Scholarly Work - Plant Sciences & Plant Pathology
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/8870
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Item First Report of Powdery Mildew Caused by Erysiphe cruciferarum on Camelina sativa in Montana(Scientific Societies, 2022-07) Fu, Benzhong; Yan, QingCamelina sativa, also known as false flax, is an annual flowering plant in the family Brassicaceae that originated in Europe and Asia. In recent years, it has been cultivated as an important biofuel crop in Europe, Canada, and the northwest United States. In June 2021, severe powdery mildew disease was observed on C. sativa ‘Suneson’ plants under greenhouse conditions (temperature 18.3*C/22.2*C, night/day) in Bozeman, Montana (45*409 N, 111*29 W).Item Effect of the Monothiol Glutaredoxin GrxD on 2,4-Diacetylphloroglucinol Biosynthesis and Biocontrol Activity of Pseudomonas fluorescens 2P24(Frontiers Media SA, 2022-07) Dong, Qiuling; Yan, Qing; Zhang, Bo; Zhang, Li-qun; Wu, XiaogangPseudomonas fluorescens 2P24 is a plant root-associated bacterium that suppresses several soilborne plant diseases due to its production of the antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG). The biosynthesis of 2,4-DAPG is controlled by many regulatory elements, including the global regulator of the Gac/Rsm regulon and the pathway-specific repressor PhlF. In this work, a novel genetic element grxD, which encodes the monothiol glutaredoxin GrxD, was identified and characterized in the production of 2,4-DAPG in P. fluorescens 2P24. Our data showed that the mutation of grxD remarkably decreased 2,4-DAPG production. GrxD lost its ability to alter the production of 2,4-DAPG when the active-site CGFS motif of GrxD was mutated by site-directed mutagenesis. Further studies showed that the RsmA and RsmE proteins were essential for the GrxD-mediated regulation of 2,4-DAPG and exoprotease production. In addition, our data revealed that the deletion of grxD increased the expression of phlF, which negatively regulated the production of 2,4-DAPG. In addition, the grxD mutant was severely impaired in the biocontrol effect against the bacterial wilt of tomato. Overall, our results indicated that the monothiol glutaredoxin GrxD is involved in the production of 2,4-DAPG of P. fluorescens by influencing the Gac/Rsm global signaling pathway and transcriptional regulator PhlF and is essential for the biocontrol properties.Item Identification and Characterization of Bacteria-Derived Antibiotics for the Biological Control of Pea Aphanomyces Root Rot(MDPI AG, 2022-08) Lai, Xiao; Niroula, Dhirendra; Burrows, Mary; Wu, Xiaogang; Yan, QingAntibiosis has been proposed to contribute to the beneficial bacteria-mediated biocontrol against pea Aphanomyces root rot caused by the oomycete pathogen Aphanomyces euteiches. However, the antibiotics required for disease suppression remain unknown. In this study, we found that the wild type strains of Pseudomonas protegens Pf-5 and Pseudomonas fluorescens 2P24, but not their mutants that lack 2,4-diacetylphloroglucinol, strongly inhibited A. euteiches on culture plates. Purified 2,4-diacetylphloroglucinol compound caused extensive hyphal branching and stunted hyphal growth of A. euteiches. Using a GFP-based transcriptional reporter assay, we found that expression of the 2,4-diacetylphloroglucinol biosynthesis gene phlAPf-5 is activated by germinating pea seeds. The 2,4-diacetylphloroglucinol producing Pf-5 derivative, but not its 2,4-diacetylphloroglucinol non-producing mutant, reduced disease severity caused by A. euteiches on pea plants in greenhouse conditions. This is the first report that 2,4-diacetylphloroglucinol produced by strains of Pseudomonas species plays an important role in the biocontrol of pea Aphanomyces root rot.Item Citrate Synthase GltA Modulates the 2,4-Diacetylphloroglucinol Biosynthesis of Pseudomonas fluorescens 2P24 and is Essential for the Biocontrol Capacity(American Chemical Society, 2023-07) Yang, Qingqing; Yan, Qing; Zhang, Bo; Zhang, Li-qun; Wu, XiaogangCarbon metabolism is critical for microbial physiology and remarkably affects the outcome of secondary metabolite production. The production of 2,4-diacetylphloroglucinol (2,4-DAPG), a bacterial secondary metabolite with a broad spectrum of antibiotic activity, is a major mechanism used by the soil bacterium Pseudomonas fluorescens 2P24 to inhibit the growth of plant pathogens and control disease occurrence. Strain 2P24 has evolved a complex signaling cascade to regulate the production of 2,4-DAPG. However, the role of the central carbon metabolism in modulating 2,4-DAPG production has not been fully determined. In this study, we report that the gltA gene, which encodes citrate synthase, affects the expression of the 2,4-DAPG biosynthesis gene and is essential for the biocontrol capacity of strain 2P24. Our data showed that the mutation of gltA remarkably decreased the biosynthesis of 2,4-DAPG. Consistent with this result, the addition of citrate in strain 2P24 resulted in increased 2,4-DAPG production and decreased levels of RsmA and RsmE. In comparison with the wild-type strain, the gltA mutant was severely impaired in terms of biocontrol activity against the bacterial wilt disease of tomato plants caused by Ralstonia solanacearum. Moreover, the gltA mutant exhibited increased antioxidant activity, and the expression of oxidative, stress-associated genes, including ahpB, katB, and oxyR, was significantly upregulated in the gltA mutant compared to the wild-type strain. Overall, our data indicate that the citrate synthase GltA plays an important role in the production of 2,4-DAPG and oxidative stress and is required for biocontrol capacity.Item Exopolysaccharide is required for motility, stress tolerance, and plant colonization by the endophytic bacterium Paraburkholderia phytofirmans PsJN(Frontiers Media SA, 2023-08) Fu, Benzhong; Yan, QingParaburkholderia phytofirmans PsJN is an endophytic bacterium and has been shown to promote the growth and health of many different plants. Exopolysaccharide (EPS) plays important roles in plant-bacteria interaction and tolerance to environmental stresses. However, the function of EPS in PsJN and its interaction with plants remain largely unknown. In this study, a deletion mutation of bceQ gene, encoding a putative flippase for the EPS biosynthesis, was introduced in the genome of PsJN. The ΔbceQ mutant produced a significantly lower level of EPS than the wild type strain in culture media. Compared to the wild type PsJN, the ΔbceQ mutant was more sensitive to desiccation, UV damage, salt (NaCl) and iron (FeCl3) stresses, and bacteriophage infection. More importantly, the mutation of bceQ decreased the endophytic colonization of PsJN in camelina (Camelina sativa) and pea (Camelina sativa) under plant drought stress conditions. To the best of our knowledge, this is the first report that EPS production is required for the maximal colonization of an endophytic bacterium in the plant tissues under stress conditions.Item Optimized High Throughput Ascochyta Blight Screening Protocols and Immunity to A. pisi in Pea(MDPI AG, 2023-03) Annan, Emmanuel N.; Nyamesorto, Bernard; Yan, Qing; McPhee, Kevin; Huang, LiAscochyta blight (AB) is a destructive disease of the field pea (Pisum sativum L.) caused by necrotrophic fungal pathogens known as the AB-disease complex. To identify resistant individuals to assist AB resistance breeding, low-cost, high throughput, and reliable protocols for AB screening are needed. We tested and optimized three protocols to determine the optimum type of pathogen inoculum, the optimal development stage for host inoculation, and the timing of inoculation for detached-leaf assays. We found that different plant development stages do not affect AB infection type on peas, but the timing of inoculation affects the infection type of detached leaves due to wound-induced host defense response. After screening nine pea cultivars, we discovered that cultivar Fallon was immune to A. pisi but not to A. pinodes or the mixture of the two species. Our findings suggest that AB screening can be done with any of the three protocols. A whole-plant inoculation assay is necessary for identifying resistance to stem/node infection. Pathogen inoculation must be completed within 1.5 h post-detachment to avoid false positives of resistance for detach-leaf assays. It is essential to use a purified single-species inoculum for resistant resource screenings to identify the host resistance to each single species.