Genome-wide transcript expression analysis reveals major chickpea and lentil genes associated with plant branching.

The search for elite cultivars with better architecture has been a demand by farmers of the chickpea and lentil crops, which aims to systematize their mechanized planting and harvesting on a large scale. Therefore, the identification of genes associated with the regulation of the branching and architecture of these plants has currently gained great importance. Herein, this work aimed to gain insight into transcriptomic changes of two contrasting chickpea and lentil cultivars in terms of branching pattern (little versus highly branched cultivars). In addition, we aimed to identify candidate genes involved in the regulation of shoot branching that could be used as future targets for molecular breeding. The axillary and apical buds of chickpea cultivars Blanco lechoso and FLIP07-318C, and lentil cultivars Castellana and Campisi, considered as little and highly branched, respectively, were harvested. A total of 1,624 and 2,512 transcripts were identified as differentially expressed among different tissues and contrasting cultivars of chickpea and lentil, respectively. Several gene categories were significantly modulated such as cell cycle, DNA transcription, energy metabolism, hormonal biosynthesis and signaling, proteolysis, and vegetative development between apical and axillary tissues and contrasting cultivars of chickpea and lentil. Based on differential expression and branching-associated biological function, ten chickpea genes and seven lentil genes were considered the main players involved in differentially regulating the plant branching between contrasting cultivars. These collective data putatively revealed the general mechanism and high-effect genes associated with the regulation of branching in chickpea and lentil, which are potential targets for manipulation through genome editing and transgenesis aiming to improve plant architecture.

Nitrogen inhibition of nitrogenase activity involves the modulation of cytosolic invertase in soybean nodule.

Legume symbiotic nitrogen fixation (SNF) is suppressed by inorganic N in the soil. High N inhibition of nitrogenase activity is associated with the deprivation of carbon allocation and metabolism in nodules. However, the underlying molecular mechanisms remain unclear. Here, we identify GmCIN1 which encodes a cytosolic invertase, as a gateway for the N-tuning of sucrose utilization in nodules. GmCIN1 is enriched in mature soybean nodules and its expression is regulated by nitrogen status. The knockout of GmCIN1 using genome editing partially mimicks the inhibitory effects of N on nitrogenase activity and sugar content and the impact of high N on nodule transcriptomes. This indicates that GmCIN1 partially mediates the high N inhibition of nodule activity. Moreover, ChIP-qPCR and EMSA reveal that SNAP1/2 transcription factors directly bind to the GmCIN1 promoter. In addition, SNAP1/2 may be involved in the repression of GmCIN1 expression in mature nodules at high N concentrations. Our findings provide insights into the involvement of the transcriptional tuning of C metabolism genes by N-signaling modulators in the N-induced inhibition of nitrogenase activity.

The growth-promoting and disease-suppressing mechanisms of Trichoderma inoculation on peanut seedlings.

Trichoderma spp. is known for its ability to enhance plant growth and suppress disease, but the mechanisms for its interaction with host plants and pathogens remain unclear. This study investigated the transcriptomics and metabolomics of peanut plants (Arachis hypogaea L.) inoculated with Trichoderma harzianum QT20045, in the absence and presence of the stem rot pathogen Sclerotium rolfsii JN3011. Under the condition without pathogen stress, the peanut seedlings inoculated with QT20045 showed improved root length and plant weight, increased indole acetic acid (IAA) production, and reduced ethylene level, with more active 1-aminocyclopropane-1-carboxylate acid (ACC) synthase (ACS) and ACC oxidase (ACO), compared with the non-inoculated control. Under the pathogen stress, the biocontrol efficacy of QT20045 against S. rolfsii was 78.51%, with a similar effect on plant growth, and IAA and ethylene metabolisms to the condition with no biotic stress. Transcriptomic analysis of peanut root revealed that Trichoderma inoculation upregulated the expression of certain genes in the IAA family but downregulated the genes in the ACO family (AhACO1 and AhACO) and ACS family (AhACS3 and AhACS1) consistently in the absence and presence of pathogens. During pathogen stress, QT20045 inoculation leads to the downregulation of the genes in the pectinesterase family to keep the host plant's cell wall stable, along with upregulation of the AhSUMM2 gene to activate plant defense responses. In vitro antagonistic test confirmed that QT20045 suppressed S. rolfsii growth through mechanisms of mycelial entanglement, papillary protrusions, and decomposition. Our findings highlight that Trichoderma inoculation is a promising tool for sustainable agriculture, offering multiple benefits from pathogen control to enhanced plant growth and soil health.

Effects of nitrogen addition and Bothriochloa ischaemum and Lespedeza davurica mixture on plant chlorophyll fluorescence and community production in semi-arid grassland.

Background: Grass-legume mixture can effectively improve productivity and stimulate overyielding in artificial grasslands, but may be N-limited in semi-arid regions. This study investigated the effects of N addition on chlorophyll fluorescence and production in the grass-legume mixtures community. Methods: An N addition experiment was conducted in the Bothriochloa ischaemum and Lespedeza davurica mixture community, with seven mixture ratios (B0L10, B2L8, B4L6, B5L5, B6L4, B8L2, and B10L0) according to the sowing abundance of B.ischaemum and L.davurica and four N addition levels, N0, N25, N50, and N75 (0,25,50,75kgNhm-2 a-1), respectively. We analyzed the response of chlorophyll fluorescence parameters of the two species, the rapid light-response curves of chlorophyll fluorescence, as well as aboveground biomass (AGB) and overyielding. Results: Our results showed that the two species showed different photosynthetic strategies, with L.davurica having significantly higher initial fluorescence (Fo), effective photochemical quantum yield of PSII (ΦPSII), and coefficient of photochemical fluorescence quenching (qP) than B. ischaemum, consisting with results of rapid light-response curves. N addition and mixture ratio both had significant effects on chlorophyll fluorescence and AGB (p<0.001). The ΦPSII and qP of L.davurica were significantly lowest in B5L5 and B6L4 under N addition, and the effect of N varied with mixture ratio. The photosynthetic efficiency of B. ischaemum was higher in mixture than in monoculture (B10L0), and ΦPSII was significantly higher in N50 than in N25 and N50 at mixture communities except at B5L5. The community AGB was significantly higher in mixture communities than in two monocultures and highest at B6L4. In the same mixture ratio, the AGB was highest under the N50. The overyielding effects were significantly highest under the N75 and B6L4 treatments, mainly attributed to L.davurica. The partial least squares path models demonstrated that adding N increased soil nutrient content, and complementary utilization by B.ischaemum and L.davurica increased the photosynthetic efficiency. However, as the different photosynthetic strategies of these two species, the effect on AGB was offset, and the mixture ratio's effects were larger than N. Our results proposed the B6L4 and N50 treatments were the optimal combination, with the highest AGB and overyielding, moderate grass-legume ratio, optimal community structure, and forage values.

Unraveling the dynamic interplay of microbial communities associated to Lupinus angustifolius in response to environmental and cultivation conditions.

Microorganisms form dynamic communities with plants, providing benefits such as nutrient acquisition and stress resilience. Understanding how these microorganisms are affected by environmental factors such as growth conditions and soil characteristics are essential for harnessing these communities for sustainable agriculture practices and their response to climate change. The microbiome associated to Lupinus angustifolius, a legume native in Europe, with a high protein value and stress resilience was characterized for the first time. Using 16S rRNA gene and ITS amplicon sequencing, we characterized the compositional and temporal changes of the bacterial and fungal communities associated to the soil, rhizosphere, and plant compartments where Lupinus angustifolius grows naturally. Our results suggest that the main difference in the soil microbial communities is related to the edaphic properties, although environmental factors such as temperature, humidity or rainfall also influenced the composition of the soil microbial communities. We also characterized the bacterial communities associated with the rhizosphere, roots, nodules, and leaves of wild plants collected in the field and compared them against plants obtained under greenhouse conditions. In the plant compartments, the bacterial composition appeared to be more affected by the growing conditions (field vs greenhouse), than by soil characteristics or location. These results can be used to identify key taxa that may play crucial roles in the development and adaptation of the host plant and its associated microbiota to environmental changes and highlight the importance of characterizing the plant microbiomes in their natural habitats. Soil, influenced by climatic seasons, shapes the plant microbiome assembly. Lupinus recruits a core microbiome across rhizosphere, roots, nodules, and leaves, that is stable across locations. However, cultivation conditions may alter microbiome dynamics, impacting the adaptability of its components. Wild plants show a resilient and adaptable microbiome while germination and cultivation in greenhouse conditions alter its composition and vulnerability.

Unlocking the Nutraceutical Potential of Legumes and Their By-Products: Paving the Way for the Circular Economy in the Agri-Food Industry.

Legumes, including beans, peas, chickpeas, and lentils, are cultivated worldwide and serve as important components of a balanced and nutritious diet. Each legume variety contains unique levels of protein, starch, fiber, lipids, minerals, and vitamins, with potential applications in various industries. By-products such as hulls, rich in bioactive compounds, offer promise for value-added utilization and health-focused product development. Various extraction methods are employed to enhance protein extraction rates from legume by-products, finding applications in various foods such as meat analogs, breads, and desserts. Moreover, essential fatty acids, carotenoids, tocols, and polyphenols are abundant in several residual fractions from legumes. These bioactive classes are linked to reduced incidence of cardiovascular diseases, chronic inflammation, some cancers, obesity, and type 2 diabetes, among other relevant health conditions. The present contribution provides a comprehensive review of the nutritional and bioactive composition of major legumes and their by-products. Additionally, the bioaccessibility and bioavailability aspects of legume consumption, as well as in vitro and in vivo evidence of their health effects are addressed.

Legume-grass mixtures improve biological nitrogen fixation and nitrogen transfer by promoting nodulation and altering root conformation in different ecological regions of the Qinghai-Tibet Plateau.

Introduction: Biological nitrogen fixation (BNF) plays a crucial role in nitrogen utilization in agroecosystems. Functional characteristics of plants (grasses vs. legumes) affect BNF. However, little is still known about how ecological zones and cropping patterns affect legume nitrogen fixation. This study's objective was to assess the effects of different cropping systems on aboveground dry matter, interspecific relationships, nodulation characteristics, root conformation, soil physicochemistry, BNF, and nitrogen transfer in three ecological zones and determine the main factors affecting nitrogen derived from the atmosphere (Ndfa) and nitrogen transferred (Ntransfer). Methods: The 15N labeling method was applied. Oats (Avena sativa L.), forage peas (Pisum sativum L.), common vetch (Vicia sativa L.), and fava beans (Vicia faba L.) were grown in monocultures and mixtures (YS: oats and forage peas; YJ: oats and common vetch; YC: oats and fava beans) in three ecological regions (HZ: Huangshui Valley; GN: Sanjiangyuan District; MY: Qilian Mountains Basin) in a split-plot design. Results: The results showed that mixing significantly promoted legume nodulation, optimized the configuration of the root system, increased aboveground dry matter, and enhanced nitrogen fixation in different ecological regions. The percentage of nitrogen derived from the atmosphere (%Ndfa) and percentage of nitrogen transferred (%Ntransfer) of legumes grown with different legume types and in different ecological zones were significantly different, but mixed cropping significantly increased the %Ndfa of the legumes. Factors affecting Ndfa included the cropping pattern, the ecological zone (R), the root nodule number, pH, ammonium-nitrogen, nitrate-nitrogen, microbial nitrogen mass (MBN), plant nitrogen content (N%), and aboveground dry biomass. Factors affecting Ntransfer included R, temperature, altitude, root surface area, nitrogen-fixing enzyme activity, organic matter, total soil nitrogen, MBN, and N%. Discussion: We concluded that mixed cropping is beneficial for BNF and that mixed cropping of legumes is a sustainable and effective forage management practice on the Tibetan Plateau.

The Compact Root Architecture 2 systemic pathway is required for the induction of cytokinins and of the miR399 in Medicago truncatula N-satisfied plants.

Plants use a combination of sophisticated local and systemic pathways to optimize growth depending on heterogeneous nutrient availability in the soil. Legume plants can acquire mineral nitrogen (N) either through their roots or via a symbiotic interaction with N-fixing rhizobia bacteria housed in so-called root nodules. To identify shoot-to-root systemic signals acting in Medicago truncatula plants at N-deficit or N-satiety, plants were grown in a split-root experimental design, in which either high or low N was provided to a half of the root system, allowing the analysis of systemic pathways independently of any local N response. Among the plant hormone families analyzed, the cytokinin trans-Zeatin accumulated in plants at N-satiety. Cytokinin application by petiole feeding led to an inhibition of both root growth and nodulation. In addition, an exhaustive analysis of miRNAs revealed that miR2111 accumulates systemically under N-deficit in both shoots and non-treated distant roots, whereas a miRNA related to inorganic Phosphate (Pi)-acquisition, the miR399, does so in plants grown at N-satiety. These two accumulation patterns are dependent on CRA2 (Compact Root Architecture 2), a receptor required for CEP (C-terminally Encoded Peptide) signaling. Constitutive ectopic expression of the miR399 reduced nodule numbers and root biomass depending on Pi availability, suggesting that the miR399-dependent Pi-acquisition regulatory module controlled by N-availability affects the development of the whole legume plant root system.

afila, the origin and nature of a major innovation in the history of pea breeding.

The afila (af) mutation causes the replacement of leaflets by a branched mass of tendrils in the compound leaves of pea - Pisum sativum L. This mutation was first described in 1953, and several reports of spontaneous af mutations and induced mutants with a similar phenotype exist. Despite widespread introgression into breeding material, the nature of af and the origin of the alleles used remain unknown. Here, we combine comparative genomics with reverse genetic approaches to elucidate the genetic determinants of af. We also investigate haplotype diversity using a set of AfAf and afaf cultivars and breeding lines and molecular markers linked to seven consecutive genes. Our results show that deletion of two tandemly arranged genes encoding Q-type Cys(2)His(2) zinc finger transcription factors, PsPALM1a and PsPALM1b, is responsible for the af phenotype in pea. Eight haplotypes were identified in the af-harbouring genomic region on chromosome 2. These haplotypes differ in the size of the deletion, covering more or less genes. Diversity at the af locus is valuable for crop improvement and sheds light on the history of pea breeding for improved standing ability. The results will be used to understand the function of PsPALM1a/b and to transfer the knowledge for innovation in related crops.

Inheritance of Resistance to Chickpea Fusarium Wilt Disease (Fusarium oxysporum f. sp. ciceris Race 2) in a Wide-Cross Cicer arietinum × Cicer reticulatum Mapping Family.

Chickpea (Cicer arietinum) is a major food legume providing high quality nutrition, especially in developing regions. Chickpea wilt (Fusarium oxysporum f. sp. ciceris) causes significant annual losses. Integrated disease management of Fusarium wilt is supported by resistant varieties. Relatively few resistance genes are known so there is value in exploring genetic resources in chickpea wild relatives. This study investigates the inheritance of Fusarium wilt resistance (race 2) in recombinant inbred lines (RILs) from a cross between a cultivated susceptible chickpea variety (Gokce) and a wild resistant Cicer reticulatum line (Kayat-077). RILs, parents, resistant and susceptible tester lines were twice grown in the greenhouse with inoculation and disease symptoms scored. DNA was extracted from dried leaves and individuals were single nucleotide polymorphism (SNP) genotyped. SNPs were placed on the reference chickpea genome and quantitative trait locus (QTL) mapping was performed. Significant QTL regions were examined using PulseDB to identify candidate genes. The results showed the segregation of Fusarium wilt resistance conforming to a single gene inheritance. One significant QTL was found at the start of chromosome 8, containing 138 genes, three of which were disease-resistance candidates for chickpea breeding.

Relationships of the wild peanut species, section Arachis: A resource for botanical classification, crop improvement, and germplasm management.

PREMISE: Wild species are strategic sources of valuable traits to be introduced into crops through hybridization. For peanut, the 33 currently described wild species in the section Arachis are particularly important because of their sexual compatibility with the domesticated species, Arachis hypogaea. Although numerous wild accessions are carefully preserved in seed banks, their morphological similarities pose challenges to routine classification. METHODS: Using a high-density array, we genotyped 272 accessions encompassing all diploid species in section Arachis. Detailed relationships between accessions and species were revealed through phylogenetic analyses and interpreted using the expertise of germplasm collectors and curators. RESULTS: Two main groups were identified: one with A genome species and the other with B, D, F, G, and K genomes. Species groupings generally showed clear boundaries. Structure within groups was informative, for instance, revealing the history of the proto-domesticate A. stenosperma. However, some groupings suggested multiple sibling species. Others were polyphyletic, indicating the need for taxonomic revision. Annual species were better defined than perennial ones, revealing limitations in applying classical and phylogenetic species concepts to the genus. We suggest new species assignments for several accessions. CONCLUSIONS: Curated by germplasm collectors and curators, this analysis of species relationships lays the foundation for future species descriptions, classification of unknown accessions, and germplasm use for peanut improvement. It supports the conservation and curation of current germplasm, both critical tasks considering the threats to the genus posed by habitat loss and the current restrictions on new collections and germplasm transfer.

Legume-supplemented feed for children hospitalised with severe malnutrition: A Phase II trial.

Children hospitalised with severe malnutrition have high mortality and readmission rates post-discharge. Current milk-based formulations target restoring ponderal growth but not modification of gut barrier integrety or microbiome which increase risk of gram-negative sepsis and poor outcomes. We propose that legume-based feeds rich in fermentable carbohydrates will promote better gut health and improve overall outcomes.We conducted an open-label Phase II trial at Mbale and Soroti Regional Referral Hospitals, Uganda involving 160 children aged 6 months-5 years with severe malnutrition (mid-upper arm circumference (MUAC) <11.5cm and/or nutritional oedema). Children were randomised to a lactose-free, chickpea-enriched legume paste feed (LF) (n=80) versus WHO standard F75/F100 feeds (n=80). Co-primary outcomes were change in MUAC and mortality to Day 90. Secondary outcomes included weight gain (>5 g/kg/day), de novo development of diarrhoea, time to diarrhoea and oedema resolution.Day 90 MUAC increase was marginally lower in LF versus WHO arm (1.1 cm (IQR 1.1) vs 1.4cm (IQR 1.40) p=0.09; Day 90 mortality was similar 11/80 (13.8%) vs 12/80 (15%) respectively OR 0.91 (95% CI 0.40 -2.07) p=0.83. There were no differences in any of the other secondary outcomes. Owing to initial poor palatability of the legume feed 10 children switched to WHO feeds. Per protocol analysis indicated a trend to lower Day 90 mortality and readmission rates in the legume feed (6/60: (10%) and (2/60: 3%) vs WHO feeds (12/71: 17.5%) and (4/71: 6%) respectively.Further refinement of legume feeds and clinical trials are warrented given the poor outcomes in children with severe malnutrition.Trial registration ISRCTN 10309022.

Applying a non-GMO breeding approach with an identified natural variation to reduce food allergen Len c3 in Lens culinaris seeds.

Lentils (Lens culinaris) are produced in diverse agroecological regions and are consumed as one of the most important food legumes worldwide. Lentils possess a nutritional profile from a human health perspective that is not only nutrient dense but also offers a better balance between protein and carbohydrates. However, lentil causes food allergy, which has been a significant concern due to increased consumption in parts of the world. Len c3, a non-specific lipid transfer protein (LTP), was identified as one of the allergens in lentil seeds. In this study, we identified an LTP gene Lcu.2RBY.4g013600 that encodes the lentil allergen Len c3. We then focused on gene screening from a collection of natural accessions to search for natural mutations of the Len c3 allergen-encoding gene. A natural lentil line M11 was identified with mutations at LcLTP3b and low accumulation of vicilin through genomic-assisted approaches. Furthermore, we generated a pool of lentil germplasms with LcLTP3b mutation background through crossing the identified lentil plant M11 with two lentil cultivars, CDC Redmoon and CDC Gold. These generated lentil hybrids can be used as a breeding resource targeting at reducing allergen risk in lentil consumption.

Recent progress and potential future directions to enhance biological nitrogen fixation in faba bean (Vicia faba L.).

The necessity for sustainable agricultural practices has propelled a renewed interest in legumes such as faba bean (Vicia faba L.) as agents to help deliver increased diversity to cropped systems and provide an organic source of nitrogen (N). However, the increased cultivation of faba beans has proven recalcitrant worldwide as a result of low yields. So, it is hoped that increased and more stable yields would improve the commercial success of the crop and so the likelihood of cultivation. Enhancing biological N fixation (BNF) in faba beans holds promise not only to enhance and stabilize yields but also to increase residual N available to subsequent cereal crops grown on the same field. In this review, we cover recent progress in enhancing BNF in faba beans. Specifically, rhizobial inoculation and the optimization of fertilizer input and cropping systems have received the greatest attention in the literature. We also suggest directions for future research on the subject. In the short term, modification of crop management practices such as fertilizer and biochar input may offer the benefits of enhanced BNF. In the long term, natural variation in rhizobial strains and faba bean genotypes can be harnessed. Strategies must be optimized on a local scale to realize the greatest benefits. Future research must measure the most useful parameters and consider the economic cost of strategies alongside the advantages of enhanced BNF.

Hydration and Fortification of Common Bean (Phaseolus vulgaris L.) with Grape Skin Phenolics-Effects of Ultrasound Application and Heating.

Ultrasound (US)-assisted soaking combined with fortification with red grape skin (GS) phenolics was applied on two Phaseolus varieties, namely White Kidney Bean (WKB) and Cranberry Bean (CB), before heat treatment. The aims were to investigate: (a) the effect of US application on the kinetic of hydration; (b) the extent of absorption of different phenolic classes of GS into the beans and the resulting effect on antioxidant activity; (c) the effects of heat treatment on the phenolic fraction and antioxidant activity of GS extract- and water-soaked beans. US fastened the soaking step of both WKB and CB beans, which showed the sigmoidal and the downward concave shape hydration curves, respectively. Anthocyanins, flavonols, flavanol and phenolic acids levels increased with GS soaking, but US application was effective only for increasing the level of flavonols, while it favored the loss of endogenous phenolic acids and it did not affect the uptake of anthocyanins and flavanols. Heat treatment decreased the levels of most of phenolic compounds, but increased the levels of monomeric flavanols. Overall, the antioxidant activity was 40% higher in WKB and 53% higher in CB upon GS-fortification than in the control beans, despite the effects of heating. This fortification strategy could be applied for value addition of varieties low in phenolics or as a pre-treatment before intensive processing.

The genome of Lespedeza potaninii reveals biased subgenome evolution and drought adaptation.

Lespedeza potaninii, a xerophytic subshrub belonging to the legume family, is native to the Tengger Desert and is highly adapted to drought. It has important ecological value due to its drought adaptability, but the underlying molecular mechanisms remain largely unknown. Here, we report a 1.24 Gb chromosome-scale assembly of the L. potaninii genome (contig N50=15.75 Mb). Our results indicate that L. potaninii underwent an allopolyploid event with two subgenomes, A and B, presenting asymmetric evolution and B subgenome dominance. We estimate that the two diploid progenitors of L. potaninii diverged around 3.6 MYA and merged around 1.0 MYA. We revealed that the expansion of hub genes associated with drought responses, such as the binding partner 1 of accelerated cell death 11 (ACD11) (BPA1), facilitated environmental adaptations of L. potaninii to desert habitats. We found a novel function of the BPA1 family in abiotic stress tolerance in addition to the known role in regulating the plant immune response, which could improve drought tolerance by positively regulating reactive oxygen species homeostasis in plants. We revealed that bZIP transcription factors could bind to the BPA1 promoter and activate its transcription. Our work fills the genomic data gap in the Lespedeza genus and the tribe Desmodieae, which should provide both theoretical support in the study of drought tolerance and in the molecular breeding of legume crops.

Green manuring alters reactive N losses and N pools in arable soils: A meta-regression study.

Green manuring is a conservation agricultural practice that improves soil quality and crop yield. However, increasing the active nitrogen (N) and carbon (C) pools during green manure (GM) amendment may accelerate soil N transformation and stimulate N loss. Previous studies have reported the effects of cover crop incorporation on N2O emission; however, the driving mechanisms and other N losses remain unclear. Therefore, we conducted a comprehensive meta-analysis of 109 published articles (517 paired observations) to clarify the effects of GM amendment on soil reactive N (Nr) losses (N2O emissions, NH3 volatilization, and N leaching and runoff), N pools, and N cycling functional gene abundance. The results showed that green manuring increased soil microbial biomass N (MBN) and NO3--N concentrations and stimulated N2O emission but significantly lowered N leaching and yield-scaled NH3 volatilization. Practices of green manuring made a dominant contribution to the variation in N2O emissions and NH3 volatilization after GM application. Furthermore, applying legume-based GM, using N derived from GM (GMN) as an additional input, and short-term GM amendment each stimulated N2O emissions. In contrast, adopting non-legume GM, using GMN to partially substitute mineral N, and applying GM to the soil surface or paddy field mitigated NH3 loss during GM amendment. Additionally, the variation in NH3 volatilization was positively related to soil pH and N application rate (NAR) but had a negative relationship with mean annual precipitation (MAP). This study highlighted the marked effects of green manuring on soil N retention and loss. Agricultural operations that adopt GM amendment should select suitable GM species and optimize mineral N inputs to minimize N loss.

Rhizobium determinants of rhizosphere persistence and root colonization.

Bacterial persistence in the rhizosphere and colonization of root niches are critical for the establishment of many beneficial plant-bacteria interactions including those between Rhizobium leguminosarum and its host legumes. Despite this, most studies on R. leguminosarum have focused on its symbiotic lifestyle as an endosymbiont in root nodules. Here, we use random barcode transposon sequencing to assay gene contributions of R. leguminosarum during competitive growth in the rhizosphere and colonization of various plant species. This facilitated the identification of 189 genes commonly required for growth in diverse plant rhizospheres, mutation of 111 of which also affected subsequent root colonization (rhizosphere progressive), and a further 119 genes necessary for colonization. Common determinants reveal a need to synthesize essential compounds (amino acids, ribonucleotides, and cofactors), adapt metabolic function, respond to external stimuli, and withstand various stresses (such as changes in osmolarity). Additionally, chemotaxis and flagella-mediated motility are prerequisites for root colonization. Many genes showed plant-specific dependencies highlighting significant adaptation to different plant species. This work provides a greater understanding of factors promoting rhizosphere fitness and root colonization in plant-beneficial bacteria, facilitating their exploitation for agricultural benefit.

Timely symbiosis: circadian control of legume-rhizobia symbiosis.

Legumes house nitrogen-fixing endosymbiotic rhizobia in specialised polyploid cells within root nodules. This results in a mutualistic relationship whereby the plant host receives fixed nitrogen from the bacteria in exchange for dicarboxylic acids. This plant-microbe interaction requires the regulation of multiple metabolic and physiological processes in both the host and symbiont in order to achieve highly efficient symbiosis. Recent studies have showed that the success of symbiosis is influenced by the circadian clock of the plant host. Medicago and soybean plants with altered clock mechanisms showed compromised nodulation and reduced plant growth. Furthermore, transcriptomic analyses revealed that multiple genes with key roles in recruitment of rhizobia to plant roots, infection and nodule development were under circadian control, suggesting that appropriate timing of expression of these genes may be important for nodulation. There is also evidence for rhythmic gene expression of key nitrogen fixation genes in the rhizobium symbiont, and temporal coordination between nitrogen fixation in the bacterial symbiont and nitrogen assimilation in the plant host may be important for successful symbiosis. Understanding of how circadian regulation impacts on nodule establishment and function will identify key plant-rhizobial connections and regulators that could be targeted to increase the efficiency of this relationship.