Tissue-specific expression analysis of Na+ and Cl- transporter genes associated with salt removal ability in rice leaf sheath

Sodium stress-induced oxidative damage and antioxidant responses during grain filling in Indica rice

KEY MESSAGE

Sodium treatment caused the sodium ion accumulation at the milk stage of immature rice grains which in turn triggered the overproduction of reactive oxygen species and oxidative damage. The tolerant cultivar showed an enhanced antioxidative response and induced expressions of OsNHX and OsHKT ion-transporters. Sodium chloride-(NaCl) induced soil salinity is a major constraint hindering global rice production. Amongst its constituent ions, sodium (Na+) is known to be the main driver of toxicity under salt stress. The present investigation aims to measure the impacts of excess Na+ during rice grain filling using two Indica rice cultivars with opposite tolerances to salt (salt tolerant: Panvel-3, salt-sensitive: Sahyadri-3) mainly via oxidative and responsive antioxidative pathways. Plants were treated with Na+-specific treatments and NaCl with equimolar Na+ levels (100 mM) at the initiation of the reproductive phase. Stressed and control plants were harvested at three different grain-filling stages- early milk, milk, and dough and assessed for ion accumulation and oxidative damage/antioxidant responses under Na+ stress. Na+ toxicity triggered reactive oxygen species (ROS) production and upregulated the responsive enzymatic antioxidants. Na+ stress also increased the nitric oxide (NO) levels and the activity of nitrate reductase in immature grains. Differential expression levels of OsNHX and OsHKT transporters were observed in response to Na+ stress. Mature grains displayed a high accumulation of Na+ along with reduced K+ content and elevated Na+/K+ under high Na+ availability. The alterations in mature grains' sugar, starch, and protein content were also observed in response to the Na+ stress. Overall, the salt-tolerant cultivar displayed higher antioxidant activities and a lower rate of ROS generation in response to the Na+ stress. Results suggested a link between Na+ accumulation, Na+-mediated stress responses via anti/-oxidant pathways, and the grain-filling process in both rice cultivars.

Polylactic acid microplastics have stronger positive effects on the qualitative traits of rice (Oryza sativa L.) than polyethylene microplastics: Evidence from a simulated field experiment

Soil pollution by microplastics (MPs) from different types of agricultural films has received substantial attention due to its potential effects on crop quality. To date, the effects of different types of MPs on rice grain quality and their underlying molecular mechanisms have not been clarified. In this study, we examined the effects of polyethylene MPs (PE-MPs) and biodegradable polylactic acid MPs (PLA-MPs) on rice grain quality at the environmental level (0.5 %) and evaluated the molecular mechanism through transcriptome analysis. PE- and PLA-MPs increased the number of rice grains per plant by 19.83 % and 24.66 %, respectively, and decreased the rice empty-shell rate by 55.89 % and 26.53 %, respectively. However, PLA-MPs increased the 1000-seed weight by 11.37 %, whereas PE-MPs had no obvious impact in this respect. Furthermore, MP exposure, especially that of PE-MPs, affected the content of mineral elements, fatty acids, and amino acids of rice grains by disturbing the expression of genes related to these functions and metabolism. Our findings provide insights into the response of rice grains to the stress caused by different MPs.

Tissue-specific proteome profile analysis reveals regulatory and stress responsive networks in passion fruit during storage

Passiflora edulis, commonly known as passion fruit, is a crop with a fragrant aroma and refreshingly tropical flavor that is a valuable source of antioxidants. It offers a unique opportunity for growers because of its adaptability to tropical and subtropical climates. Passion fruit can be sold in the fresh market or used in value-added products, but its postharvest shelf life has not been well-researched, nor have superior cultivars been well-developed. Understanding the proteins expressed at the tissue level during the postharvest stage can help improve fruit quality and extend shelf life. In this study, we carried out comparative proteomics analysis on four passion fruit tissues, the epicarp, mesocarp, endocarp, and pulp, using multiplexed isobaric tandem mass tag (TMT) labeling quantitation. A total of 3352 proteins were identified, including 295 differentially expressed proteins (DEPs). Of these DEPs, 213 showed a fold increase greater than 1.45 (50 proteins) or a fold decrease less than 0.45 (163 proteins) with different patterns among tissue types. Among the DEPs, there were proteins expressed with functions in oxygen scavenging, lipid peroxidation, response to heat stress, and pathogen resistance. Thirty-six proteins were designated as hypothetical proteins were characterized for potential functions in immunity, cell structure, homeostasis, stress response, protein metabolism and miraculin biosynthesis. This research provides insight into tissue-specific pathways that can be further studied within fruit physiology and postharvest shelf life to aid in implementing effective plant breeding programs. Knowing the tissue-specific function of fruit is essential for improving fruit quality, developing new varieties, identifying health benefits, and optimizing processing techniques.

A review of plants strategies to resist biotic and abiotic environmental stressors

Plants exposed to a variety of abiotic and biotic stressors including environmental pollution and global warming pose significant threats to biodiversity and ecosystem services. Despite substantial literature documenting how plants adapt to distinct stressors, there still is a lack of knowledge regarding responses to multiple stressors and how these affects growth and development. Exposure of plants to concurrent biotic and abiotic stressors such as cadmium and drought, leads to pronounced inhibition in above ground biomass, imbalance in oxidative homeostasis, nutrient assimilation and stunted root growth, elucidating the synergistic interactions of multiple stressors culminating in adverse physiological outcomes. Impact of elevated heavy metal and water deficit exposure extends beyond growth and development, influencing the biodiversity of the microenvironment including the rhizosphere nutrient profile and microbiome. These findings have significant implications for plant-stress interactions and ecosystem functioning that prompt immediate action in order to eliminate effect of pollution and address global environmental issues to promote sustainable tolerance for multiple stress combinations in plants. Here, we review plant tolerance against stress combinations, highlighting the need for interdisciplinary approaches and advanced technologies, such as omics and molecular tools, to achieve a comprehensive understanding of underlying stress tolerance mechanisms. To accelerate progress towards developing stress-tolerance in plants against multiple environmental stressors, future research in plant stress tolerance should adopt a collaborative approach, involving researchers from multiple disciplines with diverse expertise and resources.

Exploring Salinity Tolerance Mechanisms in Diverse Wheat Genotypes Using Physiological, Anatomical, Agronomic and Gene Expression Analyses

Salinity is a widespread abiotic stress that devastatingly impacts wheat growth and restricts its productivity worldwide. The present study is aimed at elucidating biochemical, physiological, anatomical, gene expression analysis, and agronomic responses of three diverse wheat genotypes to different salinity levels. A salinity treatment of 5000 and 7000 ppm gradually reduced photosynthetic pigments, anatomical root and leaf measurements and agronomic traits of all evaluated wheat genotypes (Ismailia line, Misr 1, and Misr 3). In addition, increasing salinity levels substantially decreased all anatomical root and leaf measurements except sclerenchyma tissue upper and lower vascular bundle thickness compared with unstressed plants. However, proline content in stressed plants was stimulated by increasing salinity levels in all evaluated wheat genotypes. Moreover, Na+ ions content and antioxidant enzyme activities in stressed leaves increased the high level of salinity in all genotypes. The evaluated wheat genotypes demonstrated substantial variations in all studied characters. The Ismailia line exhibited the uppermost performance in photosynthetic pigments under both salinity levels. Additionally, the Ismailia line was superior in the activity of superoxide dismutase (SOD), catalase activity (CAT), peroxidase (POX), and polyphenol oxidase (PPO) enzymes followed by Misr 1. Moreover, the Ismailia line recorded the maximum anatomical root and leaf measurements under salinity stress, which enhanced its tolerance to salinity stress. The Ismailia line and Misr 3 presented high up-regulation of H+ATPase, NHX2 HAK, and HKT genes in the root and leaf under both salinity levels. The positive physiological, anatomical, and molecular responses of the Ismailia line under salinity stress were reflected on agronomic performance and exhibited superior values of all evaluated agronomic traits.

The UDP-glucuronic acid decarboxylase OsUXS3 regulates Na+ ion toxicity tolerance under salt stress by interacting with OsCATs in rice

Overly Na⁺ ion in soil caused by salt stress has a significant negative impact on the growth and production of crops, especially rice (Oryza sativa L.). Therefore, it is vital for us to clarify how salt stress tolerance in rice is caused by Na⁺ ion toxicity. The UDP-glucuronic acid decarboxylase (UXS) is a critical enzyme in the biosynthesis of UDP-xylose, which is the key substrate of cytoderm synthesis in plants. In this study, we found that OsUXS3, a rice UXS, is a positive regulator to regulate Na⁺ ion toxicity under salt stress by interacting with OsCATs (Oryza sativa catalase; OsCAT). The expression of OsUXS3 was significantly up-regulated under NaCl and NaHCO₃ treatments of rice seedlings. Meanwhile, by the genetic and biochemical evidence, knockout of OsUXS3 significantly increased reactive oxygen species (ROS) levels and decreased CAT activity under NaCl and NaHCO₃ treatments in tissue. Furthermore, knockout of OsUXS3 caused excessive accumulation of Na ⁺ ion and rapid loss of K⁺ ion and disrupts Na⁺/K⁺ homeostasis under NaCl and NaHCO₃ treatments. Based on the results above, we can conclude that OsUXS3 might regulate CAT activity by interacting with OsCATs, which is not only characterized for the first time but also regulating Na⁺/K⁺ homeostasis, positively regulating the Na⁺ ion toxicity tolerance under salt stress in rice.

Identification of a DEAD-box RNA Helicase BnRH6 Reveals Its Involvement in Salt Stress Response in Rapeseed (Brassica napus)

Rapeseed (Brassica napus) is one of the most important vegetable oil crops worldwide. Abiotic stresses such as salinity are great challenges for its growth and productivity. DEAD-box RNA helicase 6 (RH6) is a subfamily member of superfamily 2 (SF2), which plays crucial roles in plant growth and development. However, no report is available on RH6 in regulating plant abiotic stress response. This study investigated the function and regulatory mechanism for BnRH6. BnRH6 was targeted to the nucleus and cytoplasmic processing body (P-body), constitutively expressed throughout the lifespan, and induced by salt stress. Transgenic overexpressing BnRH6 in Brassica and Arabidopsis displayed salt hypersensitivity, manifested by lagging seed germination (decreased to 55−85% of wild-type), growth stunt, leaf chlorosis, oxidative stress, and over-accumulation of Na ions with the K+/Na+ ratio being decreased by 18.3−28.6%. Given the undesirable quality of knockout Brassica plants, we utilized an Arabidopsis T-DNA insertion mutant rh6-1 to investigate downstream genes by transcriptomics. We constructed four libraries with three biological replicates to investigate global downstream genes by RNA sequencing. Genome-wide analysis of differentially expressed genes (DEGs) (2-fold, p < 0.05) showed that 41 genes were upregulated and 66 genes were downregulated in rh6-1 relative to wild-type under salt stress. Most of them are well-identified and involved in transcription factors, ABA-responsive genes, and detoxified components or antioxidants. Our research suggests that BnRH6 can regulate a group of salt-tolerance genes to negatively promote Brassica adaptation to salt stress.

QTL analysis for sodium removal ability in rice leaf sheaths under salinity using an IR-44595/318 F2 population

Over-accumulation of salt in rice plants is an effect of salt stress which decreases growth and grain yield. Salt removal ability in leaf sheaths is a tolerance mechanism to decrease salt entry and accumulation in leaf blades and maintain photosynthesis under salinity. In this study, a QTL analysis of removal ability of sodium ions (Na⁺) in leaf sheaths and Na⁺ accumulation-related traits, was conducted using F₂ population between two rice varieties, IR-44595 with superior Na⁺ removal ability, and 318 with contrasting Na⁺ removal ability in leaf sheaths under salinity. Suggestive QTLs for Na⁺ removal ability in leaf sheaths were found on chromosomes 4 and 11. The suggestive QTL on chromosome 11 overlapped with other significant QTLs for Na⁺ concentration in shoots, leaf blades and leaf sheaths, and Na⁺/K⁺ ratio in leaf blades. Correlation analysis indicated that Na⁺ removal ability in leaf sheaths is important in reducing Na⁺ accumulation in leaf blades. The varietal difference of Na⁺ removal ability in leaf sheaths at the whole plant level was greater at lower NaCl concentrations and became smaller as the treatment NaCl concentration increased. Although the Na⁺ removal ability in leaf sheath was comparable between IR-44595 and 318 under high salinity at the whole plant level, the younger leaves of IR-44595 still showed a higher Na⁺ sheath-blade ratio than 318, which implied the Na⁺ removal ability functions in the younger leaves in IR-44595 to reduce Na⁺ entry in young leaf blades even under high salinity.

Impact of Single and Combined Salinity and High-Temperature Stresses on Agro-Physiological, Biochemical, and Transcriptional Responses in Rice and Stress-Release

Here, for the first time, we aimed to identify in rice the key mechanisms and processes underlying tolerance to high-temperature (HT) or salt stress (SS) alone, the co-occurrence of both stresses, and recovery using physiological and biochemical measurements and gene expression analysis. We also investigated whether recovery from the two stressors depended on the relative intensities/relief of each stressor. Wild type ('Yukinkomai') rice plants were found to be more susceptible to salinity or heat applied individually. SS leads to a depletion of cellular water content, higher accumulation of Na⁺, and alterations in photosynthetic pigments. The stress-tolerant cultivar 'YNU31-2-4' (YNU) displayed a lower Na⁺/K⁺ ratio, higher water content in cells and improved photosynthetic traits, antioxidant system, and expression of defence genes. Strikingly, the SS + HT combination provided a significant level of protection to rice plants from the effects of SS alone. The expression pattern of a selected set of genes showed a specific response and dedicated pathways in plants subjected to each of the different stresses, while other genes were explicitly activated when the stresses were combined. Aquaporin genes were activated by SS, while stress-related (P5CS, MSD1, HSPs, and ions transporters) genes were shaped by HT. Hierarchical clustering and principal component analyses showed that several traits exhibited a gradually aggravating effect as plants were exposed to the combined stresses and identified heat as a mitigating factor, clearly separating heat + salt-stressed from salt-non-heat-stressed plants. Furthermore, seedling recovery was far more dependent on the relative intensities of stressors and cultivars, demonstrating the influence of one stressor over another upon stress-release. Taken together, our data show the uniqueness and complexity of the physiological and molecular network modules used by rice plants to respond to single and combined stresses and recovery.

Synergistic effect of floatable hydroxyapatite-modified biochar adsorption and low-level CaCl2 leaching on Cd removal from paddy soil

The utilization of recycled biochar combined with chemical leaching is an appropriate method to remove cadmium (Cd) from paddy soil. Some Cd-rich soil clay particulates (particulate Cd) are reported to be removed via biochar adsorption and the potential impact of biochar on soil properties need further study. The removal efficiencies and mechanisms of Cd from soil by using floatable hydroxyapatite modified biochar (HBC) combined with CaCl₂ were studied. Synergetic removal efficiencies of total Cd (46.5%) and bioavailable Cd (37.9%) from the paddy soil were achieved with 2% HBC and 1 mM CaCl₂. The increased soluble Cd in soil pore water by CaCl₂ leaching could be efficiently adsorbed on HBC, and removed by HBC collection, reducing the risk of the residual soluble Cd in soil pore water to rice plants caused by the inefficient drainage in the field. The suspendability of clay particulates in overlying water was little affected by the low-level CaCl₂ based on Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation. Moreover, low-level CaCl₂ facilitated the accumulation of particulate Cd on the floating HBC via decreasing the interaction energy (by 25%) between clay particulates and HBC. HBC-mediated Cd migration contributed ~70% of total Cd removal, while soluble and particulate Cd removed through the drainage accounted for ~30%. Soil clay proportion maintained at 25.3% due to the replenishment of HBC residues. In addition, soil nutrient and physicochemical conditions were improved with HBC residues. This work provides a novel soil remediation method by using floatable biochar combined with low-level CaCl₂ for Cd-contaminated paddy soil remediation.

Rapid Accumulation of Proline Enhances Salinity Tolerance in Australian Wild Rice Oryza australiensis Domin

Proline has been reported to play an important role in helping plants cope with several stresses, including salinity. This study investigates the relationship between proline accumulation and salt tolerance in an accession of Australian wild rice Oryza australiensis Domin using morphological, physiological, and molecular assessments. Seedlings of O. australiensis wild rice accession JC 2304 and two other cultivated rice Oryza sativa L. cultivars, Nipponbare (salt-sensitive), and Pokkali (salt-tolerant), were screened at 150 mM NaCl for 14 days. The results showed that O. australiensis was able to rapidly accumulate free proline and lower osmotic potential at a very early stage of salt stress compared to cultivated rice. The qRT-PCR result revealed that O. australiensis wild rice JC 2304 activated proline synthesis genes OsP5CS1, OsP5CS2, and OsP5CR and depressed the expression of proline degradation gene OsProDH as early as 1 h after exposure to salinity stress. Wild rice O. australiensis and Pokkali maintained their relative water content and cell membrane integrity during exposure to salinity stress, while the salt-sensitive Nipponbare failed to do so. An analysis of the sodium and potassium contents suggested that O. australiensis wild rice JC 2304 adapted to ionic stress caused by salinity by maintaining a low Na+ content and low Na+/K+ ratio in the shoots and roots. This demonstrates that O. australiensis wild rice may use a rapid accumulation of free proline as a strategy to cope with salinity stress.

Genome-wide identification of the DUF668 gene family in cotton and expression profiling analysis of GhDUF668 in Gossypium hirsutum under adverse stress

Background

Domain of unknown function 668 (DUF668) may play a crucial role in the plant growth and developmental response to adverse stress. However, our knowledge of the function of the DUF668 gene family is limited.

Results

Our study was conducted based on the DUF668 gene family identified from cotton genome sequencing. Phylogenetic analysis showed that the DUF668 family genes can be classified into four subgroups in cotton. We identified 32 DUF668 genes, which are distributed on 17 chromosomes and most of them located in the nucleus of Gossypium hirsutum. Gene structure and motif analyses revealed that the members of the DUF668 gene family can be clustered in G. hirsutum into two broad groups, which are relatively evolutionarily conserved. Transcriptome data analysis showed that the GhDUF668 genes are differentially expressed in different tissues under various stresses (cold, heat, drought, salt, and Verticillium dahliae), and expression is generally increased in roots and stems. Promoter and expression analyses indicated that Gh_DUF668–05, Gh_DUF668–08, Gh_DUF668–11, Gh_DUF668–23 and Gh_DUF668–28 in G. hirsutum might have evolved resistance to adverse stress. Additionally, qRT-PCR revealed that these 5 genes in four cotton lines, KK1543 (drought resistant), Xinluzao 26 (drought sensitive), Zhongzhimian 2 (disease resistant) and Simian 3 (susceptible), under drought and Verticillium wilt stress were all significantly induced. Roots had the highest expression of these 5 genes before and after the treatment. Among them, the expression levels of Gh_DUF668–08 and Gh_DUF668–23 increased sharply at 6 h and reached a maximum at 12 h under biotic and abiotic stress, which showed that they might be involved in the process of adverse stress resistance in cotton.

Conclusion

The significant changes in GhDUF668 expression in the roots after adverse stress indicate that GhDUF668 is likely to increase plant resistance to stress. This study provides an important theoretical basis for further research on the function of the DUF668 gene family and the molecular mechanism of adverse stress resistance in cotton.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07716-w.

Recent progress in understanding salinity tolerance in plants: Story of Na+/K+ balance and beyond

High salt concentrations in the growing medium can severely affect the growth and development of plants. It is imperative to understand the different components of salt-tolerant network in plants in order to produce the salt-tolerant cultivars. High-affinity potassium transporter- and myelocytomatosis proteins have been shown to play a critical role for salinity tolerance through exclusion of sodium (Na⁺) ions from sensitive shoot tissues in plants. Numerous genes, that limit the uptake of salts from soil and their transport throughout the plant body, adjust the ionic and osmotic balance of cells in roots and shoots. In the present review, we have tried to provide a comprehensive report of major research advances on different mechanisms regulating plant tolerance to salinity stress at proteomics, metabolomics, genomics and transcriptomics levels. Along with the role of ionic homeostasis, a major focus was given on other salinity tolerance mechanisms in plants including osmoregulation and osmo-protection, cell wall remodeling and integrity, and plant antioxidative defense. Major proteins and genes expressed under salt-stressed conditions and their role in enhancing salinity tolerance in plants are discussed as well. Moreover, this manuscript identifies and highlights the key questions on plant salinity tolerance that remain to be discussed in the future.