Tolerant Rice Research Articles

OsLSC6 Regulates Leaf Sheath Color and Cold Tolerance in Rice Revealed by Metabolite Genome Wide Association Study.

Plant metabolites including anthocyanins play an important role in the growth of plants, as well as in regulating biotic and abiotic stress responses to the environment. Here we report comprehensive profiling of 3315 metabolites and a further metabolic-based genome-wide association study (mGWAS) based on 292,485 SNPs obtained from 311 rice accessions, including 160 wild and 151 cultivars. We identified hundreds of common variants affecting a large number of secondary metabolites with large effects at high throughput. Finally, we identified a novel gene namely OsLSC6 (Oryza sativa leaf sheath color 6), which encoded a UDP 3-O-glucosyltransferase and involved in the anthocyanin biosynthesis of Cyanidin-3-Galc (sd1825) responsible for leaf sheath color, and resulted in significant different accumulation of sd1825 between wild (purple) and cultivars (green). The results of knockout transgenic experiments showed that OsLSC6 regulated the biosynthesis and accumulation of sd1825, controlled the purple leaf sheath. Our further research revealed that OsLSC6 also confers resistance to cold stress during the seedling stage in rice. And we identified that a SNP in OsLSC6 was responsible for the leaf sheath color and chilling tolerance, supporting the importance of OsLSC6 in plant adaption. Our study could not only demonstrate that OsLSC6 is a vital regulator during anthocyanin biosynthesis and abiotic stress responses, but also provide a powerful complementary tool based on metabolites-to-genes analysis by mGWAS for functional gene identification andpromising candidate in future rice breeding and improvement.

Evaluation of anaerobic germination and submergence tolerance in rice (Oryza sativa L.) suitable for direct seeded condition

Evaluation of anaerobic germination and submergence tolerance in rice (Oryza sativa L.) suitable for direct seeded condition

MpNAC1, a transcription factor from the mangrove associate Millettia pinnata, confers salt and drought stress tolerance in transgenic Arabidopsis and rice

Pongamia (Millettia pinnata Syn. Pongamia pinnata), a mangrove associate plant, exhibits good stress tolerance, making it a treasure of genetic resources for crop improvement. NAC proteins are plant-specific transcription factors, which have been elucidated to participate in the regulation and tolerance of abiotic stresses (such as salt and drought). Here, we identified a salt-induced gene from Pongamia, MpNAC1, which encodes an NAC factor sharing five highly conserved domains with other NACs and exhibits close homology to AtNAC19/AtNAC55/AtNAC72 in Arabidopsis. MpNAC1 showed nuclear localization and transcriptional activator activity. MpNAC1-overexpressing Arabidopsis exhibited significantly stronger salt and drought tolerance compared with wild-type plants. The expression levels of stress-responsive genes were activated in transgenic Arabidopsis. Furthermore, the heterologous expression of MpNAC1 also enhanced the salt and drought tolerance of transgenic rice. The major agronomic traits, such as plant height and tiller number, panicle length, grain size, and yield, were similar between the transgenic lines and wild type under normal field growth conditions. RNA-Seq analysis revealed that MpNAC1 significantly up-regulated stress-responsive genes and activated the biosynthesis of secondary metabolites such as flavonoids, resulting in increased stress tolerance. Taken together, the MpNAC1 increased salt and drought stress tolerance in transgenic plants and did not retard the plant growth and development under normal growth conditions, suggesting the potential of MpNAC1 in breeding stress-resilient crops.

Physiological Responses of Stress Tolerant Rice Varieties across Different Cropping Systems under Rainfed Stress

Rice, sustaining half of the world's population, is traditionally cultivated through transplanting, particularly in Asia. However, challenges like excessive water use, labour demands, and environmental stresses like drought prompt the search for alternatives. Our study evaluates the impact of various crop establishment methods (CEs) – conventional puddled transplanting, direct drill seeding on flatbeds (DSR), and direct seeding on raised beds (FIRB) – on five stress-tolerant rice varieties (V): DRR 42, DRR 44, Sukha Dhan 5, Sukha Dhan 6, and Sarjoo 52. The key physiological parameters like Relative Water Content, Membrane Stability Index, and Chlorophyll content were analysed across different CE and V combinations. Notably, FIRB consistently surpasses other methods, suggesting its potential in bolstering stress tolerance and yield. Among the five varieties, Sukha Dhan 5 (V3) displays the highest RWC, Sarjoo 52 (V5) in MSI, and DRR 44 (V2) demonstrates superior chlorophyll content. These varieties underscore their pivotal role in maintaining plant water status, facilitating robust photosynthesis, and enhancing stress resilience, thereby ensuring stable yields. Our findings underscore FIRB's promise in curbing water waste and mitigating drawbacks associated with conventional transplanting practices.

A bamboo 'PeSAPK4-PeMYB99-PeTIP4-3' regulatory model involved in water transport.

Water plays crucial roles in expeditious growth and osmotic stress of bamboo. Nevertheless, the molecular mechanism of water transport remains unclear. In this study, an aquaporin gene, PeTIP4-3, was identified through a joint analysis of root pressure and transcriptomic data in moso bamboo (Phyllostachys edulis). PeTIP4-3 was highly expressed in shoots, especially in the vascular bundle sheath cells. Overexpression of PeTIP4-3 could increase drought and salt tolerance in transgenic yeast and rice. A co-expression pattern of PeSAPK4, PeMYB99 and PeTIP4-3 was revealed by WGCNA. PeMYB99 exhibited an ability to independently bind to and activate PeTIP4-3, which augmented tolerance to drought and salt stress. PeSAPK4 could interact with and phosphorylate PeMYB99 in vivo and in vitro, wherein they synergistically accelerated PeTIP4-3 transcription. Overexpression of PeMYB99 and PeSAPK4 also conferred drought and salt tolerance in transgenic rice. Further ABA treatment analysis indicated that PeSAPK4 enhanced water transport in response to stress via ABA signaling. Collectively, an ABA-mediated cascade of PeSAPK4-PeMYB99-PeTIP4-3 is proposed, which governs water transport in moso bamboo.

Utilizing transcriptomics and proteomics to unravel key genes and proteins of Oryza sativa seedlings mediated by selenium in response to cadmium stress

BackgroundCadmium (Cd) pollution has declined crop yields and quality. Selenium (Se) is a beneficial mineral element that protects plants from oxidative damage, thereby improving crop tolerance to heavy metals. The molecular mechanism of Se-induced Cd tolerance in rice (Oryza sativa) is not yet understood. This study aimed to elucidate the beneficial mechanism of Se (1 mg/kg) in alleviating Cd toxicity in rice seedlings.ResultsExogenous selenium addition significantly improved the toxic effect of cadmium stress on rice seedlings, increasing plant height and fresh weight by 20.53% and 34.48%, respectively, and increasing chlorophyll and carotenoid content by 16.68% and 15.26%, respectively. Moreover, the MDA, ·OH, and protein carbonyl levels induced by cadmium stress were reduced by 47.65%, 67.57%, and 56.43%, respectively. Cell wall metabolism, energy cycling, and enzymatic and non-enzymatic antioxidant systems in rice seedlings were significantly enhanced. Transcriptome analysis showed that the expressions of key functional genes psbQ, psbO, psaG, psaD, atpG, and PetH were significantly up-regulated under low-concentration Se treatment, which enhanced the energy metabolism process of photosystem I and photosystem II in rice seedlings. At the same time, the up-regulation of LHCA, LHCB family, and C4H1, PRX, and atp6 functional genes improved the ability of photon capture and heavy metal ion binding in plants. Combined with proteome analysis, the expression of functional proteins OsGSTF1, OsGSTU11, OsG6PDH4, OsDHAB1, CP29, and CabE was significantly up-regulated under Se, which enhanced photosynthesis and anti-oxidative stress mechanism in rice seedlings. At the same time, it regulates the plant hormone signal transduction pathway. It up-regulates the expression response process of IAA, ABA, and JAZ to activate the synergistic effect between each cell rapidly and jointly maintain the homeostasis balance.ConclusionOur results revealed the regulation process of Se-mediated critical metabolic pathways, functional genes, and proteins in rice under cadmium stress. They provided insights into the expression rules and dynamic response process of the Se-mediated plant resistance mechanism. This study provided the theoretical basis and technical support for crop safety in cropland ecosystems and cadmium-contaminated areas.

The UDP-glycosyltransferase OsUGT706D2 positively regulates cold and submergence stress tolerance in rice

In a genome-wide association study, we identified a rice UDP-glycosyltransferase gene, OsUGT706D2, whose transcription was activated in response to cold and submergence stress and to exogenous abscisic acid (ABA). OsUGT706D2 positively regulated the biosynthesis of tricin-4′-O-(syringyl alcohol) ether-7-O-glucoside at both the transcriptional and metabolic levels. OsUGT706D2 mediated cold and submergence tolerance by modulating the expression of stress-responsive genes as well as the abscisic acid (ABA) signaling pathway. Gain of function of OsUGT706D2 increased cold and submergence tolerance and loss of function of OsUGT706D2 reduced cold tolerance. ABA positively regulated OsUGT706D2-mediated cold tolerance but reduced submergence tolerance. These findings suggest the potential use of OsUGT706D2 for improving abiotic stress tolerance in rice.

A calmodulin-like protein PvCML9 negatively regulates salt tolerance

Calmodulin-like proteins (CMLs) are unique Ca2+ sensors and play crucial roles in response to abiotic stress in plants. A salt-repressed PvCML9 from halophyte seashore paspalum (Paspalum vaginatum O. Swartz) was identified. PvCML9 was localized in the cytoplasm and nucleus and highly expressed in roots and stems. Overexpression of PvCML9 led to reduced salt tolerance in rice and seashore paspalum, whereas downregulating expression of PvCML9 showed increased salt tolerance in seashore paspalum as compared with the wild type (WT), indicating that PvCML9 regulated salt tolerance negatively. Na+ and K+ homeostasis was altered by PvCML9 expression. Lower level of Na+/K+ ratio in roots and shoots was maintained in PvCML9-RNAi lines compared with WT under salt stress, but higher level in overexpression lines. Moreover, higher levels of SOD and CAT activities and proline accumulation were observed in PvCML9-RNAi lines compared with WT under salt stress, but lower levels in overexpression lines, which altered ROS homeostasis. Based on the above data, mutation of its homolog gene OsCML9 in rice by CRISPR/Cas9 was performed. The mutant had enhanced salt tolerance without affecting rice growth and development, suggesting that OsCML9 gene is an ideal target gene to generate salt tolerant cultivars by genome editing in the future.

Drought Tolerance in Rice (Oryza sativa L.): Impact, Performance and Recent Trends

Drought poses a significant challenge to rice cultivation in Asia's rain-fed regions, which is expected to worsen with climate change. This article presents a comprehensive review of the current state of knowledge on drought tolerance in rice, based on a literature review of 52 relevant articles. The articles were chosen based on their relevance to the topic of drought tolerance in rice. The selected articles were then analyzed using a qualitative approach to summarize and synthesize their findings into three main sections: impact, performance, and recent trends. The article highlights several key findings on the development of drought-tolerant rice cultivars, including the identification of genes that control responses to water availability, the use of submergence-tolerant varieties in flood-prone lowlands, and the importance of physiological, biochemical, and molecular adaptation processes in improving rice's tolerance to drought stress. The article emphasizes the importance of marker-assisted breeding and cultivation in semi-arid and rainfed environments to develop more drought-tolerant cultivars. The development of drought-tolerant rice cultivars is crucial to ensure food security and mitigate the effects of climate change in Asia's rain-fed regions. The article also discusses various types of droughts and their effects on different plant species and drought pressures. As the global population increases, the demand for rice as a dependable food crop also rises. To meet this demand, rice cultivation must be expanded to rainfed areas. However, rice's adaptation mechanisms and habitat make it one of the most challenging crops for breeders to develop drought-tolerant varieties. Overall, this article provides important insights and recommendations to improve rice productivity and address the challenges associated with drought in rice cultivation.

Association Analysis in Rice Germplasm Lines for High Temperature Tolerance

Background: Relative to other abiotic factors like salinity and drought, breeding rice cultivars that are resistant of high temperatures has received a little attention. The purpose of this study is to find parents and genotypes that are suitable for utilizing in high temperature stress breeding program. Methods: The genetic material for this study comprised of a set of germplasm collections (293 accessions) from different sources such as International Rice Research Institute germplasm. These populations were raised at the Department of Rice, Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural University, Coimbatore. The Heat tolarance Indices (TOL) viz., Heat tolerance index (HTI) and Heat susceptibility index (HSI) and association analysis were estimated among germplasm lines for yield attributes under normal and high temperature stress condition. Result: Out of 293 genotypes, sixty nine genotypes significantly exceeded for both HTI and HSI. Association studies revealed that, single plant yield had highly significant and positive association with panicle exertion, number of total tillers per plant, number of productive tillers per plant, panicle length, number of filled grains per panicle and total dry matter production. Spikelet sterility and high temperature susceptibility index had highly significant and negative association with single plant yield. Number of productive tillers had significant and positive correlation with total dry matter production, panicle length, number of filled grains per panicle, days to maturity, hundred grain weight, grain breadth and high temperature susceptible index. Hence these traits may be considered as selection indices for yield and high temperature tolerance improvement programme. Hence it may be possible to combine single plant yield and heat susceptibility index by specific breeding programme for high temperature tolerance in rice.

Alginate Oligosaccharides Alleviate Salt Stress in Rice Seedlings by Regulating Cell Wall Metabolism to Maintain Cell Wall Structure and Improve Lodging Resistance.

Salt stress is one of the major abiotic stresses that damage the structure and composition of cell walls. Alginate oligosaccharides (AOS) have been advocated to significantly improve plant stress tolerance. The metabolic mechanism by which AOS induces salt tolerance in rice cell walls remains unclear. Here, we report the impact of AOS foliar application on the cell wall composition of rice seedlings using the salt-tolerant rice variety FL478 and the salt-sensitive variety IR29. Data revealed that salt stress decreased biomass, stem basal width, stem breaking strength, and lodging resistance; however, it increased cell wall thickness. In leaves, exogenous AOS up-regulated the expression level of OSCESA8, increased abscisic acid (ABA) and brassinosteroids (BR) content, and increased β-galacturonic activity, polygalacturonase activity, xylanase activity, laccase activity, biomass, and cellulose content. Moreover, AOS down-regulated the expression levels of OSMYB46 and OSIRX10 and decreased cell wall hemicellulose, pectin, and lignin content to maintain cell wall stability under salt stress. In stems, AOS increased phenylalamine ammonia-lyase and tyrosine ammonia-lyase activities, while decreasing cellulase, laccase, and β-glucanase activities. Furthermore, AOS improved the biomass and stem basal width and also enhanced the cellulose, pectin, and lignin content of the stem, As a result, increased resistance to stem breakage strength and alleviated salt stress-induced damage, thus enhancing the lodging resistance. Under salt stress, AOS regulates phytohormones and modifies cellulose, hemicellulose, lignin, and pectin metabolism to maintain cell wall structure and improve stem resistance to lodging. This study aims to alleviate salt stress damage to rice cell walls, enhance resistance to lodging, and improve salt tolerance in rice by exogenous application of AOS.

Identification of Candidate Genes for Salt Tolerance at Seedling Stage in Rice Using QTL-Seq and Chromosome Segment Substitution Line-Derived Population

Rice is a staple food for more than half of the world’s population. However, the pervasive problem of salinity is severely undermining rice production, especially in coastal and low-lying areas where soil salinization is widespread. This stress, exacerbated by climate change, necessitates the development of salt-tolerant rice varieties to ensure food security. In this study, an F2:3 population (n = 454) from a cross of KDML105 and its chromosome segment substitution line (CSSL) was used to identify genomic regions associated with salt tolerance at the seedling stage. Using the QTL-seq approach, a QTL significantly associated with salt tolerance was identified on chromosome 1. Annotation of candidate genes in this region revealed the potential regulators of salt tolerance, including MIKC-type MADS domain proteins, calmodulin-binding transcription factors, and NB-ARC domain-containing proteins. These and other identified genes provide insights into the genetic basis of salt tolerance. This study underscores the importance of using advanced genomics tools and CSSL populations in the study of complex traits such as salt tolerance in rice. Several candidate genes identified in this study could be used in further studies on molecular or physiological mechanisms related to the salt response and tolerance mechanism in rice. Additionally, these genes could also be utilized in plant breeding programs for salt tolerance.

Flooding Tolerance of Rice: Regulatory Pathways and Adaptive Mechanisms.

Rice is a major food crop for more than half of the world's population, while its production is seriously threatened by flooding, a common environmental stress worldwide. Flooding leads to oxygen deficiency, which is a major problem for submerged plants. Over the past three decades, significant progress has been made in understanding rice adaptation and molecular regulatory mechanisms in response to flooding. At the seed germination and seedling establishment stages, the CIPK15-SnRK1A-MYBS1 signaling cascade plays a central role in determining rice submergence tolerance. However, from seedlings to mature plants for harvesting, SUB1A- and SK1/SK2-regulated pathways represent two principal and opposite regulatory mechanisms in rice. In addition, phytohormones, especially gibberellins, induce adaptive responses to flooding throughout the rice growth period. This review summarizes the significant adaptive traits observed in flooded rice varieties and updates the molecular genetics and mechanisms of submergence tolerance in rice.

Marker assisted breeding of Sub1 introgressed rice (Oryza sativa L.) lines and identification of stable variety MTU 1232 suitable for flood prone ecosystem

The Development of flood-tolerant rice varieties is a prerequisite for climate resilience in flood-prone areas. The present study aimed to develop a stable, high, yielding, and tolerant rice variety against flash floods and stagnant flooding across multiple environments. Sub1A was incorporated into a popular rice variety MTU 1075 using Swarna-sub1 as a donor to generate BC3F5 families. Sub1BC2 was used as a foreground marker for selection, a proxy for the Sub1A gene. RM23865 and RM464 on Chromosome 9 were used as recombinant markers. Backcross families from the BC3F2 generation were evaluated under two weeks of flash floods 15 days after transplanting. This was followed by stagnant flooding and survived BC3F4 families were used for background selection using a 50K high-density SNP chip. The nine best families identified were included in the field trial evaluation under eight environments. Consequently, MTU Rice 1232 was identified as a high-yielding, flood-tolerant rice variety using Additive Main effects and Multiplicative Interaction stability analysis. The MTU Rice 1232 ranked first by the Best linear unbiased prediction (BLUP) based ranking parameters and 4th based on stability parameters ranking. This flood-tolerant rice variety can tolerate both flash floods and stagnant flooding and possesses an 80% survival rate. It has a yield potential of 3792 Kg ha-1 under severe floods and 6000 Kg ha-1 under normal conditions.

A bamboo bHLH transcription factor PeRHL4 has dual functions in enhancing drought and phosphorus starvation tolerance.

ROOTHAIRLESS (RHL) is a typical type of basic helix-loop-helix (bHLH) transcription factor (TF), which has been reported to participate in various aspects of plant growth and in response to stress. However, the functions of RHL subfamily members in moso bamboo (Phyllostachys edulis) remain unknown. In this study, we identified 14 bHLH genes (PeRHL1-PeRHL14) in moso bamboo. Phylogenetic tree and conserved motif analyses showed that PeRHLs were clustered into three clades. The expression analysis suggested that PeRHL4 was co-expressed with PeTIP1-1 and PePHT1-1 in moso bamboo. Moreover, these three genes were all up-regulated in moso bamboo under drought stress and phosphate starvation. Y1H, DLRand EMSA assays demonstrated that PeRHL4 could activate the expression of PeTIP1-1 and PePHT1-1. Furthermore, overexpression of PeRHL4 could increase both drought and phosphate starvation tolerance in transgenic rice, in which the expression of OsTIPs and OsPHT1s was significantly improved, respectively. Overall, our results indicated that drought stress and phosphate starvation could induce the expression of PeRHL4, which in turn activated downstream genes involved in water and phosphate transport. Collectively, our findings reveal that PeRHL4 acting as a positive regulator contributes to enhancing the tolerance of moso bamboo under drought stress and phosphate starvation.

Targeting OsNIP3;1 via CRISPR/Cas9: A strategy for minimizing arsenic accumulation and boosting rice resilience

Arsenic (As) contamination in rice poses a significant threat to human health due to its toxicity and widespread consumption. Identifying and manipulating key genes governing As accumulation in rice is crucial for reducing this threat. The large NIP gene family of aquaporins in rice presents a promising target due to functional redundancy, potentially allowing for gene manipulation without compromising plant growth. This study aimed to utilize genome editing to generate knock-out (KO) lines of genes of NIP family (OsLsi1, OsNIP3;1) and an anion transporter family (OsLsi2), in order to assess their impact on As accumulation and stress tolerance in rice. KO lines were created using CRISPR/Cas9 technology, and the As accumulation patterns, physiological performance, and grain yield were compared against wild-type (WT) under As-treated conditions. KO lines exhibited significantly reduced As accumulation in grain compared to WT. Notably, Osnip3;1 KO line displayed reduced As in xylem sap (71–74%) and grain (32–46%) upon treatment. Additionally, these lines demonstrated improved silicon (23%) uptake, photosynthetic pigment concentrations (Chl a: 77%; Chl b: 79%, Total Chl: 79% & Carotenoid: 49%) overall physiological and agronomical performance under As stress compared to WT. This study successfully utilized genome editing for the first time to identify OsNIP3;1 as a potential target for manipulating As accumulation in rice without compromising grain yield or plant vigor.

Combined Transcriptome and Proteome Analysis Reveals the Molecular Mechanism by Which ZmPDI Improves Salt Resistance in Rice (Oryza sativa)

As one of the most salt-tolerant grasses, characterizing salt-tolerance genes of Zoysia matrella [L.] Merr. not only broaden the theoretical information of salt tolerance, but also provide new salt-resistant genetic resources for crop breeding. The salt-inducible protein disulfide isomerase (ZmPDI) of Zoysia matrella [L.] Merr. was proved to enhance salt tolerance in homologous overexpression transgenic plants. In order to evaluate its potential application in crops, we conducted the salt tolerance evaluation in heterologous overexpression transgenic rice (OX-ZmPDI), Wild-type (WT) rice, and LOC_Os11g09280 (OsPDI, homologous gene of ZmPDI in rice) knock-out rice generated by CRISPR-Cas9 system (CR-OsPDI). Our findings revealed that OX-ZmPDI rice was higher and exhibited longer main root length, more proline (Pro) and malondialdehyde (MDA) and peroxidase (POD) activity than WT control after salt treatment, while CR-OsPDI resulted in contrary phenotypes. These results indicated that ZmPDI can significantly enhance the salt tolerance in rice, whereas loss-of-function of OsPDI reduces the salt tolerance. To further investigate these differences at the molecular level, we collected roots from OX-ZmPDI transgenic, CR-OsPDI transgenic, and wild-type (WT) plants at 0 and 24 h after salt treatment for RNA-seq and data-independent acquisition (DIA) proteome sequencing. Combined analysis of the transcriptome and proteome revealed that ZmPDI has the potential to enhance the salt tolerance of rice by modulating the expression of laccase-6, zingipain-2, WIP3, FKBP65, AKR4C10, GBSSII, Pho1, and TRXf1. Those results provided new information for the molecular regulation mechanism by which ZmPDI improves salt tolerance, and prove the potential of ZmPDI for application in crop breeding.

Partial root-zone drying combined with nitrogen treatments mitigates drought responses in rice.

Drought is a major stress affecting rice yields. Combining partial root-zone drying (PRD) and different nitrogen fertilizers reduces the damage caused by water stress in rice. However, the underlying molecular mechanisms remain unclear. In this study, we combined treatments with PRD and ammonia:nitrate nitrogen at 0:100 (PRD0:100) and 50:50 (PRD50:50) ratios or PEG and nitrate nitrogen at 0:100 (PEG0:100) ratios in rice. Physiological, transcriptomic, and metabolomic analyses were performed on rice leaves to identify key genes involved in water stress tolerance under different nitrogen forms and PRD pretreatments. Our results indicated that, in contrast to PRD0:100, PRD50:50 elevated the superoxide dismutase activity in leaves to accelerate the scavenging of ROS accumulated by osmotic stress, attenuated the degree of membrane lipid peroxidation, stabilized photosynthesis, and elevated the relative water content of leaves to alleviate the drought-induced osmotic stress. Moreover, the alleviation ability was better under PRD50:50 treatment than under PRD0:100. Integrated transcriptome and metabolome analyses of PRD0:100 vs PRD50:50 revealed that the differences in PRD involvement in water stress tolerance under different nitrogen pretreatments were mainly in photosynthesis, oxidative stress, nitrogen metabolism process, phytohormone signaling, and biosynthesis of other secondary metabolites. Some key genes may play an important role in these pathways, including OsGRX4, OsNDPK2, OsGS1;1, OsNR1.2, OsSUS7, and YGL8. Thus, the osmotic stress tolerance mediated by PRD and nitrogen cotreatment is influenced by different nitrogen forms. Our results provide new insights into osmotic stress tolerance mediated by PRD and nitrogen cotreatment, demonstrate the essential role of nitrogen morphology in PRD-induced molecular regulation, and identify genes that contribute to further improving stress tolerance in rice.

Effect of Cd(II) adsorption onto rice roots on its uptake by different indica and japonica rice varieties and toxicity effect of Cd(II) under acidic conditions.

The rapid increase in soil acidity coupled with the deleterious effects of cadmium (Cd) toxicity had led to a decline in worldwide agricultural production. Rice absorbs and accumulates Cd(II) from polluted paddy soils, increasing human health risks throughout the food chain. A 35-day hydroponic experiment with four japonica and four indica (two each of them tolerant and sensitive cultivars) was conducted in this study to investigate the adsorption and absorption of Cd(II) by rice roots as related with surface chemical properties of the roots. The results showed that the three chemical forms of exchangeable, complexed, and precipitated Cd(II) increased with the increase in Cd(II) concentration for all rice cultivars. The roots of indica rice cultivars carried more negative charges and had greater functional groups and thus adsorbed more exchangeable and complexed Cd(II) than those of japonica rice cultivars. This led to more absorption of Cd(II) by the roots and greater toxicity of Cd(II) to the roots of indica rice cultivars and more inhibition of Cd(II) stress on the growth of the roots and whole plants of indica rice cultivars compared with japonica rice cultivars, which was one of the main reasons for more declines in the biomass and length of indica rice roots and shoots than japonica rice cultivars. Cd(II) stress showed more toxicity to the sensitive rice cultivars and thus greater inhibition on the growth of the cultivars due to more exchangeable and complexed Cd(II) adsorbed by their roots induced by more negative charges and functional groups on the roots compared with tolerant rice cultivar for both indica and japonica, which resulted in greater decreases in the biomass and length of roots and shoots as well as chlorophyll contents of the sensitive cultivars than the tolerant cultivars. The roots of sensitive rice cultivars also absorbed more Cd(II) than tolerant rice cultivars due to the same reasons as above. These findings will provide useful references for the safe utilization and health risk prevention of Cd-contaminated paddy fields.

Screening of Rice (Oryza sativa L.) Genotypes for Salinity Tolerance and Dissecting Determinants of Tolerance Mechanism.

Soil salinity imposes osmotic, ionic, and oxidative stresses on plants, resulting in growth inhibition, developmental changes, metabolic adaptations, and ion sequestration or exclusion. Identifying salinity-tolerant resources and understanding physiological and molecular mechanisms of salinity tolerance could lay a foundation for the improvement of salinity tolerance in rice. In this study, a series of salinity-tolerance-related morphological and physiological traits were investigated in 46 rice genotypes, including Sea Rice 86, to reveal the main strategies of rice in responding to salinity stress at the seedling stage. No genotypes showed the same tolerance level as the two landraces Pokkali and Nona Bokra, which remain the donors for improving the salinity tolerance of rice. However, due to undesirable agronomic traits of these donors, alternative cultivars such as JC118S and R1 are recommended as novel source of salinity tolerance. Correlation and principal component analyses revealed that the salinity tolerance of rice seedlings is not only controlled by growth vigor but also regulated by ion transport pathways such as long-distance Na+ transport, root Na+ sequestration, and root K+ retention. Therefore, such key traits should be targeted in future breeding programs as the strategy of obtaining better Na+ exclusion is still the bottleneck for improving salinity tolerance in rice.