The composition of the arbuscular mycorrhizal fungal bacteriome is species dependent.

BACKGROUND: In addition to their role as endosymbionts for plant roots, arbuscular mycorrhizal fungi (AMF) engage in complex interactions with various soil microorganisms, the rhizosphere, and the root endosphere of host plants. They also host diverse prokaryotic groups within their mycelia, contributing to what is termed multipartite symbiosis. In this study, we examined the impact of three AMF species-Rhizophagus irregularis, R. clarus, and R. cerebriforme-combined with microbial bioaugmentation on the diversity and composition of bacterial communities in the mycelia and hyphosphere. Using a microcosm design to separate the influence of host plant roots from AMF mycelia and Illumina MiSeq amplicon sequencing to analyze the bacterial communities. RESULTS: Our results revealed that, while AMF identity and microbial bioaugmentation did not affect the structure of bacterial communities in the hyphosphere soil, they significantly altered the communities associated with their mycelia. Although all three AMF species belong to the same genus, with R. irregularis and R. clarus being closely related compared to R. cerebriforme, we observed variations in the bacterial communities associated with their mycelia. Interestingly, the mycelial bacterial community of R. cerebriforme contained 60 bacteriome core taxa exclusive to it, while R. clarus and R. irregularis had 25 and 9 exclusive taxa, respectively. CONCLUSION: This study suggests that organismal phylogeny influences the bacterial communities associated with AMF mycelia. These findings provide new insights into AMF and bacterial interactions, which are crucial for the successful deployment of AMF inoculants. The taxonomic diversity of AMF inoculants is important for engineering the plant microbiome and enhancing ecosystem services.

Response of Alternaria and Fusarium Species to Low Precipitation in a Drought-Tolerant Plant in Morocco.

The plant mycobiome plays a crucial role in the host life cycle, influencing both healthy and diseased states, and is essential for plant tolerance to drought. In this study, we used ITS metabarcoding to investigate the fungal community of the drought-resistant plant Malva sylvestris L. in Morocco along a gradient of precipitation, encompassing subhumid and semi-arid environments. We sampled three biotopes: rhizosphere, bulk soil, and root endosphere. Our findings revealed an absence of beta-diversity differences between bulk soil and rhizosphere, indicating that the plant does not selectively influence its rhizosphere mycobiome. Additionally, ASVs belonging to the genus Alternaria represented up to 30% of reads in the plant's roots and correlated with drought (p = 0.006), indicating a potential role for this fungal genus in mitigating drought, possibly as part of the dark septate endophyte group. Root staining and microscopic observation revealed extensive colonization by fungal hyphae and microsclerotia-like structures. Furthermore, ASVs identified as Fusarium equiseti were also correlated with low precipitation and recognized as a hub taxon in the roots. However, it remains uncertain whether this species is pathogenic or beneficial to the plant. These insights contribute to our understanding of the plant mycobiome's role in drought tolerance and highlight the importance of specific fungal taxa in supporting plant health under varying environmental conditions. Future research should focus on characterizing these taxa's functional roles and their interactions with the host plant to further elucidate their contributions to drought resistance.

Potential Plant-To-Plant Transmission: Shared Endophytic Bacterial Community Between Ziziphus lotus and Its Parasite Cuscuta epithymum.

Microbiota associated with host-parasite relationships offer an opportunity to explore interactions among plants, parasites, and microbes, thereby contributing to the overall complexity of community structures. The dynamics of ecological interactions between parasitic plants and their hosts in arid environments remain largely understudied, especially in Africa. This study aimed to examine the bacterial communities of Cuscuta epithymum L. (clover dodder), an epiphytic parasitic plant, and its host, Ziziphus lotus L. (jujuba), in an arid environment. Our goal was to uncover the ecological complexities of microbial communities within the framework of plant-plant interactions. We conducted a comprehensive analysis of the bacterial composition and diversity within populations of the C. epithymum parasite, the infected- and non-infected jujuba host, and their interface at the shoots of the host. This involved amplicon sequencing, targeting the V5-V6 regions of the 16S rRNA gene. A total of 5680 amplicon sequence variants (ASVs) were identified, with Pseudomonadota, Bacillota, and Actinobacteriota being prevalent phyla. Among the bacterial communities, three genera were dominant: Cutibacterium, Staphylococcus, and Acinetobacter. Interestingly, analyses of alpha-diversity (p = 0.3 for Shannon index and p = 0.5 for Simplon index) and beta-diversity (PERMANOVA, with p-values of 0.6 and 0.3) revealed no significant differences between Cuscuta-infected and non-infected jujube shrubs, suggesting a shared shoot endophytic bacteriome. This finding advances our comprehension of microbial communities linked to plant-parasite interactions in the arid environments of Africa. Further research on various hosts is required to confirm plant-to-plant bacterial transmission through Cuscuta infection. Additionally, studies on functional diversity, cytology, ecophysiology and the mechanisms by which bacterial communities transferred between host and parasite are necessary.

The rhizosphere of a drought-tolerant plant species in Morocco: A refuge of high microbial diversity with no taxon preference.

Arid and semi-arid areas are facing increasingly severe water deficits that are being intensified by global climate changes. Microbes associated with plants native to arid regions provide valuable benefits to plants, especially in water-stressed environments. In this study, we used 16S rDNA metabarcoding analysis to examine the bacterial communities in the bulk soil, rhizosphere and root endosphere of the plant Malva sylvestris L. in Morocco, along a gradient of precipitation. We found that the rhizosphere of M. sylvestris did not show significant differences in beta-diversity compared to bulk soil, although, it did display an increased degree of alpha-diversity. The endosphere was largely dominated by the genus Rhizobium and displayed remarkable variation between plants, which could not be attributed to any of the variables observed in this study. Overall, the effects of precipitation level were relatively weak, which may be related to the intense drought in Morocco at the time of sampling. The dominance of Rhizobium in a non-leguminous plant is particularly noteworthy and may permit the utilization of this bacterial taxon to augment drought tolerance; additionally, the absence of any notable selection of the rhizosphere of M. sylvestris suggests that it is not significatively affecting its soil environment.

A Comprehensive Insight of Current and Future Challenges in Large-Scale Soil Microbiome Analyses.

In the last decade, various large-scale projects describing soil microbial diversity across large geographical gradients have been undertaken. However, many questions remain unanswered about the best ways to conduct these studies. In this review, we present an overview of the experience gathered during these projects, and of the challenges that future projects will face, such as standardization of protocols and results, considering the temporal variation of microbiomes, and the legal constraints limiting such studies. We also present the arguments for and against the exhaustive description of soil microbiomes. Finally, we look at future developments of soil microbiome studies, notably emphasizing the important role of cultivation techniques.

Surprising low diversity of the plant pathogen Phytophthora in Amazonian forests.

The genus Phytophthora represents a group of plant pathogens with broad global distribution. The majority of them cause the collar and root-rot of diverse plant species. Little is known about Phytophthora communities in forest ecosystems, especially in the Neotropical forests where natural enemies could maintain the huge plant diversity via negative density dependence. We characterized the diversity of soil-borne Phytophthora communities in the North French Guiana rainforest and investigated how they are structured by host identity and environmental factors. In this little-explored habitat, 250 soil cores were sampled from 10 plots hosting 10 different plant families across three forest environments (Terra Firme, Seasonally Flooded and White Sand). Phytophthora diversity was studied using a baiting approach and metabarcoding (High-Throughput Sequencing) on environmental DNA extracted from both soil samples and baiting-leaves. These three approaches revealed very similar communities, characterized by an unexpected low diversity of Phytophthora species, with the dominance of two cryptic species close to Phytophthora heveae. As expected, the Phytophthora community composition of the French Guiana rainforest was significantly impacted by the host plant family and environment. However, these plant pathogen communities are very small and are dominated by generalist species, questioning their potential roles as drivers of plant diversity in these Amazonian forests.

Phenotyping Thermal Responses of Yeasts and Yeast-like Microorganisms at the Individual and Population Levels: Proof-of-Concept, Development and Application of an Experimental Framework to a Plant Pathogen.

Deciphering the responses of microbial populations to spatiotemporal changes in their thermal environment is instrumental in improving our understanding of their eco-evolutionary dynamics. Recent studies have shown that current phenotyping protocols do not adequately address all dimensions of phenotype expression. Therefore, these methods can give biased assessments of sensitivity to temperature, leading to misunderstandings concerning the ecological processes underlying thermal plasticity. We describe here a new robust and versatile experimental framework for the accurate investigation of thermal performance and phenotypic diversity in yeasts and yeast-like microorganisms, at the individual and population levels. In addition to proof-of-concept, the application of this framework to the fungal wheat pathogen Zymoseptoria tritici resulted in detailed characterisations for this yeast-like microorganism of (i) the patterns of temperature-dependent changes in performance for four fitness traits; (ii) the consistency in thermal sensitivity rankings of strains between in planta and in vitro growth assessments; (iii) significant interindividual variation in thermal responses, with four principal thermotypes detected in a sample of 66 strains; and (iv) the ecological consequences of this diversity for population-level processes through pairwise competition experiments highlighting temperature-dependent outcomes. These findings extend our knowledge and ability to quantify and categorise the phenotypic heterogeneity of thermal responses. As such, they lay the foundations for further studies elucidating local adaptation patterns and the effects of temperature variations on eco-evolutionary and epidemiological processes.

Multicomponent synthesis of unsymmetrical unsaturated N-heterocyclic carbene precursors and their related transition-metal complexes.

A low-cost, modular, and easily scalable multicomponent procedure affording access in good yields and excellent selectivity (up to 93%) to a wide range of (a)chiral unsymmetrical 1-aryl-3-cycloalkyl-imidazolium salts is disclosed. Electronic and steric properties of the corresponding unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands were evaluated and evidenced strong electron donor ability, high steric discrimination, and modular steric demand.

Two-directional ring-opening cross-metathesis.

Two-directional ring-opening cross-metathesis of a range of cyclic alkenes with a variety of electron deficient alkenes has been accomplished; it was found that the process is quite general and gives complete selectivity for the E,E-dienes, making this a very useful and high-yielding protocol for two-directional chain synthesis.

Two-directional cross-metathesis.

Two-directional cross-metathesis of a range of alpha,omega dienes with a variety of electron deficient alkenes has been accomplished. It was found that the process is quite general and gives complete selectivity for the E,E-dienes, making this a very useful and high yielding protocol for two-directional chain elongation.

Combining two-directional synthesis and tandem reactions: new access to 3,5-disubstituted pyrrolizidines and first total synthesis of alkaloid cis-223B.

Two new tandem reactions for the synthesis of 3,5-disubstituted pyrrolizidines and the first total synthesis of alkaloid cis-223B (in 7 steps and 43% overall yield), involving a double cross metathesis and double Michael addition as key steps, are presented.

Nitrone [2+3]-cycloadditions in stereocontrolled synthesis of a potent proteasome inhibitor: (-)-omuralide.

A new stereocontrolled synthetic route to omuralide has been developed from methyl pyroglutamate. This route involves regio- and stereoselective N-methylnitrone 1,3-dipolar cycloadditions to appropriate pyrrolinones, beta-eliminations, and highly selective hydrogenations as the main steps.

Liquid-phase synthesis of polyhydroquinoline using task-specific ionic liquid technology.

A new strategy for the synthesis of polyhydroquinolines from task-specific ionic liquids (TSIL) as a soluble support was developed. The preparation of the polyhydroquinolines by a three-component reaction was achieved by using ionic liquid-phase bound beta-oxo esters. These starting functionalized esters were synthesized by a solventless transesterification without catalyst under microwave irradiation. The structure of the intermediates in each step was verified routinely by spectroscopic analysis, and after oxidation of the polyhydroquinolines grafted on the TSIL with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone or after cleavage (transesterification, saponification-acidification), the target compounds were obtained in good yields and high purities.