Plant diseases are often thought to be caused by one species or even by a specific strain. Microbes in nature, however, mostly occur as part of complex communities and this has been noted since the ...time of van Leeuwenhoek. Interestingly, most laboratory studies focus on single microbial strains grown in pure culture; we were therefore unaware of possible interspecies and/or inter-kingdom interactions of pathogenic microbes in the wild. In human and animal infections, it is now being recognized that many diseases are the result of multispecies synergistic interactions. This increases the complexity of the disease and has to be taken into consideration in the development of more effective control measures. On the other hand, there are only a few reports of synergistic pathogen-pathogen interactions in plant diseases and the mechanisms of interactions are currently unknown. Here we review some of these reports of synergism between different plant pathogens and their possible implications in crop health. Finally, we briefly highlight the recent technological advances in diagnostics as these are beginning to provide important insights into the microbial communities associated with complex plant diseases. These examples of synergistic interactions of plant pathogens that lead to disease complexes might prove to be more common than expected and understanding the underlying mechanisms might have important implications in plant disease epidemiology and management.
Studies of chemical signaling between plants and bacteria in the past have been largely confined to two models: the rhizobial-legume symbiotic association and pathogenesis between agrobacteria and ...their host plants. Recent studies are beginning to provide evidence that many plant-associated bacteria undergo chemical signaling with the plant host via low-molecular-weight compounds. Plant-produced compounds interact with bacterial regulatory proteins that then affect gene expression. Similarly, bacterial quorum-sensing signals result in a range of functional responses in plants. This review attempts to highlight current knowledge in chemical signaling that takes place between pathogenic bacteria and plants. This chemical communication between plant and bacteria, also referred to as interkingdom signaling, will likely become a major research field in the future, as it allows the design of specific strategies to create plants that are resistant to plant pathogens.
Marine natural products with antibiotic activity have been a rich source of drug discovery; however, the emergence of antibiotic-resistant bacterial strains has turned attention towards the discovery ...of alternative innovative strategies to combat pathogens. In many pathogenic bacteria, the expression of virulence factors is under the regulation of quorum sensing (QS). QS inhibitors (QSIs) present a promising alternative or potential synergistic treatment since they disrupt the signaling pathway used for intra- and interspecies coordination of expression of virulence factors. This review covers the set of molecules showing QSI activity that were isolated from marine organisms, including plants (algae), animals (sponges, cnidarians, and bryozoans), and microorganisms (bacteria, fungi, and cyanobacteria). The compounds found and the methods used for their isolation are the emphasis of this review.
Signaling in the Rhizosphere Venturi, Vittorio; Keel, Christoph
Trends in plant science,
March 2016, 2016-Mar, 2016-03-00, 20160301, Letnik:
21, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Signaling studies in the rhizosphere have focused on close interactions between plants and symbiotic microorganisms. However, this focus is likely to expand to other microorganisms because the ...rhizomicrobiome is important for plant health and is able to influence the structure of the microbial community. We discuss here the shaping of the rhizomicrobiome and define which aspects can be considered signaling. We divide signaling in the rhizosphere into three categories: (i) between microbes, (ii) from plants to microorganisms, and (iii) from microorganisms to plants. Signals act on diverse organisms including the plant. Mycorrhizal and rhizobial interkingdom signaling has revealed its pivotal role in establishing associations, and the recent discovery of signaling with non-symbiotic microorganisms indicates the important role of communication in shaping the rhizomicrobiome.
The plant and the rhizomicrobiome strongly influence each other via the secretion and detection of signaling compounds.
Signaling between plants and rhizosphere microorganisms has been mainly studied in intimate symbiotic associations, in particular those involving mycorrhizal fungi and rhizobial bacteria; it is now evident that this is a more widespread phenomenon also involving non-symbiotic microorganisms.
The rhizomicrobiome is a very rich and complex microbial community which undergoes intraspecies as well as interspecies signaling.
Thus far, plant molecules including flavonoids, strigolactones, cutin momoners, and as yet unidentified low molecular weight compounds have been recognized as signals which are sensed by microorganisms.
Microorganisms produce signals which affect plant growth and induce plant systemic resistance mainly via a process called priming.
Bacterial Panicle Blight caused by
is a major disease of rice, which has dramatically affected rice production around the world in the last years. In this study we describe the assessment of three
...isolates as biocontrol agents for
. Additionally, the presence of other plant-growth promoting abilities and their possible beneficial effects upon their inoculation on rice plants was evaluated as an ecological analysis for their future inoculation in rice crops. Two isolates (A20 and 5.1) inhibited growth of virulent
strains, as well as a wide range of bacterial and fungal species, while a third strain (7.1) showed only antifungal activity.
tests demonstrated the ability of these strains to produce siderophores, Indoleacetic acid (IAA), extracellular enzymes and solubilizing phosphate. Greenhouse experiments with two rice cultivars indicated that
A20 is able to colonize rice plants and promote plant growth in both cultivars. Furthermore, an
tagged mutant was generated and colonization experiments were performed, indicating that
A20 -GFP was strongly associated with root hairs, which may be related to the plant growth promotion observed in the gnotobiotic experiments. In order to characterize the antimicrobial compounds produced by strain A20 bacteria, mass spectrometry analyses were performed. This technique indicated that A20 produced several antimicrobial compounds with sizes below 3 kDa and three of these molecules were identified as Streptotricins D, E and F. These findings indicate the potential of
A20 as a biocontrol inoculant to protect rice plants against bacterial diseases.
Many proteobacteria possess LuxR solos which are quorum sensing LuxR-type regulators that are not paired with a cognate LuxI-type synthase. LuxR solos have been implicated in intraspecies, ...interspecies, and interkingdom communication by sensing endogenous and exogenous acyl-homoserine lactones (AHLs) as well as non-AHL signals. LuxR solos are likely to play a major role in microbiome formation, shaping, and maintenance through many different cell-cell signaling mechanisms. This review intends to assess the different types and discuss the possible functional roles of the widespread family of LuxR solo regulators. In addition, an analysis of LuxR solo types and variability among the totality of publicly available proteobacterial genomes is presented. This highlights the importance of these proteins and will encourage scientists to mobilize and study them in order to increase our knowledge of novel cell-cell mechanisms that drive bacterial interactions in the context of complex bacterial communities.
Rice sheath rot has been mainly associated with the bacterial pathogen Pseudomonas fuscovaginae and in some cases to the fungal pathogen Sarocladium oryzae; it is yet unclear if they are part of a ...complex disease. The bacterial and fungal community associated with rice sheath rot symptomatic and asymptomatic rice plants was determined/studied with the main aim to shed light on the pathogen(s) causing rice sheath rot. Plant samples were collected from different rice varieties in two locations (highland and lowland) in two rice-growing seasons (wet and dry season) in Burundi. Our results showed that the bacterial Pseudomonas genus was prevalent in highland in both rice-growing seasons and was not affected by rice plant varieties. Pseudomonas sequence reads displayed a significant high similarity to Pseudomonas fuscovaginae indicating that it is the causal agent of rice sheath rot as previously reported. The fungal Sarocladium genus was on the other hand prevalent in lowland only in the wet season; the sequence reads were most significantly similar to Sarocladium oryzae. These studies showed that plant microbiome analysis is very useful in determining the microorganisms involved in a plant disease. P. fuscovaginae and S. oryzae were prevalent in symptomatic samples in highland and lowland respectively being present independently and hence are not part of a complex disease. The significant presence of other bacterial and fungal taxa in symptomatic samples is also discussed possibly making this disease more complex. Finally, we also report the microbial communities that are associated with the plant sheath in symptomatic and asymptomatic plants from the same rice fields.
The genus Burkholderia comprises more than 60 species isolated from a wide range of niches. Although they have been shown to be diverse and ubiquitously distributed, most studies have thus far ...focused on the pathogenic species due to their clinical importance. However, the increasing number of recently described Burkholderia species associated with plants or with the environment has highlighted the division of the genus into two main clusters, as suggested by phylogenetical analyses. The first cluster includes human, animal, and plant pathogens, such as Burkholderia glumae, Burkholderia pseudomallei, and Burkholderia mallei, as well as the 17 defined species of the Burkholderia cepacia complex, while the other, more recently established cluster comprises more than 30 nonpathogenic species, which in most cases have been found to be associated with plants, and thus might be considered to be potentially beneficial. Several species from the latter group share characteristics that are of use when associating with plants, such as a quorum sensing system, the presence of nitrogen fixation and/or nodulation genes, and the ability to degrade aromatic compounds. This review examines the commonalities in this growing subgroup of Burkholderia species and discusses their prospective biotechnological applications.
Summary
In Escherichia coli, the stationary phase alternative sigma factor σs controls the expression of genes involved cell survival in response to cessation of growth (stationary phase) and ...provides cross‐protection to various stresses. Levels of σs increase dramatically at the onset of stationary phase and are regulated at the transcriptional, post‐transcriptional and post‐translational level, making this one of the most complex regulatory systems in bacteria. The basic mechanisms for the control of translation and σs proteolysis have been understood. However, studies on the transcriptional control in E. coli lag behind and are controversial. The cAMP‐CRP complex and the two component BarA/UvrY system have been implicated and, ppGpp and polyphosphate appear to have a signalling role. σs has also been reported to be a general stress regulator in the fluorescent pseudomonads (Pseudomonas aeruginosa, P. fluorescens and P. putida) and recent studies on σs regulation highlight that transcriptional regulation in these bacteria apparently plays a major role. Global regulatory systems, the GacA/GacS two component system and quorum sensing all affect rpoS expression, as does the TetR family PsrA regulator that directly binds to‐ and activates the rpoS promoter in stationary phase. This striking difference in regulation between E. coli and Pseudomonas can be partly attributed to the differences in the functional role of σs in the two bacterial species. This report will review mainly recent studies on rpoS transcriptional regulation and will try to rationalize the current knowledge into a working model.
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