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Summary: The plant rapid alkalinization factor (RALF) peptides function as key regulators in cell growth and immune responses through the receptor kinase FERONIA (FER). In this study, we report that the transcription factor FgPacC binds directly to the promoter of FgRALF gene, which encodes a functional homologue of the plant RALF peptides from the wheat head blight fungus Fusarium graminearum (FgRALF). More importantly, FgPacC promotes fungal infection via host immune suppression by activating the expression of FgRALF. The FgRALF peptide also exhibited typical activities of plant RALF functions, such as inducing plant alkalinization and inhibiting cell growth, including wheat (Triticum aestivum), tomato (Solanum lycopersicum) and Arabidopsis thaliana. We further identified the wheat receptor kinase FERONIA (TaFER), which is capable of restoring the defects of the A. thaliana FER mutant. In addition, we found that FgRALF peptide binds to the extracellular malectin‐like domain (ECD) of TaFER (TaFERECD) to suppress the PAMP‐triggered immunity (PTI) and cell growth. Overexpression of TaFERECD in A. thaliana confers plant resistance to F. graminearum and protects from FgRALF‐induced cell growth inhibition. Collectively, our results demonstrate that the fungal pathogen‐secreted RALF mimic suppresses host immunity and inhibits cell growth via plant FER receptor. This establishes a novel pathway for the development of disease‐resistant crops in the future without compromising their yield potential. [ABSTRACT FROM AUTHOR]

Simple Summary: Microbial volatile organic compounds (VOCs) play a crucial role in promoting plant growth and causing systemic resistance to a variety of diseases caused by fungus, bacteria, nematodes, and oomycetes. However, the role of Bacillus VOCs in growth promotion is still limited. In the present work, we aim to examine the growth promotion mechanisms of cold-tolerant Bacillus strains RJGP41 and GBAC46 from the Qinghai-Tibet Plateau and the well-known PGPR strain FZB42 and their VOCs on tomato plants. Our experiment results revealed that both Bacillus isolates and their pure VOCs positively improve PGPR activities in tomato plants by triggering antioxidant enzyme activity and expression of the PGPR genes. In our future research, the selected Bacillus strains and their novel pure VOCs will be further explored to find the possible mechanisms for the safe and green control of tomato disease in sustainable agriculture. The interaction between plant and bacterial VOCs has been extensively studied, but the role of VOCs in growth promotion still needs to be explored. In the current study, we aim to explore the growth promotion mechanisms of cold-tolerant Bacillus strains GBAC46 and RJGP41 and the well-known PGPR strain FZB42 and their VOCs on tomato plants. The result showed that the activity of phytohormone (IAA) production was greatly improved in GBAC46 and RJGP41 as compared to FZB42 strains. The in vitro and in-pot experiment results showed that the Bacillus VOCs improved plant growth traits in terms of physiological parameters as compared to the CK. The VOCs identified through gas chromatography-mass spectrometry (GC-MS) analysis, namely 2 pentanone, 3-ethyl (2P3E) from GBAC46, 1,3-cyclobutanediol,2,2,4,4-tetramethyl (CBDO) from RJGP41, and benzaldehyde (BDH) from FZB42, were used for plant growth promotion. The results of the partition plate (I-plate) and in-pot experiments showed that all the selected VOCs (2P3E, CBDO, and BDH) promoted plant growth parameters as compared to CK. Furthermore, the root morphological factors also revealed that the selected VOCs improved the root physiological traits in tomato plants. The plant defense enzymes (POD, APX, SOD, and CAT) and total protein contents were studied, and the results showed that the antioxidant enzymes and protein contents significantly increased as compared to CK. Similarly, plant growth promotion expression genes (IAA4, ARF10A, GA2OX2, CKX2, and EXP1) were significantly upregulated and the ERF gene was downregulated as compared to CK. The overall findings suggest that both Bacillus isolates and their pure VOCs positively improved plant growth promotion activities by triggering the antioxidant enzyme activity, protein contents, and relative gene expressions in tomato plants. [ABSTRACT FROM AUTHOR]

BACKGROUND: Bacterial wilt (BW) caused by Ralstonia solanacearum (RS) is considered as one of the most destructive plant diseases. An avirulent strain of RS, FJAT1458, is a potential biocontrol agent of BW. In this study, the mechanism of FJAT1458 against BW was evaluated. RESULTS: FJAT1458 was tagged with the red fluorescent protein gene, and the resulting strain was named as FJAT1458‐RFP. When FJAT1458‐RFP and FJAT91‐GFP (a virulent strain of RS labelled with the green fluorescent protein gene), were co‐inoculated in potted tomato plants, the colonization of FJAT91‐GFP reached an almost undetectable level at 7 days post‐inoculation (dpi) in the roots and at 9 dpi in rhizosphere soil. When they were co‐inoculated in a hydroponic tomato growing system, numbers of the two strains were similar at 3 dpi in the root tissues; however, FJAT91‐GFP was not detected at 9 dpi while FJAT1458‐RFP maintained 1.77 × 105 CFU g−1. The inoculation of FJAT1458‐RFP alone or combination with FJAT91‐GFP significantly increased tomato root activity. Moreover, expression levels of the defense‐related genes PR‐1a, GLUA, and CHI3 in tomato roots were significantly up‐regulated by FJAT1458‐RFP and co‐inoculation of FJAT1458‐RFP and FJAT91‐GFP at 5 dpi, compared to the control (water, CK) treatment. Noteworthy, expression levels of GLUA in the treatments of FJAT1458‐RFP and FJAT1458‐RFP + FJAT91‐GFP were 12.22‐ and 12.05‐fold higher than that in the CK at 5 dpi, respectively. CONCLUSIONS: The results suggested that the avirulent strain FJAT1458‐RFP could suppress colonization of the virulent strain in tomato roots, and induce tomato plant resistance against BW. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Soil salinity is a major constraint adversely affecting agricultural crops including wheat worldwide. The use of plant growth promoting rhizobacteria (PGPR) to alleviate salt stress in crops has attracted the focus of many researchers due to its safe and eco-friendly nature. The current study aimed to study the genetic potential of high halophilic Bacillus strains, isolated from the rhizosphere in the extreme environment of the Qinghai–Tibetan plateau region of China, to reduce salt stress in wheat plants. The genetic analysis of high halophilic strains, NMCN1, LLCG23, and moderate halophilic stain, FZB42, revealed their key genetic features that play an important role in salt stress, osmotic regulation, signal transduction and membrane transport. Consequently, the expression of predicted salt stress-related genes were upregulated in the halophilic strains upon NaCl treatments 10, 16 and 18%, as compared with control. The halophilic strains also induced a stress response in wheat plants through the regulation of lipid peroxidation, abscisic acid and proline in a very efficient manner. Furthermore, NMCN1 and LLCG23 significantly enhanced wheat growth parameters in terms of physiological traits, i.e., fresh weight 31.2% and 29.7%, dry weight 28.6% and 27.3%, shoot length 34.2% and 31.3% and root length 32.4% and 30.2%, respectively, as compared to control plants under high NaCl concentration (200 mmol). The Bacillus strains NMCN1 and LLCG23 efficiently modulated phytohormones, leading to the substantial enhancement of plant tolerance towards salt stress. Therefore, we concluded that NMCN1 and LLCG23 contain a plethora of genetic features enabling them to combat with salt stress, which could be widely used in different bio-formulations to obtain high crop production in saline conditions. [ABSTRACT FROM AUTHOR]

Many representatives of the Bacillus subtilis species complex are known as plant growth-promoting rhizobacteria (PGPR) and are widely used in agriculture as biofertilizers and biocontrol agents. Two bacterial strains, "Korea isolate" and ZL918, taxonomically classified as being Bacillus amyloliquefaciens, isolated from disease-damaged plant organs, were alleged to cause bacterial rot in starchy storage plant organs. The aim of this study was to elucidate whether these findings have consequences for the general use of beneficial Bacilli in agriculture. Whole genome sequencing revealed that the pathogenic ZL918 was a representative of Bacillus velezensis. B. velezensis FZB42 and other representatives of the B. subtilis species complex caused the same symptoms of bacterial rot only when injected inside of potato tubers and onion bulbs, but not when inoculated onto the surface of the storage organs. It seemed that the pathogenic effect was due to starch hydrolyzing activity that likely stimulates propagation of endophytic bacteria inside of starchy tissues. After removing the inherent microbiota via Co60 γ-ray irradiation, the storage organs inoculated by either FZB42 or purified α-amylase did not develop rot symptoms. Two opportunistic pathogens, Pantoea ananatis and Pantoea agglomerans, isolated from the rotted area, were shown to cause bacterial rot in x-ray treated potato tuber and onion starchy tissues when the proteobacteria were applied in high concentration. This suggests that opportunistic pathogenic bacteria residing inside of the starchy storage organ are the causal agents of bacterial soft rot disease in potato tubers and other starchy plant storage organs. [ABSTRACT FROM AUTHOR]

Plant growth-promoting rhizobacteria (PGPR) are beneficial soil microorganisms that colonize plant roots for nutritional purposes and benefit plants by increasing plant growth or reducing plant disease. To clarify the complex mechanisms underlying plant-PGPR interactions, transcriptomic analyses of the response of rice ( Oryza sativa ) 9311 to Bacillus amyloliquefaciens FZB42 were carried out using RNA-Seq technology. This resulted in the identification of 379 differentially expressed genes in rice roots and 719 in rice leaves following FZB42 interaction that are likely to be related to plant-PGPR interactions, plant stress-resistance, pathogen-resistance, growth and development and basic and energy metabolism. We focused on plant disease-resistance mechanisms induced by FZB42. Variations in the expression of crucial genes COI1 , MEKK1 , WRKY, and PR that are involved in signal transduction following plant-pathogen interaction at different interaction time points were examined. Significantly up-regulated expression of PR , LOX, and ERF genes involved in the salicylic acid, jasmonic acid, and ethylene signal transduction pathways, respectively, were detected, suggest that defense reactions in rice were induced following interaction with FZB42. Phytoalexin changes in rice induced by FZB42 were examined and momilactone A, phytocassane A, phytocassane D, phytocassane E levels were low at 12 h, rose between 24 and 48 h, suggesting a PGPR-mediated mechanism of plant pathogen resistance. The study indicated that plant responses to PGPR in multi-metabolism pathways, which includes improving plant pathogen-resistance by mediating multi-signal transduction that regulates the expression of PRs and other defense genes, as well as influencing fundamental metabolic pathways to enhance the plant’s physical condition. [ABSTRACT FROM AUTHOR]