The nitric oxide suppressed Arabidopsis mutants- Atnoa1 and Atnia1nia2noa1-2 produce nitric oxide in MS growth medium and on uranium exposure

Nitric oxide controls shoot meristem activity via regulation of DNA methylation

Despite the importance of Nitric Oxide (NO) as signaling molecule in both plant and animal development, the regulatory mechanisms downstream of NO remain largely unclear. Here, we show that NO is involved in Arabidopsis shoot stem cell control via modifying expression and activity of ARGONAUTE 4 (AGO4), a core component of the RNA-directed DNA Methylation (RdDM) pathway. Mutations in components of the RdDM pathway cause meristematic defects, and reduce responses of the stem cell system to NO signaling. Importantly, we find that the stem cell inducing WUSCHEL transcription factor directly interacts with AGO4 in a NO dependent manner, explaining how these two signaling systems may converge to modify DNA methylation patterns. Taken together, our results reveal that NO signaling plays an important role in controlling plant stem cell homeostasis via the regulation of de novo DNA methylation.

Nitric Oxide in Plant Functioning: Metabolism, Signaling, and Responses to Infestation with Ecdysozoa Parasites

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological processes in plants, including responses to biotic and abiotic stresses. Changes in endogenous NO concentration lead to activation/deactivation of NO signaling and NO-related processes. This paper presents the current state of knowledge on NO biosynthesis and scavenging pathways in plant cells and highlights the role of NO in post-translational modifications of proteins (S-nitrosylation, nitration, and phosphorylation) in plants under optimal and stressful environmental conditions. Particular attention was paid to the interactions of NO with other signaling molecules: reactive oxygen species, abscisic acid, auxins (e.g., indole-3-acetic acid), salicylic acid, and jasmonic acid. In addition, potential common patterns of NO-dependent defense responses against attack and feeding by parasitic and molting Ecdysozoa species such as nematodes, insects, and arachnids were characterized. Our review definitely highlights the need for further research on the involvement of NO in interactions between host plants and Ecdysozoa parasites, especially arachnids.

Abscisic acid is required for root elongation associated with Ca2+ influx in response to water stress

Abscisic acid (ABA) is a critical hormone for plant survival upon water stress. In this study, a large-scale mutants of Arabidopsis ecotype Columbia-0 (Col-0) by ethyl methanesulfonate (EMS)-mutagenesis were generated, and an improved root elongation under water-stress 1 (irew1) mutant showing significantly enhanced root growth was isolated upon a water potential gradient assay. Then, irew1 and ABA-related mutants in Arabidopsis or tomato plants were observed under water potential gradient assay or water-deficient condition. ABA pathway, Ca²⁺ response and primary root (PR) elongation rate were monitored in addition to DNA- and RNA-Seq analyses. We found that based on phenotyping and transcriptional analyses, irew1 exhibited the enhanced PR growth, ABA and Ca²⁺ responses compared to wild-type subjected to water stress. Interestingly, exogenous Ca²⁺ application enhanced PR growth of irew1, ABA-biosynthesis deficient mutants in Arabidopsis and tomato plants in response to water potential gradients or water-deficient condition. In combination with other ABA-related mutants and pharmacological study, our results suggest that ABA is required for root elongation associated with Ca²⁺ influx in response to water stress.

Abiotic mechanism changing tetracycline resistance in root mucus layer of floating plant: The role of antibiotic-exudate complexation

Antibiotic contamination and antibiotic resistance have caused growing concerns in different aquatic environments. This work investigated the complexation between tetracycline chloride (TCH) and the molecular weight (MW)-fractionated root exudates - the key abiotic mechanism impacting antibiotic fate and antibiotic resistance in rhizosphere. Results show that the affinity of TCH to the high MW exudates (≥10 kDa) facilitated the TCH deposition on roots and meanwhile reinforced the expression of certain tetracycline resistance genes (i.e. tetA) and the growth of tetracycline resistant bacteria. The interaction between TCH and the lower MW exudates (<10 kDa) completely inhibited the bacteria growth even below the minimum inhibitory concentration of TCH. In microcosms, the abiotic interaction between TCH and root exudates made effects along with biotic processes. Persistent TCH stimulation (≥50 µg/L, 7 d) induced the change of tet gene abundance and bacteria phyla composition though the mediation of root exudates made the rhizosphere less sensitive to the TCH stress. Summarily, the affinity of antibiotics to root exudates varied with MWs, which was closely related to (i) the antibiotic fate in the root mucus layer, (ii) the bacteria inhibition capacity of antibiotics, and (iii) the antibiotic resistance and bacterial community.

Evidence for a role of nitric oxide in iron homeostasis in plants

Nitric oxide (NO), once regarded as a poisonous air pollutant, is now understood as a regulatory molecule essential for several biological functions in plants. In this review, we summarize NO generation in different plant organs and cellular compartments, and also discuss the role of NO in iron (Fe) homeostasis, particularly in Fe-deficient plants. Fe is one of the most limiting essential nutrient elements for plants. Plants often exhibit Fe deficiency symptoms despite sufficient tissue Fe concentrations. NO appears to not only up-regulate Fe uptake mechanisms but also makes Fe more bioavailable for metabolic functions. NO forms complexes with Fe, which can then be delivered into target cells/tissues. NO generated in plants can alleviate oxidative stress by regulating antioxidant defense processes, probably by improving functional Fe status and by inducing post-translational modifications in the enzymes/proteins involved in antioxidant defense responses. It is hypothesized that NO acts in cooperation with transcription factors such as bHLHs, FIT, and IRO to regulate the expression of enzymes and proteins essential for Fe homeostasis. However, further investigations are needed to disentangle the interaction of NO with intracellular target molecules that leads to enhanced internal Fe availability in plants.

Genome-Wide Analysis of Ribosomal Protein GhRPS6 and Its Role in Cotton Verticillium Wilt Resistance

Verticillium wilt is threatening the world’s cotton production. The pathogenic fungus Verticillium dahliae can survive in the soil in the form of microsclerotia for a long time, colonize through the root of cotton, and invade into vascular bundles, causing yellowing and wilting of cotton leaves, and in serious cases, leading to plant death. Breeding resistant varieties is the most economical and effective method to control Verticillium wilt. In previous studies, proteomic analysis was carried out on different cotton varieties inoculated with V. dahliae strain Vd080. It was found that GhRPS6 was phosphorylated after inoculation, and the phosphorylation level in resistant cultivars was 1.5 times than that in susceptible cultivars. In this study, knockdown of GhRPS6 expression results in the reduction of SA and JA content, and suppresses a series of defensive response, enhancing cotton plants susceptibility to V. dahliae. Overexpression in Arabidopsis thaliana transgenic plants was found to be more resistant to V. dahliae. Further, serines at 237 and 240 were mutated to phenylalanine, respectively and jointly. The transgenic Arabidopsis plants demonstrated that seri-237 compromised the plant resistance to V. dahliae. Subcellular localization in Nicotiana benthamiana showed that GhRPS6 was localized in the nucleus. Additionally, the pathogen inoculation and phosphorylation site mutation did not change its localization. These results indicate that GhRPS6 is a potential molecular target for improving resistance to Verticillium wilt in cotton. This lays a foundation for breeding disease-resistant varieties.

Calcium-Dependent Protein Kinase GhCDPK28 Was Dentified and Involved in Verticillium Wilt Resistance in Cotton

Verticillium dahliae is a soil-borne fungus that causes vascular wilt through the roots of plants. Verticillium wilt caused by V. dahliae is one of the main diseases in cotton producing areas of the world, resulting in huge economic losses. Breeding resistant varieties is the most economical and effective method to control Verticillium wilt. Calcium-dependent protein kinases (CDPKs) play a pivotal role in plant innate immunity, including regulation of oxidative burst, gene expression as well as hormone signal transduction. However, the function of cotton CDPKs in response to V. dahliae stress remains unexplored. In this study, 96, 44 and 57 CDPKs were identified from Gossypium hirsutum, Gossypium raimondii and Gossypium arboretum, respectively. Phylogenetic analysis showed that these CDPKs could be divided into four branches. All GhCDPKs of the same clade are generally similar in gene structure and conserved domain arrangement. Cis-acting elements related to hormones, stress response, cell cycle and development were predicted in the promoter region. The expression of GhCDPKs could be regulated by various stresses. Gh_D11G188500.1 and Gh_A11G186100.1 was up-regulated under Vd0738 and Vd991 stress. Further phosphoproteomics analysis showed that Gh_A11G186100.1 (named as GhCDPK28-6) was phosphorylated under the stress of V. dahliae. Knockdown of GhCDPK28-6 expression, the content of reactive oxygen species was increased, a series of defense responses were enhanced, and the sensitivity of cotton to V. dahliae was reduced. Moreover, overexpression of GhCDPK28-6 in Arabidopsis thaliana weakened the resistance of plants to this pathogen. Subcellular localization revealed that GhCDPK28-6 was localized in the cell membrane. We also found that GhPBL9 and GhRPL12C may interact with GhCDPK28-6. These results indicate that GhCDPK28-6 is a potential molecular target for improving resistance to Verticillium wilt in cotton. This lays a foundation for breeding disease-resistant varieties.

A metabolomic, transcriptomic profiling, and mineral nutrient metabolism study of the phytotoxicity mechanism of uranium

Uranium (U) is a nonessential element that is readily adsorbed and retained in plant roots, causing root damage plants, rather than being translocated to other parts of the plant. The phytotoxicity mechanism of U is poorly understood. In this study, Vicia faba, a model plant for toxicological research, was selected as experimental material to investigate the phytotoxicity mechanism of U. In this study, the effects of U on the growth and development, methonome, transcriptome and mineral nutrient metabolism of V. faba were studied under different U treatments (0-25 μM) by integrating metabolomics, transcriptomic, and mineral nutrient metabolism analysis techniques. The results showed that U accumulation in roots and aboveground parts reached 164.34-927.90 μg/pot, and 0.028-0.119 μg/pot, respectively. U was mainly accumulated in the cell wall of roots, which damaged the root microstructure and inhibited root growth and development. In terms of mineral nutrient metabolism, U treatment (0-25 μM) led to changes in mineral metabolic profiles of seedlings. In total, 612 different metabolites were identified in nontargeted metabolomics, including 309 significantly upregulated metabolites and 303 significantly downregulated metabolites. Using RNA-seq, 4974 differentially expressed genes (DEGs) were identified under the high-concentration U treatment (25 μM), including 1654 genes significantly upregulated genes and 3320 genes significantly downregulated genes. Metabolic pathway analysis showed that a high concentration of U led to an imbalance of mineral nutrient metabolism in plants and changes in the metabolism and transcriptome pathway of plants, including alterations in the function of plasmodesmata and auxin signal transduction pathway. The latter finding may potentially explain the toxic effect of U on plant roots.

Abscisic Acid Is Required for Root Elongation Associated With Ca2+ Influx in Response to Water Stress

Abscisic acid (ABA) is a critical hormone for plant survival under water stress. In this study, large-scale mutants of the Arabidopsis ecotype Columbia-0 (Col-0) were generated by ethyl methanesulfonate (EMS)-mutagenesis, and an improved root elongation under water-stress 1 (irew1) mutant showing significantly enhanced root growth was isolated under a water potential gradient assay. Then, irew1 and ABA-related mutants in Arabidopsis or tomato plants were observed under water potential gradient assay or water-deficient conditions. ABA pathway, Ca²⁺ response, and primary root (PR) elongation rate were monitored in addition to DNA- and RNA-Seq analyses. We found that based on phenotyping and transcriptional analyses, irew1 exhibited enhanced PR growth, ABA, and Ca²⁺ responses, compared to wild type subjected to water stress. Interestingly, exogenous Ca²⁺ application enhanced PR growth of irew1, ABA-biosynthesis deficient mutants in Arabidopsis, and tomato plants, in response to water potential gradients or water-deficient conditions. In combination with other ABA-related mutants and pharmacological studies, our results suggest that ABA is required for root elongation associated with Ca²⁺ influx in response to water stress.