Physiological and molecular implications of plant polyamine metabolism during biotic interactions

"During ontogeny, plants interact with a wide variety of microorganisms. The association with mutualistic microbes results in benefits for the plant. By contrast, pathogens may cause a remarkable impairment of plant growth and development. Both types of plant microbe interactions provoke notable changes in the polyamine (PA) metabolism of the host and/or the microbe, being each interaction a complex and dynamic process. It has been well documented that the levels of free and conjugated PAs undergo profound changes in plant tissues during the interaction with microorganisms. In general, this is correlated with a precise and coordinated regulation of PA biosynthetic and catabolic enzymes. Interestingly, some evidence suggests that the relative importance of these metabolic pathways may depend on the nature of the microorganism, a concept that stems from the fact that these amines mediate the activation of plant defense mechanisms. This effect is mediated mostly through PA oxidation, even though part of the response is activated by non-oxidized PAs. In the last years, a great deal of effort has been devoted to profile plant gene expression following microorganism recognition. In addition, the phenotypes of transgenic and mutant plants in PA metabolism genes have been assessed. In this review, we integrate the current knowledge on this field and analyze the possible roles of these amines during the interaction of plants with microbes.

Phosphatidylinositol 3-kinase function at very early symbiont perception: a local nodulation control under stress conditions?

Root hair curling is an early and essential morphological change required for the success of the symbiotic interaction between legumes and rhizobia. At this stage rhizobia grow as an infection thread within root hairs and are internalized into the plant cells by endocytosis, where the PI3K enzyme plays important roles. Previous observations show that stress conditions affect early stages of the symbiotic interaction, from 2 to 30 min post-inoculation, which we term as very early host responses, and affect symbiosis establishment. Herein, we demonstrated the relevance of the very early host responses for the symbiotic interaction. PI3K and the NADPH oxidase complex are found to have key roles in the microsymbiont recognition response, modulating the apoplastic and intracellular/endosomal ROS induction in root hairs. Interestingly, compared with soybean mutant plants that do not perceive the symbiont, we demonstrated that the very early symbiont perception under sublethal saline stress conditions induced root hair death. Together, these results highlight not only the importance of the very early host-responses on later stages of the symbiont interaction, but also suggest that they act as a mechanism for local control of nodulation capacity, prior to the abortion of the infection thread, preventing the allocation of resources/energy for nodule formation under unfavorable environmental conditions.Instituto de Fisiología y Recursos Genéticos VegetalesFil: Robert, German. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Fisiología y Recursos Genéticos Vegetales; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Cátedra de Fisiología Vegetal; ArgentinaFil: Muñoz, Nacira Belen. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Fisiología y Recursos Genéticos Vegetales; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Cátedra de Fisiología Vegetal; ArgentinaFil: Alvarado-Affantranger, Xochitl. Universidad Nacional Autónoma de México. Instituto de Biotecnología. Departamento de Biología Molecular de Plantas; MéxicoFil: Saavedra, Laura. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Cátedra de Fisiología Vegetal; ArgentinaFil: Davidenco, Vanina. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Fisiología y Recursos Genéticos Vegetales; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Cátedra de Fisiología Vegetal; ArgentinaFil: Rodríguez-Kessler, Margarita. Universidad Nacional Autónoma de México. Instituto de Biotecnología. Departamento de Biología Molecular de Plantas; MéxicoFil: Estrada-Navarrete, Georgina. Universidad Nacional Autónoma de México. Instituto de Biotecnología. Departamento de Biología Molecular de Plantas; MéxicoFil: Sanchez, Federico. Universidad Nacional Autónoma de México. Instituto de Biotecnología. Departamento de Biología Molecular de Plantas; MéxicoFil: Lascano, Hernan Ramiro. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Cátedra de Fisiología Vegetal; Argentin

Overexpression of AtGRDP2, a novel glycine-rich domain protein, accelerates plant growth and improves stress tolerance

"Proteins with glycine-rich signatures have been reported in a wide variety of organisms including plants, mammalians, fungi, and bacteria. Plant glycine-rich protein genes exhibit developmental and tissue-specific expression patterns. Herein, we present the characterization of the AtGRDP2 gene using Arabidopsis null and knockdown mutants and, Arabidopsis and lettuce over-expression lines. AtGRDP2 encodes a short glycine-rich domain protein, containing a DUF1399 domain and a putative RNA recognition motif (RRM). AtGRDP2 transcript is mainly expressed in Arabidopsis floral organs, and its deregulation in Arabidopsis Atgrdp2 mutants and 35S::AtGRDP2 over-expression lines produces alterations in development. The 35S::AtGRDP2 over-expression lines grow faster than the WT, while the Atgrdp2 mutants have a delay in growth and development. The over-expression lines accumulate higher levels of indole-3-acetic acid and, have alterations in the expression pattern of ARF6, ARF8, and miR167 regulators of floral development and auxin signaling. Under salt stress conditions, 35S::AtGRDP2 over-expression lines displayed higher tolerance and increased expression of stress marker genes. Likewise, transgenic lettuce plants over-expressing the AtGRDP2 gene manifest increased growth rate and early flowering time. Our data reveal an important role for AtGRDP2 in Arabidopsis development and stress response, and suggest a connection between AtGRDP2 and auxin signaling.

Nodulin 41, a novel late nodulin of common bean with peptidase activity

<p>Abstract</p> <p>Background</p> <p>The legume-rhizobium symbiosis requires the formation of root nodules, specialized organs where the nitrogen fixation process takes place. Nodule development is accompanied by the induction of specific plant genes, referred to as nodulin genes. Important roles in processes such as morphogenesis and metabolism have been assigned to nodulins during the legume-rhizobium symbiosis.</p> <p>Results</p> <p>Here we report the purification and biochemical characterization of a novel nodulin from common bean (<it>Phaseolus vulgaris </it>L.) root nodules. This protein, called nodulin 41 (PvNod41) was purified through affinity chromatography and was partially sequenced. A genomic clone was then isolated via PCR amplification. PvNod41 is an atypical aspartyl peptidase of the A1B subfamily with an optimal hydrolytic activity at pH 4.5. We demonstrate that PvNod41 has limited peptidase activity against casein and is partially inhibited by pepstatin A. A PvNod41-specific antiserum was used to assess the expression pattern of this protein in different plant organs and throughout root nodule development, revealing that PvNod41 is found only in bean root nodules and is confined to uninfected cells.</p> <p>Conclusions</p> <p>To date, only a small number of atypical aspartyl peptidases have been characterized in plants. Their particular spatial and temporal expression patterns along with their unique enzymatic properties imply a high degree of functional specialization. Indeed, PvNod41 is closely related to CDR1, an <it>Arabidopsis thaliana </it>extracellular aspartyl protease involved in defense against bacterial pathogens. PvNod41's biochemical properties and specific cell-type localization, in uninfected cells of the common bean root nodule, strongly suggest that this aspartyl peptidase has a key role in plant defense during the symbiotic interaction.</p

The Epl1 and Sm1 proteins from Trichoderma atroviride and Trichoderma virens differentially modulate systemic disease resistance against different life style pathogens in Solanum lycopersicum

"Fungi belonging to the genus Trichoderma, commonly found in soil or colonizing plant roots, exert beneficial effects on plants, including the promotion of growth and the induction of resistance to disease. T virens and T atroviride secrete the proteins Sm1 and Epl1, respectively, which elicit local and systemic disease resistance in plants. In this work, we show that these fungi promote growth in tomato (Solanum lycopersicum) plants. T virens was more effective than T atroviride in promoting biomass gain, and both fungi were capable of inducing systemic protection in tomato against Altemaria solani, Botrytis cinerea, and Pseudomonas syringae pv. tomato (Pst DC3000). Deletion (KO) of epl1 in T atroviride resulted in diminished systemic protection against A. solani and B. cinerea, whereas the T virens sm1 KO strain was less effective in protecting tomato against Pst DC3000 and B. cinerea. Importantly, overexpression (OE) of epl1 and sm1 led to an increase in disease resistance against all tested pathogens. Although the Trichoderma WT strains induced both systemic acquired resistance (SAR)-and induced systemic resistance (ISR)-related genes in tomato, inoculation of plants with OE and KO strains revealed that Epl1 and Sm1 play a minor role in the induction of these genes. However, we found that Epl1 and Sm I induce the expression of a peroxidase and an alpha-dioxygenase encoding genes, respectively, which could be important for tomato protection by Trichoderma spp. Altogether, these observations indicate that colonization by beneficial and or infection by pathogenic microorganisms dictates many of the outcomes in plants, which are more complex than previously thought.

Peripheral T-cell lymphoma: Molecular profiling recognizes subclasses and identifies prognostic markers

Peripheral T-cell lymphoma (PTCL) is a clinically aggressive disease, with a poor response to therapy and a low overall survival rate of approximately 30% after 5 years. We have analyzed a series of 105 cases with a diagnosis of PTCL using a customized NanoString platform (NanoString Technologies, Seattle, WA) that includes 208 genes associated with T-cell differentiation, oncogenes and tumor suppressor genes, deregulated pathways, and stromal cell subpopulations. A comparative analysis of the various histological types of PTCL (angioimmunoblastic T-cell lymphoma [AITL]; PTCL with T follicular helper [TFH] phenotype; PTCL not otherwise specified [NOS]) showed that specific sets of genes were associated with each of the diagnoses. These included TFH markers, cytotoxic markers, and genes whose expression was a surrogate for specific cellular subpopulations, including follicular dendritic cells, mast cells, and genes belonging to precise survival (NF-κB) and other pathways. Furthermore, the mutational profile was analyzed using a custom panel that targeted 62 genes in 76 cases distributed in AITL, PTCL-TFH, and PTCL-NOS. The main differences among the 3 nodal PTCL classes involved the RHOAG17V mutations (P < .0001), which were approximately twice as frequent in AITL (34.09%) as in PTCL-TFH (16.66%) cases but were not detected in PTCL-NOS. A multivariate analysis identified gene sets that allowed the series of cases to be stratified into different risk groups. This study supports and validates the current division of PTCL into these 3 categories, identifies sets of markers that can be used for a more precise diagnosis, and recognizes the expression of B-cell genes as an IPI-independent prognostic factor for AITL

Análisis del metabolismo de poliaminas de maíz bajo condiciones de estrés biótico y abiótico

Tesis (Doctorado en Ciencias en Biología Molecular)"La salinidad, junto con la sequía y las bajas temperaturas, constituyen los factores ambientales más adversos que afectan dramáticamente el desarrollo de las plantas. Además, el ataque por patógenos e insectos constituye un factor más en la pérdida de los cultivos. Las poliaminas, putrescina, espermidina y espermina (Put, Spd y Spm), son policationes alifáticos de bajo peso molecular involucrados en múltiples procesos fisiológicos y de desarrollo en plantas, y también en respuesta a factores de estrés biótico y abiótico. En el presente trabajo, se analizaron cambios en el metabolismo de las poliaminas de maíz bajo dos condiciones de estrés, uno abiótico que comprende el efecto del NaCl y el otro biótico, que incluye la interacción del maíz con el hongo biotrófico Ustilago maydis. Pocos genes involucrados en la biosíntesis de poliaminas de maíz han sido aislados y caracterizados. En este sentido, se aisló la secuencia completa del ADNc y la secuencia genómica equivalente al marco de lectura abierto de la espermidina sintasa 2 (Zmspds2) de maíz. Este gen participa en la biosíntesis de Spd a partir de Put. De manera interesante, la organización genómica del gen de la Zmspds2 es altamente homologa a otros genes que codifican para aminopropil transferasas de plantas (espermidina o espermina sintasas), manteniendo conservados el tamaño y la secuencia de la mayoría de los exones. Respecto a los intrones, se observó que también mantienen una similitud elevada, y conservan los bordes típicos entre las secuencias exon/intron de plantas. A nivel transcripcional, se analizó la expresión del gen Zmspds2 junto con la de otros genes involucrados en la biosíntesis de poliaminas (adc, odc y samdc) en diferentes órganos de la planta de maíz, encontrándose una expresión mayoritaria de estos transcritos en hojas. En el caso del estrés salino, se observó una regulación positiva de los genes Zmspds2, Zmspds1 y samdc. Sugerimos, que principalmente, el gen que codifica para la ZmSPDS2 podría jugar un papel muy importante en la respuesta del maíz a este tipo de estrés, ya que su expresión. aumenta con la subsecuente acumulación y/o mantenimiento de los niveles intracelulares de espermina. Además, se aisló una variante de procesamiento alternativo (“splicing”) del transcrito del Zmspds2 (Zmspds2B), la cual se expresa únicamente en presencia de cloruro de sodio. Se encontró que el gen de la Zmspds2 se induce en respuesta a ácido abscísico (ABA), choque osmótico y altas temperaturas lo que sugiere la presencia de elementos de respuesta como ABRE, DRE/CRT, HSE en el promotor de este gen. Estas evidencias sugieren una conexión importante entre el estrés salino, el ácido abscísico y las poliaminas. En el caso del estrés biótico, se analizó el metabolismo de las poliaminas de maíz durante la interacción con Ustilago maydis, incluyendo etapas de la infección como clorosis y la formación de tumores. Esta interacción dió lugar a un aumento en la expresión de los genes adc, samdc1, samdc2 y samdc3 en los tejidos infectados. Además, un aumento notorio en la actividad ADC en los tejidos infectados, se asoció a la acumulación de Put libre y conjugada en estos sitios. La formación de conjugados podría estar asociada directamente con la infección. Estos conjugados participarían en la generación de agentes anti-fúngicos y también en la reducción de la concentración poliaminas libres que podrían estar involucradas en el desarrollo del tumor. Por otro lado, el catabolismo de poliaminas (espermidina y espermina) mediado por la enzima PAO, fue estimulado durante la interacción, sugiriendo un papel importante de este proceso en la lignificación y la formación de la pared durante el desarrollo del tumor. Este trabajo, constituye el primer reporte de regulación transcripcional de la espermidina sintasa en respuesta a estrés salino en plantas y la presencia de una variante de splicing asociada a este proceso. Por otro lado, la evidente acumulación de putrescina libre y conjugada durante el desarrollo de tumores inducidos por Ustilago maydis en maíz, sugiere un papel sumamente importante para la putrescina en estrés biótico.""Soil salinity, in conjunction with drought, high and low temperatures, constitute the major abiotic stresses affecting plant growth and development. In addition, pathogen and insect attack contribute to another percentage of losses in crop productivity. Polyamines, putrescine, spermidine and spermine (Put, Spd and Spm), are low molecular weight aliphatic polycations involved in multiple physiological and developmental processes in plants, and also in response to biotic and abiotic stress conditions. In the present work, we analysed changes in maize polyamine metabolism under two different stress conditions. On one side, we analyzed the effect of salinity (abiotic stress) and on the other side, the interaction of the maize plant with the biotrophic fungus Ustilago maydis. Up to now few sequences coding maize polyamine biosynthetic genes have been isolated and characterized. In these sense, we isolated the full length cDNA sequence and also the genomic sequence equivalent to the open reading frame of the maize spermidine synthase 2 (Zmspds2) gene. This gene participates in Spd biosynthesis from Put. Interestingly, the genomic organization of this gene is highly homologous to other genes encoding plant aminopropyl transferases (spermidine and spermine synthases), conserving size and sequence similarity of most of the exons. In addition, introns also present a considerable sequence homology, including conservation of plant exon/intron boundaries. At the transcriptional level, we analysed the expression of the Zmspds2 gene and that of other genes involved in polyamine biosynthesis (adc, odc and samdc), in different maize organs, finding a predominant expression in leaves. In the case of salt stress, we observed an up-regulation of the Zmspds2, Zmspds1 and samdc genes. Our results suggest an important role of the Zmspds2 gene in the response of maize plants to salt stress, in which transcript accumulation might be related to spermine accumulation and/or maintenance of the intracellular levels of this polyamine under stress. In addition, a splicing variant of the Zmspds2 gene (Zmspds2B) was identified to be induced only in response to NaCl. We observed that the Zmspds2 gene is responsive to abscisic acid (ABA), osmotic stress and heat shock suggesting the presence of cis acting elements such as ABRE, DRE/CTR and HSE in the promoter region of this gene.