Auxin Crosstalk with Reactive Oxygen and Nitrogen Species in Plant Development and Abiotic Stress

Ectopic Expression of AetPGL from Aegilops tauschii Enhances Cadmium Tolerance and Accumulation Capacity in Arabidopsis thaliana

Cadmium (Cd) is a toxic heavy metal that accumulates in plants, negatively affecting their physiological processes, growth, and development, and poses a threat to human health through the food chain. 6-phosphogluconolactonase (PGL) is a key enzyme in the Oxidative Pentose Phosphate Pathway(OPPP) in plant cells, essential for cellular metabolism. The OPPP pathway provides energy and raw materials for organisms and is involved in antioxidant reactions, lipid metabolism, and DNA synthesis. This study describes the Cd responsive gene AetPGL from Aegilops tauschii. Overexpression of AetPGL under Cd stress increased main root length and germination rate in Arabidopsis. Transgenic lines showed higher antioxidant enzyme activities and lower malondialdehyde (MDA) content compared to the wild type. The transgenic Arabidopsis accumulated more Cd in the aboveground part but not in the underground part. Expression levels of AtHMA3, AtNRAMP5, and AtZIP1 in the roots of transgenic plants increased under Cd stress, suggesting AetPGL may enhance Cd transport from root to shoot. Transcriptome analysis revealed enrichment of differentially expressed genes (DEGs) in the plant hormone signal transduction pathway in AetPGL-overexpressing plants. Brassinosteroids (BR), Gibbenellin acid (GA), and Jasmonic acid (JA) contents significantly increased after Cd treatment. These results indicate that AetPGL may enhance Arabidopsis' tolerance to Cd by modulating plant hormone content. In conclusion, AetPGL plays a critical role in improving cadmium tolerance and accumulation and mitigating oxidative stress by regulating plant hormones, providing insights into the molecular mechanisms of plant Cd tolerance.

HD-ZIP IV Gene ROC1 Regulates Leaf Rolling and Drought Response Through Formation of Heterodimers with ROC5 and ROC8 in Rice

Leaf morphology is a crucial agronomic characteristic of rice that influences crop yield directly. One primary cause of rice leaf rolling can be attributed to alterations in bulliform cells. Several HD-ZIP IV genes have been identified to be epidemical characterized and function in leaf rolling in rice. Still others need to be studied to fully understand the overall function of HD-ZIP IV family. Among the nine ROC genes encoding HD-ZIP IV family transcription factors in rice, ROC1 exhibits the highest expression in the leaves. Overexpression of ROC1 decreased the size of bulliform cells, and thus resulted in adaxially rolled leaves. To the contrary, knockout of ROC1 (ROC1KO) through Crispr-cas9 system enlarged bulliform cells, and thus led to abaxially rolled leaves. Moreover, ROC1KO plants were sensitive to drought. ROC1 could form homodimers on its own, and heterodimers with ROC5 and ROC8 respectively. Compared to ROC1KO plants, leaves of the ROC1 and ROC8 double knocked out plants (ROC1/8DKO) were more severely rolled abaxially due to enlarged bulliform cells, and ROC1/8DKO plants were more drought sensitive. However, overexpression of ROC8 could not restore the abaxial leaf phenotype of ROC1KO plants. Therefore, we proved that ROC1, a member of the HD-ZIP IV family, regulated leaf rolling and drought stress response through tight association with ROC5 and ROC8.

Nitric oxide signal is required for glutathione-induced enhancement of photosynthesis in salt-stressed Solanum lycopersicum L

Reduced glutathione (γ-glutamyl-cysteinyl-glycine, GSH), the primary non-protein sulfhydryl group in organisms, plays a pivotal role in the plant salt stress response. This study aimed to explore the impact of GSH on the photosynthetic apparatus, and carbon assimilation in tomato plants under salt stress, and then investigate the role of nitric oxide (NO) in this process. The investigation involved foliar application of 5 mM GSH, 0.1% (w/v) hemoglobin (Hb, a nitric oxide scavenger), and GSH+Hb on the endogenous NO levels, rapid chlorophyll fluorescence, enzyme activities, and gene expression related to the Calvin cycle in tomato seedlings (Solanum lycopersicum L. cv. 'Zhongshu No. 4') subjected short-term salt stress (100 mM NaCl) for 24, 48 and 72 hours. GSH treatment notably boosted nitrate reductase (NR) and NO synthase (NOS) activities, elevating endogenous NO signaling in salt-stressed tomato seedling leaves. It also mitigated chlorophyll fluorescence (OJIP) curve distortion and damage to the oxygen-evolving complex (OEC) induced by salt stress. Furthermore, GSH improved photosystem II (PSII) electron transfer efficiency, reduced QA - accumulation, and countered salt stress effects on photosystem I (PSI) redox properties, enhancing the light energy absorption index (PIabs). Additionally, GSH enhanced key enzyme activities in the Calvin cycle and upregulated their genes. Exogenous GSH optimized PSII energy utilization via endogenous NO, safeguarded the photosynthetic reaction center, improved photochemical and energy efficiency, and boosted carbon assimilation, ultimately enhancing net photosynthetic efficiency (Pn) in salt-stressed tomato seedling leaves. Conversely, Hb hindered Pn reduction and NO signaling under salt stress and weakened the positive effects of GSH on NO levels, photosynthetic apparatus, and carbon assimilation in tomato plants. Thus, the positive regulation of photosynthesis in tomato seedlings under salt stress by GSH requires the involvement of NO.

Silicon regulates phosphate deficiency through involvement of auxin and nitric oxide in barley roots

MAIN CONCLUSION

Silicon application mitigates phosphate deficiency in barley through an interplay with auxin and nitric oxide, enhancing growth, photosynthesis, and redox balance, highlighting the potential of silicon as a fertilizer for overcoming nutritional stresses. Silicon (Si) is reported to attenuate nutritional stresses in plants, but studies on the effect of Si application to plants grown under phosphate (Pi) deficiency are still very scarce, especially in barley. Therefore, the present work was undertaken to investigate the potential role of Si in mitigating the adverse impacts of Pi deficiency in barley Hordeum vulgare L. (var. BH902). Further, the involvement of two key regulatory signaling molecules--auxin and nitric oxide (NO)--in Si-induced tolerance against Pi deficiency in barley was tested. Morphological attributes, photosynthetic parameters, oxidative stress markers (O2·-, H2O2, and MDA), antioxidant system (enzymatic--APX, CAT, SOD, GR, DHAR, MDHAR as well as non-enzymatic--AsA and GSH), NO content, and proline metabolism were the key traits that were assessed under different treatments. The P deficiency distinctly declined growth of barley seedlings, which was due to enhancement in oxidative stress leading to inhibition of photosynthesis. These results were also in parallel with an enhancement in antioxidant activity, particularly SOD and CAT, and endogenous proline level and its biosynthetic enzyme (P5CS). The addition of Si exhibited beneficial effects on barley plants grown in Pi-deficient medium as reflected in increased growth, photosynthetic activity, and redox balance through the regulation of antioxidant machinery particularly ascorbate-glutathione cycle. We noticed that auxin and NO were also found to be independently participating in Si-mediated improvement of growth and other parameters in barley roots under Pi deficiency. Data of gene expression analysis for PHOSPHATE TRANSPORTER1 (HvPHT1) indicate that Si helps in increasing Pi uptake as per the need of Pi-deficient barley seedlings, and also auxin and NO both appear to help Si in accomplishing this task probably by inducing lateral root formation. These results are suggestive of possible application of Si as a fertilizer to correct the negative effects of nutritional stresses in plants. Further research at genetic level to understand Si-induced mechanisms for mitigating Pi deficiency can be helpful in the development of new varieties with improved tolerance against Pi deficiency, especially for cultivation in areas with Pi-deficient soils.

Carrier-based delivery system of phytohormones in plants: stepping outside of the ordinary

Climate change is increasing the stresses on crops, resulting in reduced productivity and further augmenting global food security issues. The dynamic climatic conditions are a severe threat to the sustainability of the ecosystems. The role of technology in enhancing agricultural produce with the minimum environmental impact is hence crucial. Active molecule/Plant growth regulators (PGRs) are molecules helping plants' growth, development, and tolerance to abiotic and biotic stresses. However, their degradation, leaching in surrounding soil and ground water, as well as the assessment of the correct dose of application etc., are some of the technical disadvantages faced. They can be resolved by encapsulation/loading of PGRs on polymer matrices. Micro/nanoencapsulation is a revolutionary tool to deliver bioactive compounds in an economically affordable and environmentally friendly way. Carrier-based smart delivery systems could be a better alternative to PGRs application in the agriculture field than conventional methods (e.g., spraying). The physiochemical properties and release kinetics of PGRs from the encapsulating system are being explored. Therefore, the present review emphasizes the current status of PGRs encapsulation approach and their potential benefits to plants. This review also addressed the mechanistic action of carrier-based delivery systems for release, which may aid in developing smart delivery systems with specific tailored properties in future research.

Characterization of leucine aminopeptidase (LAP) activity in sweet pepper fruits during ripening and its inhibition by nitration and reducing events

KEY MESSAGE

Pepper fruits contain two leucine aminopeptidase (LAP) genes which are differentially modulated during ripening and by nitric oxide. The LAP activity increases during ripening but is negatively modulated by nitration. Leucine aminopeptidase (LAP) is an essential metalloenzyme that cleaves N-terminal leucine residues from proteins but also metabolizes dipeptides and tripeptides. LAPs play a fundamental role in cell protein turnover and participate in physiological processes such as defense mechanisms against biotic and abiotic stresses, but little is known about their involvement in fruit physiology. This study aims to identify and characterize genes encoding LAP and evaluate their role during the ripening of pepper (Capsicum annuum L.) fruits and under a nitric oxide (NO)-enriched environment. Using a data-mining approach of the pepper plant genome and fruit transcriptome (RNA-seq), two LAP genes, designated CaLAP1 and CaLAP2, were identified. The time course expression analysis of these genes during different fruit ripening stages showed that whereas CaLAP1 decreased, CaLAP2 was upregulated. However, under an exogenous NO treatment of fruits, both genes were downregulated. On the contrary, it was shown that during fruit ripening LAP activity increased by 81%. An in vitro assay of the LAP activity in the presence of different modulating compounds including peroxynitrite (ONOO-), NO donors (S-nitrosoglutathione and nitrosocyteine), reducing agents such as reduced glutathione (GSH), L-cysteine (L-Cys), and cyanide triggered a differential response. Thus, peroxynitrite and reducing compounds provoked around 50% inhibition of the LAP activity in green immature fruits, whereas cyanide upregulated it 1.5 folds. To our knowledge, this is the first characterization of LAP in pepper fruits as well as of its regulation by diverse modulating compounds. Based on the capacity of LAP to metabolize dipeptides and tripeptides, it could be hypothesized that the LAP might be involved in the GSH recycling during the ripening process.

Encapsulated nanopesticides application in plant protection: Quo vadis?

The increased global food insecurity due to the growing population can be addressed with precision and sustainable agricultural practices. To tackle the issues regarding food insecurity, farmers used different agrochemicals that improved plant growth and protection. Among these agrochemicals, synthetic pesticides used for plant protection in the agricultural field have various disadvantages. Conventional applications of synthetic pesticides have drawbacks such as rapid degradation, poor solubility, and non-target effects, as well as increased pesticide runoff that pollutes the environment. Nanotechnology has evolved as a potential solution to increase agricultural productivity through the development of different nanoforms of agrochemicals such as nanopesticides, nano-fabricated fertilizers, nanocapsules, nanospheres, nanogels, nanofibers, nanomicelles, and nano-based growth promoters. Encapsulation of these pesticides inside the nanomaterials has provided good biocompatibility over conventional application by inhibiting the early degradation of active ingredients (AI), increasing the uptake and adhesion of pesticides, improving the stability, solubility, and permeability of the pesticides, and decreasing the environmental impacts due to the pesticide runoff. In this review, different nanoforms of encapsulated pesticides and their smart delivery systems; nanocarriers in RNA interference (RNAi) based pesticides; environmental fate, practical implications, management of nanopesticides; and future perspectives are discussed.

Can nutrients act as signals under abiotic stress?

Plant cells are in constant communication to coordinate development processes and environmental reactions. Under stressful conditions, such communication allows the plant cells to adjust their activities and development. This is due to intercellular signaling events which involve several components. In plant development, cell-to-cell signaling is ensured by mobile signals hormones, hydrogen peroxide (H2O2), nitric oxide (NO), or hydrogen sulfide (H2S), as well as several transcription factors and small RNAs. Mineral nutrients, including macro and microelements, are determinant factors for plant growth and development and are, currently, recognized as potential signal molecules. This review aims to highlight the role of nutrients, particularly calcium, potassium, magnesium, nitrogen, phosphorus, and iron as signaling components with special attention to the mechanism of response against stress conditions.

Overexpression of ApHIPP26 from the Hyperaccumulator Arabis paniculata Confers Enhanced Cadmium Tolerance and Accumulation to Arabidopsis thaliana

Cadmium (Cd) is a toxic heavy metal that seriously affects metabolism after accumulation in plants, and it also causes adverse effects on humans through the food chain. The HIPP gene family has been shown to be highly tolerant to Cd stress due to its special domain and molecular structure. This study described the Cd-induced gene ApHIPP26 from the hyperaccumulator Arabis paniculata. Its subcellular localization showed that ApHIPP26 was located in the nucleus. Transgenic Arabidopsis overexpressing ApHIPP26 exhibited a significant increase in main root length and fresh weight under Cd stress. Compared with wild-type lines, Cd accumulated much more in transgenic Arabidopsis both aboveground and underground. Under Cd stress, the expression of genes related to the absorption and transport of heavy metals underwent different changes in parallel, which were involved in the accumulation and distribution of Cd in plants, such as AtNRAMP6 and AtNRAMP3. Under Cd stress, the activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) in the transgenic lines were higher than those in the wild type. The physiological and biochemical indices showed that the proline and chlorophyll contents in the transgenic lines increased significantly after Cd treatment, while the malondialdehyde (MDA) content decreased. In addition, the gene expression profile analysis showed that ApHIPP26 improved the tolerance of Arabidopsis to Cd by regulating the changes of related genes in plant hormone signal transduction pathway. In conclusion, ApHIPP26 plays an important role in cadmium tolerance by alleviating oxidative stress and regulating plant hormones, which provides a basis for understanding the molecular mechanism of cadmium tolerance in plants and provides new insights for phytoremediation in Cd-contaminated areas.

H2 O2 , NO, and H2 S networks during root development and signalling under physiological and challenging environments: Beneficial or toxic?

Hydrogen peroxide (H₂ O₂ ) is a reactive oxygen species (ROS) and a key modulator of the development and architecture of the root system under physiological and adverse environmental conditions. Nitric oxide (NO) and hydrogen sulphide (H₂ S) also exert myriad functions on plant development and signalling. Accumulating pieces of evidence show that depending upon the dose and mode of applications, NO and H₂ S can have synergistic or antagonistic actions in mediating H₂ O₂ signalling during root development. Thus, H₂ O₂ -NO-H₂ S crosstalk might essentially impart tolerance to elude oxidative stress in roots. Growth and proliferation of root apex involve crucial orchestration of NO and H₂ S-mediated ROS signalling which also comprise other components including mitogen-activated protein kinase, cyclins, cyclin-dependent kinases, respiratory burst oxidase homolog (RBOH), and Ca²⁺ flux. This assessment provides a comprehensive update on the cooperative roles of NO and H₂ S in modulating H₂ O₂ homoeostasis during root development, abiotic stress tolerance, and root-microbe interaction. Furthermore, it also analyses the scopes of some fascinating future investigations associated with strigolactone and karrikins concerning H₂ O₂ -NO-H₂ S crosstalk in plant roots.