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Molecular Research on Plant-Associated Nitrogen-Fixing Bacteria

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A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Molecular Plant Sciences".

Deadline for manuscript submissions: 30 May 2024 | Viewed by 3271

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Prof. Dr. Stefanie Kautz

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Department of Biology, Portland State University, Portland, OR 97201, USA
Interests: interspecific interactions; chemical biology; insects, plants, and microbes

Special Issue Information

Dear Colleagues,

Modulating nitrogen-fixing microbial plant symbionts have a profound influence on ecosystem dynamics and global nitrogen cycles. Beyond the classical examples of legume–Rhizobia interactions, several other—and less studied—plant–microbe symbioses perform biological nitrogen fixation at large quantitative scales. For example, Frankia–alder symbioses rival legume–Rhizobia interactions in the amount of fixed atmospheric nitrogen. Nonetheless, we often lack knowledge around the identity, diversity, and physiology of plant-associated nitrogen-fixing microbes. Furthermore, recent work has shown that microorganisms inhabiting root nodules are more taxonomically and functionally diverse than previously thought and make complex multiplayer microbial communities. Effects on plant fitness, competitiveness, and stress tolerance of nodule communities has been predicted but only experimentally shown in isolated cases. To better understand these systems and their impact on the ecosystem, ample opportunities of studies in the fields of molecular and functional biology arise. We hope to capture an encompassing picture of these multilayer systems in this Special Issue of the International Journal of Molecular Sciences to better understand the diversity and functional role of these multiplayer systems and their impact on local and global ecosystems.

Prof. Dr. Stefanie Kautz
Guest Editor

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Keywords

plants
microbes
rhizobia
frankia
symbiosis
chemical biology
interspecific interactions
nitrogen fixation

Published Papers (3 papers)

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Research

21 pages, 2053 KiB

Open AccessArticle

Calcium Induces the Cleavage of NopA and Regulates the Expression of Nodulation Genes and Secretion of T3SS Effectors in Sinorhizobium fredii NGR234

by Wonseok Kim, Sebastián Acosta-Jurado, Sunhyung Kim and Hari B. Krishnan

Int. J. Mol. Sci. 2024, 25(6), 3443; https://doi.org/10.3390/ijms25063443 - 19 Mar 2024

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Abstract

The type III secretion system (T3SS) is a key factor for the symbiosis between rhizobia and legumes. In this study, we investigated the effect of calcium on the expression and secretion of T3SS effectors (T3Es) in Sinorhizobium fredii NGR234, a broad host range rhizobial strain. We performed RNA-Seq analysis of NGR234 grown in the presence of apigenin, calcium, and apigenin plus calcium and compared it with NGR234 grown in the absence of calcium and apigenin. Calcium treatment resulted in a differential expression of 65 genes, most of which are involved in the transport or metabolism of amino acids and carbohydrates. Calcium had a pronounced effect on the transcription of a gene (NGR_b22780) that encodes a putative transmembrane protein, exhibiting a 17-fold change when compared to NGR234 cells grown in the absence of calcium. Calcium upregulated the expression of several sugar transporters, permeases, aminotransferases, and oxidoreductases. Interestingly, calcium downregulated the expression of nodABC, genes that are required for the synthesis of nod factors. A gene encoding a putative outer membrane protein (OmpW) implicated in antibiotic resistance and membrane integrity was also repressed by calcium. We also observed that calcium reduced the production of nodulation outer proteins (T3Es), especially NopA, the main subunit of the T3SS pilus. Additionally, calcium mediated the cleavage of NopA into two smaller isoforms, which might affect the secretion of other T3Es and the symbiotic establishment. Our findings suggest that calcium regulates the T3SS at a post-transcriptional level and provides new insights into the role of calcium in rhizobia–legume interactions. Full article

(This article belongs to the Special Issue Molecular Research on Plant-Associated Nitrogen-Fixing Bacteria)

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18 pages, 2690 KiB

Open AccessArticle

Bioprospecting for Rhizobacteria with the Ability to Enhance Drought Tolerance in Lessertia frutescens

by Mokgadi M. Hlongwane, Felix D. Dakora, Mustapha Mohammed and Ntebogeng S. Mokgalaka-Fleischmann

Int. J. Mol. Sci. 2023, 24(24), 17585; https://doi.org/10.3390/ijms242417585 - 18 Dec 2023

Cited by 1 | Viewed by 830

Abstract

Lessertia frutescens is a multipurpose medicinal plant indigenous to South Africa that is used for the management of cancer, stomach ulcers, wounds, etc. The use and demand for the raw materials from this plant have been increasing steadily over the years, putting strain on the dwindling wild populations. Although cultivation may provide relief to the strained supply, the persistent drought climate poses a threat to the plant’s growth and productivity. This study explored three plant-growth-promoting rhizobacteria isolates, TUTLFNC33, TUTLFNC37 and TUTLFWC74, obtained from the root nodules of Lessertia frutescens as potential bioinoculants that can improve yield, biological activities and the production of secondary metabolites in the host plant. Isolate TUTLFNC37 was identified as the most promising isolate for inoculation of Lessertia frutescens under drought conditions as it induced drought tolerance through enhanced root proliferation, osmolyte proline accumulation and stomatal closure. Superior biomass yield, phenolics, triterpenes and antioxidant activity were evident in the extracts of Lessertia frutescens inoculated with TUTLFNC37 and under different levels of drought. Furthermore, the metabolomics of the plant extracts demonstrated the ability of the isolate to withstand drastic changes in the composition of unique metabolites, sutherlandiosides A–D and sutherlandins A–D. Molecular families which were never reported in the plant (peptides and glycerolipids) were detected and annotated in the molecular networks. Although drought had deleterious effects on Lessertia frutescens, isolate TUTLFNC37 alleviated the impact of the stress. Isolate TUTLFNC37 is therefore the most promising, environmentally friendly alternative to harmful chemicals such as nitrate-based fertilizers. The isolate should be studied to establish its field performance, cross infectivity with other medicinal plants and competition with inherent soil microbes. Full article

(This article belongs to the Special Issue Molecular Research on Plant-Associated Nitrogen-Fixing Bacteria)

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19 pages, 9975 KiB

Open AccessArticle

CRK12: A Key Player in Regulating the Phaseolus vulgaris-Rhizobium tropici Symbiotic Interaction

by Antonino M. Lecona, Kalpana Nanjareddy, Lourdes Blanco, Valeria Piazza, José Antonio Vera-Núñez, Miguel Lara and Manoj-Kumar Arthikala

Int. J. Mol. Sci. 2023, 24(14), 11720; https://doi.org/10.3390/ijms241411720 - 21 Jul 2023

Cited by 1 | Viewed by 1330

Abstract

Cysteine-rich receptor-like kinases (CRKs) are a type of receptor-like kinases (RLKs) that are important for pathogen resistance, extracellular reactive oxygen species (ROS) signaling, and programmed cell death in plants. In a previous study, we identified 46 CRK family members in the Phaseolus vulgaris genome and found that CRK12 was highly upregulated under root nodule symbiotic conditions. To better understand the role of CRK12 in the Phaseolus–Rhizobia symbiotic interaction, we functionally characterized this gene by overexpressing (CRK12-OE) and silencing (CRK12-RNAi) it in a P. vulgaris hairy root system. We found that the constitutive expression of CRK12 led to an increase in root hair length and the expression of root hair regulatory genes, while silencing the gene had the opposite effect. During symbiosis, CRK12-RNAi resulted in a significant reduction in nodule numbers, while CRK12-OE roots showed a dramatic increase in rhizobial infection threads and the number of nodules. Nodule cross sections revealed that silenced nodules had very few infected cells, while CRK12-OE nodules had enlarged infected cells, whose numbers had increased compared to controls. As expected, CRK12-RNAi negatively affected nitrogen fixation, while CRK12-OE nodules fixed 1.5 times more nitrogen than controls. Expression levels of genes involved in symbiosis and ROS signaling, as well as nitrogen export genes, supported the nodule phenotypes. Moreover, nodule senescence was prolonged in CRK12-overexpressing roots. Subcellular localization assays showed that the PvCRK12 protein localized to the plasma membrane, and the spatiotemporal expression patterns of the CRK12-promoter::GUS-GFP analysis revealed a symbiosis-specific expression of CRK12 during the early stages of rhizobial infection and in the development of nodules. Our findings suggest that CRK12, a membrane RLK, is a novel regulator of Phaseolus vulgaris-Rhizobium tropici symbiosis. Full article

(This article belongs to the Special Issue Molecular Research on Plant-Associated Nitrogen-Fixing Bacteria)

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