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ABSTRACT.- Background: Eucalyptus globulus Labill. is a species of great interest to the pulp industry. However, it has a low rooting capacity, which makes it difficult to clone on a commercial scale. In micropropagation, the supply of cytokinins is necessary to stimulate proliferation, but the type and concentration of cytokinins can negatively affect adventitious rooting. This study evaluated the effect of metatopoline (mT) and benzyladenine (BA) on in vitro multiplication, elongation, and rooting of E. globulus clones. In the multiplication medium, concentrations of 0.44 and 0.88 µmol BA, 0.41 and 0.83 µmol mT, and a control medium without cytokinins were supplied. Results: During the multiplication phase, mT increased the proliferation rate. In addition, mT presented lower production of small explants, less than 0.5 cm in height. In the rooting phase, easy rooting clones treated with 0.41 µmol of mT reached rooting percentages of 91%, while with the use of BA it was 50%. However, in clones with difficult rooting, no differences were observed in relation to the type of cytokinin. Explants treated with mT developed longer roots than those originated with BA, which presented roots similar to those of the control treatment (T). Conclusion: With the use of mT in the multiplication medium, the in vitro elongation, proliferation and rooting of E. globulus was improved, therefore improving the quality of the in vitro explants for the acclimatization stage. © 2024, Federal University of Lavras. All rights reserved.

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ABSTRACT.- Paspalum L. is a genus of the Poaceae family, with many species serving as well-adapted forage plants in subtropical climates and continuous grazing systems. However, Claviceps paspali, an ascomycete of the order Hypocreales, represents a major threat to Paspalum species. This fungus induces ergot disease, characterized by the replacement of infected flower seeds with sclerotia, which adversely affects seed production and animal health through mycotoxin production. Although ergot disease is reported in many countries, no totally resistant Paspalum cultivars have been reported for commercial use. This study comparatively evaluated disease development in six Paspalum species under greenhouse conditions with three specific isolates of C. paspali, along with field trials. In addition, field isolates of C. paspali were analyzed for phenotypic characteristics and phylogenetic relationships. Greenhouse evaluation revealed variable susceptibility among Paspalum species, with P. malacophyllum,P. notatum and P. umbrosum being the most resistant. In field trials P. dilatatum showed the highest severity index, while P. umbrosum and P. malacophyllum were less affected. Phenotypic characterization of 22 C. paspali isolates showed variability in pigmentation and growth rates, with PDA being the culture medium where the highest growth rate was observed. Phylogenetic analysis of the isolates identified two well-supported lineages between C. paspali species. This research reports an ergot resistance gradient among Paspalum species, identifying genuine sources of resistance. In addition, virulent isolates of C. paspali potentially useful for rapid screening of accessions or crosses in Paspalum breeding programs were identified. © 2024 The American Phytopathological Society

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ABSTRACT.- In a previous study, we reported the in vitro potential probiotic and gamma-aminobutyric acid (GABA) production, of several strains from a collection of Lactiplantibacillus (Lpb) strains within the community of natural whey starters from the artisanal cheese industry. GABA is a non-protein amino acid widely distributed in nature and produced in animals, plants, and microorganisms. However, the best known role of GABA is its function as the major inhibitory neurotransmitter of the central nervous system. Preclinical and clinical evidence suggests that the GABAergic system has a relevant role in mental health disorders, such as anxiety and major depression. The modulation of the GABAergic system has been suggested as a potential strategy for treatment, one such mechanism of modulation is the influence of the microbiota-gut-brain axis through probiotic treatments. The present study was designed to investigate the in vivo probiotic potential of LPB145, a Lactiplantibacillus strain previously characterised as a GABA-producing potentially probiotic strain. Therefore, we evaluated the behavioural effects of chronic oral administration of LPB145 on rats' anxiety- and depression-like behaviours, using the elevated plus maze, open field, and the forced swimming test. The impact of LPB145 strain treatment on the gut microbiota structure and diversity was assessed to discern a possible mechanism of action of the LPB145 treatment through the microbiota-gut-brain axis. Our results showed that LPB145 administration induced an antidepressive-like behaviour without changes in locomotor activity. In contrast, the treatment did not modify the experimental anxiety. The structure and diversity of the intestinal microbiota remained unaffected by the treatment when compared to the control. However, specific clades that could be implicated in the behavioural changes did show differences in their relative abundance. These findings provide evidence regarding the potential of probiotic strains isolated from alimentary sources, to modulate the microbiota-gut-brain axis and positively impact mental health. © J. LOZANO et al., 2024.

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ABSTRACT.- The intensification of droughts due to climate change is a global concern, and many plant species face increasing water deficits. Understanding the role of phenotypic plasticity in plant adaptation to these changing conditions is crucial. This research focuses on Bromopsis erecta, a dominant perennial grass in European and Mediterranean grasslands, to predict its potential adaptation to climate change. We assessed plants from shallow and deep soils (i.e., with contrasting water reserves) of a Mediterranean rangeland in southern France, and tested the effect of six years of experimentally increased summer drought compared to the ambient conditions on plant traits, survival and abundance. In both field and common garden experiments, we measured water-related traits, including static traits under non-limiting water conditions, and dynamic traits, such as rates of trait variation during drought. Trait plasticity was determined as a reaction norm to increasing soil water stress and was tested against changes in B. erecta abundance over the past decade, including the study period. Trait plasticity was detected only for leaf dry matter content (LDMC), revealing that the resource strategy of B. erecta became more conservative over less than a decade with higher LDMC and leaf thickness according to the plant economic spectrum. No plasticity was found for osmotic potential or specific leaf area. The variability of other traits was ascribed to the possible lagging effect of previous water stress and was associated more with soil depth than with previous summer drought intensity. The abundance decline of B. erecta, which dropped from 20 % to around 5 % in shallow soils, was not associated with the plasticity of LDMC but was positively correlated with variations in leaf base membrane damage, meaning unexpectedly, that plants exposed to the most severe summer drought also had the most sensitive leaf base membranes, a possible sign of maladaptive trait plasticity in the population. This key trait response reveals boundaries to the adaptive capacity of this perennial grass to survive pluri-annual drought. © 2024 The Authors

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ABSTRACT.- The impact of forestry practices was evaluated on Eucalyptus?s growth variables and mortality dynamics. An experiment was conducted in Uruguay over sixteen years, sixteen spacing and thinning treatments were compared depending on the genetic material and productive objective. Tree height and diameter at breast height were assessed annually. All variables were analyzed using linear mixed models. Kaplan-Meier survival analysis and the Log Rank test were used to compare tree survival. © (2024), (Universidade Federal Rural do Rio de Janeiro (UFRRJ)). All Rights Reserved.

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ABSTRACT.- The present article describes the development of an improved Pinus taeda clonal seed orchard adapted to the edaphoclimatic conditions of Uruguay. Initially, 2068 hectares distributed in nine companies were prospected, and 124 plus trees were identified based on growth, straightness, and health traits. These trees were clonally propagated via grafting to establish a clonal seed orchard. For the genetic evaluation of the orchard, two progeny tests were carried out in the Rivera and Paysandú municipalities. Quantitative genetic analyses allowed us to identify a simple genotype-environment interaction and an expected genetic gain for volumes of 17%, 13%, and 8% for selection intensities of 12%, 25%, and 50%, respectively. Moreover, the genetic diversity of the 124 clones of the orchard was assessed using 10 microsatellite markers. The fingerprinting profiles allowed us to identify a total of 224 alleles. The polymorphism information content of the different markers was in the range of 0.594 to 0.895. The combined probability of identity and probability of identity among siblings had a discrimination power of 8.26 × 10-14 and 5.91 × 10-5, respectively. Analysis of the genetic structure demonstrated that the seed orchard population was not structured by the supplier. Copyright: © 2024 by the authors.

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ABSTRACT.- Crop type classification with satellite imageries is widely applied to support sustainable agricultural practices and for continuous crop monitoring [1], [2], [3]. In this work, we present a study for the classification of winter crops on a nationwide perspective for Uruguay. We have analyzed Uruguay's three most widely extended winter crops: wheat, barley, and rapeseed. We have trained a classifier based on XGBoost that uses temporal series built from Sentinel-2 image data. For training, we used the information from previous years and reported the results the following year. To our knowledge, this is the first work that proposes a clear and systematic way to classify winter crops in Uruguay based on historical data without needing samples of the actual year. We have obtained high precision and recall values for rapeseed and results comparable with other regions' work for wheat and barley. © 2024 IEEE.

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ABSTRACT.- The transformation of the existing agrifood system towards more sustainable systems requires sociotechnical strategies that can boost radical changes. In Uruguay there is a community of practice committed to the sustainable development of family livestock farming which has developed alternative production practices, that improve the sustainability of farms based on ecological intensification, for more than fifteen years. Co-innovation as a modality of intervention was a fundamental aspect in the results achieved, being the work on farms a key factor, with a very special bond between extensionist and family. Taking this community of practice as a case study, this text characterizes co-innovation as a modality of intervention for farm technical assistance, offering a vision to enhance the scaling of the interventions and contribute to the sustainable transformation of livestock farming. Results are presented on: 1) general characteristics of the intervention modality, 2) stages of work and practices on farms, 3) characteristics of the family-extensionist bond and 4) lessons learned. Finally, key aspects are pointed out to scale co-innovation, in order to contribute to a sustainability transition of Uruguayan family livestock farming. -.-.-.-.-.-.-.-.-.-.-.-.-. RESUMEN.- La transformación del sistema agroalimentario actual hacia sistemas más sostenibles requiere estrategias sociotécnicas que puedan impulsar cambios radicales. En Uruguay existe una comunidad de práctica comprometida con el desarrollo sostenible de la ganadería familiar que ha desarrollado prácticas productivas alternativas, que mejoran la sostenibilidad de los establecimientos con base en la intensificación ecológica, durante más de quince años. La coinnovación como modalidad de intervención fue un aspecto fundamental en los resultados alcanzados, fue clave el trabajo situado en los predios, con un vínculo muy especial entre extensionistas y familias. Tomando la comunidad de práctica como un estudio de caso, este texto caracteriza a la coinnovación como modalidad de intervención para la asistencia técnica predial, ofreciendo una visión para potenciar el escalamiento de las intervenciones y contribuir a la transformación sostenible de la ganadería. Se presentan resultados sobre: 1) características generales de la modalidad de intervención, 2) etapas de trabajo y prácticas en predios, 3) características del vínculo familia-extensionista y 4) lecciones aprendidas. Finalmente, se señalan aspectos clave para escalar la coinnovación, de manera de contribuir a una transición sostenible de la ganadería familiar uruguaya. © (2024), (SciELO-Scientific Electronic Library Online). All Rights Reserved.

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ABSTRACT.- Tree plantations are expanding in southern South America and their effects on ecosystem services, particularly climate regulation, are still not well understood. Here, we used remote sensing techniques and a paired design to analyze 33,000 ha of Pinus plantations along a broad geographical and environmental gradient (26-43° South latitude, 54?72° West longitude). Radiation interception, surface temperature, evapotranspiration, and albedo were assessed both in tree plantations stands and in adjacent uncultivated areas. Additionally, the climatic impact of tree plantations was quantified by analyzing changes in atmospheric radiative forcing and its carbon (C) equivalent. Tree plantations intercepted more radiation when replacing steppes, grasslands, and shrublands but not when replacing forests. The control exerted on radiation interception by precipitation decreased in both space and time after tree plantation. Furthermore, evapotranspiration notably increased in tree plantations. The lower albedo of tree plantations compared to uncultivated adjacent areas induces global warming through the biophysical pathway. Thus, the climate benefits of afforestation through C sequestration can be counteracted by 18 to 83 % due to albedo changes. It is necessary to fully consider the biophysical effects and water footprint of tree plantations in public policies that promote them, as well as in international carbon accounting mechanisms. © 2024 Elsevier B.V.

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ABSTRACT.- We described the first case of rhinofacial pythiosis with dissemination in an adult horse in Uruguay. The affected horse presented a partially circumscribed mass measuring 30 x 23 x 9 cm affecting the right side of the face with involvement of cutaneous, subcutaneous, and muscular tissues, the right nasal cavity, and adjacent structures. At postmortem examination, the main lesions were "kunkers" characterized by pyogranulomatous and eosinophilic dermatitis, Splendore-Hoeppli reaction and numerous intralesional hyphae immunolabeling with polyclonal anti-Pythium insidiosum antibody. Similar lesions were observed in the lung and submandibular lymph nodes. The diagnosis was made by the characteristic histological lesions and the strong immunolabelling by anti-P. insidiosum antibody. ------------------ RESUMO.- Descreve-se o primeiro caso de pitiose rinofacial com disseminação em um equino adulto no Uruguai. O animal apresentava uma massa parcialmente circunscrita medindo 30 x 23 x 9 cm acometendo o lado direito da face e com envolvimento dos tecidos cutâneo, subcutâneo e muscular, cavidade nasal direita e estruturas adjacentes. Os principais achados patológicos incluem a formação de kunkers microscopicamente caracterizados por dermatite piogranulomatosa e eosinofilica, reação de Splendore-Hoeppli, e numerosas hifas intralesionais imunomarcadas com anticorpo policlonal anti-Pythium insidiosum. Lesões semelhantes foram observadas no pulmão e nos linfonodos submandibulares. O diagnóstico foi baseado nas lesões histológicas características e imunomarcação com anticorpo anti-P. insidiosum. © 2025, Universidade Federal de Santa Maria. All rights reserved.

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ABSTRACT.- Question: Understanding the patterns of alien plant invasions and their underlying drivers is a key step in conserving the remaining native grasslands of Uruguay. We addressed the level of invasion by considering the four invasive alien plants of these ecosystems, Cynodon dactylon, Eragrostis plana, Senecio madagascariensis and Ulex europaeus, throughout the country. Location: Remnant native grasslands of Uruguay, constituting part of the Río de la Plata grasslands. Methods: Extensive fieldwork was carried out over five years of data collection, including hierarchically randomized observations (around 2000) nested in 137 10 × 10-km2 squares covering different geomorphological regions. For each invasive alien species, we constructed distribution maps to show their patterns; for the two most abundant, we fitted models to identify the main explanatory variables at different spatial scales. Results: We found that 77% of the squares were invaded by at least one target species. The level of invasion varied between regions and target plants. The most abundant invasive alien species were Cynodon dactylon and Senecio madagascariensis; while Eragrostis plana and Ulex europaeus were scarce. Cynodon dactylon cover was related to a set of variables at different spatial scales, including climate, topography and several local community descriptors. Senecio madagascariensis cover was positively associated with grassland fragmentation and anthropic disturbance at the landscape, and a few local descriptors. Conclusions: The large sampling effort at the country level, with a randomized design, allowed for a reliable assessment of the level of invasion of Uruguayan grasslands and its possible drivers. This is an important step in the design of policies to conserve Uruguay's remaining native grasslands. We suggest that the prevention should focus on the Basaltic Cuestas region, while control and containment should prioritize the eastern and south-central parts of the country, focusing mainly on Cynodon dactylon management. © 2024 International Association for Vegetation Science.

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ABSTRACT.- Waterlogging is a critical abiotic stress increasing in importance due to more intense, erratic rainfall associated with climate change. Waterlogging leads to significant yield losses in sensitive crops, such as soybean (Glycine max [L.] Merr.). Identifying soybean genotypes and traits associated with better waterlogging tolerance is of high interest. We assessed the response of six soybean genotypes, selected from a field screening of over 190 genotypes, to 10 days of waterlogging at the R1 (onset of flowering) and R4 (grain filling) stages. We evaluated yield and its components, as well as shoot and root dry weights (DW) at the end of the waterlogging treatments and at maturity, along with morphological traits such as plant branch number, stem diameter and plant height. By integrating all these traits, a waterlogging tolerance index (WTI) was calculated for each genotype to rank their sensitivity. The WTI showed variations among genotypes from 0.61 to 0.77, indicating genotypic variation in response to waterlogging. Greater reductions in root DW compared to shoot DW were observed immediately after waterlogging. By maturity, shoot DW of waterlogged plants was more severely reduced than root DW in all genotypes. Despite similar DW losses at R1 and R4 at physiological maturity, seed number per plant and 100-seed weight responses differed between the treatments. Genotypes that performed well under control conditions suffered significant yield reductions of 70%-85% after waterlogging, mainly due to fewer fertile nodes and seeds per pod, with some also experiencing a notable decrease in 100-seed weight. In contrast, other genotypes had milder responses, with less severe reductions in seed and pod traits. Identifying breeding soybean genotypes tolerant to waterlogging during reproductive stages that maintain the number of fertile nodes and pods per node without changes in seeds per pod could significantly mitigate yield losses from waterlogging. © 2024 Wiley-VCH GmbH. Published by John Wiley & Sons Ltd.

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ABSTRACT.- This study aimed to estimate variance components (VCs) for growth and reproductive traits in Nellore cattle using two relationship matrices (pedigree relationship A matrix and pedigree plus genomic relationship H matrix), and records collected before and after genomic selection (GS) implementation. The study also evaluated how genomic breeding values (GEBV) are affected by variance components and discarding old records. The analysed traits were weight at 120 days (W120), weight and scrotal circumference at 450 days (W450 and SC450, respectively). Three datasets were used to estimate VCs, including all phenotypic information (All) or records for animals born before or after GS implementation (Before or After datasets, respectively). Both relationship matrices were considered for VC estimation, the A matrix was used in all three datasets and VC from each combination were named as A_Before, A_After, and A_All). The H was used in two datasets: H_All and H_After. Different VCs were used for GEBV prediction through ssGBLUP. This step used two possible Datasets, using all available phenotypic data (Dataset 1) or just records collected since GS implementation (Dataset 2). Validation was conducted using accuracy, bias and dispersion according to the LR method and prediction accuracy from corrected phenotypes. The heritability of all traits increased from A_Before to A_After, while estimates for A_All were intermediary. In the previous order, the estimates were 0.16, 0.17, and 0.15 for W120; 0.31, 0.39, and 0.35 for W450; 0.35, 0.47, and 0.41 for SC. For W450 and SC, using the H matrix reduced the heritability (0.33 and 0.32 for W450; 0.41 and 0.38 for SC for H_After and H_All, respectively). For W120, Dataset1 and VCs from A_After showed the highest accuracy for direct and maternal GEBV (0.953 and 0.868). For W450, Dataset 1 and VC from H_After allowed the highest accuracy (0.854) but use Dataset 2 and same VC source yield similar value (0.846). For SC, Dataset 2 with VC from H_After showed the highest accuracy (0.925). To use Dataset 2 does not cause important changes in bias or dispersion with respect to Dataset 1. The VC and genetic parameters changed for W120, W450, and SC450, using records before or after the GS implementation. For W450 and SC450, genetic variance and heritability estimates increased with the use of GS. For W120, genomic predictions were more accurate using A for VC estimation. Accuracy gains were observed for W450 and SC450 using H in VC estimation and/or discarding records before GS. It is possible to discard phenotypic records before GS implementation without generating bias or dispersion in the GEBV of young candidates. © 2024 Wiley-VCH GmbH. Published by John Wiley & Sons Ltd.

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ABSTRACT.- South American beef production varies due to diverse climates, environmental conditions, animal breeds (Bos indicus, Bos taurus and crossbreeds), management strategies, and nutritional sources. Applying technology in the South American beef production system can significantly enhance efficiency, sustainability, and profitability. Reproductive efficiency is a significant challenge, especially in cow-calf operation systems conducted under adverse conditions. Consequently, implementing effective assisted reproduction technologies (ART) can make a significant contribution. In the last two decades, the development of fixed-time artificial insemination (FTAI) protocols permitted the widespread application of artificial insemination for breeding management and genetic improvement in beef herds in South America. Nowadays, FTAI is being applied in South America in large-scale programs, with around 20 % of heifers and cows receiving this technology every year. This results in a greater calving rate and significant genetic gain occurring in this territory. Also, in vitro embryo production, mainly using sex-selected sperm has been widely applied in this region, leading to significant improvements in herd genetics and productivity. Recently, 94 % of all embryo transfers in South America consist of in vitro-produced embryos (41,429 being in vivo-derived and 650,782 being in vitro-produced embryos), mainly using fixed-time embryo transfer technology (FTET). Genomic selection combined with in vitro embryo production with oocytes from heifer calves provides a powerful technology platform to reduce generation interval and significantly increase the rate of genetic gain in beef cattle. Emerging biotechnologies, such as genome editing via the CRISPR/Cas system, are being developed to enhance productivity, confer resilience to adverse environmental conditions, increase disease resistance, and control pest species that affect livestock. Finally, while all these technologies offer significant potential, further progresses are needed to transform livestock production. The vast geographical scale and diverse climates of South America make regional knowledge crucial for aligning beef production with sustainability goals and supporting global food security. © 2024

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ABSTRACT.- Numerous conservation and regeneration practices are recognized as effective strategies in the management of soil health (SH), a critical factor for ensuring the sustainability of food production systems. Despite their acknowledged importance, the multifaceted impacts of these practices often lead to confounding effects, and reliance on generic categorization of agronomic practices often falls short in portraying the drivers of SH. We advocate for a paradigm shift from a label-centric approach to one rooted in processes. Our study underscores the pivotal role of aboveground biomass cycling as an indicator for assessing the potential of agronomic management practices to instigate shifts in carbon balances, and, consequently SH. © 2024 The Authors. Published by Elsevier B.V.

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ABSTRACT.- Achieving sustainable food and nutritional security requires a transformation of the existing agrifood system. In livestock farming based on natural grassland in Uruguay, an ecological intensification strategy could play a radical role in the transition towards more sustainable systems. This study analyzes the continuity of interconnected projects that used co-innovation approaches to promote and evaluate ecological intensification strategies over a period of 15 years (2004-2019). The purpose of the article is to provide evidence on the development of a socio-technical niche in sustainable livestock farming and to identify anchoring points for further regime transformation. Our contention is that interactive research in the context of application based on a sequence of co-innovation projects has the potential to trigger a sustainability transition through ecological intensification of livestock farming based on natural grassland. The research followed a single-case study design with multiple units of analysis, based on the study of documents produced by the different projects and semi-structured interviews. In addition, network analysis was used to examine the linkage of persons and projects. Results show that a socio-technical niche in sustainable livestock farming base on natural grassland was developed in Uruguay, promoted by research institutions and progressively involving other social actors throughout the process. The continuity of projects over 15 years, was fundamental to achieve the three essential processes for a niche conformation: i) an alignment of expectations and the development of a common vision, linked to the sustainable development of family-farming; ii) the creation and expansion of a network of stakeholders, comprising researchers, farmers, extensionists, and other relevant actors; iii) the development of learning processes through interaction, accumulating knowledge around two main axes: a new way of promoting innovation through research in application contexts associated with co-innovation, and a new way of sustainable livestock farming associated with ecological intensification. This study reveals the importance of sequencing co-innovation projects and continuity in the negotiation of visions of change, the creation of a community committed with the direction of change, and the promotion of interdisciplinarity and interactive learning, that foster changes at a socio-technical level. Anchoring challenges, and therefore advancement of the transition process, face the need for significantly expanding trained research and extension personnel to implement co-innovation and ecological intensification practices in livestock systems, and the organization of an extension program to sustain long term transformation of livestock farming in Uruguay. © 2022 Elsevier Ltd. All rights reserved.

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ABSTRACT.- Heme and iron metabolic pathways are highly intertwined, both compounds being essential for key biological processes, yet becoming toxic if overabundant.Their concentrations are exquisitely regulated, including via dedicated two-component systems (TCSs) that sense signals and regulate adaptive responses.HemKR is a TCS present in both saprophytic and pathogenic Leptospira species, involved in the control of heme metabolism.However, the molecular means by which HemKR is switched on/off in a signal-dependent way, are still unknown.Moreover, a comprehensive list of HemKR-regulated genes, potentially overlapped with iron-responsive targets, is also missing. © 2024 Imelio et al.

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ABSTRACT.- Symbiosis plays a critical role in plant biology. Temperate grasses often associate with several symbiotic fungi simultaneously, including Epichloë endophytes and arbuscular mycorrhizal (AM) fungi, in shoots and roots, respectively. These symbionts often modulate plant-herbivore interactions by influencing nutritional traits (i.e. AM fungi-mediated nutrient uptake) and/or the secondary chemistry (i.e. endophytic alkaloids) of their host plant. Moreover, such grasses also accumulate large amounts of silicon (Si) from the soil, which can be deposited in tissues to act as a physical anti-herbivore defence. Recent evidence suggests that both endophytes and AM fungi independently facilitate Si uptake. However, the consequences of their interactions with piercing-sucking insects (i.e. aphids), or whether Si supply, endophytes, and AM fungi interact in this regard, are currently unknown. While Si deposition may be less effective against aphids than other herbivores (i.e. chewing caterpillars), Si supply can also alter plant secondary metabolite defences, which could affect sucking insects. In a factorial greenhouse experiment, we evaluated whether these components, acting alone or in combination, altered (1) foliar primary chemistry, (2) Si and symbiont-chemical (endophytic alkaloids) defences, as well as (3) performance of the bird cherry-oat aphid (Rhopalosiphum padi) feeding on tall fescue (Festuca arundinacea). Endophytes decreased all aphid performance parameters, including population growth and reproduction by 40%, but their impact was reversed by the presence of AM fungi, leading to a 52% increase in aphid performance compared with plants solely hosting endophytes. This improvement in performance was associated with reduced loline alkaloid levels and higher shoot nitrogen in AM-endophytic plants. Endophytes and AM fungi exhibited antagonism, with endophytes reducing AM colonization by 34% and AM presence decreasing endophyte loline alkaloids by 44%. While both fungi jointly increased Si accumulation by 39% under Si-supplied conditions, Si had no noticeable effects on aphids. Moreover, although Si supply had no identifiable effects on AM colonization, it reduced endophyte peramine alkaloids by 24%. Synthesis. Our findings indicate that symbiotic fungal partnerships and silicon provision may benefit plants but could weaken anti-herbivore defences when combined. Revealing the complex interactions among diverse fungal symbionts and showcasing their effects on different anti-herbivore defences (chemical and physical) and herbivore performance for the first time. © 2024 The Author(s). Journal of Ecology published by John Wiley & Sons Ltd on behalf of British Ecological Society.