Glycolate oxidase-dependent H2O2 production regulates IAA biosynthesis in rice

Enhanced Rice Resistance to Sheath Blight through Nitrate Transporter 1.1B Mutation without Yield Loss under NH4+ Fertilization

Nitrogen fertilization can promote rice yield but decrease resistance to sheath blight (ShB). In this study, the nitrate transporter 1.1b (nrt1.1b) mutant that exhibited less susceptibility to ShB but without compromising yield under NH4+ fertilization was screened. NRT1.1B's regulation of ShB resistance was independent of the total nitrogen concentration in rice under NH4+ conditions. In nrt1.1b mutant plants, the NH4+ application modulated auxin signaling, chlorophyll content, and phosphate signaling to promote ShB resistance. Furthermore, the findings indicated that NRT1.1B negatively regulated ShB resistance by positively modulating the expression of H+-ATPase gene OSA3 and phosphate transport gene PT8. The mutation of OSA3 and PT8 promoted ShB resistance by increasing the apoplastic pH in rice. Our study identified the ShB resistance mutant nrt1.1b, which maintained normal nitrogen use efficiency without compromising yield.

Wounding induces a peroxisomal H2 O2 decrease via glycolate oxidase-catalase switch dependent on glutamate receptor-like channel-supported Ca2+ signaling in plants

Sensing of environmental challenges, such as mechanical injury, by a single plant tissue results in the activation of systemic signaling, which attunes the plant's physiology and morphology for better survival and reproduction. As key signals, both calcium ions (Ca2+ ) and hydrogen peroxide (H2 O2 ) interplay with each other to mediate plant systemic signaling. However, the mechanisms underlying Ca2+ -H2 O2 crosstalk are not fully revealed. Our previous study showed that the interaction between glycolate oxidase and catalase, key enzymes of photorespiration, serves as a molecular switch (GC switch) to dynamically modulate photorespiratory H2 O2 fluctuations via metabolic channeling. In this study, we further demonstrate that local wounding induces a rapid shift of the GC switch to a more interactive state in systemic leaves, resulting in a sharp decrease in peroxisomal H2 O2 levels, in contrast to a simultaneous outburst of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived apoplastic H2 O2 . Moreover, the systemic response of the two processes depends on the transmission of Ca2+ signaling, mediated by glutamate-receptor-like Ca2+ channels 3.3 and 3.6. Mechanistically, by direct binding and/or indirect mediation by some potential biochemical sensors, peroxisomal Ca2+ regulates the GC switch states in situ, leading to changes in H2 O2 levels. Our findings provide new insights into the functions of photorespiratory H2 O2 in plant systemic acclimation and an optimized systemic H2 O2 signaling via spatiotemporal interplay between the GC switch and NADPH oxidases.

Mitogen-activated protein kinase 2 specifically regulates photorespiration in rice

Photorespiration begins with the oxygenation reaction catalyzed by Rubisco and is the second highest metabolic flux in plants after photosynthesis. Although the core biochemical pathway of photorespiration has been well characterized, little is known about the underlying regulatory mechanisms. Some rate-limiting regulation of photorespiration has been suggested to occur at both the transcriptional and posttranslational levels, but experimental evidence is scarce. Here, we found that mitogen-activated protein kinase 2 (MAPK2) interacts with photorespiratory glycolate oxidase and hydroxypyruvate reductase, and the activities of these photorespiratory enzymes were regulated via phosphorylation modifications in rice (Oryza sativa L.). Gas exchange measurements revealed that the photorespiration rate decreased in rice mapk2 mutants under normal growth conditions, without disturbing photosynthesis. Due to decreased photorespiration, the levels of some key photorespiratory metabolites, such as 2-phosphoglycolate, glycine, and glycerate, significantly decreased in mapk2 mutants, but those of photosynthetic metabolites were not altered. Transcriptome assays also revealed that the expression levels of some flux-controlling genes in photorespiration were significantly downregulated in mapk2 mutants. Our findings provide molecular evidence for the association between MAPK2 and photorespiration and suggest that MAPK2 regulates the key enzymes of photorespiration at both the transcriptional and posttranslational phosphorylation levels in rice.

Transcriptome Analysis Revealed the Potential Molecular Mechanism of Anthocyanidins' Improved Salt Tolerance in Maize Seedlings

Anthocyanin, a kind of flavonoid, plays a crucial role in plant resistance to abiotic stress. Salt stress is a kind of abiotic stress that can damage the growth and development of plant seedlings. However, limited research has been conducted on the involvement of maize seedlings in salt stress resistance via anthocyanin accumulation, and its potential molecular mechanism is still unclear. Therefore, it is of great significance for the normal growth and development of maize seedlings to explore the potential molecular mechanism of anthocyanin improving salt tolerance of seedlings via transcriptome analysis. In this study, we identified two W22 inbred lines (tolerant line pur-W22 and sensitive line bro-W22) exhibiting differential tolerance to salt stress during seedling growth and development but showing no significant differences in seedling characteristics under non-treatment conditions. In order to identify the specific genes involved in seedlings' salt stress response, we generated two recombinant inbred lines (RILpur-W22 and RILbro-W22) by crossing pur-W22 and bro-W22, and then performed transcriptome analysis on seedlings grown under both non-treatment and salt treatment conditions. A total of 6100 and 5710 differentially expressed genes (DEGs) were identified in RILpur-W22 and RILbro-W22 seedlings, respectively, under salt-stressed conditions when compared to the non-treated groups. Among these DEGs, 3160 were identified as being present in both RILpur-W22 and RILbro-W22, and these served as commonly stressed EDGs that were mainly enriched in the redox process, the monomer metabolic process, catalytic activity, the plasma membrane, and metabolic process regulation. Furthermore, we detected 1728 specific DEGs in the salt-tolerant RILpur-W22 line that were not detected in the salt-sensitive RILbro-W22 line, of which 887 were upregulated and 841 were downregulated. These DEGs are primarily associated with redox processes, biological regulation, and the plasma membrane. Notably, the anthocyanin synthesis related genes in RILpur-W22 were strongly induced under salt treatment conditions, which was consistented with the salt tolerance phenotype of its seedlings. In summary, the results of the transcriptome analysis not only expanded our understanding of the complex molecular mechanism of anthocyanin in improving the salt tolerance of maize seedlings, but also, the DEGs specifically expressed in the salt-tolerant line (RILpur-W22) provided candidate genes for further genetic analysis.

Exploring Exogenous Indole-3-acetic Acid's Effect on the Growth and Biochemical Profiles of Synechocystis sp. PAK13 and Chlorella variabilis

Microalgae have garnered scientific interest for their potential to produce bioactive compounds. However, the large-scale industrial utilization of microalgae faces challenges related to production costs and achieving optimal growth conditions. Thus, this study aimed to investigate the potential role of exogenous indole-3-acetic acid (IAA) application in improving the growth and production of bioactive metabolites in microalgae. To this end, the study employed different concentrations of exogenously administered IAA ranging from 0.36 µM to 5.69 µM to assess its influence on the growth and biochemical composition of Synechocystis and Chlorella. IAA exposure significantly increased IAA levels in both strains. Consequentially, improved biomass accumulation in parallel with increased total pigment content by approximately eleven-fold in both strains was observed. Furthermore, the application of IAA stimulated the accumulation of primary metabolites. Sugar levels were augmented, providing a carbon source that facilitated amino acid and fatty acid biosynthesis. As a result, amino acid levels were enhanced as well, leading to a 1.55-fold increase in total amino acid content in Synechocystis and a 1.42-fold increase in Chlorella. Total fatty acids content increased by 1.92-fold in Synechocystis and by 2.16-fold in Chlorella. Overall, the study demonstrated the effectiveness of exogenously adding IAA as a strategy for enhancing the accumulation of microalgae biomass and biomolecules. These findings contribute to the advancement of microalgae-based technologies, opening new avenues to produce economically important compounds derived from microalgae.

Effects of exogenous glycine betaine and cycloleucine on photosynthetic capacity, amino acid composition, and hormone metabolism in Solanum melongena L

Although exogenous glycine betaine (GB) and cycloleucine (Cyc) have been reported to affect animal cell metabolism, their effects on plant growth and development have not been studied extensively. Different concentrations of exogenous glycine betaine (20, 40, and 60 mmol L^-1) and cycloleucine (10, 20, and 40 mmol L^-1), with 0 mmol L^-1 as control, were used to investigate the effects of foliar spraying of betaine and cycloleucine on growth, photosynthesis, chlorophyll fluorescence, Calvin cycle pathway, abaxial leaf burr morphology, endogenous hormones, and amino acid content in eggplant. We found that 40 mmol L^-1 glycine betaine had the best effect on plant growth and development; it increased the fresh and dry weight of plants, increased the density of abaxial leaf hairs, increased the net photosynthetic rate and Calvin cycle key enzyme activity of leaves, had an elevating effect on chlorophyll fluorescence parameters, increased endogenous indoleacetic acid (IAA) content and decreased abscisic acid (ABA) content, and increased glutamate, serine, aspartate, and phenylalanine contents. However, cycloleucine significantly inhibited plant growth; plant apical dominance disappeared, plant height and dry and fresh weights decreased significantly, the development of abaxial leaf hairs was hindered, the net photosynthetic rate and Calvin cycle key enzyme activities were inhibited, the endogenous hormones IAA and ABA content decreased, and the conversion and utilization of glutamate, arginine, threonine, and glycine were affected. Combined with the experimental results and plant growth phenotypes, 20 mmol L^-1 cycloleucine significantly inhibited plant growth. In conclusion, 40 mmol L^-1 glycine betaine and 20 mmol L^-1 cycloleucine had different regulatory effects on plant growth and development.

SEMI-ROLLED LEAF 10 stabilizes catalase isozyme B to regulate leaf morphology and thermotolerance in rice (Oryza sativa L.)

Plant architecture and stress tolerance play important roles in rice breeding. Specific leaf morphologies and ideal plant architecture can effectively improve both abiotic stress resistance and rice grain yield. However, the mechanism by which plants simultaneously regulate leaf morphogenesis and stress resistance remains elusive. Here, we report that SRL10, which encodes a double-stranded RNA-binding protein, regulates leaf morphology and thermotolerance in rice through alteration of microRNA biogenesis. The srl10 mutant had a semi-rolled leaf phenotype and elevated sensitivity to high temperature. SRL10 directly interacted with catalase isozyme B (CATB), and the two proteins mutually increased one other's stability to enhance hydrogen peroxide (H₂ O₂ ) scavenging, thereby contributing to thermotolerance. The natural Hap3 (AGC) type of SRL10 allele was found to be present in the majority of aus rice accessions, and was identified as a thermotolerant allele under high temperature stress in both the field and the growth chamber. Moreover, the seed-setting rate was 3.19 times higher and grain yield per plant was 1.68 times higher in near-isogenic line (NIL) carrying Hap3 allele compared to plants carrying Hap1 allele under heat stress. Collectively, these results reveal a new locus of interest and define a novel SRL10-CATB based regulatory mechanism for developing cultivars with high temperature tolerance and stable yield. Furthermore, our findings provide a theoretical basis for simultaneous breeding for plant architecture and stress resistance.

A Single Nucleotide Variation of CRS2 Affected the Establishment of Photosynthetic System in Rice

Chloroplasts are essential sites for plant photosynthesis, and the biogenesis of the photosynthetic complexes involves the interaction of nuclear genes and chloroplast genes. In this study, we identified a rice pale green leaf mutant, crs2. The crs2 mutant showed different degrees of low chlorophyll phenotypes at different growth stages, especially at the seedling stage. Fine mapping and DNA sequencing of crs2 revealed a single nucleotide substitution (G4120A) in the eighth exons of CRS2, causing a G-to-R mutation of the 229th amino acid of CRS2 (G229R). The results of complementation experiments confirmed that this single-base mutation in crs2 is responsible for the phenotype of the crs2 mutant. CRS2 encodes a chloroplast RNA splicing 2 protein localized in the chloroplast. Western blot results revealed an abnormality in the abundance of the photosynthesis-related protein in crs2. However, the mutation of CRS2 leads to the enhancement of antioxidant enzyme activity, which could reduce ROS levels. Meanwhile, with the release of Rubisco activity, the photosynthetic performance of crs2 was improved. In summary, the G229R mutation in CRS2 causes chloroplast protein abnormalities and affects photosystem performance in rice; the above findings facilitate the elucidation of the physiological mechanism of chloroplast proteins affecting photosynthesis.

Functional Characterization of Sugar Beet M14 Antioxidant Enzymes in Plant Salt Stress Tolerance

Salt stress can cause cellular dehydration, which induces oxidative stress by increasing the production of reactive oxygen species (ROS) in plants. They may play signaling roles and cause structural damages to the cells. To overcome the negative impacts, the plant ROS scavenging system plays a vital role in maintaining the cellular redox homeostasis. The special sugar beet apomictic monosomic additional M14 line (BvM14) showed strong salt stress tolerance. Comparative proteomics revealed that six antioxidant enzymes (glycolate oxidase (GOX), peroxiredoxin (PrxR), thioredoxin (Trx), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase3 (DHAR3)) in BvM14 were responsive to salt stress. In this work, the full-length cDNAs of genes encoding these enzymes in the redox system were cloned from the BvM14. Ectopic expression of the six genes reduced the oxidative damage of transgenic plants by regulating the contents of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), ascorbic acid (AsA), and glutathione (GSH), and thus enhanced the tolerance of transgenic plants to salt stress. This work has charecterized the roles that the antioxidant enzymes play in the BvM14 response to salt stress and provided useful genetic resources for engineering and marker-based breeding of crops that are sensitive to salt stress.

Dynamic and fluctuating generation of hydrogen peroxide via photorespiratory metabolic channeling in plants

The homeostasis of hydrogen peroxide (H₂ O₂ ), a key regulator of basic biological processes, is a result of the cooperation between its generation and scavenging. However, the mechanistic basis of this balance is not fully understood. We previously proposed that the interaction between glycolate oxidase (GLO) and catalase (CAT) may serve as a molecular switch that modulates H₂ O₂ levels in plants. In this study, we demonstrate that the GLO-CAT complex in plants exists in different states, which are dynamically interchangeable in response to various stimuli, typically salicylic acid (SA), at the whole-plant level. More crucially, changes in the state of the complex were found to be closely linked to peroxisomal H₂ O₂ fluctuations, which were independent of the membrane-associated NADPH oxidase. Furthermore, evidence suggested that H₂ O₂ channeling occurred even in vitro when GLO and CAT worked cooperatively. These results demonstrate that dynamic changes in H₂ O₂ levels are physically created via photorespiratory metabolic channeling in plants, and that such H₂ O₂ fluctuations may serve as signals that are mechanistically involved in the known functions of photorespiratory H₂ O₂ . In addition, our study also revealed a new way for SA to communicate with H₂ O₂ in plants.

Phytochemical analysis reveals an antioxidant defense response in Lonicera japonica to cadmium-induced oxidative stress

Cadmium (Cd), though potentially beneficial at lower levels to some plant species, at higher levels is a toxic metal that is detrimental to plant growth and development. Cd is also a carcinogen to humans and other contaminated plant consumers, affecting the kidneys and reducing bone strength. In this study we investigated responses of growth, chlorophyll content, reactive oxygen species levels, and antioxidant responses to Cd in honeysuckle leaves (Lonicera japonica Thunb.), a potential Cd hyperaccumulator. Results indicated that plant height, dry weight, leaf area, and chlorophyll content increased when honeysuckle was exposed to 10 mg kg^-1 or 30 mg kg^-1 Cd (low concentration). However, in response to 150 mg kg^-1 or 200 mg kg^-1 Cd (high concentration) these growth parameters and chlorophyll content significantly decreased relative to untreated control plant groups. Higher levels of superoxide radical (O₂^·-) and hydrogen peroxide (H₂O₂) were observed in high concentration Cd groups. The activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase were enhanced with exposure to increasing levels of Cd. Additionally, the Ascorbate-Glutathione (AsA-GSH) cycle was activated for the removal of H₂O₂ in honeysuckle in response to elevated Cd. The Pearson correlation analysis, a redundancy analysis, and a permutation test indicated that proline and APX were dominant antioxidants for removing O₂^·- and H₂O₂. The antioxidants GSH and non-protein thiols (NPTs) also increased as the concentration of Cd increased.