Special Issue "Plant Control of Symbiotic Microbe Behavior and Reproduction"

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Environmental Microbiology".

Deadline for manuscript submissions: 30 July 2019

Special Issue Editors

Guest Editor
Prof. James White

Department of Plant Biology, Rutgers University, New Brunswick, New Jersey, USA
Website | E-Mail
Interests: microbial endophytes of plants; rhizophagy cycle; plant defensive symbioses; plant nutritional symbioses
Guest Editor
Dr. Charles W. Bacon

Agricultural Research Service, United States Department of Agriculture, Russell Research Center, 950 College Station Road, Athens, GA 30604, USA
Website | E-Mail
Fax: +1 706 546 3116
Interests: regulation and biosynthesis of mycotoxins; fungal endophyte-grass relationships; bacterial endophytes, and the coevolution of secondary products; primarily mycotoxins, with grasses and other plants, as an adaptive strategy for mutualistic associations

Special Issue Information

Dear Colleagues,

Plants are host to numerous microbes (mutualists, pathogens and saprobes), on and within their tissues. It is becoming increasingly clear that these associations are not mere chance interactions between plants and microbes—but, rather, are functional and under host selection, control, and regulation. Host plants select microbes that they will permit to enter into their tissues, then they cultivate them, controlling their behaviors and regulating their numbers. Collaboration with microbes is a key way that plants interface with the environment to obtain nutrients and defend themselves from biotic and abiotic stresses—and plants rely on microbes to modulate plant development. Since intimate association with microbes that enter into plant tissues is "playing with fire" in the sense that microbes retain a parasitism capacity, virulence and reproduction of endophytic microbes must be managed by the host plant. In this topic we will explore the functions of microbes in plant tissues and the ways that plant hosts select and manage the microbes in their tissues.

Prof. James White
Dr. Charles W. Bacon
Guest Editors

Manuscript Submission Information

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Keywords

  • Actinorhizae
  • Bacteria
  • Dark septate endophytes
  • Epichloe
  • Fungi
  • Quorum quenching/sensing
  • Rhizosphere
  • Rhizobia
  • Plant secondary metabolites
  • Plant antimicrobials
  • Rhizophagy cycle

Published Papers (3 papers)

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Research

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Open AccessArticle Variovorax sp. Has an Optimum Cell Density to Fully Function as a Plant Growth Promoter
Microorganisms 2019, 7(3), 82; https://doi.org/10.3390/microorganisms7030082
Received: 18 February 2019 / Revised: 6 March 2019 / Accepted: 13 March 2019 / Published: 15 March 2019
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Abstract
Utilization of plant growth-promoting bacteria colonizing roots is environmentally friendly technology instead of using chemicals in agriculture, and understanding of the effects of their colonization modes in promoting plant growth is important for sustainable agriculture. We herein screened the six potential plant growth-promoting [...] Read more.
Utilization of plant growth-promoting bacteria colonizing roots is environmentally friendly technology instead of using chemicals in agriculture, and understanding of the effects of their colonization modes in promoting plant growth is important for sustainable agriculture. We herein screened the six potential plant growth-promoting bacteria isolated from Beta vulgaris L. (Rhizobium sp. HRRK 005, Polaromonas sp. HRRK 103, Variovorax sp. HRRK 170, Mesorhizobium sp. HRRK 190, Streptomyces sp. HRTK 192, and Novosphingobium sp. HRRK 193) using a series of biochemical tests. Among all strains screened, HRRK 170 had the highest potential for plant growth promotion, given its ability to produce plant growth substances and enzymes such as siderophores and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, respectively, concomitantly with active growth in a wider range of temperatures (10–30 °C) and pH (5.0–10.0). HRRK 170 colonized either as spots or widely on the root surface of all vegetable seedlings tested, but significant growth promotion occurred only in two vegetables (Chinese cabbage and green pepper) within a certain cell density range localized in the plant roots. The results indicate that HRRK 170 could function as a plant growth promoter, but has an optimum cell density for efficient use. Full article
(This article belongs to the Special Issue Plant Control of Symbiotic Microbe Behavior and Reproduction)
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Open AccessArticle Root-Associated Endophytic Bacterial Community Composition of Pennisetum sinese from Four Representative Provinces in China
Microorganisms 2019, 7(2), 47; https://doi.org/10.3390/microorganisms7020047
Received: 24 December 2018 / Revised: 16 January 2019 / Accepted: 30 January 2019 / Published: 11 February 2019
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Abstract
Pennisetum sinese, a source of bio-energy with high biomass production, is a species that contains high crude protein and will be useful for solving the shortage of forage grass after the implementation of “Green for Grain” project in the Loess plateau of [...] Read more.
Pennisetum sinese, a source of bio-energy with high biomass production, is a species that contains high crude protein and will be useful for solving the shortage of forage grass after the implementation of “Green for Grain” project in the Loess plateau of Northern Shaanxi in 1999. Plants may receive benefits from endophytic bacteria, such as the enhancement of plant growth or the reduction of plant stress. However, the composition of the endophytic bacterial community associated with the roots of P. sinese is poorly elucidated. In this study, P. sinese from five different samples (Shaanxi province, SX; Fujian province, FJ; the Xinjiang Uyghur autonomous prefecture, XJ and Inner Mongolia, including sand (NS) and saline-alkali land (NY), China) were investigated by high-throughput next-generation sequencing of the 16S rDNA V3-V4 hypervariable region of endophytic bacteria. A total of 313,044 effective sequences were obtained by sequencing five different samples, and 957 effective operational taxonomic units (OTUs) were yielded at 97% identity. The phylum Proteobacteria, the classes Gammaproteobacteria and Alphaproteobacteria, and the genera Pantoea, Pseudomonas, Burkholderia, Arthrobacter, Psychrobacter, and Neokomagataea were significantly dominant in the five samples. In addition, our results demonstrated that the Shaanxi province (SX) sample had the highest Shannon index values (3.795). We found that the SX (308.097) and NS (126.240) samples had the highest and lowest Chao1 richness estimator (Chao1) values, respectively. Venn graphs indicated that the five samples shared 39 common OTUs. Moreover, according to results of the canonical correlation analysis (CCA), soil total carbon, total nitrogen, effective phosphorus, and pH were the major contributing factors to the difference in the overall composition of the bacteria community in this study. Our data provide insights into the endophytic bacteria community composition and structure of roots associated with P. sinese. These results might be useful for growth promotion in different samples, and some of the strains may have the potential to improve plant production in future studies. Full article
(This article belongs to the Special Issue Plant Control of Symbiotic Microbe Behavior and Reproduction)
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Review

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Open AccessReview Rhizophagy Cycle: An Oxidative Process in Plants for Nutrient Extraction from Symbiotic Microbes
Microorganisms 2018, 6(3), 95; https://doi.org/10.3390/microorganisms6030095
Received: 22 August 2018 / Revised: 1 September 2018 / Accepted: 5 September 2018 / Published: 17 September 2018
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Abstract
In this paper, we describe a mechanism for the transfer of nutrients from symbiotic microbes (bacteria and fungi) to host plant roots that we term the ‘rhizophagy cycle.’ In the rhizophagy cycle, microbes alternate between a root intracellular endophytic phase and a free-living [...] Read more.
In this paper, we describe a mechanism for the transfer of nutrients from symbiotic microbes (bacteria and fungi) to host plant roots that we term the ‘rhizophagy cycle.’ In the rhizophagy cycle, microbes alternate between a root intracellular endophytic phase and a free-living soil phase. Microbes acquire soil nutrients in the free-living soil phase; nutrients are extracted through exposure to host-produced reactive oxygen in the intracellular endophytic phase. We conducted experiments on several seed-vectored microbes in several host species. We found that initially the symbiotic microbes grow on the rhizoplane in the exudate zone adjacent the root meristem. Microbes enter root tip meristem cells—locating within the periplasmic spaces between cell wall and plasma membrane. In the periplasmic spaces of root cells, microbes convert to wall-less protoplast forms. As root cells mature, microbes continue to be subjected to reactive oxygen (superoxide) produced by NADPH oxidases (NOX) on the root cell plasma membranes. Reactive oxygen degrades some of the intracellular microbes, also likely inducing electrolyte leakage from microbes—effectively extracting nutrients from microbes. Surviving bacteria in root epidermal cells trigger root hair elongation and as hairs elongate bacteria exit at the hair tips, reforming cell walls and cell shapes as microbes emerge into the rhizosphere where they may obtain additional nutrients. Precisely what nutrients are transferred through rhizophagy or how important this process is for nutrient acquisition is still unknown. Full article
(This article belongs to the Special Issue Plant Control of Symbiotic Microbe Behavior and Reproduction)
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