Phosphorus deprivation affects composition and spatial distribution of membrane lipids in legume nodules

Soil microbial functional profiles of P-cycling reveal drought-induced constraints on P-transformation in a hyper-arid desert ecosystem

Soil water conditions are known to influence soil nutrient availability, but the specific impact of different conditions on soil phosphorus (P) availability through the modulation of P-cycling functional microbial communities in hyper-arid desert ecosystems remains largely unexplored. To address this knowledge gap, we conducted a 3-year pot experiment using a typical desert plant species (Alhagi sparsifolia Shap.) subjected to two water supply levels (25 %-35 % and 65 %-75 % of maximum field capacity, MFC) and four P-supply levels (0, 1, 3, and 5 g P m-2 y-1). Our investigation focused on the soil Hedley-P pool and the four major microbial groups involved in the critical phases of soil microbial P-cycling. The results revealed that the drought (25 %-35 % MFC) and no P-supply treatments reduced soil resin-P and NaHCO3-Pi concentrations by 87.03 % and 93.22 %, respectively, compared to the well-watered (65 %-75 % MFC) and high P-supply (5 g P m-2 y-1) treatments. However, the P-supply treatment resulted in a 12 %-22 % decrease in the soil NH4+-N concentration preferred by microbes compared to the no P-supply treatment. Moreover, the abundance of genes engaged in microbial P-cycling (e.g. gcd and phoD) increased under the drought and no P-supply treatments (p < 0.05), suggesting that increased NH4+-N accumulation under these conditions may stimulate P-solubilizing microbes, thereby promoting the microbial community's investment in resources to enhance the P-cycling potential. Furthermore, the communities of Steroidobacter cummioxidans, Mesorhizobium alhagi, Devosia geojensis, and Ensifer sojae, associated with the major P-cycling genes, were enriched in drought and no or low-P soils. Overall, the drought and no or low-P treatments stimulated microbial communities and gene abundances involved in P-cycling. However, this increase was insufficient to maintain soil P-bioavailability. These findings shed light on the responses and feedback of microbial-mediated P-cycling behaviors in desert ecosystems under three-year drought and soil P-deficiency.

Nitrogen-fixing and non-nitrogen-fixing legume plants differ in leaf nutrient concentrations and relationships between photosynthetic and hydraulic traits

Legumes account for a significant proportion of plants in the terrestrial ecosystems. Nitrogen (N)-fixing capability of certain legumes is a pivotal trait that contributes to their ecological dominance. Yet, the functional traits and trait relationships between N-fixer and non-N-fixer legumes are poorly understood. Here, we investigated 27 functional traits associated with morphology, nutrients, hydraulic conductance and photosynthesis in 42 woody legumes (19 N-fixers and 23 non-N-fixers) in a common garden. Our results showed that N-fixers had higher specific leaf area, photosynthetic phosphorus (P)-use efficiency, leaf N, and iron concentrations on both area and mass basis, N/P ratio, and carbon (C) to P ratio, but lower wood density, area-based maximum photosynthetic rate (Aa), photosynthetic N-use efficiency, leaf mass- and area-based P and molybdenum and area-based boron concentrations, and C/N ratio, compared with non-N-fixers. The mass-based maximum photosynthetic rate (Am), stomatal conductance (gs), intrinsic water-use efficiency (WUEi), mass- and area-based leaf potassium and mass-based boron concentrations, leaf hydraulic conductance (Kleaf), and whole-shoot hydraulic conductance (Kshoot) showed no difference between N-fixers and non-N-fixers. Significant positive associations between all hydraulic and photosynthetic trait pairs were found in N-fixers, but only one pair (Kshoot-Aa) in non-N-fixers, suggesting that hydraulic conductance plays a more important role in mediating photosynthetic capacity in N-fixers compared with non-N-fixers. Higher mass-based leaf N was linked to lower time-integrated gs and higher WUEi among non-N-fixer legumes or all legumes pooled after phylogeny was considered. Moreover, mass-based P concentration was positively related to Am and gs in N-fixers, but not in non-N-fixers, indicating that the photosynthetic capacity and stomatal conductance in N-fixers were more dependent on leaf P status than in non-N-fixers. These findings expand our understanding of the trait-based ecology within and across N-fixer and non-N-fixer legumes in tropics.

Imaging plant metabolism in situ

Mass spectrometry imaging (MSI) has emerged as an invaluable analytical technique for investigating the spatial distribution of molecules within biological systems. In the realm of plant science, MSI is increasingly employed to explore metabolic processes across a wide array of plant tissues, including those in leaves, fruits, stems, roots, and seeds, spanning various plant systems such as model species, staple and energy crops, and medicinal plants. By generating spatial maps of metabolites, MSI has elucidated the distribution patterns of diverse metabolites and phytochemicals, encompassing lipids, carbohydrates, amino acids, organic acids, phenolics, terpenes, alkaloids, vitamins, pigments, and others, thereby providing insights into their metabolic pathways and functional roles. In this review, we present recent MSI studies that demonstrate the advances made in visualizing the plant spatial metabolome. Moreover, we emphasize the technical progress that enhances the identification and interpretation of spatial metabolite maps. Within a mere decade since the inception of plant MSI studies, this robust technology is poised to continue as a vital tool for tackling complex challenges in plant metabolism.

Comparative analysis of the rhizosphere microbiome and medicinally active ingredients of Atractylodes lancea from different geographical origins

This study aimed to explore the important role of the rhizosphere microbiome in the quality of Atractylodes lancea (Thunb.) DC. (A. lancea). The rhizosphere microbial community of A. lancea at two sampling sites was studied using metagenomic technology. The results of α-diversity analysis showed that the rhizosphere microbial richness and diversity were higher in the Maoshan area. The higher abundance of core microorganisms of the rhizosphere, especially Penicillium and Streptomyces, in the Maoshan area compared with those in the Yingshan area might be an important factor affecting the yield of A. lancea. Redundancy analysis illustrated that the available phosphorus had a significant effect on the rhizosphere microbial community structure of A. lancea. We also showed that the plant-microbe and microbe-microbe interactions were closer in the Maoshan area than in the Yingshan area, and Streptomyces were the main contributors to the potential functional difference between the two regions. A. lancea in the Maoshan area had a high content of atractylodin and atractylon, which might be related to the enhanced abundance of Streptomyces, Candidatus-Solibacter, and Frankia. Taken together, this study provided theoretical insights into the interaction between medicinal plants and the rhizosphere microbiome and provides a valuable reference for studying beneficial microbes of A. lancea.

VPT-like genes modulate Rhizobium-legume symbiosis and phosphorus adaptation

Although vacuolar phosphate transporters (VPTs) are essential for plant phosphorus adaptation, their role in Rhizobium-legume symbiosis is unclear. In this study, homologous genes of VPT1 (MtVPTs) were identified in Medicago truncatula to assess their roles in Rhizobium-legume symbiosis and phosphorus adaptation. MtVPT2 and MtVPT3 mainly positively responded to low and high phosphate, respectively. However, both mtvpt2 and mtvpt3 mutants displayed shoot phenotypes with high phosphate sensitivity and low phosphate tolerance. The root-to-shoot phosphate transfer efficiency was significantly enhanced in mtvpt3 but weakened in mtvpt2, accompanied by lower and higher root cytosolic inorganic phosphate (Pi) concentration, respectively. Low phosphate induced MtVPT2 and MtVPT3 expressions in nodules. MtVPT2 and MtVPT3 mutations markedly reduced the nodule number and nitrogenase activity under different phosphate conditions. Cytosolic Pi concentration in nodules was significantly lower in mtvpt2 and mtvpt3 than in the wildtype, especially in tissues near the base of nodules, probably due to inhibition of long-distance Pi transport and cytosolic Pi supply. Also, mtvpt2 and mtvpt3 could not maintain a stable cytosolic Pi level in the nodule fixation zone as the wildtype under low phosphate stress. These findings show that MtVPT2 and MtVPT3 modulate phosphorus adaptation and rhizobia-legume symbiosis, possibly by regulating long-distance Pi transport.

Resilient and sustainable production of peanut (Arachis hypogaea) in phosphorus-limited environment by using exogenous gamma-aminobutyric acid to sustain photosynthesis

Globally, many low to medium yielding peanut fields have the potential for further yield improvement. Low phosphorus (P) limitation is one of the significant factors curtailing Arachis hypogaea productivity in many regions. In order to demonstrate the effects of gamma-aminobutyric acid (GABA) on peanuts growing under P deficiency, we used a pot-based experiment to examine the effects of exogenous GABA on alleviating P deficiency-induced physiological changes and growth inhibition in peanuts. The key physiological parameters examined were foliar gas exchange, photochemical efficiency, proton motive force, reactive oxygen species (ROS), and adenosine triphosphate (ATP) synthase activity of peanuts under cultivation with low P (LP, 0.5 mM P) and control conditions. During low P, the cyclic electron flow (CEF) maintained the high proton gradient (∆pH) induced by low ATP synthetic activity. Applying GABA during low P conditions stimulated CEF and reduced the concomitant ROS generation and thereby protecting the foliar photosystem II (PSII) from photoinhibition. Specifically, GABA enhanced the rate of electronic transmission of PSII (ETRII) by pausing the photoprotection mechanisms including non-photochemical quenching (NPQ) and ∆pH regulation. Thus, GABA was shown to be effective in restoring peanut growth when encountering P deficiency. Exogenous GABA alleviated two symptoms (increased root-shoot ratio and photoinhibition) of P-deficient peanuts. This is possibly the first report of using exogenous GABA to restore photosynthesis and growth under low P availability. Therefore, foliar applications of GABA could be a simple, safe and effective approach to overcome low yield imposed by limited P resources (low P in soils or P-fertilizers are unavailable) for sustainable peanut cultivation and especially in low to medium yielding fields.

Seeing plants as never before

Imaging has long supported our ability to understand the inner life of plants, their development, and response to a dynamic environment. While optical microscopy remains the core tool for imaging, a suite of novel technologies is now beginning to make a significant contribution to visualize plant metabolism. The purpose of this review was to provide the scientific community with an overview of current imaging methods, which rely variously on either nuclear magnetic resonance (NMR), mass spectrometry (MS) or infrared (IR) spectroscopy, and to present some examples of their application in order to illustrate their utility. In addition to providing a description of the basic principles underlying these technologies, the review discusses their various advantages and limitations, reveals the current state of the art, and suggests their potential application to experimental practice. Finally, a view is presented as to how the technologies will likely develop, how these developments may encourage the formulation of novel experimental strategies, and how the enormous potential of these technologies can contribute to progress in plant science.

A modified aeroponic system for growing small-seeded legumes and other plants to study root systems

BACKGROUND

Various growth systems are available for studying plant root growth and plant-microbe interactions including hydroponics and aeroponics. Although some of these systems work well with Arabidopsis thaliana and smaller cereal model plants, they may not scale up as well for use with hundreds of plants at a time from a larger plant species. The aim of this study is to present step-by-step instructions for fabricating an aeroponic system, also called a "caisson," that has been in use in several legume research labs studying the development of symbiotic nitrogen fixing nodules, but for which detailed directions are not currently available. The aeroponic system is reusable and is adaptable for many other types of investigations besides root nodulation.

RESULTS

An aeroponic system that is affordable and reusable was adapted from a design invented by French engineer René Odorico. It consists of two main components: a modified trash can with a lid of holes and a commercially available industrial humidifier that is waterproofed with silicon sealant. The humidifier generates a mist in which plant roots grow, suspended from holes in trash can lid. Results from use of the aeroponic system have been available in the scientific community for decades; it has a record as a workhorse in the lab.

CONCLUSIONS

Aeroponic systems present a convenient way for researchers to grow plants for studying root systems and plant-microbe interactions in root systems. They are particularly attractive for phenotyping roots and following the progress of nodule development in legumes. Advantages include the ability to precisely control the growth medium in which the plants grow and easy observations of roots during growth. In this system, mechanical shear potentially killing microbes found in some other types of aeroponic devices is not an issue. Disadvantages of aeroponic systems include the likelihood of altered root physiology compared to root growth on soil and other solid substrates and the need to have separate aeroponic systems for comparing plant responses to different microbial strains.

Metabolite shift in Medicago truncatula occurs in phosphorus deprivation

Symbiotic nitrogen (N) fixation entails successful interaction between legume hosts and rhizobia that occur in specialized organs called nodules. N-fixing legumes have a higher demand for phosphorus (P) than legumes grown on mineral N. Medicago truncatula is an important model plant for characterization of effects of P deficiency at the molecular level. Hence, a study was carried out to address the alteration in metabolite levels of M. truncatula grown aeroponically and subjected to 4 weeks of P stress. First, GC-MS-based untargeted metabolomics initially revealed changes in the metabolic profile of nodules, with increased levels of amino acids and sugars and a decline in amounts of organic acids. Subsequently, LC-MS/MS was used to quantify these compounds including phosphorylated metabolites in the whole plant. Our results showed a drastic reduction in levels of organic acids and phosphorylated compounds in -P leaves, with a moderate reduction in -P roots and nodules. Additionally, sugars and amino acids were elevated in the whole plant under P deprivation. These findings provide evidence that N fixation in M. truncatula is mediated through a N feedback mechanism that in parallel is related to carbon and P metabolism.

Unravel the Local Complexity of Biological Environments by MALDI Mass Spectrometry Imaging

Classic metabolomic methods have proven to be very useful to study functional biology and variation in the chemical composition of different tissues. However, they do not provide any information in terms of spatial localization within fine structures. Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) does and reaches at best a spatial resolution of 0.25 μm depending on the laser setup, making it a very powerful tool to analyze the local complexity of biological samples at the cellular level. Here, we intend to give an overview of the diversity of the molecules and localizations analyzed using this method as well as to update on the latest adaptations made to circumvent the complexity of samples. MALDI MSI has been widely used in medical sciences and is now developing in research areas as diverse as entomology, microbiology, plant biology, and plant–microbe interactions, the rhizobia symbiosis being the most exhaustively described so far. Those are the fields of interest on which we will focus to demonstrate MALDI MSI strengths in characterizing the spatial distributions of metabolites, lipids, and peptides in relation to biological questions.