Healthy Photosynthetic Mechanism Suggests ISR Elicited by Bacillus spp. in Capsicum chinense Plants Infected with PepGMV

Induced Systemic Resistance in the Bacillus spp.-Capsicum chinense Jacq.-PepGMV Interaction, Elicited by Defense-Related Gene Expression

Induced systemic resistance (ISR) is a mechanism involved in the plant defense response against pathogens. Certain members of the Bacillus genus are able to promote the ISR by maintaining a healthy photosynthetic apparatus, which prepares the plant for future stress situations. The goal of the present study was to analyze the effect of the inoculation of Bacillus on the expression of genes involved in plant responses to pathogens, as a part of the ISR, during the interaction of Capsicum chinense infected with PepGMV. The effects of the inoculation of the Bacillus strains in pepper plants infected with PepGMV were evaluated by observing the accumulation of viral DNA and the visible symptoms of pepper plants during a time-course experiment in greenhouse and in in vitro experiments. The relative expression of the defense genes CcNPR1, CcPR10, and CcCOI1 were also evaluated. The results showed that the plants inoculated with Bacillus subtilis K47, Bacillus cereus K46, and Bacillus sp. M9 had a reduction in the PepGMV viral titer, and the symptoms in these plants were less severe compared to the plants infected with PepGMV and non-inoculated with Bacillus. Additionally, an increase in the transcript levels of CcNPR1, CcPR10, and CcCOI1 was observed in plants inoculated with Bacillus strains. Our results suggest that the inoculation of Bacillus strains interferes with the viral replication, through the increase in the transcription of pathogenesis-related genes, which is reflected in a lowered plant symptomatology and an improved yield in the greenhouse, regardless of PepGMV infection status.

Glomus sp. and Bacillus sp. strains mitigate the adverse effects of drought on maize (Zea mays L.)

Maize (Zea mays L.) is an economically important source of food and feed. This species is highly sensitive to drought, which is the most limiting factor for the biomass yield of a crop. Thus, maize cultivation methods should be improved, especially by environment-friendly agricultural practices, such as microorganisms. Here, we provide evidence that Glomus sp. and Bacillus sp. modulate maize response to drought. Inoculation of maize seeds by these microorganisms restored the proper photosynthetic activity of the plant under drought and stabilized the osmoprotectant content of the leaf. The beneficial effect of Glomus sp. and Bacillus sp. was also related to the stabilization of cell redox status reflected by hydrogen peroxide content, antioxidant enzymes, and malondialdehyde level in leaves. As we revealed by several methods, shaping maize response to drought is mediated by both microorganism-mediated modifications of cell wall composition and structure of leaves, such as downregulating pectin, affecting their methylation degree, and increasing hemicellulose content. Overall, we provide new information about the mechanisms by which Glomus sp. and Bacillus sp. induce drought tolerance in maize, which is a promising approach for mitigating abiotic stresses.

Ambiguities of PGPR-Induced Plant Signaling and Stress Management

The growth and stress responses developed by the plant in virtue of the action of PGPR are dictated by the changes in hormone levels and related signaling pathways. Each plant possesses its specific type of microbiota that is shaped by the composition of root exudates and the signal molecules produced by the plant and microbes. Plants convey signals through diverse and complex signaling pathways. The signaling pathways are also controlled by phytohormones wherein they regulate and coordinate various defense responses and developmental stages. On account of improved growth and stress tolerance provided by the PGPR to plants, there exist crosstalk of signaling events between phytohormones and other signaling molecules secreted by the plants and the PGPR. This review discusses some of the important aspects related to the ambiguities of signaling events occurring in plants, allowing the interaction of PGPR with plants and providing stress tolerance to the plant.