of salinity tolerance in wheat, and then applying the available knowledge to deliver salt-resilient crop varieties. We review the research around salinity tolerance in wheat in context of historical and rapidly evolving breeding technologies and discuss the future prospects. The extensive research on identifying promising resources of salinity tolerance in durum wheat, synthetic hexaploid wheats and tertiary gene pool species such as those of Thinopyrum have been explored to transfer salinity tolerance traits to bread wheat. As the last few years witnessed leading-edge transformations where we have now (i) new and improved genotyping assays in form of SNP arrays and next-generation sequencing to facilitate gene discovery, (ii) new generation turn-over methods to get five to six generations per year by “speed breeding” facilitating gene deployment, (iii) gene-editing tools to precisely manipulate the effects of causal genes, and (iv) new phenomic platforms for capturing salinity effects in field and glass-house conditions. Integration of all these technologies will help in understanding the complex genetic architecture of wheat adaptability in saline soils and will accelerate the delivery of our future potential wheat cultivars.