Symbiotic Plants Research Articles

Maternal Exposure to Ozone Modulates the Endophyte-Conferred Resistance to Aphids in Lolium multiflorum Plants.

Simple SummaryGlobal change is driving the incidence of novel stress factors such as the tropospheric pollutant ozone. Plants can overcome the environmental challenges by adjusting their phenotypes that eventually, can be transmitted to the progeny. Plants also establish symbiotic interactions with beneficial fungal endophytes, some of which can be transmitted to the progeny through the seeds. We worked with the grass Lolium multiflorum and its common endophyte, Epichloë occultans that benefits the host by coffering resistance to herbivores. Specifically, we studied the effect of exposing endophyte-symbiotic and non-symbiotic plants to ozone on the level of resistance to herbivorous aphids in the progeny. The ozone history impaired the endophyte-conferred resistance to aphids in progeny. This was evident at individual weight level of aphids but not so at population level. Defensive compounds were higher in endophyte-symbiotic seeds but depressed by mother plants exposure to ozone. Despite the negative effect of maternal ozone on the resistance level of plants, symbiotic plants showed a superior biomass compared to endophyte-free plants. Our work illustrates how the environment explored by parent plants can persist transgenerationally and, depending on the symbiotic state, will affect the fate of the progeny.Plants are challenged by biotic and abiotic stress factors and the incidence of one can increase or decrease resistance to another. These relations can also occur transgenerationally. For instance, progeny plants whose mothers experienced herbivory can be more resistant to herbivores. Certain fungal endophytes that are vertically transmitted endow plants with alkaloids and resistance to herbivores. However, endophyte-symbiotic plants exposed to the oxidative agent ozone became susceptible to aphids. Here, we explored whether this effect persists transgenerationally. We exposed Lolium multiflorum plants with and without fungal endophyte Epichloë occultans to ozone (120 or 0 ppb), and then, challenged the progeny with aphids (Rhopalosiphum padi). The endophyte was the main factor determining the resistance to aphids, but its importance diminished in plants with ozone history. This negative ozone effect on the endophyte-mediated resistance was apparent on aphid individual weights. Phenolic compounds in seeds were increased by the symbiosis and diminished by the ozone. The endophyte effect on phenolics vanished in progeny plants while the negative ozone effect persisted. Independently of ozone, the symbiosis increased the plant biomass (≈24%). Although ozone can diminish the importance of endophyte symbiosis for plant resistance to herbivores, it would be compensated by host growth stimulation.

Transcriptomic and Proteomic Analysis Revealed the Effect of Funneliformis mosseae in Soybean Roots Differential Expression Genes and Proteins.

Glycine max is easily infected with root rot in continuous cropping systems, which can severely affect crop yield. Arbuscular mycorrhizal fungi (AMF) can reduce the incidence of root rot and increase plant height and biomass indices. However, the molecular changes that occur during soybean symbiosis with AMF remain largely unknown. To better understand the molecular mechanism underlying soybean symbiosis with AMF, we performed transcriptomic and proteomic analyses to explore the changes in protein expression during a high-incidence period (79 days) in asymbiotic and symbiotic plants and to identify the key proteins that regulate the mechanism of soybean symbiosis with AMF. A total of 10 104 genes were identified in the CK-vs-F comparison, and 11 562 genes were significantly differentially expressed in the AF group compared with the F group. A total of 9488 proteins were identified, with 256 differentially expressed proteins (DEPs) in the CK-vs-F comparison and 651 DEPs in the F-vs-AF comparison. Key pathways and DEPs were found to be involved in processes associated with "phenylalanine metabolism", "plant hormone signal transduction", "plant-pathogen interaction", and "metabolic pathways". The expression of phenylalanine ammonia-lyase (PAL), calcium-dependent protein kinase (CPK), and other defense-related proteins was upregulated by Funneliformis mosseae, indicating that inoculation promotes the development of soybean and increases disease resistance. Our results suggest that symbiosis promotes the growth and development of soybean and increases disease resistance. This study provides new insight into the molecular basis of the mechanism by which AMF affect plant disease resistance.

Daño, producción de semillas y persistencia del hongo endófito Epichloë occultans en plantas de Lolium multiflorum bajo un ataque de herbívoros lepidópteros y contaminación por ozono

Plants are expected to face novel challenges as consequence of human-driven global change. Outbreaks of pests and higher incidence of contaminants are increasing. Plants can improve tolerance to stress factors through associations with symbiotic microorganisms. Certain grasses establish persistent and asymptomatic symbioses with Epichloe fungal endophytes, which are known to confer protection against Herbivores and improve plant tolerance to abiotic stress factors. Nonetheless, accumulating evidence suggests the symbiosis outcome is context-dependent. We evaluated the capacity of the endophyte fungus E. occultans in protecting the annual grass Lolium multiflorum against a spontaneous larva attack of the generalist herbivore Agrotis ipsilon under episodic exposure of plants to ozone. Symbiotic and non-symbiotic plants were individually grown outdoors and exposed to ozone at different stages resulting in four treatments: control (plant never exposed to ozone), plant exposed to ozone at the vegetative stage, plant exposed to ozone at reproductive stage, and plant exposed to ozone at both stages. After the last exposure, there was an outbreak of A. ipsilon larvae. We evaluated herbivore damage, seed production per plant, and endophyte transmission to the seeds. Frequency of attacked plants was irrespective of both the endophyte and ozone exposure. However, the damage level per plant was only reduced by the endophyte. Seed production was slightly lower in endophyte-symbiotic plants and not affected by ozone. Interestingly, herbivore damaged and undamaged endophyte-symbiotic plants contributed equally to seed production. However, in plants exposed to ozone once at the vegetative or reproductive stage, endophyte-free undamaged plants had higher seed production than endophyte-free damaged plants. Ozone treatments did not affect the transmission efficiency of endophytes to the seeds. Mean endophyte transmission efficiency per plant was 95%. Medium doses of ozone seem to have undetectable effects on grass-endophyte symbiosis, not affecting the defensive mutualism nor the persistence of the symbiont across generations.

A linkage disequilibrium-based statistical test for Genome-Wide Epistatic Selection Scans in structured populations.

The quest for signatures of selection using single nucleotide polymorphism (SNP) data has proven efficient to uncover genes involved in conserved and/or adaptive molecular functions, but none of the statistical methods were designed to identify interacting alleles as targets of selective processes. Here, we propose a statistical test aimed at detecting epistatic selection, based on a linkage disequilibrium (LD) measure accounting for population structure and heterogeneous relatedness between individuals. SNP-based ([Formula: see text]) and window-based ([Formula: see text]) statistics fit a Student distribution, allowing to test the significance of correlation coefficients. As a proof of concept, we use SNP data from the Medicago truncatula symbiotic legume plant and uncover a previously unknown gene coadaptation between the MtSUNN (Super Numeric Nodule) receptor and the MtCLE02 (CLAVATA3-Like) signaling peptide. We also provide experimental evidence supporting a MtSUNN-dependent negative role of MtCLE02 in symbiotic root nodulation. Using human HGDP-CEPH SNP data, our new statistical test uncovers strong LD between SLC24A5 (skin pigmentation) and EDAR (hairs, teeth, sweat glands development) world-wide, which persists after correction for population structure and relatedness in Central South Asian populations. This result suggests that epistatic selection or coselection could have contributed to the phenotypic make-up in some human populations. Applying this approach to genome-wide SNP data will facilitate the identification of coadapted gene networks in model or non-model organisms.

Epichloë endophyte modifies the foliar anatomy of Lolium multiflorum Lam.

Systemic fungal endophytes may increase the adaptive potential of their hosts to different environmental conditions. However, the mechanisms involved in the adjustment are still an area of active inquiry. Considering that anatomical features in plants are the result of adaptation to different environments, this aspect of plants response to the symbionts deserves further research. In this work we investigated whether an asexual Epichloe endophyte modifies the foliar anatomy of symbiotic plants (E+) of its host grass with respect to endophyte-free plants (E-), using the Epichloe occultans–Lolium multiflorum system. The experiment was carried out in a greenhouse and plants were grown under benign, non-stressful (controlled) conditions. Symbiotic plants showed thinner leaf blades and lower mesophyll thickness. Likewise, the endophyte is associated with a greater number of vascular bundles. The stomatal density on the lower epidermis was higher in symbiotic plants than non-symbiotic plants. Our study reveals that Epichloe occultans modifies the foliar anatomy of Lolium multiflorum. Considering that leaf anatomy exhibits characters that were selected as a result of evolution in relation to specific environmental conditions, these results are promising since they can offer information about the mechanisms involved in the adaptive adjustment of symbiotic plants.

Functional roles of microbial symbionts in plant cold tolerance.

In this review, we examine the functional roles of microbial symbionts in plant tolerance to cold and freezing stresses. The impacts of symbionts on antioxidant activity, hormonal signaling and host osmotic balance are described, including the effects of the bacterial endosymbionts Burkholderia, Pseudomonas and Azospirillum on photosynthesis and the accumulation of carbohydrates such as trehalose and raffinose that improve cell osmotic regulation and plasma membrane integrity. The influence of root fungal endophytes and arbuscular mycorrhizal fungi on plant physiology at low temperatures, for example their effects on nutrient acquisition and the accumulation of indole-3-acetic acid and antioxidants in tissues, are also reviewed. Meta-analyses are presented showing that aspects of plant performance (shoot biomass, relative water content, sugar and proline concentrations and Fv /Fm ) are enhanced in symbiotic plants at low (-1 to 15°C), but not at high (20-26°C), temperatures. We discuss the implications of microbial symbionts for plant performance at low and sub-zero temperatures in the natural environment and propose future directions for research into the effects of symbionts on the cold and freezing tolerances of plants, concluding that further studies should routinely incorporate symbiotic microbes in their experimental designs.

Combined Effects of Water Deficit, Exogenous Ethylene Application and Root Symbioses on Trigonelline and ABA Accumulation in Fenugreek

Secondary metabolites (SMs) have high economic impact thanks to their exploitability in chemical, pharmaceutical and cosmetic industries. Trigonella foenum-graecum has an importance due to the production of bioactive compounds with pharmaceutical values. Among them, the alkaloid trigonelline is known for its role in the treatment of different human diseases. SM accumulation is influenced by environmental factors but is modulated by the application of exogenous compounds. Ethephon, a precursor of the phytohormone ethylene, was already used to influence SM accumulation. Our work is aimed at evaluating the accumulation of trigonelline and the phytohormone abscisic acid (ABA) when three factors were combined: i) two levels of water regimes (well-watered and water deficit), ii) ethephon treatments and iii) inoculation with an arbuscular mycorrhizal (AM)-based inoculum also leading to nodulation. The content of trigonelline and ABA was significantly affected by symbioses, showing high accumulation in AM-colonized plants irrespective of the water regimes applied. In terms of trigonelline accumulation with respect to ethephon treatments, while symbiotic plants showed a dose-dependent trend, non-symbiotic plants showed a significantly difference only when 550 ppm of ethephon was applied. In conclusion, our work provides new information on the effects of both ethephon and symbioses on plant growth and accumulation of valuable compounds, such as trigonelline, in fenugreek.

Draft Genome Sequence of Mesorhizobium sp. Strain SARCC-RB16n, an Effective Nodulating and Nitrogen-Fixing Symbiont of Rooibos [Aspalathus linearis (Burm. f.)] in South Africa

The draft genome sequence of Mesorhizobium sp. strain SARCC-RB16n reveals the presence of major symbiotic (nod and nif) and additional plant growth-promoting (PGPR) genes associated with enhanced growth of Aspalathus linearis (Burm. f.) in South Africa. The genome sequence provides vital information for the development of a commercial inoculant for rooibos cultivation.

Seasonal nitrogen uptake strategies in a temperate desert ecosystem depends on N form and plant species.

Symbiotic plants might be able to regulate a limited nitrogen (N) pool, thus avoiding and reducing competition for resources, through the uptake of different chemical N forms. Our aim was to see whether coexisting herbs showed preference for different forms of N in a temperate desert. We conducted a situ experiment using the 15 N labeling method in the Gurbantunggut Desert of Northwestern China dominated by Erodium oxyrrhynchum, Hyalea pulchella, Nonea caspica and Lactuca undulata during their growing period (April and May). Four desert herb species preferentially relied on 15 N-NO3 for their N nutrition. Multi-factor analysis of variance (ANOVA) analysis results showed that species, N forms, months, and soil depths strongly affected N uptake rate. The uptake rate by herbs was higher in May than in April, and higher at 0-5 cm than at 5-15 cm soil layers. Erodium oxyrrhynchum, N. caspica and L. undulata showed different preference on N form over months. Erodium oxyrrhynchum and L. undulata changed their uptake preference from more 15 N-Glycine in April to more 15 N-NH4 in May. Although the N uptake rate of four desert herbs varied across different soil depths and months, all species absorbed more inorganic N compared with organic N. The higher preference for 15 N-NO3 and 15 N-NH4 over 15 N-Gly possibly reflects adaptation to different N forms in temperate desert.

Impact of arbuscular mycorrhizal fungi (AMF) on gene expression of some cell wall and membrane elements of wheat (Triticum aestivum L.) under water deficit using transcriptome analysis.

Mycorrhizal symbiotic relationship is one of the most common collaborations between plant roots and the arbuscular mycorrhizal fungi (AMF). The first barrier for establishing this symbiosis is plant cell wall which strongly provides protection against biotic and abiotic stresses. The aim of this study was to investigate the gene expression changes in cell wall of wheat root cv. Chamran after inoculation with AMF, Funneliformis mosseae under two different irrigation regimes. To carry out this investigation, total RNA was extracted from the roots of mycorrhizal and non-mycorrhizal plants, and analyzed using RNA-Seq in an Illumina Next-Seq500 platform. The results showed that symbiotic association between wheat and AMF and irrigation not only affect transcription profile of the plant growth, but also cell wall and membrane components. Of the 114428 genes expressed in wheat roots, the most differentially expressed genes were related to symbiotic plants under water stress. The most differentially expressed genes were observed in carbohydrate metabolic process, lipid metabolic process, cellulose synthase activity, membrane transports, nitrogen compound metabolic process and chitinase activity related genes. Our results indicated alteration in cell wall and membrane composition due to mycorrhization and irrigation regimes might have a noteworthy effect on the plant tolerance to water deficit.

The \u03b415N value of N2 fixing actinorhizal plants and legumes grown with N2 as the only nitrogen source

The aim of this study was to investigate the effects of different plant parts and the age of plants at harvest as well as N2 fixing bacterial strains on the N concentration in symbiotic plant parts, especially on the δ15N signature of the actinorhizal plants and legumes. The 15N natural abundance method was used. Two actinorhizal plants were studied: Alnus incana (L.) infected with the Frankia strains ArI3 or “lsF” (local source of Frankia) and Hippophaë rhamnoides (L.) infected with the Frankia strains T1 or E15b. Two legume species were studied: Hedysarum coronarium (L.), infected with a soil suspension, and Robinia pseudoacacia (L.), infected with a crushed nodule suspension. It was particularly interesting that in A. incana, the two Frankia strains affected not only N concentration and δ15N signature of leaves and roots, but also had an impact on plant growth at first harvest. In Hippophaë rhamnoides plants inoculated with the Frankia strains T1 and E15b, N concentrations and δ15N values did not differ at any harvest time. However, plants nodulated by the Frankia strain T1 showed a higher nitrogen fixation rate and higher plant dry matter at all harvesting times. Based on our results for the quantification of N2 fixation with the “B” value, that is the δ15N value of the N2 fixing plants relying only on N2 fixation, plant parts, ages and strains should be carefully considered.

High Prevalence of Integrative and Conjugative Elements Encoding Transcription Activator-Like Effector Repeats in Mycoplasma hominis.

Integrative and conjugative elements (ICEs) are modular mobile genetic elements that can disseminate through excision, circularization, and transfer. Mycoplasma ICEs have recently been found distributed among some mycoplasma species and there is accumulating evidence that they play a pivotal role in horizontal gene transfers. The occurrence of ICEs has not been documented in Mycoplasma hominis, a human urogenital pathogen responsible for urogenital infections, neonatal infections and extragenital infections. In this study, we searched for, characterized, and compared ICEs by genome analyses of 12 strains of M. hominis. ICEs of 27–30 kb were found in one or two copies in seven of the 12 M. hominis strains sequenced. Only five of these ICEs seemed to be functional, as assessed by detection of circular forms of extrachromosomal ICE. Moreover, the prevalence of ICEs in M. hominis was estimated to be 45% in a collection of 120 clinical isolates of M. hominis, including 27 tetracycline-resistant tet(M)-positive isolates. The proportion of ICEs was not higher in isolates carrying the tet(M) gene, suggesting that ICEs are not involved in tetracycline resistance. Notably, all M. hominis ICEs had a very similar structure, consisting of a 4.0–5.1 kb unusual module composed of five to six juxtaposed CDSs. All the genes forming this module were specific to M. hominis ICEs as they had no homologs in other mycoplasma ICEs. In each M. hominis ICE, one to three CDSs encode proteins that share common structural features with transcription activator-like (TAL) effectors involved in polynucleotide recognition and signal transduction in symbiotic plant pathogen bacteria. The conserved and specific structure of M. hominis ICEs and the high prevalence in clinical strains suggest that these ICEs may confer a selective advantage for the physiology or pathogenicity of this human pathogenic bacterium. These data open the way for further studies aiming at unraveling horizontal gene transfers and virulence factors in M. hominis.

EFFECT OF GOAT’S-RUE RHIZOBIA ON THE FORMATION AND FUNCTIONING OF THE SOYBEAN – BRADYRHIZOBIUM JAPONICUM 634B SYMBIOSIS

Objective. Study the peculiarities of nodule formation upon the formation of the symbiotic sys-tem soybean-Bradyrhizobium japonicum 634b, as well as the symbiotic nitrogen-fixation ability and plant growth and development under the influence of goat’s-rue rhizobia. Methods. Microbiologi-cal, physiological, statistical, gas chromatography. Results. In green house experiments, using sand as a substrate for growing plants, the mixed microbial cultures combining soybean nodule bacteria B. japonicum 634b and goat’s-rue nodule bacteria R. galegae 0702 or R. galegae 0703 in the ratio of 1 : 1 differed from the monoculture bradyrhizobium by their influence on the nodulation, nitro-gen-fixation ability of soybean-rhizobial symbiosis and development of soybean plants (variety Almaz). Increased nodulation activity in the primordial leaf and budding phases, as well as a signif-icant decrease in the level of symbiosis nitrogen fixation during budding, were observed when used in binary bacterial compositions of strain R. galegae 0703. These rhizobia of goat’s-rue suppressed the development of the root system of soybeans, but had no significant effect on the formation of the aerial part of the plants throughout the observation period. R. galegae 0702 strain slightly slowed the formation of nodules by bacteria in the primordial leaf phase, which caused a decrease in the number of soybean plants that formed symbiosis with B. japonicum 634b. Goat’s-rue nodule bacte-ria R. galegae 0702 improved the formation of the root system, and stimulated the growth and de-velopment of the aerial part of the macro symbiont in the phase of two trigeminal leaves. Conclu-sion. Combined inoculation of the rhizobia of goat’s-rue with nodule bacteria B. japonicum 634b showed a multidirectional effect on the formation of symbiosis by soybean plants of variety Almaz and functioning of soybean rhizobial symbiosis. The nature of the influence of R. galegae depended on their strain affiliation.

Deciphering the Symbiotic Plant Microbiome: Translating the Most Recent Discoveries on Rhizobia for the Improvement of Agricultural Practices in Metal-Contaminated and High Saline Lands

Rhizosphere and plant-associated microorganisms have been intensely studied for their beneficial effects on plant growth and health. These mainly include nitrogen-fixing bacteria (NFB) and plant-growth promoting rhizobacteria (PGPR). This beneficial fraction is involved in major functions such as plant nutrition and plant resistance to biotic and abiotic stresses, which include water deficiency and heavy-metal contamination. Consequently, crop yield emerges as the net result of the interactions between the plant genome and its associated microbiome. Here, we provide a review covering recent studies on PGP rhizobia as effective inoculants for agricultural practices in harsh soil, and we propose models for inoculant combinations and genomic manipulation strategies to improve crop yield.

Plant-Microbe Symbiosis: What Has Proteomics Taught Us?

Beneficial microbes have a positive impact on the productivity and fitness of the host plant. A better understanding of the biological impacts and underlying mechanisms by which the host derives these benefits will help to address concerns around global food production and security. The recent development of omics-based technologies has broadened our understanding of the molecular aspects of beneficial plant-microbe symbiosis. Specifically, proteomics has led to the identification and characterization of several novel symbiosis-specific and symbiosis-related proteins and post-translational modifications that play a critical role in mediating symbiotic plant-microbe interactions and have helped assess the underlying molecular aspects of the symbiotic relationship. Integration of proteomic data with other "omics" data can provide valuable information to assess hypotheses regarding the underlying mechanism of symbiosis and help define the factors affecting the outcome of symbiosis. Herein, an update is provided on the current and potential applications of symbiosis-based "omic" approaches to dissect different aspects of symbiotic plant interactions. The application of proteomics, metaproteomics, and secretomics as enabling approaches for the functional analysis of plant-associated microbial communities is also discussed.

Metabolic reprogramming in nodules, roots, and leaves of symbiotic soybean in response to iron deficiency.

To elucidate the mechanism of adaptation of leguminous plants to iron (Fe)-deficient environment, comprehensive analyses of soybean (Glycine max) plants (sampled at anthesis) were conducted under Fe-sufficient control and Fe-deficient treatment using metabolomic and physiological approach. Our results show that soybeans grown under Fe-deficient conditions showed lower nitrogen (N) fixation efficiency; however, ureides increased in different tissues, indicating potential N-feedback inhibition. N assimilation was inhibited as observed in the repressed amino acids biosynthesis and reduced proteins in roots and nodules. In Fe-deficient leaves, many amino acids increased, accompanied by the reduction of malate, fumarate, succinate, and α-ketoglutarate, which implies the N reprogramming was stimulated by the anaplerotic pathway. Accordingly, many organic acids increased in roots and nodules; however, enzymes involved in the related metabolic pathway (e.g., Krebs cycle) showed opposite activity between roots and nodules, indicative of different mechanisms. Sugars increased or maintained at constant level in different tissues under Fe deficiency, which probably relates to oxidative stress, cell wall damage, and feedback regulation. Increased ascorbate, nicotinate, raffinose, galactinol, and proline in different tissues possibly helped resist the oxidative stress induced by Fe deficiency. Overall, Fe deficiency induced the coordinated metabolic reprogramming in different tissues of symbiotic soybean plants.

Genomic insights into plant growth promoting rhizobia capable of enhancing soybean germination under drought stress

BackgroundThe role of soil microorganisms in plant growth, nutrient utilization, drought tolerance as well as biocontrol activity cannot be over-emphasized, especially in this era when food crisis is a global challenge. This research was therefore designed to gain genomic insights into plant growth promoting (PGP) Rhizobium species capable of enhancing soybean (Glycine max L.) seeds germination under drought condition.ResultsRhizobium sp. strain R1, Rhizobium tropici strain R2, Rhizobium cellulosilyticum strain R3, Rhizobium taibaishanense strain R4 and Ensifer meliloti strain R5 were found to possess the entire PGP traits tested. Specifically, these rhizobial strains were able to solubilize phosphate, produce exopolysaccharide (EPS), 1-aminocyclopropane-1-carboxylate (ACC), siderophore and indole-acetic-acid (IAA). These strains also survived and grew at a temperature of 45 °C and in an acidic condition with a pH 4. Consequently, all the Rhizobium strains enhanced the germination of soybean seeds (PAN 1532 R) under drought condition imposed by 4% poly-ethylene glycol (PEG); nevertheless, Rhizobium sp. strain R1 and R. cellulosilyticum strain R3 inoculations were able to improve seeds germination more than R2, R4 and R5 strains. Thus, genomic insights into Rhizobium sp. strain R1 and R. cellulosilyticum strain R3 revealed the presence of some genes with their respective proteins involved in symbiotic establishment, nitrogen fixation, drought tolerance and plant growth promotion. In particular, exoX, htrA, Nif, nodA, eptA, IAA and siderophore-producing genes were found in the two rhizobial strains.ConclusionsTherefore, the availability of the whole genome sequences of R1 and R3 strains may further be exploited to comprehend the interaction of drought tolerant rhizobia with soybean and other legumes and the PGP ability of these rhizobial strains can also be harnessed for biotechnological application in the field especially in semiarid and arid regions of the globe.

Potency of Commercial Symbiotic Bio-Fertilizer Consortium for Mitigating the Olive Quick Decline Syndrome (OQDS)

The inoculation of soil with a bio-fertilizer (BF), with arbuscular mycorrhiza fungi, characterizes a Symbiotic (S) agriculture mode, aimed at promoting the yield and health of crops through modifications in the rhizosphere as well as in the plant phenotype. The main objective of this study was to reduce the incidence of Olive Quick Decline Syndrome (OQDS, involving Xylella fastidiosasubsp.pauca) that afflicts the olive groves in Apulia (Italy). Non-inoculated control (C) plants were compared with Symbiotic (S) plants inoculated with 20 kg ha-1 of Micosat F ®, through a 15 cm deep scarification, in the groves of seven farms covering an area of 27 ha. In addition to a visual observation of 484 plants, to obtain a gradation of the disease severity, some objective rapid type methods were utilized to survey the plants and soil , namely leaf pH, NIR tomoscopy of the leaves, hay-litter-bag probes coupled with NIR spectroscopy and the prediction of soil induced respiration. The fingerprinting of the S and C types of leaves and litter-bags was ascertained by means of the use of a random forest algorithm in the classification matrices. The results on the symptoms appeared variable: they were significantly mitigated in two groves out of six, but they were aggravated in one. All the rapid measurements became essentials in a “holistic” model which was able to explain over 95% of the average mitigation / null / aggravation response to BF inoculation. The holistic model gathers differential and compositional analyses of the leaf (pH, crude protein, water) and of the soil (respiration), but depends mainly on the fingerprinting of the C and S leaves and litter-bags. Two keys were identified for a successful inoculation: a high degree of variability of the soil conditions permitting hospitality for the BF with enhancement of the microbial activity in the S soil (lowering the fingerprint of the control litter-bags) and homogeneity of the leaves (with increases in the fingerprint of the S leaves treated with BF). In short, the inoculation of diseased plants with one BF consortium is far from being the ultimate remedy to mitigate OQDS in all situations. Further studies are needed, at a field level, to clarify the soil hosting capacity and to define the mycorrhizal and / or endophytic * plant * pathogen interactions, even using rapid methods.

Nutritional status of soils from KwaZulu-Natal modulate symbiotic interactions and plant performance in Vigna unguiculata L. (Walp)

Vigna unguiculata L. (Walp) has high nutritional value. It thrives in semi-arid regions with low nutrient requirements thanks to the establishment of efficient symbiosis with soil borne bacteria. We investigated legume-plant-microbe symbiosis, nitrogen nutrition and associated C construction costs of V. unguiculata grown in nutrient-poor soils from savannah and grassland ecosystems. V. unguiculata seeds were germinated and grown in natural soils from the KwaZulu-Natal (KZN) province. Studied soils showed significant differences in soil nutrition status and microbial diversity. A combination of Rhizobium sp. and Bacillus sp. strains were isolated from root nodules together with arbuscular mycorrhizal (AM) fungi. V. unguiculata efficiently fixed 53–79% of their total plant N from the atmosphere and proved to rely on soil available N. Hluhluwe and Izingolweni soil grown V. unguiculata increased plant biomass compared to other soils. Carbon (C) construction costs were significantly higher in V. unguiculata grown in Bergville and Ashburton soils, whereas no differences in total N and P contents were observed among soils. For the first time we have proven that V. unguiculata may adapt to nutrient-poor soils by establishing multiple symbiosis with soil microorganisms and shifting N source preference.

Symbiotic Plant Biomass Decomposition in Fungus-Growing Termites.

Termites are among the most successful animal groups, accomplishing nutrient acquisition through long-term associations and enzyme provisioning from microbial symbionts. Fungus farming has evolved only once in a single termite sub-family: Macrotermitinae. This sub-family has become a dominant decomposer in the Old World; through enzymatic contributions from insects, fungi, and bacteria, managed in an intricate decomposition pathway, the termites obtain near-complete utilisation of essentially any plant substrate. Here we review recent insights into our understanding of the process of plant biomass decomposition in fungus-growing termites. To this end, we outline research avenues that we believe can help shed light on how evolution has shaped the optimisation of plant-biomass decomposition in this complex multipartite symbiosis.