RESUMEN
Many plant-encoded E3 ligases are known to be involved in plant defense. Here, we report a novel role of E3 ligase SALT- AND DROUGHT-INDUCED RING FINGER1 (SDIR1) in plant immunity. Even though SDIR1 is reasonably well-characterized, its role in biotic stress response is not known. The silencing of SDIR1 in Nicotiana benthamiana reduced the multiplication of the virulent bacterial pathogen Pseudomonas syringae pv. tabaci. The Arabidopsis sdir1 mutant is resistant to virulent pathogens, whereas SDIR1 overexpression lines are susceptible to both host and nonhost hemibiotrophic bacterial pathogens. However, sdir1 mutant and SDIR1 overexpression lines showed hypersusceptibility and resistance, respectively, against the necrotrophic pathogen Erwinia carotovora. The mutant of SDIR1 target protein, i.e., SDIR-interacting protein 1 (SDIR1P1), also showed resistance to host and nonhost pathogens. In SDIR1 overexpression plants, transcripts of NAC transcription factors were less accumulated and the levels of jasmonic acid (JA) and abscisic acid were increased. In the sdir1 mutant, JA signaling genes JAZ7 and JAZ8 were downregulated. These data suggest that SDIR1 is a susceptibility factor and its activation or overexpression enhances disease caused by P. syringae pv. tomato DC3000 in Arabidopsis. Our results show a novel role of SDIR1 in modulating plant defense gene expression and plant immunity.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Resistencia a la Enfermedad , Interacciones Huésped-Patógeno , Ubiquitina-Proteína Ligasas , Arabidopsis/enzimología , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Resistencia a la Enfermedad/genética , Regulación de la Expresión Génica de las Plantas , Interacciones Huésped-Patógeno/genética , Pectobacterium carotovorum/fisiología , Enfermedades de las Plantas/microbiología , Pseudomonas syringae/fisiología , Nicotiana/enzimología , Nicotiana/microbiología , Ubiquitina-Proteína Ligasas/genética , Ubiquitina-Proteína Ligasas/metabolismoRESUMEN
Alfalfa (Medicago sativa L.) is one of the most important forage crops throughout the world. Maximizing leaf retention during the haymaking process is critical for achieving superior hay quality and maintaining biomass yield. Leaf abscission process affects leaf retention. Previous studies have largely focused on the molecular mechanisms of floral organ, pedicel and seed abscission but scarcely touched on leaf and petiole abscission. This study focuses on leaf and petiole abscission in the model legume Medicago truncatula and its closely related commercial species alfalfa. By analysing the petiolule-like pulvinus (plp) mutant in M. truncatula at phenotypic level (breakstrength and shaking assays), microscopic level (scanning electron microscopy and cross-sectional analyses) and molecular level (expression level and expression pattern analyses), we discovered that the loss of function of PLP leads to an absence of abscission zone (AZ) formation and PLP plays an important role in leaflet and petiole AZ differentiation. Microarray analysis indicated that PLP affects abscission process through modulating genes involved in hormonal homeostasis, cell wall remodelling and degradation. Detailed analyses led us to propose a functional model of PLP in regulating leaflet and petiole abscission. Furthermore, we cloned the PLP gene (MsPLP) from alfalfa and produced RNAi transgenic alfalfa plants to down-regulate the endogenous MsPLP. Down-regulation of MsPLP results in altered pulvinus structure with increased leaflet breakstrength, thus offering a new approach to decrease leaf loss during alfalfa haymaking process.
Asunto(s)
Medicago truncatula , Pulvino , Estudios Transversales , Regulación de la Expresión Génica de las Plantas/genética , Medicago sativa/genética , Medicago sativa/metabolismo , Medicago truncatula/genética , Medicago truncatula/metabolismo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Pulvino/metabolismoRESUMEN
Leaves are derived from the shoot apical meristem with three distinct axes: dorsoventral, proximodistal and mediolateral. Different regulators are involved in the establishment of leaf polarity. Members of the class III homeodomain-leucine zipper (HD-ZIPIII) gene family are critical players in the determination of leaf adaxial identity mediated by microRNA165/166. However, their roles in compound leaf development are still unclear. By screening of a retrotransposon-tagged mutant population of the model legume plant Medicago truncatula, a mutant line with altered leaflet numbers was isolated and characterized. Mutant leaves partially lost their adaxial identity. Leaflet numbers in the mutant were increased along the proximodistal axis, showing pinnate pentafoliate leaves in most cases, in contrast to the trifoliate leaves of the wild type. Detailed characterization revealed that a lesion in a HD-ZIPIII gene, REVOLUTA (MtREV1), resulted in the defects of the mutant. Overexpression of MtMIR166-insensitive MtREV1 led to adaxialized leaves and ectopic leaflets along the dorsoventral axis. Accompanying the abnormal leaf patterning, the free auxin content was affected. Our results demonstrate that MtREV1 plays a key role in determination of leaf adaxial-abaxial polarity and compound leaf patterning, which is associated with proper auxin homeostasis.
Asunto(s)
Tipificación del Cuerpo/genética , Ácidos Indolacéticos/metabolismo , Medicago truncatula/genética , MicroARNs/genética , Reguladores del Crecimiento de las Plantas/metabolismo , Proteínas de Plantas/metabolismo , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Homeostasis , Leucina Zippers , Medicago truncatula/citología , Medicago truncatula/fisiología , Filogenia , Hojas de la Planta/citología , Hojas de la Planta/genética , Hojas de la Planta/fisiología , Proteínas de Plantas/genética , ARN de Planta/genéticaRESUMEN
AGD1, a plant ACAP-type ADP-ribosylation factor-GTPase activating protein (ARF-GAP), functions in specifying root hair polarity in Arabidopsis thaliana To better understand how AGD1 modulates root hair growth, we generated full-length and domain-deleted AGD1-green fluorescent protein (GFP) constructs, and followed their localization during root hair development. AGD1-GFP localized to the cytoplasm and was recruited to specific regions of the root hair plasma membrane (PM). Distinct PM AGD1-GFP signal was first detected along the site of root hair bulge formation. The construct continued to mark the PM at the root hair apical dome, but only during periods of reduced growth. During rapid tip growth, AGD1-GFP labeled the PM of the lateral flanks and dissipated from the apical-most PM. Deletion analysis and a single domain GFP fusion revealed that the pleckstrin homology (PH) domain is the minimal unit required for recruitment of AGD1 to the PM. Our results indicate that differential recruitment of AGD1 to specific PM domains is an essential component of the membrane trafficking machinery that facilitates root hair developmental phase transitions and responses to changes in the root microenvironment.
Asunto(s)
Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/metabolismo , Membrana Celular/metabolismo , Proteínas Activadoras de GTPasa/química , Proteínas Activadoras de GTPasa/metabolismo , Raíces de Plantas/metabolismo , Eliminación de Secuencia , Citoplasma/metabolismo , Proteínas Fluorescentes Verdes/metabolismo , Mutación/genética , Fosfatos de Fosfatidilinositol/metabolismo , Raíces de Plantas/crecimiento & desarrollo , Dominios Proteicos , Proteínas Recombinantes de Fusión/metabolismo , Relación Estructura-ActividadRESUMEN
Symbiotic nitrogen fixation by rhizobia in legume root nodules is a key source of nitrogen for sustainable agriculture. Genetic approaches have revealed important roles for only a few of the thousands of plant genes expressed during nodule development and symbiotic nitrogen fixation. Previously, we isolated >100 nodulation and nitrogen fixation mutants from a population of Tnt1-insertion mutants of Medigaco truncatula Using Tnt1 as a tag to identify genetic lesions in these mutants, we discovered that insertions in a M. truncatula nodule-specific polycystin-1, lipoxygenase, α-toxin (PLAT) domain-encoding gene, MtNPD1, resulted in development of ineffective nodules. Early stages of nodule development and colonization by the nitrogen-fixing bacterium Sinorhizobium meliloti appeared to be normal in the npd1 mutant. However, npd1 nodules ceased to grow after a few days, resulting in abnormally small, ineffective nodules. Rhizobia that colonized developing npd1 nodules did not differentiate completely into nitrogen-fixing bacteroids and quickly degraded. MtNPD1 expression was low in roots but increased significantly in developing nodules 4 d postinoculation, and expression accompanied invading rhizobia in the nodule infection zone and into the distal nitrogen fixation zone. A functional MtNPD1:GFP fusion protein localized in the space surrounding symbiosomes in infected cells. When ectopically expressed in tobacco (Nicotiana tabacum) leaves, MtNPD1 colocalized with vacuoles and the endoplasmic reticulum. MtNPD1 belongs to a cluster of five nodule-specific single PLAT domain-encoding genes, with apparent nonredundant functions.
Asunto(s)
Regulación de la Expresión Génica de las Plantas , Fijación del Nitrógeno/genética , Proteínas de Plantas/genética , Nódulos de las Raíces de las Plantas/genética , Simbiosis/genética , Medicago truncatula/genética , Medicago truncatula/metabolismo , Medicago truncatula/microbiología , Mutación , Nitrógeno/metabolismo , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Nodulación de la Raíz de la Planta/genética , Raíces de Plantas/genética , Raíces de Plantas/metabolismo , Raíces de Plantas/microbiología , Plantas Modificadas Genéticamente , Dominios Proteicos , Rhizobium/fisiología , Nódulos de las Raíces de las Plantas/metabolismo , Sinorhizobium meliloti/fisiología , Nicotiana/genética , Nicotiana/metabolismo , Nicotiana/microbiologíaRESUMEN
Plant lateral organ development is a complex process involving both transcriptional activation and repression mechanisms. The WOX transcriptional repressor WOX1/STF, the LEUNIG (LUG) transcriptional corepressor and the ANGUSTIFOLIA3 (AN3) transcriptional coactivator play important roles in leaf blade outgrowth and flower development, but how these factors coordinate their activities remains unclear. Here we report physical and genetic interactions among these key regulators of leaf and flower development. We developed a novel in planta transcriptional activation/repression assay and suggest that LUG could function as a transcriptional coactivator during leaf blade development. MtLUG physically interacts with MtAN3, and this interaction appears to be required for leaf and flower development. A single amino acid substitution at position 61 in the SNH domain of MtAN3 protein abolishes its interaction with MtLUG, and its transactivation activity and biological function. Mutations in lug and an3 enhanced each other's mutant phenotypes. Both the lug and the an3 mutations enhanced the wox1 prs leaf and flower phenotypes in Arabidopsis. Our findings together suggest that transcriptional repression and activation mediated by the WOX, LUG and AN3 regulators function in concert to promote leaf and flower development, providing novel mechanistic insights into the complex regulation of plant lateral organ development.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crecimiento & desarrollo , Flores/crecimiento & desarrollo , Proteínas de Homeodominio/metabolismo , Morfogénesis , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo , Transactivadores/metabolismo , Factores de Transcripción/metabolismo , Secuencia de Aminoácidos , Arabidopsis/metabolismo , Proteínas de Arabidopsis/química , Secuencia Conservada , Epistasis Genética , Mutación , Fenotipo , Unión Proteica , Dominios Proteicos , Transactivadores/química , Factores de Transcripción/químicaRESUMEN
Iron (Fe) is an essential micronutrient for symbiotic nitrogen fixation in legume nodules, where it is required for the activity of bacterial nitrogenase, plant leghemoglobin, respiratory oxidases, and other Fe proteins in both organisms. Fe solubility and transport within and between plant tissues is facilitated by organic chelators, such as nicotianamine and citrate. We have characterized a nodule-specific citrate transporter of the multidrug and toxic compound extrusion family, MtMATE67 of Medicago truncatula The MtMATE67 gene was induced early during nodule development and expressed primarily in the invasion zone of mature nodules. The MtMATE67 protein was localized to the plasma membrane of nodule cells and also the symbiosome membrane surrounding bacteroids in infected cells. In oocytes, MtMATE67 transported citrate out of cells in an Fe-activated manner. Loss of MtMATE67 gene function resulted in accumulation of Fe in the apoplasm of nodule cells and a substantial decrease in symbiotic nitrogen fixation and plant growth. Taken together, the results point to a primary role of MtMATE67 in citrate efflux from nodule cells in response to an Fe signal. This efflux is necessary to ensure Fe(III) solubility and mobility in the apoplasm and uptake into nodule cells. Likewise, MtMATE67-mediated citrate transport into the symbiosome space would increase the solubility and availability of Fe(III) for rhizobial bacteroids.
Asunto(s)
Hierro/metabolismo , Medicago truncatula/fisiología , Fijación del Nitrógeno/fisiología , Proteínas de Plantas/metabolismo , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Citratos/metabolismo , Regulación de la Expresión Génica de las Plantas , Hierro/farmacocinética , Medicago truncatula/microbiología , Mutación , Filogenia , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente , Nódulos de las Raíces de las Plantas/crecimiento & desarrollo , Nódulos de las Raíces de las Plantas/metabolismo , Nódulos de las Raíces de las Plantas/microbiología , Simbiosis/fisiologíaRESUMEN
Physical dormancy of seed is an adaptive trait that widely exists in higher plants. This kind of dormancy is caused by a water-impermeable layer that blocks water and oxygen from the surrounding environment and keeps embryos in a viable status for a long time. Most of the work on hardseededness has focused on morphological structure and phenolic content of seed coat. The molecular mechanism underlying physical dormancy remains largely elusive. By screening a large number of Tnt1 retrotransposon-tagged Medicago truncatula lines, we identified nondormant seed mutants from this model legume species. Unlike wild-type hard seeds exhibiting physical dormancy, the mature mutant seeds imbibed water quickly and germinated easily, without the need for scarification. Microscopic observations of cross sections showed that the mutant phenotype was caused by a dysfunctional palisade cuticle layer in the seed coat. Chemical analysis found differences in lipid monomer composition between the wild-type and mutant seed coats. Genetic and molecular analyses revealed that a class II KNOTTED-like homeobox (KNOXII) gene, KNOX4, was responsible for the loss of physical dormancy in the seeds of the mutants. Microarray and chromatin immunoprecipitation analyses identified CYP86A, a gene associated with cutin biosynthesis, as one of the downstream target genes of KNOX4 This study elucidated a novel molecular mechanism of physical dormancy and revealed a new role of class II KNOX genes. Furthermore, KNOX4-like genes exist widely in seed plants but are lacking in nonseed species, indicating that KNOX4 may have diverged from the other KNOXII genes during the evolution of seed plants.
Asunto(s)
Genes Homeobox , Genes de Plantas , Medicago/genética , Latencia en las Plantas/genética , Semillas , Regulación de la Expresión Génica de las Plantas , Medicago/embriología , MutaciónRESUMEN
The symbiosis between leguminous plants and soil rhizobia culminates in the formation of nitrogen-fixing organs called nodules that support plant growth. Two Medicago truncatula Tnt1-insertion mutants were identified that produced small nodules, which were unable to fix nitrogen effectively due to ineffective rhizobial colonization. The gene underlying this phenotype was found to encode a protein containing a putative membrane-localized domain of unknown function (DUF21) and a cystathionine-ß-synthase domain. The cbs1 mutants had defective infection threads that were sometimes devoid of rhizobia and formed small nodules with greatly reduced numbers of symbiosomes. We studied the expression of the gene, designated M truncatula Cystathionine-ß-Synthase-like1 (MtCBS1), using a promoter-ß-glucuronidase gene fusion, which revealed expression in infected root hair cells, developing nodules, and in the invasion zone of mature nodules. An MtCBS1-GFP fusion protein localized itself to the infection thread and symbiosomes. Nodulation factor-induced Ca(2+) responses were observed in the cbs1 mutant, indicating that MtCBS1 acts downstream of nodulation factor signaling. MtCBS1 expression occurred exclusively during Medicago-rhizobium symbiosis. Induction of MtCBS1 expression during symbiosis was found to be dependent on Nodule Inception (NIN), a key transcription factor that controls both rhizobial infection and nodule organogenesis. Interestingly, the closest homolog of MtCBS1, MtCBS2, was specifically induced in mycorrhizal roots, suggesting common infection mechanisms in nodulation and mycorrhization. Related proteins in Arabidopsis have been implicated in cell wall maturation, suggesting a potential role for CBS1 in the formation of the infection thread wall.
Asunto(s)
Cistationina betasintasa/metabolismo , Medicago truncatula/enzimología , Medicago truncatula/microbiología , Fijación del Nitrógeno , Proteínas de Plantas/metabolismo , Rhizobium/fisiología , Simbiosis , Cistationina betasintasa/química , Cistationina betasintasa/genética , Endocitosis , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Proteínas Fluorescentes Verdes/metabolismo , Medicago truncatula/genética , Mutación/genética , Fenotipo , Proteínas de Plantas/química , Proteínas de Plantas/genética , Nodulación de la Raíz de la Planta , Regiones Promotoras Genéticas/genética , Dominios Proteicos , Nódulos de las Raíces de las Plantas/genéticaRESUMEN
Almost all C4 plants require the co-ordination of the adjacent and fully differentiated cell types, mesophyll (M) and bundle sheath (BS). The C4 photosynthetic pathway operates through two distinct subtypes based on how malate is decarboxylated in BS cells; through NAD-malic enzyme (NAD-ME) or NADP-malic enzyme (NADP-ME). The diverse or unique cell-specific molecular features of M and BS cells from separate C4 subtypes of independent lineages remain to be determined. We here provide an M/BS cell type-specific transcriptome data set from the monocot NAD-ME subtype switchgrass (Panicum virgatum). A comparative transcriptomics approach was then applied to compare the M/BS mRNA profiles of switchgrass, monocot NADP-ME subtype C4 plants maize and Setaria viridis, and dicot NAD-ME subtype Cleome gynandra. We evaluated the convergence in the transcript abundance of core components in C4 photosynthesis and transcription factors to establish Kranz anatomy, as well as gene distribution of biological functions, in these four independent C4 lineages. We also estimated the divergence between NAD-ME and NADP-ME subtypes of C4 photosynthesis in the two cell types within C4 species, including differences in genes encoding decarboxylating enzymes, aminotransferases, and metabolite transporters, and differences in the cell-specific functional enrichment of RNA regulation and protein biogenesis/homeostasis. We suggest that C4 plants of independent lineages in both monocots and dicots underwent convergent evolution to establish C4 photosynthesis, while distinct C4 subtypes also underwent divergent processes for the optimization of M and BS cell co-ordination. The comprehensive data sets in our study provide a basis for further research on evolution of C4 species.
Asunto(s)
Diferenciación Celular , Panicum/citología , Panicum/genética , Fotosíntesis/genética , Filogenia , Transcriptoma/genética , Transporte Biológico , Carbono/metabolismo , Separación Celular , Mapeo Cromosómico , Regulación de la Expresión Génica de las Plantas , Secuenciación de Nucleótidos de Alto Rendimiento , Hibridación in Situ , Malato Deshidrogenasa/metabolismo , Células del Mesófilo/metabolismo , Modelos Biológicos , Hojas de la Planta/genética , Proteínas de Plantas/metabolismo , Haz Vascular de Plantas/genética , ARN Mensajero/genética , ARN Mensajero/metabolismo , Factores de Transcripción/metabolismoRESUMEN
Lignins are phenylpropanoid polymers, derived from monolignols, commonly found in terrestrial plant secondary cell walls. We recently reported evidence of an unanticipated catechyl lignin homopolymer (C lignin) derived solely from caffeyl alcohol in the seed coats of several monocot and dicot plants. We previously identified plant seeds that possessed either C lignin or traditional guaiacyl/syringyl (G/S) lignins, but not both. Here, we identified several dicot plants (Euphorbiaceae and Cleomaceae) that produce C lignin together with traditional G/S lignins in their seed coats. Solution-state NMR analyses, along with an in vitro lignin polymerization study, determined that there is, however, no copolymerization detectable (i.e., that the synthesis and polymerization of caffeyl alcohol and conventional monolignols in vivo is spatially and/or temporally separated). In particular, the deposition of G and C lignins in Cleome hassleriana seed coats is developmentally regulated during seed maturation; C lignin appears successively after G lignin within the same testa layers, concurrently with apparent loss of the functionality of O-methyltransferases, which are key enzymes for the conversion of C to G lignin precursors. This study exemplifies the flexible biosynthesis of different types of lignin polymers in plants dictated by substantial, but poorly understood, control of monomer supply by the cells.
Asunto(s)
Lignina/biosíntesis , Plantas/metabolismo , Polímeros/metabolismo , Semillas/metabolismo , Vías Biosintéticas , Pared Celular/química , Pared Celular/enzimología , Pared Celular/metabolismo , Cleome/química , Cleome/enzimología , Cleome/metabolismo , Euphorbiaceae/química , Euphorbiaceae/enzimología , Euphorbiaceae/metabolismo , Lignina/química , Espectroscopía de Resonancia Magnética , Magnoliopsida/química , Magnoliopsida/enzimología , Magnoliopsida/metabolismo , Metiltransferasas/metabolismo , Microscopía Confocal , Estructura Molecular , Plantas/química , Plantas/enzimología , Semillas/enzimología , Especificidad de la EspecieRESUMEN
Transcription factors (TFs) are thought to regulate many aspects of nodule and symbiosis development in legumes, although few TFs have been characterized functionally. Here, we describe regulator of symbiosome differentiation (RSD) of Medicago truncatula, a member of the Cysteine-2/Histidine-2 (C2H2) family of plant TFs that is required for normal symbiosome differentiation during nodule development. RSD is expressed in a nodule-specific manner, with maximal transcript levels in the bacterial invasion zone. A tobacco (Nicotiana tabacum) retrotransposon (Tnt1) insertion rsd mutant produced nodules that were unable to fix nitrogen and that contained incompletely differentiated symbiosomes and bacteroids. RSD protein was localized to the nucleus, consistent with a role of the protein in transcriptional regulation. RSD acted as a transcriptional repressor in a heterologous yeast assay. Transcriptome analysis of an rsd mutant identified 11 genes as potential targets of RSD repression. RSD interacted physically with the promoter of one of these genes, VAMP721a, which encodes vesicle-associated membrane protein 721a. Thus, RSD may influence symbiosome development in part by repressing transcription of VAMP721a and modifying vesicle trafficking in nodule cells. This establishes RSD as a TF implicated directly in symbiosome and bacteroid differentiation and a transcriptional regulator of secretory pathway genes in plants.
Asunto(s)
Regulación de la Expresión Génica de las Plantas , Genoma de Planta/genética , Medicago truncatula/genética , Proteínas de Plantas/metabolismo , Secuencia de Bases , Diferenciación Celular , Perfilación de la Expresión Génica , Medicago truncatula/crecimiento & desarrollo , Medicago truncatula/microbiología , Modelos Biológicos , Anotación de Secuencia Molecular , Datos de Secuencia Molecular , Mutagénesis Insercional , Fijación del Nitrógeno , Análisis de Secuencia por Matrices de Oligonucleótidos , Filogenia , Proteínas de Plantas/genética , Nodulación de la Raíz de la Planta , Nódulos de las Raíces de las Plantas/genética , Nódulos de las Raíces de las Plantas/metabolismo , Nódulos de las Raíces de las Plantas/microbiología , Vías Secretoras , Análisis de Secuencia de ADN , Sinorhizobium meliloti/fisiología , Simbiosis , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
The evolution of lignin biosynthesis was critical in the transition of plants from an aquatic to an upright terrestrial lifestyle. Lignin is assembled by oxidative polymerization of two major monomers, coniferyl alcohol and sinapyl alcohol. Although two recently discovered laccases, LAC4 and LAC17, have been shown to play a role in lignin polymerization in Arabidopsis thaliana, disruption of both genes only leads to a relatively small change in lignin content and only under continuous illumination. Simultaneous disruption of LAC11 along with LAC4 and LAC17 causes severe plant growth arrest, narrower root diameter, indehiscent anthers, and vascular development arrest with lack of lignification. Genome-wide transcript analysis revealed that all the putative lignin peroxidase genes are expressed at normal levels or even higher in the laccase triple mutant, suggesting that lignin laccase activity is necessary and nonredundant with peroxidase activity for monolignol polymerization during plant vascular development. Interestingly, even though lignin deposition in roots is almost completely abolished in the lac11 lac4 lac17 triple mutant, the Casparian strip, which is lignified through the activity of peroxidase, is still functional. Phylogenetic analysis revealed that lignin laccase genes have no orthologs in lower plant species, suggesting that the monolignol laccase genes diverged after the evolution of seed plants.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crecimiento & desarrollo , Lacasa/metabolismo , Lignina/biosíntesis , Peroxidasas/metabolismo , Arabidopsis/enzimología , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Pared Celular/metabolismo , Regulación de la Expresión Génica de las Plantas , Lacasa/genética , Peroxidasas/genética , Filogenia , Haz Vascular de Plantas/crecimiento & desarrollo , Factores de Transcripción/metabolismo , Activación TranscripcionalRESUMEN
Leaf shape elaboration and organ separation are critical for plant morphogenesis. We characterized the developmental roles of lobed leaflet1 by analyzing a recessive mutant in the model legume Medicago truncatula. An ortholog of Arabidopsis thaliana argonaute7 (AGO7), Mt-AGO7/lobed leaflet1, is required for the biogenesis of a trans-acting short interfering RNA (ta-siRNA) to negatively regulate the expression of auxin response factors in M. truncatula. Loss of function in AGO7 results in pleiotropic phenotypes in different organs. The prominent phenotype of the ago7 mutant is lobed leaf margins and more widely spaced lateral organs, suggesting that the trans-acting siRNA3 (TAS3) pathway negatively regulates the formation of boundaries and the separation of lateral organs in M. truncatula. Genetic interaction analysis with the smooth leaf margin1 (slm1) mutant revealed that leaf margin formation is cooperatively regulated by the auxin/SLM1 (ortholog of Arabidopsis PIN-formed1) module, which influences the initiation of leaf margin teeth, and the TAS3 ta-siRNA pathway, which determines the degree of margin indentation. Further investigations showed that the TAS3 ta-siRNA pathway and no apical meristem (ortholog of Arabidopsis cup-shaped cotyledon) antagonistically regulate both leaf margin development and lateral organ separation, and the regulation is partially dependent on the auxin/SLM1 module.
Asunto(s)
Medicago truncatula/crecimiento & desarrollo , Proteínas de Plantas/fisiología , ARN Interferente Pequeño/fisiología , Secuencia de Bases , Clonación Molecular , Flores/citología , Flores/genética , Flores/crecimiento & desarrollo , Medicago truncatula/citología , Medicago truncatula/genética , Datos de Secuencia Molecular , Mutación , Hojas de la Planta/citología , Hojas de la Planta/genética , Hojas de la Planta/crecimiento & desarrollo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , ARN Interferente Pequeño/química , Análisis de Secuencia de ARNRESUMEN
BACKGROUND: Switchgrass rust, caused by Puccinia emaculata, is an important disease of switchgrass, a potential biofuel crop in the United States. In severe cases, switchgrass rust has the potential to significantly affect biomass yield. In an effort to identify novel sources of resistance against switchgrass rust, we explored nonhost resistance against P. emaculata by characterizing its interactions with six monocot nonhost plant species. We also studied the genetic variations for resistance among Brachypodium inbred accessions and the involvement of various defense pathways in nonhost resistance of Brachypodium. RESULTS: We characterized P. emaculata interactions with six monocot nonhost species and identified Brachypodium distachyon (Bd21) as a suitable nonhost model to study switchgrass rust. Interestingly, screening of Brachypodium accessions identified natural variations in resistance to switchgrass rust. Brachypodium inbred accessions Bd3-1 and Bd30-1 were identified as most and least resistant to switchgrass rust, respectively, when compared to tested accessions. Transcript profiling of defense-related genes indicated that the genes which were induced in Bd21after P. emaculata inoculation also had higher basal transcript abundance in Bd3-1 when compared to Bd30-1 and Bd21 indicating their potential involvement in nonhost resistance against switchgrass rust. CONCLUSION: In the present study, we identified Brachypodium as a suitable nonhost model to study switchgrass rust which exhibit type I nonhost resistance. Variations in resistance response were also observed among tested Brachypodium accessions. Brachypodium nonhost resistance against P. emaculata may involve various defense pathways as indicated by transcript profiling of defense related genes. Overall, this study provides a new avenue to utilize novel sources of nonhost resistance in Brachypodium against switchgrass rust.
Asunto(s)
Basidiomycota/patogenicidad , Brachypodium/microbiología , Modelos Biológicos , Basidiomycota/genética , Perfilación de la Expresión Génica , Genes Fúngicos , ARN Mensajero/genéticaRESUMEN
Reduction of lignin levels in the forage legume alfalfa (Medicago sativa) by down-regulation of the monolignol biosynthetic enzyme hydroxycinnamoyl coenzyme A:shikimate hydroxycinnamoyl transferase (HCT) results in strongly increased digestibility and processing ability of lignocellulose. However, these modifications are often also associated with dwarfing and other changes in plant growth. Given the importance of nitrogen fixation for legume growth, we evaluated the impact of constitutively targeted lignin modification on the belowground organs (roots and nodules) of alfalfa plants. HCT down-regulated alfalfa plants exhibit a striking reduction in root growth accompanied by an unexpected increase in nodule numbers when grown in the greenhouse or in the field. This phenotype is associated with increased levels of gibberellins and certain flavonoid compounds in roots. Although HCT down-regulation reduced biomass yields in both the greenhouse and field experiments, the impact on the allocation of nitrogen to shoots or roots was minimal. It is unlikely, therefore, that the altered growth phenotype of reduced-lignin alfalfa is a direct result of changes in nodulation or nitrogen fixation efficiency. Furthermore, HCT down-regulation has no measurable effect on carbon allocation to roots in either greenhouse or 3-year field trials.
Asunto(s)
Lignina/metabolismo , Medicago sativa/metabolismo , Nódulos de las Raíces de las Plantas/metabolismo , Aciltransferasas/metabolismo , Biomasa , Carbono/metabolismo , Regulación hacia Abajo , Flavonoides/metabolismo , Regulación de la Expresión Génica de las Plantas , Medicago sativa/enzimología , Medicago sativa/genética , Medicago sativa/microbiología , Nitrógeno/metabolismo , Fenoles/metabolismo , Fenotipo , Reguladores del Crecimiento de las Plantas/metabolismo , Nodulación de la Raíz de la Planta , ARN sin Sentido/metabolismo , Nódulos de las Raíces de las Plantas/enzimología , Nódulos de las Raíces de las Plantas/crecimiento & desarrollo , Nódulos de las Raíces de las Plantas/microbiología , Sinorhizobium meliloti/fisiología , Solubilidad , Transcriptoma/genéticaRESUMEN
To identify genes that confer nonhost resistance to biotrophic fungal pathogens, we did a forward-genetics screen using Medicago truncatula Tnt1 retrotransposon insertion lines. From this screen, we identified an inhibitor of rust germ tube differentation1 (irg1) mutant that failed to promote preinfection structure differentiation of two rust pathogens, Phakopsora pachyrhizi and Puccinia emaculata, and one anthracnose pathogen, Colletotrichum trifolii, on the abaxial leaf surface. Cytological and chemical analyses revealed that the inhibition of rust preinfection structures in irg1 mutants is due to complete loss of the abaxial epicuticular wax crystals and reduced surface hydrophobicity. The composition of waxes on abaxial leaf surface of irg1 mutants had >90% reduction of C30 primary alcohols and a preferential increase of C29 and C31 alkanes compared with the wild type. IRG1 encodes a Cys(2)His(2) zinc finger transcription factor, PALM1, which also controls dissected leaf morphology in M. truncatula. Transcriptome analysis of irg1/palm1 mutants revealed downregulation of eceriferum4, an enzyme implicated in primary alcohol biosynthesis, and MYB96, a major transcription factor that regulates wax biosynthesis. Our results demonstrate that PALM1 plays a role in regulating epicuticular wax metabolism and transport and that epicuticular wax influences spore differentiation of host and nonhost fungal pathogens.
Asunto(s)
Medicago truncatula/metabolismo , Medicago truncatula/microbiología , Hojas de la Planta/metabolismo , Hojas de la Planta/microbiología , Proteínas de Plantas/genética , Ceras/metabolismo , Basidiomycota/patogenicidad , Colletotrichum/patogenicidad , Medicago truncatula/genética , Datos de Secuencia Molecular , Enfermedades de las Plantas/microbiología , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/metabolismo , Plantas Modificadas Genéticamente/microbiologíaRESUMEN
UNLABELLED: ⢠PREMISE OF THE STUDY: Plants will be an important component of advanced life support systems during space exploration missions. Therefore, understanding their biology in the spacecraft environment will be essential before they can be used for such systems.⢠METHODS: Seedlings of Arabidopsis thaliana were grown for 2 wk in the Biological Research in Canisters (BRIC) hardware on board the second to the last mission of the space shuttle Discovery (STS-131). Transcript profiles between ground controls and space-grown seedlings were compared using stringent selection criteria.⢠KEY RESULTS: Expression of transcripts associated with oxidative stress and cell wall remodeling was repressed in microgravity. These downregulated genes were previously shown to be enriched in root hairs consistent with seedling phenotypes observed in space. Mutations in genes that were downregulated in microgravity, including two uncharacterized root hair-expressed class III peroxidase genes (PRX44 and PRX57), led to defective polar root hair growth on Earth. PRX44 and PRX57 mutants had ruptured root hairs, which is a typical phenotype of tip-growing cells with defective cell walls and those subjected to stress.⢠CONCLUSIONS: Long-term exposure to microgravity negatively impacts tip growth by repressing expression of genes essential for normal root hair development. Whereas changes in peroxidase gene expression leading to reduced root hair growth in space are actin-independent, root hair development modulated by phosphoinositides could be dependent on the actin cytoskeleton. These results have profound implications for plant adaptation to microgravity given the importance of tip growing cells such as root hairs for efficient nutrient capture.
Asunto(s)
Proteínas de Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Arabidopsis/genética , Regulación de la Expresión Génica , Estrés Oxidativo , Peroxidasas/genética , Ingravidez , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Pared Celular/metabolismo , Peroxidasas/metabolismo , Plantones/genética , Plantones/crecimiento & desarrollo , Plantones/metabolismo , Vuelo EspacialRESUMEN
We have recently described a hitherto unsuspected catechyl lignin polymer (C-lignin) in the seed coats of Vanilla orchid and in cacti of one genus, Melocactus (Chen et al., Proc. Natl. Acad. Sci. USA. 2012, 109, 1772-1777.). We have now determined the lignin types in the seed coats of 130 different cactus species. Lignin in the vegetative tissues of cacti is of the normal guaiacyl/syringyl (G/S) type, but members of most genera within the subfamily Cactoidae possess seed coat lignin of the novel C-type only, which we show is a homopolymer formed by endwise ß-O-4-coupling of caffeyl alcohol monomers onto the growing polymer resulting in benzodioxane units. However, the species examined within the genera Coryphantha, Cumarinia, Escobaria and Mammillaria (Cactoideae) mostly had normal G/S lignin in their seeds, as did all six species in the subfamily Opuntioidae that were examined. Seed coat lignin composition is still evolving in the Cactaceae, as seeds of one Mammillaria species (M. lasiacantha) possess only C-lignin, three Escobaria species (E. dasyacantha, E. lloydii and E. zilziana) contain an unusual lignin composed of 5-hydroxyguaiacyl units, the first report of such a polymer that occurs naturally in plants, and seeds of some species contain no lignin at all. We discuss the implications of these findings for the mechanisms that underlie the biosynthesis of these newly discovered lignin types.
Asunto(s)
Cactaceae/fisiología , Lignina/metabolismo , Semillas/química , Cactaceae/genética , Regulación de la Expresión Génica de las Plantas/fisiología , Lignina/biosíntesis , Lignina/química , Filogenia , Semillas/fisiología , Especificidad de la EspecieRESUMEN
Symbiotic interaction between Medicago truncatula and Sinorhizobium meliloti results in the formation on the host roots of new organs, nodules, in which biological nitrogen fixation takes place. In infected cells, rhizobia enclosed in a plant-derived membrane, the symbiosome membrane, differentiate to nitrogen-fixing bacteroids. The symbiosome membrane serves as an interface for metabolite and signal exchanges between the host cells and endosymbionts. At some point during symbiosis, symbiosomes and symbiotic cells are disintegrated, resulting in nodule senescence. The regulatory mechanisms that underlie nodule senescence are not fully understood. Using a forward genetics approach, we have uncovered the early senescent nodule 1 (esn1) mutant from an M. truncatula fast neutron-induced mutant collection. Nodules on esn1 roots are spherically shaped, ineffective in nitrogen fixation, and senesce early. Atypical among fixation defective mutants isolated thus far, bacteroid differentiation and expression of nifH, Leghemoglobin, and DNF1 genes are not affected in esn1 nodules, supporting the idea that a process downstream of bacteroid differentiation and nitrogenase gene expression is affected in the esn1 mutant. Expression analysis shows that marker genes involved in senescence, macronutrient degradation, and remobilization are greatly upregulated during nodule development in the esn1 mutant, consistent with a role of ESN1 in nodule senescence and symbiotic nitrogen fixation.