Bacillus pumilus improved drought tolerance in Glycyrrhiza uralensis G5 seedlings through enhancing primary and secondary metabolisms

Endophytic Bacillus pumilus G5 Interacting with Silicon to Improve Drought Stress Resilience in Glycyrrhiza uralensis Fisch. by Modulating Nitrogen Absorption, Assimilation, and Metabolism Pathways

Drought stress has become the primary severe threat to global agriculture production, including medicinal plants. Plant growth-promoting bacteria (PGPB) and environmentally friendly element silicon (Si) have emerged as effective methods in alleviating drought stress in various plants. Here, the effects of the plant endophytic G5 interaction with Si on regulating nitrogen absorption, assimilation, and metabolism pathways were investigated in the morphophysiological and gene attributes of Glycyrrhiza uralensis exposed to drought. Results showed that G5+Si application improved nitrogen absorption and assimilation by increasing the available nitrogen content in the soil, further improving the nitrogen utilization efficiency. Then, G5+Si triggered the accumulation of the major adjustment substances proline, γ-aminobutyric acid, putrescine, and chlorophyll, which played an important role in contributing to maintaining balance and energy supply in G. uralensis exposed to drought. These findings will provide new ideas for the combined application of PGPR and Si on both soil and plant systems in a drought habitat.

Plant-beneficial Streptomyces dioscori SF1 potential biocontrol and plant growth promotion in saline soil within the arid and semi-arid areas

Environmental challenges like salinity, drought, fungal phytopathogens, and pesticides directly or/and indirectly influence the environment and agricultural yields. Certain beneficial endophytic Streptomyces sp. can ameliorate environmental stresses and be utilized as crop growth promoters under adverse conditions. Herein, Streptomyces dioscori SF1 (SF1) isolated from seeds of Glycyrrhiza uralensis tolerated fungal phytopathogens and abiotic stresses (drought, salt, and acid base). Strain SF1 showed multifarious plant growth promotion characteristics, including the production of indole acetic acid (IAA), ammonia, siderophores, ACC deaminase, extracellular enzymes, the ability of potassium solubilization, and nitrogen fixation. The dual plate assay showed that strain SF1 inhibited 63.21 ± 1.53%, 64.84 ± 1.35%, and 74.19 ± 2.88% of Rhizoctonia solani, Fusarium acuminatum, and Sclerotinia sclerotiorum, respectively. The detached root assays showed that strain SF1 significantly reduced the number of rotten sliced roots, and the biological control effect on sliced roots of Angelica sinensis, Astragalus membranaceus, and Codonopsis pilosula was 93.33%, 86.67%, and 73.33%, respectively. Furthermore, the strain SF1 significantly increased the growth parameters and biochemical indicators of adversity in G. uralensis seedlings under drought and/or salt conditions, including radicle length and diameter, hypocotyl length and diameter, dry weight, seedling vigor index, antioxidant enzyme activity, and non-enzymatic antioxidant content. In conclusion, the strain SF1 can be used to develop environmental protection biological control agents, improve the anti-disease activity of plants, and promote plant growth in salinity soil within arid and semi-arid regions.

Comprehensive physiological, transcriptomic, and metabolomic analyses reveal the synergistic mechanism of Bacillus pumilus G5 combined with silicon alleviate oxidative stress in drought-stressed Glycyrrhiza uralensis Fisch

Glycyrrhiza uralensis Fisch. is often cultivated in arid, semi-arid, and salt-affected regions that suffer from drought stress, which leads to the accumulation of reactive oxygen species (ROS), thus causing oxidative stress. Plant growth-promoting bacteria (PGPB) and silicon (Si) have been widely reported to be beneficial in improving the tolerance of plants to drought stress by maintaining plant ROS homeostasis. Herein, combining physiological, transcriptomic, and metabolomic analyses, we investigated the response of the antioxidant system of G. uralensis seedlings under drought stress to Bacillus pumilus (G5) and/or Si treatment. The results showed that drought stress caused the overproduction of ROS, accompanied by the low efficiency of antioxidants [i.e., superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), the ascorbate (AsA)-glutathione (GSH) pool, total carotenoids, and total flavonoids]. Inversely, supplementation with G5 and/or Si enhanced the antioxidant defense system in drought-stressed G. uralensis seedlings, and the complex regulation of the combination of G5 and Si differed from that of G5 or Si alone. The combination of G5 and Si enhanced the antioxidant enzyme system, accelerated the AsA-GSH cycle, and triggered the carotenoid and flavonoid metabolism, which acted in combination via different pathways to eliminate the excess ROS induced by drought stress, thereby alleviating oxidative stress. These findings provide new insights into the comparative and synergistic roles of PGPB and Si in the antioxidant system of plants exposed to drought and a guide for the application of PGPB combined with Si to modulate the tolerance of plants to stress.

The bacterial consortia promote plant growth and secondary metabolite accumulation in Astragalus mongholicus under drought stress

Astragalus mongholicus is a widely used Traditional Chinese Medicine. However, cultivated A. mongholicus is often threatened by water shortage at all growth stage, and the content of medicinal compounds of cultivated A. mongholicus is much lower than that of wild plants. To alleviate drought stress on A. mongholicus and improve the accumulation of medicinal components in roots of A. mongholicus, we combined different bacteria with plant growth promotion or abiotic stress resistance characteristics and evaluated the role of bacterial consortium in helping plants tolerate drought stress and improving medicinal component content in roots simultaneously. Through the determination of 429 bacterial strains, it was found that 97 isolates had phosphate solubilizing ability, 63 isolates could release potassium from potash feldspar, 123 isolates could produce IAA, 58 isolates could synthesize ACC deaminase, and 21 isolates could secret siderophore. Eight bacterial consortia were constructed with 25 bacterial isolates with more than three functions or strong growth promoting ability, and six out of eight bacterial consortia significantly improved the root dry weight. However, only consortium 6 could increase the root biomass, astragaloside IV and calycosin-7-glucoside content in roots simultaneously. Under drought challenge, the consortium 6 could still perform these functions. Compared with non-inoculated plants, the root dry weight of consortium inoculated-plants increased by 120.0% and 78.8% under mild and moderate drought stress, the total content of astragaloside IV increased by 183.83% and 164.97% under moderate and severe drought stress, calycosin-7-glucoside content increased by 86.60%, 148.56% and 111.45% under mild, moderate and severe drought stress, respectively. Meanwhile, consortium inoculation resulted in a decrease in MDA level, while soluble protein and proline content and SOD, POD and CAT activities increased. These findings provide novel insights about multiple bacterial combinations to improve drought stress responses and contribute to accumulate more medicinal compounds.

How to improve CHMs quality: Enlighten from CHMs ecological cultivation

Chinese herbal medicines (CHMs) are one of the important bioresources of medicine, which works by unlocking nature's ability to prevent diseases and recover from illnesses. Recently, it has ascended to the world stage and become a global icon. Nowadays, a considerable of researches have focused on the quality evaluation of CHMs. However, it is difficult to meet the reasonable needs of human beings for safe drug use to evaluate the quality of a huge number of inferior goods for the CHMs contaminated by pesticides and heavy metals. Hence to explore an eligible medicinal plant cultivation pattern, which can provide high quality CHMs sustainably, is most promising. This review analyzed the situation and characteristics of medicinal plant resources in different periods, including wild-harvested and cultivated resources during different stages, putting forward that ecological cultivation must be the way to develop medicinal plant cultivation and to obtain high quality CHMs.