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Author: Gwendolyn K. Kirschner.
The Plant Journal (2024)
Excerpts: "Udvardi and Sonali Roy, a former post-doctoral fellow with Udvardi at the Noble Research Institute and now an assistant professor at Tennessee State University, together with a team of experts on legume rhizobial symbiosis from Oklahoma, Cambridge and Shanghai, analysed the role of GLVs for nodule development and positioning in more detail (Roy et al., 2024)."
"Transcriptional reporter expression in transgenic hairy roots showed that the expression of the five GLVs overlapped at sites of nodule initiation (Figure 1b). Out of these, MtGLV6, MtGLV9 and MtGLV10 were induced by short-term nitrogen deprivation stress, suggesting a role in early stages of symbiosis, such as the dedifferentiation of cortical cells or the regulation of early nodulin genes."
"The nitrogen-induced GLV10 peptide could integrate the nitrogen signal from the soil to adaptation of the root architecture. GLV10p treatment also led to more microcolonies and infection thread initiations. The authors hypothesise that the increase in infection might be a compensation for the reduction in nodule number: The plant initiates more infection threads to make an optimal number of nodules and derive sufficient nitrogen."
Authors: Isabel Cristina Vélez-Bermúdez and Wolfgang Schmidt.
Nature Plants (2024)
Summary: "The functions of a small family of non-secreted peptides, originally identified as critical communicators of the plant’s iron status, have expanded. The involvement of these effectors in disparate signalling cascades underlines the pivotal role peptides have in responses to the environment."
Authors: Wenzhe Yu, Li Luo, Xiangyu Qi, Yuman Cao, Jie An, Zhiguo Xie, Tianming Hu and Peizhi Yang.
Journal of Agricultural and Food Chemistry (2024)
Abstract: "Plant growth-promoting rhizobacteria have been shown to enhance plant tolerance to drought stress through various mechanisms. However, there is limited research on improving drought resistance in alfalfa by genetically modifying PGPR to produce increased levels of cytokinins. Herein, we employed synthetic biology approaches to engineer two novel strains of Sinorhizobium meliloti capable of overproducing trans-Zeatin and investigated their potential in enhancing drought tolerance in alfalfa. Our results demonstrate that alfalfa plants inoculated with these engineered S. meliloti strains exhibited reduced wilting and yellowing while maintaining higher relative water content under drought conditions. The engineered S. meliloti-induced tZ activated the activity of antioxidant enzymes and the accumulation of osmolytes. Additionally, the increased endogenous tZ content in plants alleviated the impact of drought stress on the alfalfa photosynthetic rate. However, under nondrought conditions, inoculation with the engineered S. meliloti strains had no significant effect on alfalfa biomass and nodule formation."
Authors: Karen Velandia, Alejandro Correa-Lozano, Peter M. McGuiness, James B. Reid and Eloise Foo.
New Phytologist (2024)
Abstract: "Gibberellins (GA) have a profound influence on the formation of lateral root organs. However, the precise role this hormone plays in the cell-specific events during lateral root formation, rhizobial infection and nodule organogenesis, including interactions with auxin and cytokinin (CK), is not clear. We performed epidermal- and endodermal-specific complementation of the severely GA-deficient na pea (Pisum sativum) mutant with Agrobacterium rhizogenes. Gibberellin mutants were used to examine the spatial expression pattern of CK (TCSn)- and auxin (DR5)-responsive promoters and hormone levels. We found that GA produced in the endodermis promote lateral root and nodule organogenesis and can induce a mobile signal(s) that suppresses rhizobial infection. By contrast, epidermal-derived GA suppress infection but have little influence on root or nodule development. GA suppress the CK-responsive TCSn promoter in the cortex and are required for normal auxin activation during nodule primordia formation. Our findings indicate that GA regulate the checkpoints between infection thread (IT) penetration of the cortex and invasion of nodule primordial cells and promote the subsequent progression of nodule development. It appears that GA limit the progression and branching of IT in the cortex by restricting CK response and activate auxin response to promote nodule primordia development."
Authors: Wendell J. Pereira, Jade Boyd, Daniel Conde, Paolo M. Triozzi, Kelly M. Balmant, Christopher Dervinis, Henry W. Schmidt, Carolina Boaventura-Novaes, Sanhita Chakraborty, Sara A. Knaack, Yueyao Gao, Frank Alexander Feltus, Sushmita Roy, Jean-Michel Ané, Julia Frugoli and Matias Kirst.
Cell Reports (2024)
Editor's view: Plant nitrogen fixation by rhizobia is agriculture’s most important symbiotic association, but only a few species develop root nodules to house the bacteria. Using single-cell analysis, Pereira et al. dissect the transcriptional program necessary for nodule formation, an essential step for the future introduction of this symbiotic relationship into crops.
Highlights: • Single-cell sequencing of a Medicago mutant captures rare cell response to rhizobia • Root hair and stele cells differentiate to support infection and nodulation • Cortex-derived cellular lineages modulate phytohormone activity in their trajectory • High-dimension gene regulatory network analysis identifies RNS regulators
Abstract: "Legumes establish a symbiotic relationship with nitrogen-fixing rhizobia by developing nodules. Nodules are modified lateral roots that undergo changes in their cellular development in response to bacteria, but the transcriptional reprogramming that occurs in these root cells remains largely uncharacterized. Here, we describe the cell-type-specific transcriptome response of Medicago truncatula roots to rhizobia during early nodule development in the wild-type genotype Jemalong A17, complemented with a hypernodulating mutant (sunn-4) to expand the cell population responding to infection and subsequent biological inferences. The analysis identifies epidermal root hair and stele sub-cell types associated with a symbiotic response to infection and regulation of nodule proliferation. Trajectory inference shows cortex-derived cell lineages differentiating to form the nodule primordia and, posteriorly, its meristem, while modulating the regulation of phytohormone-related genes. Gene regulatory analysis of the cell transcriptomes identifies new regulators of nodulation, including STYLISH 4, for which the function is validated."
Authors: Momoyo Ito, Yuri Tajima, Mari Ogawa-Ohnishi, Hanna Nishida, Shohei Nosaki, Momona Noda, Naoyuki Sotta, Kensuke Kawade, Takehiro Kamiya, Toru Fujiwara, Yoshikatsu Matsubayashi and Takuya Suzaki.
Nature Communications (2024)
Editors view: The authors show IRON MAN peptides have an essential role in symbiotic nitrogen fixation during legume-rhizobium symbiosis. The peptides additionally function to regulate nitrogen homeostasis by controlling nitrogen-iron balance.
Abstract: "Legumes control root nodule symbiosis (RNS) in response to environmental nitrogen availability. Despite the recent understanding of the molecular basis of external nitrate-mediated control of RNS, it remains mostly elusive how plants regulate physiological processes depending on internal nitrogen status. In addition, iron (Fe) acts as an essential element that enables symbiotic nitrogen fixation; however, the mechanism of Fe accumulation in nodules is poorly understood. Here, we focus on the transcriptome in response to internal nitrogen status during RNS in Lotus japonicus and identify that IRON MAN (IMA) peptide genes are expressed during symbiotic nitrogen fixation. We show that LjIMA1 and LjIMA2 expressed in the shoot and root play systemic and local roles in concentrating internal Fe to the nodule. Furthermore, IMA peptides have conserved roles in regulating nitrogen homeostasis by adjusting nitrogen-Fe balance in L. japonicus and Arabidopsis thaliana. These findings indicate that IMA-mediated Fe provision plays an essential role in regulating nitrogen-related physiological processes."
Authors: Qian Wang, Mengmeng Liu, Zhifan Wang, Junrong Li, Ke Liu and Dong Huang.
Frontiers in Microbiology (2024)
Abstract: "Arbuscular mycorrhizal fungi (AMF) can penetrate plant root cortical cells, establish a symbiosis with most land plant species, and form branched structures (known as arbuscules) for nutrient exchange. Plants have evolved a complete plant–AMF symbiosis system to sustain their growth and development under various types of abiotic stress. Here, we highlight recent studies of AM symbiosis and the regulation of symbiosis process. The roles of mycorrhizal symbiosis and host plant interactions in enhancing drought resistance, increasing mineral nutrient uptake, regulating hormone synthesis, improving salt resistance, and alleviating heavy metal stress were also discussed. Overall, studies of AM symbiosis and a variety of abiotic stresses will aid applications of AMF in sustainable agriculture and can improve plant production and environmental safety."
Via Jean-Michel Ané
Authors: Mariel C. Isidra-Arellano, Jawahar Singh and Oswaldo Valdés-López.
Trends in Plant Science (2024)
Abstract: "Strigolactones (SLs) are fundamental to the ability of plants to cope with phosphate deficiency. A recent study by Yuan et al. indicates that the genetic module PHR2/NSP1/NSP2 is crucial in activating SL biosynthesis and signaling under inorganic phosphate (Pi) deficiency. Furthermore, this genetic module is essential for improving Pi and nitrogen homeostasis in rice."
Authors: Gökhan Boyno, Younes Rezaee Danesh, Semra Demir, Necmettin Teniz, José M. Mulet and Rosa Porcel.
International Journal of Molecular Sciences (2023)
Abstract: "Plants, the cornerstone of life on Earth, are constantly struggling with a number of challenges arising from both biotic and abiotic stressors. To overcome these adverse factors, plants have evolved complex defense mechanisms involving both a number of cell signaling pathways and a complex network of interactions with microorganisms. Among these interactions, the relationship between symbiotic arbuscular mycorrhizal fungi (AMF) and strigolactones (SLs) stands as an important interplay that has a significant impact on increased resistance to environmental stresses and improved nutrient uptake and the subsequent enhanced plant growth. AMF establishes mutualistic partnerships with plants by colonizing root systems, and offers a range of benefits, such as increased nutrient absorption, improved water uptake and increased resistance to both biotic and abiotic stresses. SLs play a fundamental role in shaping root architecture, promoting the growth of lateral roots and regulating plant defense responses. AMF can promote the production and release of SLs by plants, which in turn promote symbiotic interactions due to their role as signaling molecules with the ability to attract beneficial microbes. The complete knowledge of this synergy has the potential to develop applications to optimize agricultural practices, improve nutrient use efficiency and ultimately increase crop yields. This review explores the roles played by AMF and SLs in plant development and stress tolerance, highlighting their individual contributions and the synergistic nature of their interaction."
Authors: Juraj Kleman and Radoslava Matusova
Biologia (2023)
Abstract: "The discovery of strigolactones has resulted in a confluence of various research topics like parasitic plants, arbuscular mycorrhizal fungi and phytohormones, which all play a big role in current global agricultural production. Over the past few decades, strigolactone research swiftly gained a spotlight, as to reveal their possible functions within plants and also the surrounding organisms in the rhizosphere. In this review, we explore the discovered functions of strigolactones with the main focus on the chemical structure of strigolactones and how it relates to the various biological responses they cause. We highlight their involvement in plant responses to abiotic stressors, like lack of available nutrients, high salinity, drought, extreme temperatures and presence of potentially toxic elements of environmental importance, while reflecting upon the strigolactone-mediated plant associations with arbuscular mycorrhizal fungi and nodule-forming, N-fixing bacteria. Furthermore, we elaborate on the current state of applied strigolactone research in agriculture and the probable bright future these compounds have in commercial use and what hurdles need to be overcome before they can be fully utilized."
Authors: Songkui Cui, Shoko Inaba, Takuya Suzaki and Satoko Yoshida.
Current Opinion in Plant Biology (2023)
Abstract: "Plants have evolved diverse strategies to meet their nutritional needs. Parasitic plants employ haustoria, specialized structures that facilitate invasion of host plants and nutrient acquisition. Legumes have adapted to nitrogen-limited conditions by developing nodules that accommodate nitrogen-fixing rhizobia. The formation of both haustoria and nodules is induced by signals originating from the interacting organisms, namely host plants and rhizobial bacteria, respectively. Emerging studies showed that both organogenesis crucially involves plant hormones such as auxin, cytokinins, and ethylene and also integrate nutrient availability, particularly nitrogen. In this review, we discuss recent advances on hormonal and environmental control of haustoria and nodules development with side-by-side comparison. These underscore the remarkable plasticity of plant organogenesis."
Authors: Bouchra Benmrid, Cherki Ghoulam, Youssef Zeroual, Lamfeddal Kouisni and Adnane Bargaz.
Communications Biology (2023)
Abstract: "Ensuring plant resilience to drought and phosphorus (P) stresses is crucial to support global food security. The phytobiome, shaped by selective pressures, harbors stress-adapted microorganisms that confer host benefits like enhanced growth and stress tolerance. Intercropping systems also offer benefits through facilitative interactions, improving plant growth in water- and P-deficient soils. Application of microbial consortia can boost the benefits of intercropping, although questions remain about the establishment, persistence, and legacy effects within resident soil microbiomes. Understanding microbe- and plant-microbe dynamics in drought-prone soils is key. This review highlights the beneficial effects of rhizobacterial consortia-based inoculants in legume-cereal intercropping systems, discusses challenges, proposes a roadmap for development of P-solubilizing drought-adapted consortia, and identifies research gaps in crop-microbe interactions. This review discusses the intricate interactions between rhizobacterial consortia-based inoculants, cropping systems, and soil abiotic stresses, focusing specifically on drought and phosphorous deficiency.
Author: Gwendolyn K. Kirschner
The Plant Journal (2023)
Excerpts: "For the highlighted publication, Van Dingenen, Goormachtig and colleagues therefore set out to analyse the impact of strigolactone biosynthesis and signalling on nodule development in pea (Van Dingenen et al., 2023)."
"They found that the total nodule number was the same as in the wild type, but the percentage and size of red nodules - indicative of active nitrogen fixation - in mutants was higher, suggesting that strigolactone signalling and biosynthesis are involved in the regulation of nodule development and functioning."
"Transcript levels of senescence marker genes were also enhanced in all rms mutants, whereas the transcript levels of leghemoglobin genes were decreased, suggesting that the development of the nodules in rms mutants was faster than in the wild type."
"Spatial analysis showed that peak intensities of all sugars were lower in the rms4 nodule than in wild-type nodules (Figure 1b), suggesting that the faster-developing nodules in rms4 have an increased carbon turnover which could lead to accelerated senescence. In summary, strigolactones control nodule development possibly by aligning the carbon input to nodule size (Figure 1c)."
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Authors: Mengdi Fu, Xiaolei Yao, Xiaolin Li, Jing Liu, Mengyan Bai, Zijun Fang, Jiming Gong, Yuefeng Guan and Fang Xie.
The Plant Journal (2024)
Significance Statement: GmNLP1 and GmNLP4 activate nitrate-induced CLE peptides NIC1a/b to mediate nitrate-regulated root nodulation.
Abstract: "Symbiotic nitrogen fixation is an energy-intensive process, to maintain the balance between growth and nitrogen fixation, high concentrations of nitrate inhibit root nodulation. However, the precise mechanism underlying the nitrate inhibition of nodulation in soybean remains elusive. In this study, CRISPR-Cas9-mediated knockout of GmNLP1 and GmNLP4 unveiled a notable nitrate-tolerant nodulation phenotype. GmNLP1b and GmNLP4a play a significant role in the nitrate-triggered inhibition of nodulation, as the expression of nitrate-responsive genes was largely suppressed in Gmnlp1b and Gmnlp4a mutants. Furthermore, we demonstrated that GmNLP1b and GmNLP4a can bind to the promoters of GmNIC1a and GmNIC1b and activate their expression. Manipulations targeting GmNIC1a and GmNIC1b through knockdown or overexpression strategies resulted in either increased or decreased nodule number in response to nitrate. Additionally, transgenic roots that constitutively express GmNIC1a or GmNIC1b rely on both NARK and hydroxyproline O-arabinosyltransferase RDN1 to prevent the inhibitory effects imposed by nitrate on nodulation. In conclusion, this study highlights the crucial role of the GmNLP1/4-GmNIC1a/b module in mediating high nitrate-induced inhibition of nodulation."
Authors: María Isabel Puga, César Poza-Carrión, Iris Martinez-Hevia, Laura Perez-Liens and Javier Paz-Ares
Journal of Plant Research (2024)
Abstract: "Phosphorus is indispensable for plant growth and development, with its status crucial for determining crop productivity. Plants have evolved various biochemical, morphological, and developmental responses to thrive under conditions of low P availability, as inorganic phosphate (Pi), the primary form of P uptake, is often insoluble in soils. Over the past 25 years, extensive research has focused on understanding these responses, collectively forming the Pi starvation response system. This effort has not only expanded our knowledge of strategies to cope with Pi starvation (PS) but also confirmed their adaptive significance. Moreover, it has identified and characterized numerous components of the intricate regulatory network governing P homeostasis. This review emphasizes recent advances in PS signaling, particularly highlighting the physiological importance of local PS signaling in inhibiting primary root growth and uncovering the role of TORC1 signaling in this process. Additionally, advancements in understanding shoot-root Pi allocation and a novel technique for studying Pi distribution in plants are discussed. Furthermore, emerging data on the regulation of plant-microorganism interactions by the PS regulatory system, crosstalk between the signaling pathways of phosphate starvation, phytohormones and immunity, and recent studies on natural variation in Pi homeostasis are addressed.
Authors: Clare Hurst and Miriam L. Gifford.
Development (2024)
Excepts: "Legumes form a symbiotic relationship with bacteria called rhizobia. The rhizobia fix atmospheric dinitrogen, which is used by the plant as a nitrogen resource, and take up molecules, including carbon compounds, from the plant. Rhizobia are housed in nodules that develop on roots after a series of orchestrated stages that are triggered by the perception and entry of rhizobia at root hairs (reviewed by Luo et al., 2023). Study of this relationship and the mechanisms that govern nodule formation and inhibition may reveal targets to promote enhanced nodulation efficiency and increased nitrogen acquisition for the plant. Phytohormones have been shown to play a key role in both nodule formation and inhibition; therefore, a better understanding of hormonal regulatory activity could provide options for such enhancement. To address this, Drapek and colleagues (2023 preprint) focus on the dynamics of gibberellin (GA), a phytohormone previously identified as both a positive and negative regulator of nodulation (Rizza et al., 2017; Fonouni-Farde et al., 2016).
"In conclusion, this study analysed the spatial and temporal accumulation of GA, the interactions between GA and key nodule identity regulatory genes, and tested the importance of GA biosynthesis enzymes in nodule formation. The work provides strong evidence that GA is a potential determinator between lateral root formation and nodulation, and helps to explain previous contradictory findings related to the importance of GA, as well as cytokinin, in these processes."
Authors: Sonali Roy, Ivone Torres-Jerez, Shulan Zhang, Wei Liu, Katharina Schiessl, Divya Jain, Clarissa Boschiero, Hee-Kyung Lee, Nicholas Krom, Patrick X. Zhao, Jeremy D. Murray, Giles E. D. Oldroyd, Wolf-Rüdiger Scheible and Michael Udvardi.
The Plant Journal (2024)
Significance Statement: Nodule positioning is an understudied trait, yet it determines the length of the root that can support nodule formation and consequently the total number of functional nodules formed. We identify genetic factors called GOLVEN peptides that alter nodule and lateral root positioning on the primary root along with several other traits including nodule organ initiation and root architecture.
Abstract: "The conservation of GOLVEN (GLV)/ROOT MERISTEM GROWTH FACTOR (RGF) peptide encoding genes across plant genomes capable of forming roots or root-like structures underscores their potential significance in the terrestrial adaptation of plants. This study investigates the function and role of GOLVEN peptide-coding genes in Medicago truncatula. Five out of fifteen GLV/RGF genes were notably upregulated during nodule organogenesis and were differentially responsive to nitrogen deficiency and auxin treatment. Specifically, the expression of MtGLV9 and MtGLV10 at nodule initiation sites was contingent upon the NODULE INCEPTION transcription factor. Overexpression of these five nodule-induced GLV genes in hairy roots of M. truncatula and application of their synthetic peptide analogues led to a decrease in nodule count by 25–50%. Uniquely, the GOLVEN10 peptide altered the positioning of the first formed lateral root and nodule on the primary root axis, an observation we term ‘noduletaxis’; this decreased the length of the lateral organ formation zone on roots. Histological section of roots treated with synthetic GOLVEN10 peptide revealed an increased cell number within the root cortical cell layers without a corresponding increase in cell length, leading to an elongation of the root likely introducing a spatiotemporal delay in organ formation. At the transcription level, the GOLVEN10 peptide suppressed expression of microtubule-related genes and exerted its effects by changing expression of a large subset of Auxin responsive genes. These findings advance our understanding of the molecular mechanisms by which GOLVEN peptides modulate root morphology, nodule ontogeny, and interactions with key transcriptional pathways."
Authors: Tak Lee, Martina Orvosova, Morgane Batzenschlager, Marcelo Bueno Batista, Paul C. Bailey, Nadia A. Mohd-Radzman, Aram Gurzadyan, Naomi Stuer, Kirankumar S. Mysore, Jiangqi Wen, Thomas Ott, Giles E.D. Oldroyd and Katharina Schiessl.
Current Biology (2024)
Editor's view: To host N-fixing bacteria, legumes grow root nodules initiated via a lateral root program. Lee et al. show that two LSH transcription factors mediate the divergence between lateral roots and nodules by promoting the proliferation of colonizable cells. LSH1/LSH2 regulate the nodule identity genes NF-YA1 and NOOT1/NOOT2 and auxin/cytokinin dynamics.
Highlights: • LSHs are key regulators of symbiotic root nodule differentiation downstream of NIN • LSHs promote cell divisions in the root cortex that support bacterial colonization • LSHs promote expression of the nodule organ identity genes NOOT1/NOOT2 and NF-YA1 • LSHs repress PLETHORA root regulators and modulate auxin-cytokinin dynamics
Abstract: "Legumes produce specialized root nodules that are distinct from lateral roots in morphology and function, with nodules intracellularly hosting nitrogen-fixing bacteria. We have previously shown that a lateral root program underpins nodule initiation, but there must be additional developmental regulators that confer nodule identity. Here, we show two members of the LIGHT-SENSITIVE SHORT HYPOCOTYL (LSH) transcription factor family, predominantly known to define shoot meristem complexity and organ boundaries, function as regulators of nodule organ identity. In parallel to the root initiation program, LSH1/LSH2 recruit a program into the root cortex that mediates the divergence into nodules, in particular with cell divisions in the mid-cortex. This includes regulation of auxin and cytokinin, promotion of NODULE ROOT1/2 and Nuclear Factor YA1, and suppression of the lateral root program. A principal outcome of LSH1/LSH2 function is the production of cells able to accommodate nitrogen-fixing bacteria, a key feature unique to nodules."
Authors: Andrea Genre, Serena Capitanio and Paola Bonfante.
In Book: Fungal Associations (2024)
Abstract: "Mycorrhizas are mutualistic interactions that the majority of land plants establish with a heterogeneous group of soil fungi; their distribution and diversity have supported the success of plants on the planet. Among all different types of mycorrhizas, arbuscular mycorrhiza (AM) is the most ancient and the most common in host plants of all major crops. The functional core of AM is a finely branched fungal structure called the arbuscule. Arbuscules are hosted inside living root cells, within a specialized cell compartment that is generated through a precise sequence of molecular and cellular events. Over the last 10 years, the application of novel technologies, such as genome sequencing, high-throughput transcriptomics, and live cell imaging, has generated substantial advances in our knowledge of such events. Here, we present a synopsis of the recent literature on the interactions between AM fungi and their hosts, with an evolutionary-developmental focus on the intimate contact that develops between plant cells and fungal hyphae, in terms of molecular signaling, nutrient exchange, and cell organization."
Authors: Zhen Liu, Xiao-Feng Cheng, Ying-Ning Zou, Anoop Kumar Srivastava, Mashael Daghash Alqahtani and Qiang-Sheng Wu.
Environmental and Experimental Botany (2024)
Highlights • AMF boosted plant growth as well as POD and CAT activity in roots under drought. • Nine GA species were detected in roots, with GA4 only found in AMF roots. • AMF reduced GA3, but increased GA5, GA9, and GA15 levels under drought. • AMF up-regulated the expression of PtCPS, PtPKS, PtKO, PtGA20ox, PtGA3ox, and PtGA2ox under drought. • AMF increased the expression of the DELLA genes PtGaipb and PtGai under drought.
Abstract: "Gibberellins (GAs), an important endogenous hormone, serve a crucial regulatory role in plants’ resistance to environmental stress, whereas it is unclear whether and how arbuscular mycorrhizal fungi (AMF) regulate the profile of GAs in plants exposed to soil water deficit (SWD). This study aimed to analyze how Rhizoglomus intraradices inoculation affected plant growth performance, antioxidant enzyme activities, and the composition, synthesis, metabolism, and signaling pathways of GAs in the roots of trifoliate orange (Poncirus trifoliata) under a 10-week SWD. Although SWD decreased both root AMF colonization and soil hyphal length, mycorrhizal plants nevertheless outperformed non-mycorrhizal plants in terms of growth performance, as well as peroxidase (70.0%) and catalase (149.2%) activities, indicating greater drought tolerance. A total of nine GAs compositions were detected in the roots, with bioactive GA4 exclusively found in AMF roots. AMF colonization significantly reduced bioactive GA3 levels by 37.9%, while it increased inactive GA8, GA9, and GA15 levels under SWD by 522.2%, 100.0%, and 2500.0%. Inoculation with AMF also up-regulated the expression of PtCPS, PtPKS, and PtKO in GA synthesis pathways of roots and the expression of PtGA20ox, PtGA3ox, and PtGA2ox in GA metabolisms under SWD. In addition, the expression of DELLA genes PtGaipb and PtGai associated with GA signaling pathways was further up-regulated under SWD by AMF inoculation. It is concluded that AMF regulated the composition, synthesis, and deactivation of GAs in roots to promote plant growth, along with an increase in PtGaipb and PtGai expression to possibly initiate mycorrhizal signaling pathways in response to SWD."
Authors: Carole Laffont and Florian Frugier.
New Phytologist (2024)
Abstract: "C-terminally encoded peptides (CEP) signaling peptides are drivers of systemic pathways regulating nitrogen (N) acquisition in different plants, from Arabidopsis to legumes, depending on mineral N availability (e.g. nitrate) and on the whole plant N demand. Recent studies in the Medicago truncatula model legume revealed how root-produced CEP peptides control the root competence for endosymbiosis with N fixing rhizobia soil bacteria through the activity of the Compact Root Architecture 2 (CRA2) CEP receptor in shoots. Among CEP genes, MtCEP7 was shown to be tightly linked to nodulation, and the dynamic temporal regulation of its expression reflects the plant ability to maintain a different symbiotic root competence window depending on the symbiotic efficiency of the rhizobium strain, as well as to reinitiate a new window of root competence for nodulation."
Authors: Michael Taleski, Marvin Jin, Kelly Chapman, Katia Taylor, Courtney Winning, Manuel Frank, Nijat Imin and Michael A. Djordjevic.
Journal of Experimental Botany (2024)
Abstract: "A growing understanding is emerging of the roles of peptide hormones in local- and long-distance signalling that coordinates plant growth and development as well as responses to the environment. C-TERMINALLY ENCODED PEPTIDE (CEP) signalling triggered by its interaction with CEP RECEPTOR 1 (CEPR1) is known to play roles in systemic nitrogen (N)-demand signalling, legume nodulation, and root system architecture. Recent research provides further insight into how CEP signalling operates, which involves diverse downstream targets and interactions with other hormone pathways. Additionally, there is emerging evidence of CEP signalling playing roles in N-allocation, root responses to carbon levels, the uptake of other soil nutrients such as phosphorus and sulphur, root responses to arbuscular mycorrhizal fungi, plant immunity, and reproductive development. These findings suggest CEP signalling more broadly coordinates growth across the whole plant in response to diverse environmental cues. Moreover, CEP signalling and function appears to be conserved in angiosperms. In this manuscript, we review the recent advances in CEP biology with a focus on soil nutrient uptake, root system architecture and organogenesis, and roles in plant-microbe interactions. Furthermore, we address knowledge gaps and future directions in this research field."
Author: Yoshiya Seto.
Bioscience, Biotechnology, and Biochemistry (2023)
Abstract: "Strigolactones (SLs) are a class of terpenoid lactones initially identified as seed germination stimulants for root parasitic plants more than 50 years ago. Long after this initial discovery, SLs were re-characterized as the symbiotic signals for arbuscular mycorrhizal fungi that supply inorganic nutrients, such as phosphate, to their host plants. In 2008, SLs were found to be endogenous plant hormones that regulate shoot branching in plants. The discovery of SLs as a new class of plant hormones has significantly advanced research in this field. Studies over the past 15 years have elucidated almost the entire pathway of SL biosynthesis and the overall mechanism of its signalling. This review summarizes research on the SL biosynthetic pathway, and the current state of knowledge of the SL perception mechanism."
Authors: Guan-Ting Erica Chen, Jian You Wang, Cristina Votta, Justine Braguy, Muhammad Jamil, Gwendolyn K. Kirschner, Valentina Fiorilli, Lamis Berqdar, Aparna Balakrishna, Ikram Blilou, Luisa Lanfranco and Salim Al-Babili.
PNAS (2023)
Significance: Strigolactones (SLs) are multifunctional, structurally diverse secondary metabolites fulfilling the function of a hormone. Whether a particular SL exerts specific functions is one of the most important questions in SL biology. Here, we generated and characterized rice mutants lacking the common SLs 4-deoxyorobanchol and/or its derivative orobanchol, which represent one of the two SL subfamilies, i.e., canonical SLs. We show that 4-deoxyorobanchol is not a determinant of shoot branching, but has a specific function as a regulator of shoot, root, and panicle growth. Accumulation of 4-deoxyorobanchol affects auxin homeostasis and negatively impacts the symbiosis with mycorrhizal fungi. Our data reveal specific hormonal functions of canonical SLs and pave the way for targeted modulation of rice architecture and rhizospheric interactions.
Abstract: "Strigolactones (SLs) regulate many developmental processes, including shoot-branching/tillering, and mediate rhizospheric interactions. SLs originate from carlactone (CL) and are structurally diverse, divided into a canonical and a noncanonical subfamily. Rice contains two canonical SLs, 4-deoxyorobanchol (4DO) and orobanchol (Oro), which are common in different plant species. The cytochrome P450 OsMAX1-900 forms 4DO from CL through repeated oxygenation and ring closure, while the homologous enzyme OsMAX1-1400 hydroxylates 4DO into Oro. To better understand the biological function of 4DO and Oro, we generated CRISPR/Cas9 mutants disrupted in OsMAX1-1400 or in both OsMAX1-900 and OsMAX1-1400. The loss of OsMAX1-1400 activity led to a complete lack of Oro and an accumulation of its precursor 4DO. Moreover, Os1400 mutants showed shorter plant height, panicle and panicle base length, but no tillering phenotype. Hormone quantification and transcriptome analysis of Os1400 mutants revealed elevated auxin levels and changes in the expression of auxin-related, as well as of SL biosynthetic genes. Interestingly, the Os900/1400 double mutant lacking both Oro and 4DO did not show the observed Os1400 architectural phenotypes, indicating their being a result of 4DO accumulation. Treatment of wild-type plants with 4DO confirmed this assumption. A comparison of the Striga seed germinating activity and the mycorrhization of Os900, Os900/1400, and Os1400 loss-of-function mutants demonstrated that the germination activity positively correlates with 4DO content while disrupting OsMAX1-1400 has a negative impact on mycorrhizal symbiosis. Taken together, our paper deciphers the biological function of canonical SLs in rice and reveals their particular contributions to establishing architecture and rhizospheric communications."
Authors: Chihiro Miura, Yuki Furui, Tatsuki Yamamoto, Yuri Kanno, Masaya Honjo, Katsushi Yamaguchi, Kenji Suetsugu, Takahiro Yagame, Mitsunori Seo, Shuji Shigenobu, Masahide Yamato and Hironori Kaminaka.
Plant Physiology (2023)
Abstract: "Orchids parasitically depend on external nutrients from mycorrhizal fungi for seed germination. Previous findings suggest that orchids utilize a genetic system of mutualistic arbuscular mycorrhizal (AM) symbiosis, in which the plant hormone gibberellin (GA) negatively affects fungal colonization and development, to establish parasitic symbiosis. Although GA generally promotes seed germination in photosynthetic plants, previous studies have reported low sensitivity of GA in seed germination of mycoheterotrophic orchids where mycorrhizal symbiosis occurs concurrently. To elucidate the connecting mechanisms of orchid seed germination and mycorrhizal symbiosis at the molecular level, we investigated the effect of GA on a hyacinth orchid (Bletilla striata) seed germination and mycorrhizal symbiosis using asymbiotic and symbiotic germination methods. Additionally, we compared the transcriptome profiles between asymbiotically and symbiotically germinated seeds. Exogenous GA negatively affected seed germination and fungal colonization, and endogenous bioactive GA was actively converted to the inactive form during seed germination. Transcriptome analysis showed that B. striata shared many of the induced genes between asymbiotically and symbiotically germinated seeds, including GA metabolism- and signaling-related genes and AM-specific marker homologs. Our study suggests that orchids have evolved in a manner that they do not use bioactive GA as a positive regulator of seed germination and instead auto-activate the mycorrhizal symbiosis pathway through GA inactivation to accept the fungal partner immediately during seed germination."
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