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

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

Agrobacterium rhizogenes transformation of the Phaseolus spp.: A tool for functional genomics

A fast, reproducible, and efficient transformation procedure employing Agrobacterium rhizogenes was developed for Phaseolus vulgaris L. wild accessions, landraces, and cultivars and for three other species belonging to the genus Phaseolus: R coccineus, P lunatus, and P acutifolius. Induced hairy roots are robust and grow quickly. The transformation frequency is between 75 and 90% based on the 35-S promoter-driven green fluorescent protein and beta-glucuronidase expression reporter constructs. When inoculated with Rhizobium tropici, transgenic roots induce normal determinate nodules that fix nitrogen as efficiently as inoculated standard roots. The A. rhizogenes-induced hairy root transformation in the genus Phaseolus sets the foundation for functional genomics programs focused on root physiology, root metabolism, and root-microbe interactions