Alleviated cadmium toxicity in wheat (Triticum aestivum L.) by the coactive role of zinc oxide nanoparticles and plant growth promoting rhizobacteria on TaEIL1 gene expression, biochemical and physiological changes

Cadmium (Cd) contamination in agricultural soil is a major global concern among the multitude of human health and food security. Zinc oxide nanoparticles (ZnO-NPs) and plant growth promoting rhizobacteria (PGPR) have been known to combat heavy metal toxicity in crops. Herein, the study intended to explore the interactive effect of treatments mediated by inoculation of PGPR and foliar applied ZnO-NPs to alleviate Cd induced phytotoxicity in wheat plants which is rarely investigated. For this purpose, TaEIL1 expression, morpho-physiological, and biochemical traits of wheat were examined. Our results revealed that Cd reduced growth and biomass, disrupted plant physiological and biochemical traits, and further expression patterns of TaEIL1. The foliar application of ZnO-NPs improved growth attributes, photosynthetic pigments, and gas exchange parameters in a dose-additive manner, and this effect was further amplified with a combination of PGPR. The combined application of ZnO-NPs (100 mg L-1) with PGPR considerably increased the catalase (CAT; 52.4%), peroxidase (POD; 57.4%), superoxide dismutase (SOD; 60.1%), ascorbate peroxidase (APX; 47.4%), leading to decreased malondialdehyde (MDA; 47.4%), hydrogen peroxide (H2O2; 38.2%) and electrolyte leakage (EL; 47.3%) under high Cd (20 mg kg-1) stress. Furthermore, results revealed a significant reduction in roots (56.3%), shoots (49.4%), and grains (59.4%) Cd concentration after the Combined treatment of ZnO-NPs and PGPR as compared to the control. Relative expression of TaEIL1 (two homologues) was evaluated under control (Cd 0), Cd, ZnO-NPs, PGPR, and combined treatments. Expression profiling revealed a differential expression pattern of TaEIL1 under different treatments. The expression pattern of TaEIL1 genes was upregulated under Cd stress but downregulated under combined ZnO-NPs and PGPR, revealing its crucial role in Cd stress tolerance. Inferentially, ZnO-NPs and PGPR showed significant potential to alleviate Cd toxicity in wheat by modulating the antioxidant defense system and TaEIL1 expression. By inhibiting Cd uptake, and facilitating their detoxification, this innovative approach ensures food safety and security.

Rhizospheric bacteria from the Atacama Desert hyper-arid core: cultured community dynamics and plant growth promotion

The Atacama Desert is the oldest and driest desert on Earth, encompassing great temperature variations, high ultraviolet radiation, drought, and high salinity, making it ideal for studying the limits of life and resistance strategies. It is also known for harboring a great biodiversity of adapted life forms. While desertification is increasing as a result of climate change and human activities, it is necessary to optimize soil and water usage, where stress-resistant crops are possible solutions. As many studies have revealed the great impact of the rhizobiome on plant growth efficiency and resistance to abiotic stress, we set up to explore the rhizospheric soils of Suaeda foliosa and Distichlis spicata desert plants. By culturing these soils and using 16S rRNA amplicon sequencing, we address community taxonomy composition dynamics, stability through time, and the ability to promote lettuce plant growth. The rhizospheric soil communities were dominated by the families Pseudomonadaceae, Bacillaceae, and Planococcaceae for S. foliosa and Porphyromonadaceae and Haloferacaceae for D. spicata. Nonetheless, the cultures were completely dominated by the Enterobacteriaceae family (up to 98%). Effectively, lettuce plants supplemented with the cultures showed greater size and biomass accumulation. We identified 12 candidates that could be responsible for these outcomes, of which 5 (Enterococcus, Pseudomonas, Klebsiella, Paenisporosarcina, and Ammoniphilus) were part of the built co-occurrence network. We aim to contribute to the efforts to characterize the microbial communities as key for the plant's survival in extreme environments and as a possible source of consortia with plant growth promotion traits aimed at agricultural applications.IMPORTANCEThe current scenario of climate change and desertification represents a series of incoming challenges for all living organisms. As the human population grows rapidly, so does the rising demand for food and natural resources; thus, it is necessary to make agriculture more efficient by optimizing soil and water usage, thus ensuring future food supplies. Particularly, the Atacama Desert (northern Chile) is considered the most arid place on Earth as a consequence of geological and climatic characteristics, such as the naturally low precipitation patterns and high temperatures, which makes it an ideal place to carry out research that seeks to aid agriculture in future conditions that are predicted to resemble these scenarios. Our main interest lies in utilizing microorganism consortia from plants thriving under extreme conditions, aiming to promote plant growth, improve crops, and render "unsuitable" soils farmable.

Enhancement of sulfur metabolism and antioxidant machinery confers Bacillus sp. Jrh14-10-induced alkaline stress tolerance in plant

Alkaline stress is a major environmental challenge that restricts plant growth and agricultural productivity worldwide. Plant growth-promoting rhizobacteria (PGPR) can be used to effectively enhance plant abiotic stress in an environment-friendly manner. However, PGPR that can enhance alkalinity tolerance are not well-studied and the mechanisms by which they exert beneficial effects remain elusive. In this study, we isolated Jrh14-10 from the rhizosphere soil of halophyte Halerpestes cymbalaria (Pursh) Green and found that it can produce indole-3-acetic acid (IAA) and siderophore. By 16S rRNA gene sequencing, it was classified as Bacillus licheniformis. Inoculation Arabidopsis seedlings with Jrh14-10 significantly increased the total fresh weight (by 148.1%), primary root elongation (by 1121.7%), and lateral root number (by 108.8%) under alkaline stress. RNA-Seq analysis showed that 3389 genes were up-regulated by inoculation under alkaline stress and they were associated with sulfur metabolism, photosynthetic system, and oxidative stress response. Significantly, the levels of Cys and GSH were increased by 144.3% and 48.7%, respectively, in the inoculation group compared to the control under alkaline stress. Furthermore, Jrh14-10 markedly enhanced the activities of antioxidant enzymes, resulting in lower levels of O2•-, H2O2, and MDA as well as higher levels of Fv/Fm in alkaline-treated seedlings. In summary, Jrh14-10 can improve alkaline stress resistance in seedlings which was accompanied by an increase in sulfur metabolism-mediated GSH synthesis and antioxidant enzyme activities. These results provide a mechanistic understanding of the interactions between a beneficial bacterial strain and plants under alkaline stress.

Effect of Priestia endophytica on the metabolites accumulation in chicory and lettuce plants cultivated in vitro

The influence of the culture medium without bacterial cells, obtained after the cultivation of endophytic bacteria Priestia endophytica UCM B-5715, on the growth and synthesis of some metabolites in lettuce and chicory seedlings under in vitro conditions was studied. Bacteria were cultivated in liquid LB medium at 37 ºC for 24 h with periodic stirring. The culture fluid was separated from the cell biomass. For preparing the test solution, the supernatant was sterilized by filtration through a filter with a pore diameter of 0.2 µm (Sartorius, Minisart) and diluted with sterile distilled water. The 20% culture fluid (30 µl/plant) was applied to 3-day-old seedlings. In 28 days root and shoot weights of treated chicory plants were 54.3 ± 6.9 and 260.0 ± 20.2 mg, respectively (8.0 ± 0.7 and 91.4 ± 7.0 mg for the control plants). Total flavonoid content and antioxidant activity increased only in chicory plants after the addition of the test solution. Significant changes in the metabolism of treated plants were detected. In the treated lettuce plants asparagine content increased compared to the control (90 vs 22 µg/g, p < 0.1). The median content of fructose was also higher in treated lettuce and chicory plants (1469 vs 73 µg/g and 2278 vs 1051 µg/g). Therefore, the use of culture fluid obtained after the cultivation of P. endophytica UСM B-5715 stimulated the growth of lettuce and chicory plants, affecting the synthesis of some compounds in single-treated plants. These results indicate the potential of compounds excreted during bacterial growth to create natural growth stimulators.

Challenges for Plant Growth Promoting Microorganism Transfer from Science to Industry: A Case Study from Chile

Research on the plant growth promoting microorganisms (PGPM) is increasing strongly due to the biotechnological potential for the agricultural, forestry, and food industry. The benefits of using PGPM in crop production are well proven; however, their incorporation in agricultural management is still limited. Therefore, we wanted to explore the gaps and challenges for the transfer of biotechnological innovations based on PGPM to the agricultural sector. Our systematic review of the state of the art of PGPM research and knowledge transfer takes Chile as an example. Several transfer limiting aspects are identified and discussed. Our two main conclusions are: neither academia nor industry can meet unfounded expectations during technology transfer, but mutually clarifying their needs, capabilities, and limitations is the starting point for successful collaborations; the generation of a collaborative innovation environment, where academia as well as public and private stakeholders (including the local community) take part, is crucial to enhance the acceptance and integration of PGPM on the way to sustainable agriculture.

Overview of biofertilizers in crop production and stress management for sustainable agriculture

With the increase in world population, the demography of humans is estimated to be exceeded and it has become a major challenge to provide an adequate amount of food, feed, and agricultural products majorly in developing countries. The use of chemical fertilizers causes the plant to grow efficiently and rapidly to meet the food demand. The drawbacks of using a higher quantity of chemical or synthetic fertilizers are environmental pollution, persistent changes in the soil ecology, physiochemical composition, decreasing agricultural productivity and cause several health hazards. Climatic factors are responsible for enhancing abiotic stress on crops, resulting in reduced agricultural productivity. There are various types of abiotic and biotic stress factors like soil salinity, drought, wind, improper temperature, heavy metals, waterlogging, and different weeds and phytopathogens like bacteria, viruses, fungi, and nematodes which attack plants, reducing crop productivity and quality. There is a shift toward the use of biofertilizers due to all these facts, which provide nutrition through natural processes like zinc, potassium and phosphorus solubilization, nitrogen fixation, production of hormones, siderophore, various hydrolytic enzymes and protect the plant from different plant pathogens and stress conditions. They provide the nutrition in adequate amount that is sufficient for healthy crop development to fulfill the demand of the increasing population worldwide, eco-friendly and economically convenient. This review will focus on biofertilizers and their mechanisms of action, role in crop productivity and in biotic/abiotic stress tolerance.