Microbiome convergence enables siderophore-secreting-rhizobacteria to improve iron nutrition and yield of peanut intercropped with maize.

Intercropping has the potential to improve plant nutrition as well as crop yield. However, the exact mechanism promoting improved nutrient acquisition and the role the rhizosphere microbiome may play in this process remains poorly understood. Here, we use a peanut/maize intercropping system to investigate the role of root-associated microbiota in iron nutrition in these crops, combining microbiome profiling, strain and substance isolation and functional validation. We find that intercropping increases iron nutrition in peanut but not in maize plants and that the microbiota composition changes and converges between the two plants tested in intercropping experiments. We identify a Pseudomonas secreted siderophore, pyoverdine, that improves iron nutrition in glasshouse and field experiments. Our results suggest that the presence of siderophore-secreting Pseudomonas in peanut and maize intercropped plays an important role in iron nutrition. These findings could be used to envision future intercropping practices aiming to improve plant nutrition.

The active Fe chelator proline-2'-deoxymugineic acid enhances peanut yield by improving soil Fe availability and plant Fe status.

Iron (Fe) deficiency restricts crop yields in calcareous soil. Thus, a novel Fe chelator, proline-2'-deoxymugineic acid (PDMA), based on the natural phytosiderophore 2'-deoxymugineic acid (DMA), was developed to solve the Fe deficiency problem. However, the effects and mechanisms of PDMA relevant to the Fe nutrition and yield of dicots grown under field conditions require further exploration. In this study, pot and field experiments with calcareous soil were conducted to investigate the effects of PDMA on the Fe nutrition and yield of peanuts. The results demonstrated that PDMA could dissolve insoluble Fe in the rhizosphere and up-regulate the expression of the yellow stripe-like family gene AhYSL1 to improve the Fe nutrition of peanut plants. Moreover, the chlorosis and growth inhibition caused by Fe deficiency were significantly diminished. Notably, under field conditions, the peanut yield and kernel micronutrient contents were promoted by PDMA application. Our results indicate that PDMA promotes the dissolution of insoluble Fe and a rich supply of Fe in the rhizosphere, increasing yields through integrated improvements in soil-plant Fe nutrition at the molecular and ecological levels. In conclusion, the efficacy of PDMA for improving the Fe nutrition and yield of peanut indicates its outstanding potential for agricultural applications.

Root exudate signals in plant-plant interactions.

Plant-to-plant signalling is a key mediator of interactions among plant species. Plants can perceive and respond to chemical cues emitted from their neighbours, altering survival and performance, impacting plant coexistence and community assembly. An increasing number of studies indicate root exudates as key players in plant-to-plant signalling. Root exudates mediate root detection and behaviour, kin recognition, flowering and production, driving inter- and intra-specific facilitation in cropping systems and mixed-species plantations. Altered interactions may be attributed to the signalling components within root exudates. Root ethylene, strigolactones, jasmonic acid, (-)-loliolide and allantoin are signalling chemicals that convey information on local conditions in plant-plant interactions. These root-secreted signalling chemicals appear ubiquitous in plants and trigger a series of belowground responses inter- and intra-specifically, involving molecular events in biosynthesis, secretion and action. The secretion of root signals, mainly mediated by ATP-binding cassette transporters, is critical. Root-secreted signalling chemicals and their molecular mechanisms are rapidly revealing a multitude of fascinating plant-plant interactions. However, many root signals, particularly species-specific signals and their underlying mechanisms, remain to be uncovered due to methodological limitations and root-soil interactions. A thorough understanding of root-secreted chemical signals and their mechanisms will offer many ecological implications and potential applications for sustainable agriculture.

Nematicidal Effect of Methyl Palmitate and Methyl Stearate against Meloidogyne incognita in Bananas.

Banana plants (Musa spp.) are susceptible to infection by many plant-parasitic nematodes, including Meloidogyne incognita. In this study, a mixed fermentation broth of chicken manure (CM) and cassava ethanol wastewater (CEW) was used to inhibit M. incognita by reducing egg hatching and by having a lethal effect on second-stage juvenile nematodes (J2s). It also alleviated nematode damage and promoted banana plant growth. Using gas chromatography-mass spectrometry (GC-MS), we identified methyl palmitate and methyl stearate as bioactive compounds. These bioactive compounds repelled J2s and inhibited egg hatching; reduced root galls, egg masses, and nematodes in soil; and downregulated the essential parasitic nematode genes Mi-flp-18 and 16D10. A Caenorhabditis elegans offspring assay showed that low concentrations of the fermentation broth, methyl palmitate, and methyl stearate were safe for its life cycle. This study explored the effective and environmentally safe strategies for controlling root-knot nematodes.

From Leguminosae/Gramineae Intercropping Systems to See Benefits of Intercropping on Iron Nutrition.

To achieve sustainable development with a growing population while sustaining natural resources, a sustainable intensification of agriculture is necessary. Intercropping is useful for low-input/resource-limited agricultural systems. Iron (Fe) deficiency is a worldwide agricultural problem owing to the low solubility and bioavailability of Fe in alkaline and calcareous soils. Here, we summarize the effects of intercropping systems on Fe nutrition. Several cases showed that intercropping with graminaceous plants could be used to correct Fe nutrition of Leguminosae such as peanut and soybean or fruits such as Psidium guajava L., Citrus, grape and pear in calcareous soils. Intercropping systems have strong positive effects on the physicochemical and biochemical characteristics of soil and the microbial community due to interspecific differences and interactions in the rhizosphere. Rhizosphere interactions can increase the bioavailability of Fe with the help of phytosiderophores. Enriched microorganisms may also facilitate the Fe nutrition of crops. A peanut/maize intercropping system could help us understand the dynamics in rhizosphere and molecular mechanism. However, the role of microbiome in regulating Fe acquisition of root and the mechanisms underlying these phenomena in other intercropping system except peanut/maize need further work, which will help better utilize intercropping to increase the efficiency of Fe foraging.

AhNRAMP1 Enhances Manganese and Zinc Uptake in Plants.

Manganese (Mn) and zinc (Zn) play essential roles in plants. Members of the natural resistance-associated macrophage protein (NRAMP) family transport divalent metal ions. In this research, the function of peanut (Arachis hypogaea L.) AhNRAMP1 in transporting Mn and Zn, as well as its potential for iron(Fe) and Zn biofortification was examined. AhNRAMP1 transcription was strongly induced by Mn- or Zn-deficiency in roots and stems of peanut. Yeast complementation assays suggested that AhNRAMP1 encoded a functional Mn and Zn transporter. Exogenous expression of AhNRAMP1 in tobacco and rice enhanced Mn or Zn concentrations, improving tolerance to Mn or Zn deficiency. With higher Mn concentration, transgenic plants exhibited inhibited growth under Mn excess condition; similar results were obtained under excessive Zn treatment. AhNRAMP1 expression increased biomass in transgenic tobacco and rice, as well as yield in transgenic rice grown on calcareous soil. Compared with non-transformed (NT) plants, Fe and Zn concentrations were elevated whereas concentrations of Mn, copper (Cu), and cadmium (Cd) were not enhanced. These results revealed that AhNRAMP1 contributes to Mn and Zn transport in plants and may be a candidate gene for Fe and Zn biofortification.

AhFRDL1-mediated citrate secretion contributes to adaptation to iron deficiency and aluminum stress in peanuts.

Although citrate transporters are involved in iron (Fe) translocation and aluminum (Al) tolerance in plants, to date none of them have been shown to confer both biological functions in plant species that utilize Fe-absorption Strategy I. In this study, we demonstrated that AhFRDL1, a citrate transporter gene from peanut (Arachis hypogaea) that is induced by both Fe-deficiency and Al-stress, participates in both root-to-shoot Fe translocation and Al tolerance. Expression of AhFRDL1 induced by Fe deficiency was located in the root stele, but under Al-stress expression was observed across the entire root-tip cross-section. Overexpression of AhFRDL1 restored efficient Fe translocation in Atfrd3 mutants and Al resistance in AtMATE-knockout mutants. Knocking down AhFRDL1 in the roots resulted in reduced xylem citrate and reduced concentrations of active Fe in young leaves. Furthermore, AhFRDL1-knockdown lines had reduced root citrate exudation and were more sensitive to Al toxicity. Compared to an Al-sensitive variety, enhanced AhFRDL1 expression in an Fe-efficient variety contributed to higher levels of Al tolerance and Fe translocation by promoting citrate secretion. These results indicate that AhFRDL1 plays a significant role in Fe translocation and Al tolerance in Fe-efficient peanut varieties under different soil-stress conditions. Given its dual biological functions, AhFRDL1 may serve as a useful genetic marker for breeding for high Fe efficiency and Al tolerance.

The Yellow Stripe-Like (YSL) Gene Functions in Internal Copper Transport in Peanut.

Copper (Cu) is involved in fundamental biological processes for plant growth and development. However, Cu excess is harmful to plants. Thus, Cu in plant tissues must be tightly regulated. In this study, we found that the peanut Yellow Stripe-Like family gene AhYSL3.1 is involved in Cu transport. Among five AhYSL genes, AhYSL3.1 and AhYSL3.2 were upregulated by Cu deficiency in peanut roots and expressed mainly in young leaves. A yeast complementation assay suggested that the plasma membrane-localized AhYSL3.1 was a Cu-nicotianamine complex transporter. High expression of AhYSL3.1 in tobacco and rice plants with excess Cu resulted in a low concentration of Cu in young leaves. These transgenic plants were resistant to excess Cu. The above results suggest that AhYSL3.1 is responsible for the internal transport of Cu in peanut.

Comparative transcriptomic analysis of the roots of intercropped peanut and maize reveals novel insights into peanut iron nutrition.

Intercropping is a vital technology in resource-limited agricultural systems with low inputs. Peanut/maize intercropping enhances iron (Fe) nutrition in calcareous soil. In this study, the transcriptome of peanut and maize roots was analyzed by suppression subtractive hybridization (SSH) and microarray analysis separately. We constructed four SSH libraries using the cDNA of peanut roots based on two cropping patterns: monocropping and intercropping, and two growth stages: vegetative stage and reproductive stage. Lib M1, I1, M2 and I2 comprised 53, 51, 37 and 54 genes, respectively. Six and four transporters were found in the two intercropping-specific SSH libraries, which may facilitate Fe acquisition and protoplasmic homeostasis of metal ions and anions. Specifically, AhNARMP1 and MTP may play a role in boosting Fe nutrition during the vegetative stage. The expression of MYC2 was also upregulated by intercropping, while an ethylene-responsive transcription factor was downregulated during two growth periods. Microarrays indicated that homocysteine S-methyltransferase and serine acetyltransferase 1 upregulated in intercropped maize roots, which directly associated with methionine biosynthesis. It may account for the enhanced phytosiderophore released capacity in intercropping, which benefited the Fe nutrition of intercropped peanut in reproductive stage. Two aminocyclopropane-1-carboxylic acid synthase oxidase genes, which are related to ethylene biosynthesis, were downregulated in maize root by intercropping. Taken together with our previous proteomic work, the results indicated that intercropping enhances jasmonate signaling and weakens ethylene signaling in peanut and maize roots, which may improve ecological adaptation of the peanut plant to intercropping systems.

Effects of Fe-deficient conditions on Fe uptake and utilization in P-efficient soybean.

Phosphorus (P)-efficient soybean (Glycine max) plants absorb and utilize P with high efficiency. To investigate the effects of iron (Fe)-deficient conditions on the absorption and utilization of Fe in P-efficient soybean plants, two soybean cultivars with different P efficiency, the 03-3 (P-efficient variety) and Bd-2 (P-inefficient variety), were used in this study. The two soybean cultivars were grown in nutrient solution containing Fe concentrations of 0 (Fe0), 20 (Fe20), 40 (Fe40), or 80 (Fe80) µM for 7 days. The Fe reductase activity of roots was higher in 03-3 plants grown under the Fe0, Fe20, and Fe40 treatments than in Bd-2 plants and the total Fe uptake was greater in 03-3 plants under the Fe40 treatment. GmFRD3a was much more highly expressed in the stem of 03-3 than in that of Bd-2, and significantly more iron was transported to 03-3 plant shoots during Fe0 treatment. Chlorosis in young leaves caused by Fe deficiency under the Fe0 and Fe20 treatments was alleviated by increased Fe concentration in shoots. Increased levels of active Fe in young 03-3 leaves under Fe-deprivation conditions (Fe0) and maintenance of stable Fe concentrations in 03-3 shoots subjected to Fe20, Fe40, and Fe80 treatments suggested that the P-efficient 03-3 cultivar is also Fe-efficient. It is suggested that 03-3 soybean cultivar should be a good resource for application to farm field.

[Citrus boron nutrient level and its impact factors in the Three Gorges Reservoir region of Chongqing, China].

To investigate the level of boron nutrient in citrus and its impact factors, a total of 954 citrus leaf samples and 302 soil samples were collected from representative orchards in the 12 main citrus production counties in the Three Gorges Reservoir region of Chongqing to determine the boron content in citrus leaves, as well as the relationships between leaf boron content with soil available boron content, soil pH value, cultivar, rootstock and the age of tree. Results indicated that the leaf samples from 41.6% orchards (< 35 mg x kg(-1)) and the soil samples from 89.4% orchards (< 0.5 mg x kg(-1)) were boron insufficient. The correlation of leaf boron content and soil available boron content was not significant. The soil pH, cultivar, rootstock and the age of tree did affect the leaf boron content. The leaves from the orchards with soil pH of 4.5-6.4 demonstrated significantly higher boron contents than with the soil pH of 6.5-8.5. The leaf boron contents in the different cultivars was ranged as Satsuma mandarin > pomelo > valencia orange > sweet orange > tangor > navel orange. The citrus on trifoliate orange and sour pomelo rootstocks had significantly higher leaf boron contents than on Carrizo citrange and red tangerine rootstocks. Compared with the adult citrus trees (above 8 year-old), 6.6% more of leaf samples of younger trees (3 to 8 year-old) contained boron contents in the optimum range (35-100 mg x kg(-1)).

Exogenous spermine pretreatment confers tolerance to combined high-temperature and drought stress in vitro in trifoliate orange seedlings via modulation of antioxidative capacity and expression of stress-related genes.

Spermine (Spm) is thought to play an important role in drought or high-temperature (HT) tolerance. However, it is not clear whether Spm confers similar resistance in the presence of both drought and HT, which often occur simultaneously. In the present study, the trifoliate orange (Poncirus trifoliata (L.) Raf.) seedlings were pretreated with 1 mmol L-1 Spm to evaluate their tolerance to combined drought and HT (45 ºC) stress. Spm-pretreated seedlings showed less leaf wilting, less water loss and less electrolyte leakage than control leaves not treated with Spm within 180 min of treatment. Histochemical staining with diaminobenzidine and nitro blue tetrazolium showed that Spm-pretreated seedlings accumulated less hydrogen peroxide and superoxide than those of control plants 60, 120 and 180 min after treatment when exposed to both drought and HT (45 ºC). However, superoxide dismutase, peroxidase and catalase were significantly more active in Spm-pretreated seedlings than in control seedlings. In addition, Spm-pretreated seedlings showed significantly higher expression of heat shock proteins, abscisic acid (ABA)-responsive element binding factor and 9-cis-epoxycarotenoid dioxygenase 3 than controls either before (0 min) or after (60, 120 and 180 min) combined drought and HT treatment. All of these data suggest that exogenous Spm pretreatment confers tolerance to simultaneously occurring drought and HT stresses. Spm may influence this by activating antioxidant enzymes, increasing the effectiveness of scavenging of reactive oxygen species. It may also increase the expression levels of stress-related genes that protect trifoliate orange seedlings from stress damage.