Genetic variation and gene expression of anthocyanin synthesis and transport related enzymes in Oryza sativa against thiocyanate

Exogenous proline mediates OsNPR1 to regulate the innate pool of IAA in response to Cr exposure in rice plants

Indole acetic acid (IAA) orchestrates a myriad of physiological and biochemical responses in plants under stressful conditions, highlighting its indispensable role in plant resilience. The widespread contamination of chromium (Cr) poses a significant threat to rice cultivation, as its accumulation in plants disrupts various metabolic processes, consequently hindering growth. Of course, the utilization of exogenous growth regulators, including proline (Pro), has notably surged as a strategy to mitigate stress in plants. Pro can trigger the activation of other growth-regulating molecules, including IAA, to coordinate stress responses. To explore the complex interaction between exogenous Pro and the endogenous pool of IAA under Cr(VI) toxicity, a hydroponic system was established. The rice plants treated with exogenous Pro in coupled with Cr(VI) [Cr(VI)+Pro] showed significantly greater content of IAA than the plants not treated with exogenous Pro [Cr(VI)-Pro]. The expression analysis of genes involved in the speciation of IAA reactions reveals that the downregulation of OsNPR1 under "Cr(VI)+Pro" treatments might be the crucial player in increasing the IAA content in rice plants. The increase in IAA by Pro treatment under Cr toxicity might lead to an improvement in root activity and root architecture elements. Importantly, no significant difference was observed in the accumulation of Cr in [Cr(VI)-Pro]- and [Cr(VI)+Pro]-treated rice plants. These results reveal that exogenous Pro can improve plant growth by inducing IAA accumulation in plant tissues exposed to Cr(VI) toxicity, without increasing Cr toxicity in plants.

Regulatory Mechanisms of Phytohormones in Thiocyanate-Exposed Rice Plants: Integrating Multi-Omics Profiling with Mathematical Modeling

Plants experience various abiotic stresses, among which pollutant stress is one of the most damaging, threatening plant productivity and survival. Thiocyanate (SCN-), a recalcitrant byproduct of industrial processes, poses escalating threats to agroecosystems by disrupting plant hormonal homeostasis, which is critical for stress adaptation. Here, we dissect the regulatory interplay of phytohormones in rice (Oryza sativa L.) under SCN- stress (4.80-124.0 mg SCN/L) through integrated transcriptomic and metabolomic profiling. Quantitative hormonal assays revealed dose- and tissue-specific perturbations in phytohormone homeostasis, with shoots exhibiting higher sensitivity than roots. Transcriptomic analysis revealed that a number of differentially expressed genes (DEGs) mapped in different phytohormone pathways in SCN--treated rice seedlings, and their transcript abundances are tissue-specific. To identify the phytohormones governing rice's sensitivity to SCN- stress, we developed a Total Hormonal Sensitivity Index (THSI) through an integrative multivariate framework, which combines Modified Variable Importance in Projection (VIP(m)) scores to quantify hormonal fluctuations and Total Weighted Contribution Scores (TWCS) at the gene-level from hormonal pathways. This study establishes a system-level understanding of how phytohormonal crosstalk mediates rice's adaptation to SCN- stress, providing biomarkers for phytoremediation strategies in contaminated paddies.

Elevated CO2 enhances growth and cyanide assimilation in nitrogen-deficient rice: A transcriptome and metabolomic perspective

Plants face multiple challenges from environmental pollutants and higher emissions of atmospheric CO2. Therefore, a hydroponic-based experiment was used to explore the combined effects of elevated [CO2] (700 ppm) and exogenous cyanide (CN-) (3.0 mg CN/L) on rice seedlings under nitrogen deficiency, utilizing metabonomic and transcriptomic analysis. Elevated [CO2] significantly improved the growth of CN--treated rice seedlings compared to those with ambient [CO2] (350 ppm), and it also significantly affected CN- assimilation. Transcriptome analysis revealed distinct impacts on differentially expressed genes (DEGs) across treatments and tissues. KEGG analysis showed variability in DEGs enriched in amino acid (AA) and energy metabolism pathways due to elevated [CO2] and CN-. Metabonomic indicated that higher input of [CO2] and exogenous CN- more severely impacted energy metabolism elements than the individual species of AAs. Positive synergistic effects of elevated [CO2] and CN- were observed for glutamine and asparagine in shoots, and methionine in roots, wherein negative effects were noted for phenylalanine in shoots, and phenylalanine, valine, and alanine in roots. Meanwhile, positive effects on fumarate in shoots and α-ketoglutarate and succinate in roots were also found. Overall, elevated [CO2] enhanced growth in CN--treated rice seedlings under nitrogen deficiency by altering AA and energy metabolism. This is the first attempt to provide new evidence of [CO2]-based gaseous fertilization as an energy-saving strategy for rice plants fed with biodegradable N-containing pollutants as a supporting N source under N deficient conditions.

SOS! Hydrogen Sulfide Enhances the Flavonoid Early Warning System in Rice Plants to Cope with Thiocyanate Pollution

The presence of thiocyanate (SCN-) in irrigation water has adverse effects on both plant growth and crop output. Hydrogen sulfide (H2S) is an important gaseous signaling molecule that can alleviate SCN- stress. Flavonoids are secondary compounds produced by plants and are ubiquitous in the plant kingdom. They play important roles in several physiological and biochemical processes. To investigate the effect of exogenous H2S on the growth of early rice plants under SCN- stress, we carried out a hydroponic experiment focusing on the interaction of exogenous H2S with flavonoids. In this study, a hydroponic experiment was performed to investigate the behavior of SCN- when subjected to varying effective doses (EC20: 24.0 mg/L; EC50: 96.0 mg/L; and EC75: 300.0 mg/L). The findings indicated that the relative growth rate (RGR) of the plants treated with H2S + SCN- was greater than that of the plants treated with SCN- alone. Higher amounts of flavonoids were detected in the shoots than in the roots, with more variability in the shoots. The early warning level results showed that most of the flavonoids were present at levels I and II, while quercetin was present at level IV. Genetic expression variation factor (GEVF) analyses revealed an increase in the quantity of "promoter genes" with increasing SCN- concentration in both rice tissues. Furthermore, administering external H2S while exposing rice tissues to SCN- resulted in a considerable decrease in the levels of reactive oxygen species. This study provides novel insights into the regulation of flavonoid levels in rice plants by exogenous H2S, facilitating enhanced resistance to SCN- stress and promoting sustainable agriculture.

Elucidating the intricacies of the H2S signaling pathway in gasotransmitters: Highlighting the regulation of plant thiocyanate detoxification pathways

In recent decades, there has been increasing interest in elucidating the role of sulfur-containing compounds in plant metabolism, particularly emphasizing their function as signaling molecules. Among these, thiocyanate (SCN-), a compound imbued with sulfur and nitrogen, has emerged as a significant environmental contaminant frequently detected in irrigation water. This compound is known for its potential to adversely impact plant growth and agricultural yield. Although adopting exogenous SCN- as a nitrogen source in plant cells has been the subject of thorough investigation, the fate of sulfur resulting from the assimilation of exogenous SCN- has not been fully explored. There is burgeoning curiosity in probing the fate of SCN- within plant systems, especially considering the possible generation of the gaseous signaling molecule, hydrogen sulfide (H2S) during the metabolism of SCN-. Notably, the endogenous synthesis of H2S occurs predominantly within chloroplasts, the cytosol, and mitochondria. In contrast, the production of H2S following the assimilation of exogenous SCN- is explicitly confined to chloroplasts and mitochondria. This phenomenon indicates complex interplay and communication among various subcellular organelles, influencing signal transduction and other vital physiological processes. This review, augmented by a small-scale experimental study, endeavors to provide insights into the functional characteristics of H2S signaling in plants subjected to SCN--stress. Furthermore, a comparative analysis of the occurrence and trajectory of endogenous H2S and H2S derived from SCN--assimilation within plant organisms was performed, providing a focused lens for a comprehensive examination of the multifaceted roles of H2S in rice plants. By delving into these dimensions, our objective is to enhance the understanding of the regulatory mechanisms employed by the gasotransmitter H2S in plant adaptations and responses to SCN--stress, yielding invaluable insights into strategies for plant resilience and adaptive capabilities.

Thiocyanate-degrading microflora alleviates thiocyanate stress on tomato seedlings by improving plant and rhizosphere microenvironment

Thiocyanate in irrigation water can adversely affect plant growth and development. A previously constructed microflora with effective thiocyanate-degrading ability was used to investigate the potential of bacterial degradation for thiocyanate bioremediation. The root and aboveground part dry weight of plants inoculated with the degrading microflora increased by 66.67% and 88.45%, respectively, compared to those plants without the microflora. The supplementation of thiocyanate-degrading microflora (TDM) significantly alleviated the interference of thiocyanate in mineral nutrition metabolism. Moreover, the supplementation of TDM significantly reduced the activities of antioxidant enzymes, lipid peroxidation, and DNA damage and it protected plants from excessive thiocyanate, while the crucial antioxidant enzyme (peroxidase) decreased by 22.59%. Compared with the control without TDM supplementation, the soil sucrase content increased by 29.58%. The abundances of Methylophilus, Acinetobacter, unclassified Saccharimonadales, and Rhodanobacter changed from 19.92%, 6.63%, 0.79%, and 3.90%-13.19%, 0.27%, 3.06%, and 5.14%, respectively, with TDM supplementation. Caprolactam, 5,6-dimethyldecane, and pentadecanoic acid seem to have an effect on the structure of the microbial community in the rhizosphere soil. The above results indicated TDM supplementation can significantly reduce the toxic effects of thiocyanate on the tomato-soil microenvironment.

A newly developed consortium with a highly efficient thiocyanate degradation capacity: A comprehensive investigation of the degradation and detoxification potential

Thiocyanate-containing wastewater harms ecosystems and can cause serious damage to animals and plants, so it is urgent to treat it effectively. In this study, a new efficient thiocyanate-degrading consortium was developed and its degradation characteristics were studied. It was found that up to 154.64 mM thiocyanate could be completely degraded by this consortium over 6 days of incubation, with a maximum degradation rate of 1.53 mM h^-1. High-throughput sequencing analysis showed that Thiobacillus (77.78%) was the predominant thiocyanate-degrading bacterial genus. Plant toxicology tests showed that the germination index of mung bean and rice seeds cultured with media obtained after thiocyanate degradation by the consortium increased by 94% and 84.83%, respectively, compared with the control group without thiocyanate degradation. Cytotoxicity tests showed that thiocyanate without degradation significantly decreased the Neuro-2a cell activity and mitochondrial membrane potential; induced reactive oxygen species generation and apoptosis; increased the cellular Ca²⁺ concentration; and damaged the cell nucleus and DNA. Furthermore, the thiocyanate degradation products produced the consortium were almost totally non-toxic, revealing the same characteristics as those of the control using distilled water. This study shows that the consortium has a high degradation efficiency and detoxification characteristics, as well as great application potential in bioremediation of industrial thiocyanate-containing wastewater.

Individual and mutual effects of elevated carbon dioxide and temperature on salt and cadmium uptake and translocation by rice seedlings

Plant kingdoms are facing increasingly harsh environmental challenges marked by the coexposure of salinity and pollution in the pedosphere and elevated CO₂ and temperature in the atmosphere due to the rapid acceleration of industrialization and global climate change. In this study, we deployed a hydroponics-based experiment to explore the individual and mutual effects of different temperatures (low temperature, T1: 23°C; high temperature, T2: 27°C) and CO₂ concentrations (ambient CO₂: 360 ppm; medium CO₂: 450 ppm; high CO₂: 700 ppm) on the uptake and translocation of sodium chloride (NaCl, 0.0, 0.2, 0.6, and 1.1 g Na/L) and cadmium nitrate (Cd(NO₃)₂·4H₂O, 0.0, 0.2, 1.8, and 5.4 mg Cd/L) by rice seedlings. The results indicated that Cd and Na exposure significantly (P< 0.05) inhibited plant growth, but T2 and medium/high CO₂ alleviated the effects of Cd and Na on plant growth. Neither significant synergistic nor antagonistic effects of Cd and Na were observed, particularly not at T1 or high CO₂. At increasing temperatures, relative growth rates increased despite higher concentrations of Cd and Na in both rice roots and shoots. Similarly, higher CO₂ stimulated the growth rate but resulted in significantly lower concentrations of Na, while the Cd concentration was highest at medium CO₂. Coexposure experiments suggested that the concentration of Cd in roots slightly declined with additional Na and more at T2. Overall, our preliminary study suggested that global climate change may alter the distribution of mineral and toxic elements in rice plants as well as the tolerance of the plants.

HvGST plays a key role in anthocyanin accumulation in colored barley

Blue aleurone of barley is caused by the accumulation of delphinidin-based derivatives. Although these compounds are ideal nutrients for human health, they are undesirable contaminants in malt brewing. Therefore, the ability to add and remove this trait easily would facilitate breeding barley for different purposes. Here we identified a glutathione S-transferase gene (HvGST) that was responsible for the blue aleurone trait in Tibetan qingke barley by performing a genome-wide association study and RNA-sequencing analysis. Gene variation and expression analysis indicated that HvGST also participates in the transport and accumulation of anthocyanin in purple barley. Haplotype and the geographic distribution analyses of HvGST alleles revealed two independent natural variants responsible for the emergence of white aleurone: a 203-bp deletion causing premature termination of translation in qingke barley and two key single nucleotide polymorphisms in the promoter resulting in low transcription in Western barley. This study contributes to a better understanding of mechanisms of colored barley formation, and provides a comprehensive reference for marker-assisted barley breeding.

Involvement of β-cyanoalanine synthase (β-CAS) and sulfurtransferase (ST) in cyanide (CN-) assimilation in rice seedlings

In spite of available information demonstrating the assimilation of cyanide (CN^-) by β-cyanoalanine synthase (β-CAS) in plants, involvement of sulfurtransferase (ST) in CN^- assimilation in rice plants is still undefined. In this study, a microcosmic hydroponic system was used to investigate the involvement of β-cyanoalanine synthase (β-CAS) and sulfurtransferase (ST) in the CN^- assimilation in rice seedlings under the exposure of potassium cyanide (KCN) in presence or absence of 1-amino-cyclopropane-1-carboxylic acid (ACC). Our results indicated that the measurable thiocyanate (SCN^-) was detected in both rice roots and shoots under KCN exposure, and the abundances of ST-related transcripts were up-regulated significantly (p < 0.05), suggesting that the ST pathway is involved in CN^- assimilation in the rice plants. The application of exogenous ACC significantly (p < 0.05) decreased the accumulation of CN^- and SCN^- in rice tissues after KCN exposures, and also up-regulated the expression of β-CAS and ST genes and their enzymatic activities, suggesting a positive interaction between aminocyclopropane-1-carboxylate oxidase (ACO), β-CAS and ST in rice plants during the CN^- assimilation. This is the first attempt to experimentally clarify the involvement of ST in CN^- assimilation in rice seedlings.

A Survey of Enhanced Cold Tolerance and Low-Temperature-Induced Anthocyanin Accumulation in a Novel Zoysia japonica Biotype

Zoysia japonica is a warm-season turfgrass that is extensively used in landscaping, sports fields, and golf courses worldwide. Uncovering the low-temperature response mechanism of Z. japonica can help to accelerate the development of new cold-tolerant cultivars, which could be used to prolong the ornamental and usage duration of turf. A novel Z. japonica biotype, YueNong-9 (YN-9), was collected from northeastern China for this study. Phenotypic measurements, cold-tolerance investigation, and whole-transcriptome surveys were performed on YN-9 and LanYin-3 (LY-3), the most popular Z. japonica cultivar in Southern China. The results indicated the following: YN-9 has longer second and third leaves than LY-3; when exposed to the natural low temperature during winter in Guangzhou, YN-9 accumulated 4.74 times more anthocyanin than LY-3; after cold acclimation and freezing treatment, 83.25 ± 9.55% of YN-9 survived while all LY-3 leaves died, and the dark green color index (DGCI) value of YN-9 was 1.78 times that of LY-3; in YN-9, there was a unique up-regulation of Phenylalanine ammonia-lyase (PAL), Homeobox-leucine Zipper IV (HD-ZIP), and ATP-Binding Cassette transporter B8 (ABCB8) expressions, as well as a unique down-regulation of zinc-regulated transporters and iron-regulated transporter-like proteins (ZIPs) expression, which may promote anthocyanin biosynthesis, transport, and accumulation. In conclusion, YN-9 exhibited enhanced cold tolerance and is thus an excellent candidate for breeding cold-tolerant Z. japonica variety, and its unique low-temperature-induced anthocyanin accumulation and gene responses provide ideas and candidate genes for the study of low-temperature tolerance mechanisms and genetic engineering breeding.

The importance of utilizing nitrate (NO3-) over ammonium (NH4+) as nitrogen source during detoxification of exogenous thiocyanate (SCN-) in Oryza sativa

Thiocyanate (SCN^-) is a nitrogen-containing pollutant, which can be involved in the nitrogen (N) cycle and interferes with plant growth. The current study highlights a new insight into the N (nitrate [NO₃^-] and ammonium [NH₄⁺]) utilization ways in rice seedlings under SCN^- exposure to clarify the interactive effect on uptake and assimilation between these N-containing chemicals. Phenotypically, relative growth rates (RGR) of NO₃^--fed seedlings were significantly higher than NH₄⁺-fed rice seedlings at the same SCN^- concentration. Both N fertilizations have no significant influence on SCN^- content and its assimilation in rice seedlings. However, significant accumulation of NO₃^- and NH₄⁺ were detected in shoots prior to roots under SCN^- stress. Enzymatic assay and mRNA analysis showed that the carbonyl sulfide (COS) pathway of SCN^- degradation occurred in both roots and shoots of NO₃^--fed seedlings but only evident in roots of NH₄⁺-fed seedlings. Moreover, the effect of SCN^- on the activity of nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT) was negligible in NO₃^--fed seedlings, while GOGAT activity was significantly inhibited in shoots of NH₄⁺-fed seedlings. Nitrogen use efficiency (NUE) estimation provided positive evidence in utilizing NO₃^- over NH₄⁺ as the main N source to support rice seedling growth during detoxification of exogenous SCN^-. Overall, SCN^- pollution has unexpectedly changed the rice preference for N source which shifted from NH₄⁺ to NO₃^-, suggesting that the interactions of SCN^- with different N sources in terms of uptake and assimilation in rice plants should not be overlooked, especially at the plant N nutritional level.

Proline-mediated regulation on jasmonate signals repressed anthocyanin accumulation through the MYB-bHLH-WDR complex in rice under chromium exposure

Toxic metal-induced overaccumulation of anthocyanin (ATH) in plants can oxidize proteins and break DNA. Herein, the role of exogenous proline (Pro) on the repression of ATH accumulation in rice seedlings during hexavalent chromium [Cr(VI)] exposure was studied. Results indicated that exogenous Pro-mediated regulation of jasmonate signals activated the MYB-bHLH-WDR complex to repress ATH accumulation in rice tissues under Cr(VI) stress. Biochemical and transcript analysis indicated that exogenous Pro promoted the synthesis of jasmonic acid (JA) and its molecularly active metabolite jasmonic acid isoleucine (JA-Ile) in rice tissues under Cr(VI) stress. Increment in the endogenous level of jasmonates positively triggered the expression of genes responsible for the JA signaling pathway and activated the MYB-bHLH-WDR complex, eventually repressing the glycosylation of anthocyanidin to form ATH in rice tissues. In conclusion, exogenous proline-mediated regulation on jasmonate signals was tissue-specific under Cr(VI) stress and a more positive effect was detected in shoots rather than roots.