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Gühl K, Holmer R, Xiao TT, Shen D, Wardhani TAK, Geurts R, van Zeijl A, Kohlen W. The Effect of Exogenous Nitrate on LCO Signalling, Cytokinin Accumulation, and Nodule Initiation in Medicago truncatula. Genes (Basel) 2021; 12:genes12070988. [PMID: 34203444 PMCID: PMC8305252 DOI: 10.3390/genes12070988] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Revised: 06/23/2021] [Accepted: 06/24/2021] [Indexed: 01/21/2023] Open
Abstract
Nitrogen fixation by rhizobia is a highly energy-demanding process. Therefore, nodule initiation in legumes is tightly regulated. Environmental nitrate is a potent inhibitor of nodulation. However, the precise mechanism by which this agent (co)regulates the inhibition of nodulation is not fully understood. Here, we demonstrate that in Medicago truncatula the lipo-chitooligosaccharide-induced accumulation of cytokinins is reduced in response to the application of exogenous nitrate. Under permissive nitrate conditions, perception of rhizobia-secreted signalling molecules leads to an increase in the level of four cytokinins (i.e., iP, iPR, tZ, and tZR). However, under high-nitrate conditions, this increase in cytokinins is reduced. The ethylene-insensitive mutant Mtein2/sickle, as well as wild-type plants grown in the presence of the ethylene biosynthesis inhibitor 2-aminoethoxyvinyl glycine (AVG), is resistant to the inhibition of nodulation by nitrate. This demonstrates that ethylene biosynthesis and perception are required to inhibit nodule organogenesis under high-nitrate conditions.
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Affiliation(s)
- Kerstin Gühl
- Laboratory of Molecular Biology, Department of Plant Sciences, Wageningen University & Research, 6708 PB Wageningen, The Netherlands; (K.G.); (R.H.); (T.T.X.); (D.S.); (T.A.K.W.); (R.G.); (A.v.Z.)
| | - Rens Holmer
- Laboratory of Molecular Biology, Department of Plant Sciences, Wageningen University & Research, 6708 PB Wageningen, The Netherlands; (K.G.); (R.H.); (T.T.X.); (D.S.); (T.A.K.W.); (R.G.); (A.v.Z.)
- Bioinformatics Group, Department of Plant Sciences, Wageningen University, 6708 PB Wageningen, The Netherlands
| | - Ting Ting Xiao
- Laboratory of Molecular Biology, Department of Plant Sciences, Wageningen University & Research, 6708 PB Wageningen, The Netherlands; (K.G.); (R.H.); (T.T.X.); (D.S.); (T.A.K.W.); (R.G.); (A.v.Z.)
| | - Defeng Shen
- Laboratory of Molecular Biology, Department of Plant Sciences, Wageningen University & Research, 6708 PB Wageningen, The Netherlands; (K.G.); (R.H.); (T.T.X.); (D.S.); (T.A.K.W.); (R.G.); (A.v.Z.)
| | - Titis A. K. Wardhani
- Laboratory of Molecular Biology, Department of Plant Sciences, Wageningen University & Research, 6708 PB Wageningen, The Netherlands; (K.G.); (R.H.); (T.T.X.); (D.S.); (T.A.K.W.); (R.G.); (A.v.Z.)
| | - René Geurts
- Laboratory of Molecular Biology, Department of Plant Sciences, Wageningen University & Research, 6708 PB Wageningen, The Netherlands; (K.G.); (R.H.); (T.T.X.); (D.S.); (T.A.K.W.); (R.G.); (A.v.Z.)
| | - Arjan van Zeijl
- Laboratory of Molecular Biology, Department of Plant Sciences, Wageningen University & Research, 6708 PB Wageningen, The Netherlands; (K.G.); (R.H.); (T.T.X.); (D.S.); (T.A.K.W.); (R.G.); (A.v.Z.)
| | - Wouter Kohlen
- Laboratory of Molecular Biology, Department of Plant Sciences, Wageningen University & Research, 6708 PB Wageningen, The Netherlands; (K.G.); (R.H.); (T.T.X.); (D.S.); (T.A.K.W.); (R.G.); (A.v.Z.)
- Correspondence:
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Mamenko TP, Kots SY, Khomenko YO. The intensity of ethylene release by soybean plants under the influence of fungicides in the early stages of legume-rhizobial symbiosis. REGULATORY MECHANISMS IN BIOSYSTEMS 2020. [DOI: 10.15421/022014] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The effect of pre-sowing treatment of soybean seeds with fungicides on the intensity of ethylene release, the processes of nodulation and nitrogen fixation in different symbiotic systems in the early stages of ontogenesis were investigated. The objects of the study were selected symbiotic systems formed with the participation of soybean (Glycine max (L.) Merr.) Diamond variety, strains Bradyrhizobium japonicum 634b (active, virulent) and 604k (inactive, highly virulent) and fungicides Maxim XL 035 PS (fludioxonil, 25 g/L, metalaxyl, 10 g/L), and Standak Top (fipronil, 250 g/L, thiophanate methyl, 225 g/L, piraclostrobin, 25 g/L). Before sowing, the seeds of soybean were treated with solutions of fungicides, calculated on the basis of one rate of expenditure of the active substance of each preparation indicated by the producer per ton of seed. One part of the seeds treated with fungicides was inoculated with rhizobium culture for 1 h (the titre of bacteria was 107 cells/mL). To conduct the research we used microbiological, physiological, biochemical methods, gas chromatography and spectrophotometry. It is found that, regardless of the effectiveness of soybean rhizobial symbiosis, the highest level of ethylene release by plants was observed in the stages of primordial leaf and first true leaf. This is due to the initial processes of nodulation – the laying of nodule primordia and the active formation of nodules on the roots of soybeans. The results show that with the participation of fungicides in different symbiotic systems, there are characteristic changes in phytohormone synthesis in the primordial leaf stage, when the nodule primordia are planted on the root system of plants. In particular, in the ineffective symbiotic system, the intensity of phytohormone release decreases, while in the effective symbiotic system it increases. At the same time, a decrease in the number of nodules on soybean roots inoculated with an inactive highly virulent rhizobia 604k strain due to the action of fungicides and an increase in their number in variants with co-treatment of fungicides and active virulent strain 634b into the stage of the second true leaf were revealed. It was shown that despite a decrease in the mass of root nodules, there is an increase in their nitrogen-fixing activity in an effective symbiotic system with the participation of fungicides in the stage of the second true leaf. The highest intensity of ethylene release in both symbiotic systems was recorded in the stage of the first true leaf, which decreased in the stage of the second true leaf and was independent of the nature of the action of the active substances of fungicides. The obtained data prove that the action of fungicides changes the synthesis of ethylene by soybean plants, as well as the processes of nodulation and nitrogen fixation, which depend on the efficiency of the formed soybean-rhizobial systems and their ability to realize their symbiotic potential under appropriate growing conditions.
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Deinum EE, Kohlen W, Geurts R. Quantitative modelling of legume root nodule primordium induction by a diffusive signal of epidermal origin that inhibits auxin efflux. BMC PLANT BIOLOGY 2016; 16:254. [PMID: 27846795 PMCID: PMC5109694 DOI: 10.1186/s12870-016-0935-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Accepted: 10/27/2016] [Indexed: 05/08/2023]
Abstract
BACKGROUND Rhizobium nitrogen fixation in legumes takes place in specialized organs called root nodules. The initiation of these symbiotic organs has two important components. First, symbiotic rhizobium bacteria are recognized at the epidermis through specific bacterially secreted lipo-chitooligosaccharides (LCOs). Second, signaling processes culminate in the formation of a local auxin maximum marking the site of cell divisions. Both processes are spatially separated. This separation is most pronounced in legumes forming indeterminate nodules, such as model organism Medicago truncatula, in which the nodule primordium is formed from pericycle to most inner cortical cell layers. RESULTS We used computer simulations of a simplified root of a legume that can form indeterminate nodules. A diffusive signal that inhibits auxin transport is produced in the epidermis, the site of rhizobium contact. In our model, all cells have the same response characteristics to the diffusive signal. Nevertheless, we observed the fastest and strongest auxin accumulation in the pericycle and inner cortex. The location of these auxin maxima correlates with the first dividing cells of future nodule primordia in M. truncatula. The model also predicts a transient reduction of the vascular auxin concentration rootward of the induction site as is experimentally observed. We use our model to investigate how competition for the vascular auxin source could contribute to the regulation of nodule number and spacing. CONCLUSION Our simulations show that the diffusive signal may invoke the strongest auxin accumulation response in the inner root layers, although the signal itself is strongest close to its production site.
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Affiliation(s)
- Eva E. Deinum
- Mathematical and Statistical methods group, Wageningen University, Droevendaalsesteeg 1PB, Wageningen, 6708 the Netherlands
- FOM institute AMOLF, Science Park 104XG, Amsterdam, 1098 the Netherlands
| | - Wouter Kohlen
- Laboratory for Molecular Biology, Wageningen University, Droevendaalsesteeg 1, Wageningen, 6708 PB the Netherlands
| | - René Geurts
- Laboratory for Molecular Biology, Wageningen University, Droevendaalsesteeg 1, Wageningen, 6708 PB the Netherlands
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Guinel FC. Ethylene, a Hormone at the Center-Stage of Nodulation. FRONTIERS IN PLANT SCIENCE 2015; 6:1121. [PMID: 26834752 PMCID: PMC4714629 DOI: 10.3389/fpls.2015.01121] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Accepted: 11/26/2015] [Indexed: 05/19/2023]
Abstract
Nodulation is the result of a beneficial interaction between legumes and rhizobia. It is a sophisticated process leading to nutrient exchange between the two types of symbionts. In this association, within a nodule, the rhizobia, using energy provided as photosynthates, fix atmospheric nitrogen and convert it to ammonium which is available to the plant. Nodulation is recognized as an essential process in nitrogen cycling and legume crops are known to enrich agricultural soils in nitrogenous compounds. Furthermore, as they are rich in nitrogen, legumes are considered important as staple foods for humans and fodder for animals. To tightly control this association and keep it mutualistic, the plant uses several means, including hormones. The hormone ethylene has been known as a negative regulator of nodulation for almost four decades. Since then, much progress has been made in the understanding of both the ethylene signaling pathway and the nodulation process. Here I have taken a large view, using recently obtained knowledge, to describe in some detail the major stages of the process. I have not only reviewed the steps most commonly covered (the common signaling transduction pathway, and the epidermal and cortical programs), but I have also looked into steps less understood (the pre-infection step with the plant defense response, the bacterial release and the formation of the symbiosome, and nodule functioning and senescence). After a succinct review of the ethylene signaling pathway, I have used the knowledge obtained from nodulation- and ethylene-related mutants to paint a more complete picture of the role played by the hormone in nodule organogenesis, functioning, and senescence. It transpires that ethylene is at the center of this effective symbiosis. It has not only been involved in most of the steps leading to a mature nodule, but it has also been implicated in host immunity and nodule senescence. It is likely responsible for the activation of other hormonal signaling pathways. I have completed the review by citing three studies which makes one wonder whether knowledge gained on nodulation in the last decades is ready to be transferred to agricultural fields.
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Chan PK, Biswas B, Gresshoff PM. Classical ethylene insensitive mutants of the Arabidopsis EIN2 orthologue lack the expected 'hypernodulation' response in Lotus japonicus. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2013; 55:395-408. [PMID: 23452324 DOI: 10.1111/jipb.12040] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Three independent ethylene insensitive mutants were selected from an EMS- mutagenized population of Lotus japonicus MG-20 (Miyakojima). The mutants, called 'Enigma', were mutated in the LjEIN2a gene from Lotus chromosome 1, sharing significant homology with Arabidopsis EIN2 (ethylene-insensitive2). All three alleles showed classical ethylene insensitivity phenotypes (e.g., Triple Response), but lacked the increased nodulation phenotype commonly associated with ethylene insensitivity. Indeed, all showed a marginal reduction in nodule number per plant, a phenotype that is enigmatic to sickle, an ethylene-insensitive EIN2 mutant in Medicago truncatula. In contrast to wild type, but similar to an ETR1-1 ethylene ethylene-insensitive transgenic of L. japonicus, enigma mutants formed nodules in between the protoxylem poles, demonstrating the influence of ethylene on radial positioning. Suppression of nodule numbers by nitrate and colonisation by mycorrhizal fungi in the enigma-1 mutant were indistinguishable from the wild-type MG-20. However, reflecting endogenous ethylene feedback, the enigma-1 mutant released more than twice the wild-type amount of ethylene. enigma-1 had a moderate reduction in growth, greater root mass (and lateral root formation), delayed flowering and ripening, smaller pods and seeds. Expression analysis of ethylene-regulated genes, such as ETR1, NRL1 (neverripe-like 1), and EIL3 in shoots and roots of enigma-1 and MG-20 illustrated that the ethylene-insensitive mutation strongly affected transcriptional responses in the root. These mutants open the possibility that EIN2 in L. japonicus, a determinate nodulating legume, acts in a more complex fashion possibly through the presence of a duplicated copy of LjEIN2.
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Affiliation(s)
- Pick Kuen Chan
- Australian Research Council Centre of Excellence for Integrative Legume Research, The University of Queensland, St. Lucia, Brisbane QLD 4072, Australia
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