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Phytophthora betacei is an oomycete plant pathogen closely related to Phytophthora infestans. It infects tree tomato (Solanum betaceum) in northern South America, but is, under natural conditions, unable to infect potatoes or tomatoes, the main hosts of its sister species P. infestans. We characterized, and compared the effector repertoires of P. betacei and other Phytophthora species. To this end, we used in silico approaches to predict and describe the repertoire of secreted proteins in Phytophthora species and determine unique and core effectors. P. betacei has the largest proteome and secretome of all Phytophthora species evaluated. We identified between 450 and 1933 candidate effector genes in P. ramorum, P. sojae, P. cactorum, P. parasitica, P. palmivora, P. infestans, and P. betacei genomes. The P. betacei predicted secretome contains 5653 proteins, 1126 of which are apoplastic effectors and 807cytoplasmic effectors. Phytophthora betacei es un patógeno vegetal oomiceto estrechamente relacionado con Phytophthora infestans. Infecta el tomate de árbol (Solanum betaceum) en el norte de Sudamérica, pero, en condiciones naturales, no puede infectar patatas o tomates, los principales hospedadores de su especie hermana P. infestans. Caracterizamos y comparamos los repertorios efectores de P. betacei y otras especies de Phytophthora. Con este fin, utilizamos enfoques in silico para predecir y describir el repertorio de proteínas secretadas en especies de Phytophthora y determinar efectores únicos y centrales. P. betacei tiene el proteoma y secretoma más grandes de todas las especies de Phytophthora evaluadas. Identificamos entre 450 y 1933 genes efectores candidatos en los genomas de P. ramorum, P. sojae, P. cactorum, P. parasitica, P. palmivora, P. infestans y P. betacei. El secretoma predicho de P. betacei contiene 5653 proteínas, 1126 de las cuales son efectores apoplásicos y 807 efectores citoplásmicos. Magíster en Biología Computacional Maestría

Expression of the Bradyrhizobium japonicum napEDABC, nirK and norCBQD denitrification genes requires low oxygen (O2) tension and nitrate (NO3−), through a regulatory network comprised of two coordinated cascades, FixLJ-FixK2-NnrR and RegSR-NifA. To precisely understand how these signals are integrated in the FixLJ-FixK2-NnrR circuit, we analyzed β-Galactosidase activities from napE-lacZ, nirK-lacZ and norC-lacZ fusions, and performed analyses of NapC and NorC levels as well as periplasmic nitrate reductase (Nap) activity, in B. japonicum wildtype and fixK2 and nnrR mutant backgrounds. While microoxic conditions (2% O2 at headspace) were sufficient to induce expression of napEDABC and nirK genes and this control depends on FixK2, norCBQD expression requires, in addition to microoxia, nitric oxide gas (NO) and both FixK2 and NnrR transcription factors. Purified FixK2 protein directly interacted and activated transcription in collaboration with B. japonicum RNA polymerase (RNAP) from the napEDABC and nirK promoters, but not from the norCBQD promoter. Further, recombinant NnrR protein bound exclusively to the norCBQD promoter in an O2-sensitive manner. Our work suggest a disparate regulation of B. japonicum denitrifying genes expression with regard to their dependency to microoxia, nitrogen oxides (NOx), and the regulatory proteins FixK2 and NnrR. In this control, expression of napEDABC and nirK genes requires microoxic conditions and directly depends on FixK2, while expression of norCBQD genes relies on NO, being NnrR the candidate which directly interacts with the norCBQD promoter., Fondo Europeo de Desarrollo Regional (FEDER)-co-financed grants (AGL2013-45087-R and AGL2015-63651-P) from the Ministerio de Economía y Competitividad (MINECO), Spain. Grant P12-AGR-1968 and support from the Junta de Andalucía to Group BIO-275 are also acknowledged. EB was supported by grant JAEDOC-047 from the Consejo Superior de Investigaciones Cientificas JAE-DOC Programme co-financed by European Social Fund. EFR received financial support from the FPU programme (grant AP2002-3731, MINECO, Spain).

At a world scale, tomato is an important horticultural crop, but its productivity is highly reduced by drought stress. Combining the application of beneficial microbial inoculants with breeding and grafting techniques may be key to cope with reduced tomato yield under drought. This study aimed to investigate the growth responses and physiological mechanisms involved in the performance under drought stress of four tomato recombinant inbred lines (RIL) after inoculation with the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis and the plant growth promoting rhizobacteria (PGPR) Variovorax paradoxus 5C-2. Results showed a variation in the efficiency of the different tomato RILs under drought stress and a differential effect of the microbial inoculants, depending on the RIL involved. The inoculants affected plant parameters such as net photosynthetic capacity, oxidative damage to lipids, osmolyte accumulation, root hydraulic conductivity or aquaporin abundance and phosphorylation status. RIL66 was the one obtaining maximum benefit from the microbial inoculants under drought stress conditions, due likely to improved CO2-fixation capacity and root hydraulic conductivity. We propose that RIL66 could be selected as a good plant material to be used as rootstock to improve tomato growth and productivity under water limiting conditions. Since RIL66 is highly responsive to microbial inoculants, this grafting strategy should be combined with inoculation of R. irregularis and V. paradoxus in order to improve plant yield under conditions of drought stress.[EN], This research has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 289365 (ROOTOPOWER project).

"En el presente trabajo fue indispensable llevar a cabo una mutación por deleción del gen cdgE para evitar el efecto polar, siendo necesarias una serie de conjugaciones para generar el doble entrecruzamiento generador de la deleción; sin embargo, por el momento no están claras las causas de la baja frecuencia en la conjugación, así como de recombinación al utilizar el plásmido pK18mobsacB/PM-ΔcdgE-QH en A. brasilense Sp245, vector suicida con el origen de replicación oriE, mismo que tiene el plásmido pSUP202 empleado ampliamente para la obtención de mutantes por inserción en A. brasilense. El obtener mutantes por deleción es de gran ayuda para el estudio de varios genes, tal como el cdgE, por lo que es necesario seguir buscando los parámetros fisiológicos adecuados para aumentar la frecuencia de conjugación-recombinación en A. brasilense Sp245."

Wildfires are frecuent in the forest of the Mediterranean Basin and have greatly influenced this ecosystem. Changes to the physical and chemical properties of the soil, due to fire and post-fire conditions result in alterations of both the bacterial communities and the nitrgen cycle,. We explored the effetcs of a holm-oak forest wildfire on the rhizospheric bacterial communities involved in the nitrogen cycle. Metagenomic data of the genes involved in the nitrogen cycle showed that both the undistrubed and burned rhizospheres had a conservative nitrogen cycle with a larger number of sequences related to the nitrogen incorpotation pathways and lower number for nitrogen output. However, the burned rhizosphere showed a statistically significant increase in the number of sequences for nitrogen incorporation (allantoin utilization and nitrogen fixation) and a significantly lower number of sequences for denitrification and dissimilatory nitrite reductase subsystems, possibly in order to compensate for nitrogen loss from the soil after burning. The genetic potential for nitrogen incorporation into the ecosystems was assessed through the diversity of the nitrogenase reductase enzyme, wich is encoded by the nifH gene. We found that nifH gene diversity and richness were lower in burned than in undisturbed rhizospheric soils. The structure of the bacterial communities involved in the nitrogen cycle showed a statistically significant increase of Actinobacteria and Firmicutes phyla after the wildfire. Both approaches showed the important role of Gram-positive bacteria in the ecosystem after a wilfire.

Research activities of the Topic editors are supported by several funding agencies: AP by the Netherlands Organization for Scientific Research (NWO) [ALW grant No. 822.01.005], MP by the Spanish Ministry of Economy and Competitiveness (AGL2012-39923), SR by a National Science Foundation Ambizione grant PZ00P3_131956/1, and TT by the Swiss National Science Foundation (economic stimulus grant).

"La interacción bacteria-planta es una relación de convivencia que permite la promoción del crecimiento vegetal, entre los que se destaca la producción de biopelícula como parte esencial en la colonización de las plantas. Esta comunidad cooperativa permite a la planta beneficiarse de productos del metabolismo de los microorganismos, como lo es la producción de fitohormonas, fijación de nitrógeno, solubilización de fosfatos entre otros. Azospirillum brasilense es una rizobacteria promotora del crecimiento vegetal que forma biopelícula, esta matriz polimérica constituida principalmente de exopolisacáridos, DNA exógeno, proteínas, detritos productos de la lisis celular, agua y otros componentes. Se conoce que este proceso es dependiente de un segundo mensajero el di-GMPc, que a su vez depende de la actividad catalítica de dos enzimas, las diguanilato ciclasas que intervienen en la formación y por el contrario las fosfodiesterasas encargadas de la degradación de este".

In this study, the role of the recently identified class of phytohormones, strigolactones, in shaping root architecture was addressed. Primary root lengths of strigolactone-deficient and -insensitive Arabidopsis (Arabidopsis thaliana) plants were shorter than those of wild-type plants. This was accompanied by a reduction in meristem cell number, which could be rescued by application of the synthetic strigolactone analog GR24 in all genotypes except in the strigolactone-insensitive mutant. Upon GR24 treatment, cells in the transition zone showed a gradual increase in cell length, resulting in a vague transition point and an increase in transition zone size. PIN1/3/7-green fluorescent protein intensities in provascular tissue of the primary root tip were decreased, whereas PIN3-green fluorescent protein intensity in the columella was not affected. During phosphatesufficient conditions, GR24 application to the roots suppressed lateral root primordial development and lateral root forming potential, leading to a reduction in lateral root density. Moreover, auxin levels in leaf tissue were reduced. When auxin levels were increased by exogenous application of naphthylacetic acid, GR24 application had a stimulatory effect on lateral root development instead. Similarly, under phosphate-limiting conditions, endogenous strigolactones present in wild-type plants stimulated a more rapid outgrowth of lateral root primordia when compared with strigolactone-deficient mutants. These results suggest that strigolactones are able to modulate local auxin levels and that the net result of strigolactone action is dependent on the auxin status of the plant.We postulate that the tightly balanced auxin-strigolactone interaction is the basis for the mechanism of the regulation of the plants' root-to-shoot ratio. © 2010 American Society of Plant Biologists., This work was supported by the Netherlands Organization for Scientific Research (VICI grant to H.B.) and the European Commission (Intra-European Marie Curie postdoctoral fellowship FP6–MEIF–CT–2005–024345 and Reintegration grant no. PERG–02–2007–224751 to J.A.L.-R.). This project was cofinanced by the Centre for BioSystems Genomics, which is part of the Netherlands Genomics Initiative/Netherlands Organization for Scientific Research.

Strigolactones are considered a novel class of plant hormones that, in addition to their endogenous signalling function, are exuded into the rhizosphere acting as a signal to stimulate hyphal branching of arbuscular mycorrhizal (AM) fungi and germination of root parasitic plant seeds. Considering the importance of the strigolactones and their biosynthetic origin (from carotenoids), we investigated the relationship with the plant hormone abscisic acid (ABA). Strigolactone production and ABA content in the presence of specific inhibitors of oxidative carotenoid cleavage enzymes and in several tomato ABA-deficient mutants were analysed by LC-MS/MS. In addition, the expression of two genes involved in strigolactone biosynthesis was studied. The carotenoid cleavage dioxygenase (CCD) inhibitor D2 reduced strigolactone but not ABA content of roots. However, in abamineSG-treated plants, an inhibitor of 9-cis-epoxycarotenoid dioxygenase (NCED), and the ABA mutants notabilis, sitiens and flacca, ABA and strigolactones were greatly reduced. The reduction in strigolactone production correlated with the downregulation of LeCCD7 and LeCCD8 genes in all three mutants. The results show a correlation between ABA levels and strigolactone production, and suggest a role for ABA in the regulation of strigolactone biosynthesis. © The Authors (2010). Journal compilation © New Phytologist Trust (2010).