Plant polycistronic precursors containing non-homologous microRNAs target transcripts encoding functionally related proteins

Functional homologous and non-homologous clusters of MIR genes that co-regulate target mRNA transcripts have been identified in plant

MAP Kinase-Mediated Negative Regulation of Symbiotic Nodule Formation in Medicago truncatula

Mitogen-activated protein kinase (MAPK) signaling cascades play critical roles in various cellular events in plants, including stress responses, innate immunity, hormone signaling, and cell specificity. MAPK-mediated stress signaling is also known to negatively regulate nitrogen-fixing symbiotic interactions, but the molecular mechanism of the MAPK signaling cas-cades underlying the symbiotic nodule development remains largely unknown. We show that the MtMKK5-MtMPK3/6 signaling module negatively regulates the early symbiotic nodule formation, probably upstream of ERN1 (ERF Required for Nodulation 1) and NSP1 (Nod factor Signaling Pathway 1) in Medicago truncatula. The overexpression of MtMKK5 stimulated stress and defense signaling pathways but also reduced nodule formation in M. truncatula roots. Conversely, a MAPK specific inhibitor, U0126, enhanced nodule formation and the expression of an early nodulation marker gene, MtNIN. We found that MtMKK5 directly activates MtMPK3/6 by phosphorylating the TEY motif within the activation loop and that the MtMPK3/6 proteins physically interact with the early nodulation-related transcription factors ERN1 and NSP1. These data suggest that the stress signaling-mediated MtMKK5/MtMPK3/6 module sup-presses symbiotic nodule development via the action of early nodulation transcription factors.115Ysciescopuskc

Early symbiotic responses induced by Sinorhizobium meliloti ilvC mutants in alfalfa

A mutation in the ilvC gene of Sinorhizobium meliloti 1021 determines a symbiotically defective phenotype, ilvC mutants obtained from different S. meliloti wild-type strains are able to induce root hair deformation on alfalfa roots and show variable activation of the common nodulation genes nodABC. All of these mutants are noninfective. The presence of extra copies of nodD3-syrM in an IlvC‒ background does not promote nod expression but allows the detection of low levels of Nod factor production. The sulphation of the Nod factor metabolites, however, is not affected. Furthermore, IlvC‒ strains induce a specific pattern of starch accumulation on alfalfa roots as well as of early nodulin expression. Hence, the pleiotropic action of the ilvC gene in S. meliloti may reveal novel complexities involved in the symbiotic interaction.Instituto de Biotecnologia y Biologia MolecularFacultad de Ciencias Exacta

Unraveling new molecular players involved in the autoregulation of nodulation in Medicago truncatula

The number of legume root nodules resulting from a symbiosis with rhizobia is tightly controlled by the plant. Certain members of the CLAVATA3/Embryo Surrounding Region (CLE) peptide family, specifically MtCLE12 and MtCLE13 in Medicago truncatula, act in the systemic autoregulation of nodulation (AON) pathway that negatively regulates the number of nodules. Little is known about the molecular pathways that operate downstream of the AON-related CLE peptides. Here, by means of a transcriptome analysis, we show that roots ectopically expressing MtCLE13 deregulate only a limited number of genes, including three down-regulated genes encoding lysin motif receptor-like kinases (LysM-RLKs), among which are the nodulation factor (NF) receptor NF Perception gene (NFP) and two up-regulated genes, MtTML1 and MtTML2, encoding Too Much Love (TML)-related Kelch-repeat containing F-box proteins. The observed deregulation was specific for the ectopic expression of nodulation-related MtCLE genes and depended on the Super Numeric Nodules (SUNN) AON RLK. Moreover, overexpression and silencing of these two MtTML genes demonstrated that they play a role in the negative regulation of nodule numbers. Hence, the identified MtTML genes are the functional counterpart of the Lotus japonicus TML gene shown to be central in the AON pathway. Additionally, we propose that the down-regulation of a subset of LysM-RLK-encoding genes, among which is NFP, might contribute to the restriction of further nodulation once the first nodules have been formed

MtNRLK1, a CLAVATA1-like leucine-rich repeat receptor-like kinase upregulated during nodulation in Medicago truncatula

Peptides are signaling molecules regulating various aspects of plant development, including the balance between cell division and differentiation in different meristems. Among those, CLAVATA3/Embryo Surrounding Region-related (CLE-ESR) peptide activity depends on leucine-rich-repeat receptor-like-kinases (LRR-RLK) belonging to the subclass XI. In legume plants, such as the Medicago truncatula model, specific CLE peptides were shown to regulate root symbiotic nodulation depending on the LRR-RLK SUNN (Super Numeric Nodules). Amongst the ten M. truncatula LRR-RLK most closely related to SUNN, only one showed a nodule-induced expression, and was so-called MtNRLK1 (Nodule-induced Receptor-Like Kinase 1). MtNRLK1 expression is associated to root and nodule vasculature as well as to the proximal meristem and rhizobial infection zone in the nodule apex. Except for the root vasculature, the MtNRLK1 symbiotic expression pattern is different than the one of MtSUNN. Functional analyses either based on RNA interference, insertional mutagenesis, and overexpression of MtNRLK1 however failed to identify a significant nodulation phenotype, either regarding the number, size, organization or nitrogen fixation capacity of the symbiotic organs formed

Identification of transcription factors involved in root apex responses to salt stress in Medicago truncatula

The root apex contains meristematic cells that determine root growth and architecture in the soil. Specific transcription factor (TF) genes in this region may integrate endogenous signals and external cues to achieve this. Early changes in transcriptional responses involving TF genes after a salt stress in Medicago truncatula (Mt) roots were analysed using two complementary transcriptomic approaches. Forty-six salt-regulated TF genes were identified using massive quantitative real-time RT-PCR TF profiling in whole roots. In parallel, Mt16K+ microarray analysis revealed 824 genes (including 84 TF sequences) showing significant changes (p < 0.001) in their expression in root apexes after a salt stress. Analysis of salt-stress regulation in root apexes versus whole roots showed that several TF genes have more than 30-fold expression differences including specific members of AP2/EREBP, HD-ZIP, and MYB TF families. Several salt-induced TF genes also respond to other abiotic stresses as osmotic stress, cold and heat, suggesting that they participate in a general stress response. Our work suggests that spatial differences of TF gene regulation by environmental stresses in various root regions may be crucial for the adaptation of their growth to specific soil environments

Early symbiotic responses induced by Sinorhizobium meliloti ilvC mutants in alfalfa

A mutation in the ilvC gene of Sinorhizobium meliloti 1021 determines a symbiotically defective phenotype, ilvC mutants obtained from different S. meliloti wild-type strains are able to induce root hair deformation on alfalfa roots and show variable activation of the common nodulation genes nodABC. All of these mutants are noninfective. The presence of extra copies of nodD3-syrM in an IlvC‒ background does not promote nod expression but allows the detection of low levels of Nod factor production. The sulphation of the Nod factor metabolites, however, is not affected. Furthermore, IlvC‒ strains induce a specific pattern of starch accumulation on alfalfa roots as well as of early nodulin expression. Hence, the pleiotropic action of the ilvC gene in S. meliloti may reveal novel complexities involved in the symbiotic interaction.Instituto de Biotecnologia y Biologia MolecularFacultad de Ciencias Exacta

CEP receptor signalling controls root system architecture in Arabidopsis and Medicago

© 2020 The Authors. New Phytologist © 2020 New Phytologist Trust Root system architecture (RSA) influences the effectiveness of resources acquisition from soils but the genetic networks that control RSA remain largely unclear. We used rhizoboxes, X-ray computed tomography, grafting, auxin transport measurements and hormone quantification to demonstrate that Arabidopsis and Medicago CEP (C-TERMINALLY ENCODED PEPTIDE)-CEP RECEPTOR signalling controls RSA, the gravitropic set-point angle (GSA) of lateral roots (LRs), auxin levels and auxin transport. We showed that soil-grown Arabidopsis and Medicago CEP receptor mutants have a narrower RSA, which results from a steeper LR GSA. Grafting showed that CEPR1 in the shoot controls GSA. CEP receptor mutants exhibited an increase in rootward auxin transport and elevated shoot auxin levels. Consistently, the application of auxin to wild-type shoots induced a steeper GSA and auxin transport inhibitors counteracted the CEP receptor mutant’s steep GSA phenotype. Concordantly, CEP peptides increased GSA and inhibited rootward auxin transport in wild-type but not in CEP receptor mutants. The results indicated that CEP–CEP receptor-dependent signalling outputs in Arabidopsis and Medicago control overall RSA, LR GSA, shoot auxin levels and rootward auxin transport. We propose that manipulating CEP signalling strength or CEP receptor downstream targets may provide means to alter RSA

HSFA1a modulates plant heat stress responses and alters the 3D chromatin organization of enhancer-promoter interactions

The complex and dynamic three-dimensional organization of chromatin within the nucleus makes understanding the control of gene expression challenging, but also opens up possible ways to epigenetically modulate gene expression. Because plants are sessile, they evolved sophisticated ways to rapidly modulate gene expression in response to environmental stress, that are thought to be coordinated by changes in chromatin conformation to mediate specific cellular and physiological responses. However, to what extent and how stress induces dynamic changes in chromatin reorganization remains poorly understood. Here, we comprehensively investigated genome-wide chromatin changes associated with transcriptional reprogramming response to heat stress in tomato. Our data show that heat stress induces rapid changes in chromatin architecture, leading to the transient formation of promoter-enhancer contacts, likely driving the expression of heat-stress responsive genes. Furthermore, we demonstrate that chromatin spatial reorganization requires HSFA1a, a transcription factor (TF) essential for heat stress tolerance in tomato. In light of our findings, we propose that TFs play a key role in controlling dynamic transcriptional responses through 3D reconfiguration of promoter-enhancer contacts