Specific Streptomyces strain enhances the growth, defensive mechanism, and fruit quality of cucumber by minimizing its fertilizer consumption.

BACKGROUND: The required amounts of chemical fertilizers (NPK) are determined by plant yield, and product quality is given less consideration. The use of PGPRs is an environmentally friendly approach that, in addition to increasing yield, also improves fruit quality. This study examined the role of specific Streptomyces strains in aiding cucumber plants to 1) use fewer NPK fertilizers in the same quantity 2) improve the quality of cucumber fruit, and 3) promote growth and defense system. RESULTS: In this study, the effect of 17 Streptomyces strains on the vegetative traits of cucumber seedlings of the Sultan cultivar was evaluated as the first test. Four strains of Streptomyces with the highest root and shoot dry weight were selected from the strains. This experiment was performed to determine the interaction effect of selected strains and different amounts of NPK on cucumber yield, quality, physiological and biochemical responses of plants. The first experiment's results revealed that strains IC6, Y7, SS12, and SS14 increased significantly in all traits compared to the control, while the other strains dramatically improved several characteristics. Analysis of variance (ANOVA) revealed significant differences between the effect of strains, NPK concentrations, and their interactions on plant traits. The treatments containing 75% NPK + SS12, yielded the most fruit (40% more than the inoculated control). Antioxidant enzymes assay showed that SS12 substantially increased the activity of POX, PPO, and the expression of the genes related to these two enzymes. Hormone assay utilizing HPLC analysis revealed that various strains employ a specific mechanism to improve the immune system of plants. CONCLUSIONS: Treatment with strain SS12 led to the production of cucumbers with the highest quality by reducing the amount of nitrate, and soluble sugars and increasing the amount of antioxidants and firmness compared to other treatments. A specific Streptomyces strain could reduce 25% of NPK fertilizer during the vegetative and reproductive growth period. Moreover, this strain protected plants against possible pathogens and adverse environmental factors through the ISR and SAR systems.

Proteomic analysis of the meristematic root zone in contrasting genotypes reveals new insights in drought tolerance in rice.

Drought is responsible for major losses in rice production. Root tips contain meristematic and elongation zones that play major roles in determination of root traits and adaptive strategies to drought. In this study we analysed two contrasting genotypes of rice: IR64, a lowland, drought-susceptible, and shallow-rooting genotype; and Azucena, an upland, drought-tolerant, and deep-rooting genotype. Samples were collected of root tips of plants grown under control and water deficit stress conditions. Quantitative proteomics analysis resulted in the identification of 7294 proteins from the root tips of IR64 and 6307 proteins from Azucena. Data are available via ProteomeXchange with identifier PXD033343. Using a Partial Least Square Discriminant Analysis on 4170 differentially abundant proteins, 1138 statistically significant proteins across genotypes and conditions were detected. Twenty two enriched biological processes showing contrasting patterns between two genotypes in response to stress were detected through gene ontology enrichment analysis. This included identification of novel proteins involved in root elongation with specific expression patterns in Azucena, including four Expansins and seven Class III Peroxidases. We also detected an antioxidant network and a metallo-sulfur cluster assembly machinery in Azucena, with roles in reactive oxygen species and iron homeostasis, and positive effects on root cell cycle, growth and elongation.

Genome-Wide Expression Analysis of Root Tips in Contrasting Rice Genotypes Revealed Novel Candidate Genes for Water Stress Adaptation.

Root system architecture (RSA) is an important agronomic trait with vital roles in plant productivity under water stress conditions. A deep and branched root system may help plants to avoid water stress by enabling them to acquire more water and nutrient resources. Nevertheless, our knowledge of the genetics and molecular control mechanisms of RSA is still relatively limited. In this study, we analyzed the transcriptome response of root tips to water stress in two well-known genotypes of rice: IR64, a high-yielding lowland genotype, which represents a drought-susceptible and shallow-rooting genotype; and Azucena, a traditional, upland, drought-tolerant and deep-rooting genotype. We collected samples from three zones (Z) of root tip: two consecutive 5 mm sections (Z1 and Z2) and the following next 10 mm section (Z3), which mainly includes meristematic and maturation regions. Our results showed that Z1 of Azucena was enriched for genes involved in cell cycle and division and root growth and development whereas in IR64 root, responses to oxidative stress were strongly enriched. While the expansion of the lateral root system was used as a strategy by both genotypes when facing water shortage, it was more pronounced in Azucena. Our results also suggested that by enhancing meristematic cell wall thickening for insulation purposes as a means of confronting stress, the sensitive IR64 genotype may have reduced its capacity for root elongation to extract water from deeper layers of the soil. Furthermore, several members of gene families such as NAC, AP2/ERF, AUX/IAA, EXPANSIN, WRKY, and MYB emerged as main players in RSA and drought adaptation. We also found that HSP and HSF gene families participated in oxidative stress inhibition in IR64 root tip. Meta-quantitative trait loci (QTL) analysis revealed that 288 differentially expressed genes were colocalized with RSA QTLs previously reported under drought and normal conditions. This finding warrants further research into their possible roles in drought adaptation. Overall, our analyses presented several major molecular differences between Azucena and IR64, which may partly explain their differential root growth responses to water stress. It appears that Azucena avoided water stress through enhancing growth and root exploration to access water, whereas IR64 might mainly rely on cell insulation to maintain water and antioxidant system to withstand stress. We identified a large number of novel RSA and drought associated candidate genes, which should encourage further exploration of their potential to enhance drought adaptation in rice.

Corrigendum to "Plant growth promoting Streptomyces strains are selectively interacting with the wheat cultivars especially in saline conditions" [Heliyon 6 (2) (2020) e03445].

[This corrects the article DOI: 10.1016/j.heliyon.2020.e03445.].

Plant growth promoting Streptomyces strains are selectively interacting with the wheat cultivars especially in saline conditions.

Plant growth promoting (PGP) effect of Streptomyces on wheat growth in different conditions has been mostly reported although mechanisms which caused wheat cultivars differently response to a PGP Streptomyces has been less studied. In this study, the effect of two Streptomyces strains, previously reported as PGPR, on the growth of four salt-sensitive commercial wheat cultivars under normal and saline conditions was investigated. Strain C-2012 differently affected the growth of the cultivars in the normal and stress conditions. Cultivars Gonbad with the highest (63%) and Zarin without increased dry biomass upon C-2012 treatments were selected for further study. Salinity significantly decreased seedling fresh and dry weight, K+ and chlorophyll content and glutathione S-transferase activity. Moreover, the stress increased proline and Na+ content and peroxidase (POX) and ascorbate peroxidase (APX) activity in both cultivars. Strain C-2012, generally, ameliorated the negative effect of the stress with increased chlorophyll and carotenoid and reduced Na+ content and APX and SOD activity in both cultivars, however, its effect on biomass was different. Increase in SOD, APX and POX activities in bacterial inoculated-Zarin, but not Gonbad, under normal conditions suggested that this cultivar may recognize strain C-2012 as a gentle stressor and not as a PGPR. These results showed that the responses of the wheat cultivars to a defined PGPR is different in the physiological, phenotypic and molecular level. Based on the results, the evaluation of the effect of a bio-fertilizer on each wheat cultivar is necessary prior to use in a commercial field.

Proteomic and metabolomic analysis of desiccation tolerance in wheat young seedlings.

Young wheat seedlings are desiccation tolerant and have the capacity to withstand long dehydration period. In this study, we characterized the proteome and metabolome of wheat seedlings during desiccation and after recovery. Functional classification of differentially identified proteins revealed dynamic changes in the number and abundance of proteins observed during stress and recovery. Desiccation resulted in a decline in the abundance of proteins associated with photosynthesis and carbohydrate reserves, along with an increase in the presence of proteins associated with stress and defense response, such as peroxiredoxins and antioxidant enzymes. Following recovery, the abundance of stress-responsive proteins returned either partially or completely to their baseline level, confirming their importance to the seedling's desiccation response. Furthermore, proteins involved in carbohydrate metabolism, as well as fructose-bisphosphate aldolase and fructokinase-2 and phosphorylated metabolites as the substrate or the end-product, showed the inverse pattern during desiccation and after re-watering. This may reflect the fact that plants maintained energy supply during stress to protect seedlings from further damage, and for use in subsequent recovery after rewatering period. This study provides novel insights into the molecular mechanisms underlying the desiccation tolerance of wheat seedlings, and paves the way for more detailed molecular analysis of this remarkable phenomenon.

Comparative proteomic and physiological characterisation of two closely related rice genotypes with contrasting responses to salt stress.

Salinity is a limiting factor affecting crop growth. We evaluated the responses of a salt-tolerant recombinant inbred rice (Oryza sativa L.) line, FL478, and the salt-sensitive IR29. Seedlings were exposed to salt stress and the growth rate was monitored to decipher the effect of long-term stress. At Day 16, IR29 produced lower shoot biomass than FL478. Significant differences for Na+ and K+ concentrations and Na+ : K+ ratios in roots and shoots were observed between genotypes. Changes in the proteomes of control and salt-stressed plants were analysed, identifying 59 and 39 salt-responsive proteins in roots and leaves, respectively. Proteomic analysis showed greater downregulation of proteins in IR29. In IR29, proteins related to pathways involved in salt tolerance (e.g. oxidative stress response, amino acid biosynthesis, polyamine biosynthesis, the actin cytoskeleton and ion compartmentalisation) changed to combat salinity. We found significant downregulation of proteins related to photosynthetic electron transport in IR29, indicating that photosynthesis was influenced, probably increasing the risk of reactive oxygen species formation. The sensitivity of IR29 might be related to its inability to exclude salt from its transpiration stream, to compartmentalise excess ions and to maintain a healthy photosynthetic apparatus during salt stress, or might be because of the leakiness of its roots, allowing excess salt to enter apoplastically. In FL478, superoxide dismutase, ferredoxin thioredoxin reductase, fibre protein and inorganic pyrophosphatase, which may participate in salt tolerance, increased in abundance. Our analyses provide novel insights into the mechanisms behind salt tolerance and sensitivity in genotypes with close genetic backgrounds.