Draft genome sequence of Bradyrhizobium sp. strain Oc8 isolated from Crotalaria ochroleuca nodule

In this study, we report the draft genome sequence of Bradyrhizobium sp. strain Oc8, a rhizobium isolated from Crotalaria ochroleuca,efficient in C. ochroleuca, C. juncea, C. spectabilis, and Cajanus cajan. The whole genome of the strain Oc8 contains 46 scaffolds, 8,283,342 bp, and 63.27% of GC content. Bradyrhizobium sp. Oc8 is an effective nitrogen-fixing bacterium with potential use as an inoculant for legumes used as cover crops and green manures.ANII: FMV_ 3_2016_1_12549

Phenotyping Systems for Evaluating Saline Stress Response in Lotus

La tolerancia al estrés salino es un carácter complejo determinado por la sumatoria de los efectos de numerosos genes, cuya identificación es necesaria para la definición de estrategias de mejoramiento. En este sentido, el uso de plantas modelo genotipadas y la disponibilidad de métodos de fenotipado masivo son útiles para asistir a los programas de mejoramiento. Lotus japonicus (Regel) K. Larsen es un modelo de leguminosa con nodulación determinada, que puede ser utilizada en la identificación de determinantes genéticos en programas de mejoramiento de Lotus y otras leguminosas forrajeras. En este trabajo, para establecer un sistema de cultivo adecuado para el fenotipado masivo, se compararon cuatro sistemas experimentales para evaluar respuestas a estrés salino: placas, pouch, hidroponía y macetas. Los resultados obtenidos permitieron elegir el sistema de hidroponía como el más adecuado para evaluar el estrés salino, dado que se pudieron establecer diferencias en las respuestas fisiológicas basadas en parámetros de crecimiento y desarrollo en los genotipos Lotus japonicus Gifu y Lotus burttii. Además, el sistema de hidroponía permitió discriminar respuestas en una población de líneas recombinantes puras (RILs), producto del cruzamiento de Lotus japonicus Gifu x Lotus burttii. Contar con un sistema de cultivo que permita realizar de manera precisa el fenotipado masivo de plantas, es necesario para identificar regiones del genoma implicadas en las respuestas a estrés salino.Salt stress tolerance is a complex trait which is determined by the additive effects of several genes whose identification is necessary to define improvement strategies. In this sense, the use of model plants genotyped and the availability of massive phenotyping methods are useful to assist breeding programs. Lotus japonicus (Regel) K. Larsen has been adopted as a determined nodulating legume model, which can be used for identification of the genetic determinants in the breeding program of Lotus and other forage legumes. In this work, in order to establish a growth system suitable for massive phenotyping, we compared four experimental systems for evaluating saline stress responses: plates, pouch, hydroponic and pots. Results allow to choose the hydroponic system as the most suitable for evaluating saline stress, since it is able to establish differences in responses based on physiological parameters of growth and development in Lotus japonicus (Gifu) and Lotus burttii genotypes. Moreover, the hydroponic system allowed to discriminate the responses in a population of recombinant inbreed lines (RILs) originated by the crossing of Lotus japonicus Gifu x Lotus burttii. Having a culture system that allows precise and massive phenotyping is necessary for detecting genomic regions involved in the responses to saline stress.Fil: Quero, Gastón Eduardo. Universidad de la República; UruguayFil: Borsani, Omar. Universidad de la República; UruguayFil: Gutiérrez, Lucía. Universidad de la República; UruguayFil: Melchiorre, Mariana Noemi. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Fisiología y Recursos Geneticos Vegetales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Monza, Jorge. Universidad de la República; UruguayFil: Lascano, Hernan Ramiro. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Fisiología y Recursos Geneticos Vegetales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Cellular Stress Following Water Deprivation in the Model Legume Lotus japonicus

Drought stress is one of the most important factors in the limitation of plant productivity worldwide. In order to cope with water deprivation, plants have adopted several strategies that produce major changes in gene expression. In this paper, the response to drought stress in the model legume Lotus japonicus was studied using a transcriptomic approach. Drought induced an extensive reprogramming of the transcriptome as related to various aspects of cellular metabolism, including genes involved in photosynthesis, amino acid metabolism and cell wall metabolism, among others. A particular focus was made on the genes involved in the cellular stress response. Key genes involved in the control of the cell cycle, antioxidant defense and stress signaling, were modulated as a consequence of water deprivation. Genes belonging to different families of transcription factors were also highly responsive to stress. Several of them were homologies to known stress-responsive genes from the model plant Arabidopsis thaliana, while some novel transcription factors were peculiar to the L. japonicus drought stress response

Inoculantes rizobianos para alfalfa en suelos ácidos: Una propuesta para Uruguay

Ensifer meliloti establishes symbiosis with Medicago sativa (alfalfa) and other perennial species of Medicago that grow in soils with neutral to alkaline pH, whereas Ensifer medicae makes symbiosis with annual medics adapted to moderately acid soils. The new species Rhizobium favelukesii, whose strain is LPU83, belongs to an alfalfa group of inefficient rhizobia, known as the Oregon type, initially represented by Rhizobium sp. strain Or191. R. favelukesii is considered a potential risk in the acid soils where alfalfa is grown, and could explain the inefficient nodulation observed in different countries. In acidic soils from the «Dairy Basin» of Uruguay, producers inoculate alfalfa with E. melliloti U143 strain. This edaphic condition is often marginal because the maximum potential of rhizobia-alfalfa symbiosis is not achieved at acid pH. Although Uruguay has an outstanding position in the production and use of rhizobial inoculants, the commercial strains currently used in Trifolium, Lotus and alfalfa were selected about 50 years ago in different conditions that the present ones as a consequence of: i) the displacement of cultivated pastures to other sites, ii) the sowing method, and iii) the use of new cultivars. In this review, alfalfa inoculation is analyzed in some countries and a strategy for the development of an inoculant suitable for Uruguayan acid soils is proposed. This strategy is based on the selection of efficient and competitive strains, as the first selection criteria, and persistency in soil as the second one.Ensifer meliloti establece simbiosis con Medicago sativa (alfalfa) y otras especies perennes de Medicago que crecen en suelos con pH neutro a alcalino, mientras que Ensifer medicae lo hace con especies anuales adaptadas a suelos moderadamente ácidos. La nueva especie Rhizobium favelukesii, cuya cepa tipo es LPU83, pertenece a un grupo de rizobios ineficientes en alfalfa conocidos como tipo Oregon, representados inicialmente por Rhizobium sp. cepa Or191. R. favelukesii; se considera un riesgo potencial en suelos ácidos en los que se cultiva alfalfa, y podría explicar la nodulación ineficiente en diferentes países. En suelos ácidos de la «Cuenca lechera» de Uruguay los productores inoculan alfalfa con E. meliloti cepa U143. Esa condición edáfica a veces resulta marginal para la simbiosis rizobio-alfalfa porque a pH ácido no se logra su máximo potencial. Si bien Uruguay tiene una posición destacada en la producción y uso de inoculantes rizobianos, las cepas comerciales usadas actualmente en especies de Trifolium, Lotus y alfalfa se seleccionaron hace unos 50 años en condiciones diferentes a las actuales, consecuencia de: i) el desplazamiento de pasturas cultivadas a otros sitios, ii) el tipo de siembra y iii) el uso de nuevos cultivares. En esta revisión se analiza la inoculación de la alfalfa en algunos países y se propone una estrategia para el desarrollo de un inoculante apto para suelos ácidos en Uruguay. Esta estrategia se basa en la selección de cepas eficientes y competitivas como primer criterio y persistencia en suelos, como segundo.Fil: Tabares da Rosa, Sofía. Universidad de la República; UruguayFil: Signorelli, Santiago. Universidad de la República; UruguayFil: del Papa, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Biotecnología y Biología Molecular. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Biotecnología y Biología Molecular; ArgentinaFil: Sabatini, Ornella. Universidad de la República; UruguayFil: Reyno, Rafael. Instituto Nacional de Investigación Agropecuaria; UruguayFil: Lattanzi, Fernando. Instituto Nacional de Investigación Agropecuaria; UruguayFil: Rebuffo, Mónica. Instituto Nacional de Investigación Agropecuaria; UruguayFil: Sanjuán, Juan. Consejo Superior de Investigaciones Científicas; EspañaFil: Monza Galetti, Jorge. Universidad de la República; Urugua

The Rhizobia-Lotus Symbioses: Deeply Specific and Widely Diverse

The symbiosis between Lotus and rhizobia has been long considered very specific and only two bacterial species were recognized as the microsymbionts of Lotus: Mesorhizobium loti was considered the typical rhizobia for the L. corniculatus complex, whereas Bradyrhizobium sp. (Lotus) was the symbiont for L. uliginosus and related species. As discussed in this review, this situation has dramatically changed during the last 15 years, with the characterization of nodule bacteria from worldwide geographical locations and from previously unexplored Lotus spp. Current data support that the Lotus rhizobia are dispersed amongst nearly 20 species in five genera (Mesorhizobium, Bradyrhizobium, Rhizobium, Ensifer, and Aminobacter). As a consequence, M. loti could be regarded an infrequent symbiont of Lotus, and several plant–bacteria compatibility groups can be envisaged. Despite the great progress achieved with the model L. japonicus in understanding the establishment and functionality of the symbiosis, the genetic and biochemical bases governing the stringent host-bacteria compatibility pairships within the genus Lotus await to be uncovered. Several Lotus spp. are grown for forage, and inoculation with rhizobia is a common practice in various countries. However, the great diversity of the Lotus rhizobia is likely squandered, as only few bacterial strains are used as inoculants for Lotus pastures in very different geographical locations, with a great variety of edaphic and climatic conditions. The agroecological potential of the genus Lotus can not be fully harnessed without acknowledging the great diversity of rhizobia-Lotus interactions, along with a better understanding of the specific plant and bacterial requirements for optimal symbiotic nitrogen fixation under increasingly constrained environmental conditions

Rhizobia Inoculants for Alfalfa in Acid Soils: A Proposal for Uruguay

Ensifer meliloti establishes symbiosis with Medicago sativa (alfalfa) and other perennial species of Medicago that grow in soils with neutral to alkaline pH, whereas Ensifer medicae makes symbiosis with annual medics adapted to moderately acid soils. The new species Rhizobium favelukesii, whose strain is LPU83, belongs to an alfalfa group of inefficient rhizobia, known as the Oregon type, initially represented by Rhizobium sp. strain Or191. R. favelukesii is considered a potential risk in the acid soils where alfalfa is grown, and could explain the inefficient nodulation observed in different countries. In acidic soils from the «Dairy Basin» of Uruguay, producers inoculate alfalfa with E. melliloti U143 strain. This edaphic condition is often marginal because the maximum potential of rhizobia-alfalfa symbiosis is not achieved at acid pH. Although Uruguay has an outstanding position in the production and use of rhizobial inoculants, the commercial strains currently used in Trifolium, Lotus and alfalfa were selected about 50 years ago in different conditions that the present ones as a consequence of: i) the displacement of cultivated pastures to other sites, ii) the sowing method, and iii) the use of new cultivars. In this review, alfalfa inoculation is analyzed in some countries and a strategy for the development of an inoculant suitable for Uruguayan acid soils is proposed. This strategy is based on the selection of efficient and competitive strains, as the first selection criteria, and persistency in soil as the second one.Instituto de Biotecnologia y Biologia Molecula

Proline does not quench singlet oxygen: Evidence to reconsider its protective role in plants

Plants are commonly subjected to several environmental stresses that lead to an overproduction of reactive oxygen species (ROS). As plants accumulate proline in response to stress conditions, some authors have proposed that proline could act as a non-enzymatic antioxidant against ROS. One type of ROS aimed to be quenched by proline is singlet oxygen (1O2), molecular oxygen in its lowest energy electronically excited state, constitutively generated in oxygenic, photosynthetic organisms. In this study we clearly prove that proline cannot quench 1O2 in aqueous buffer, giving rise to a rethinking about the antioxidant role of proline against 1O2.This research has financial support from ANII and PEDECIBA(Uruguay), the Spanish Ministry of Economy and Competitiveness and the Research Council of Norway.Peer reviewe

Crop Performance Indexes Applied to Legume Used as Summer Cover Crops under Water Deficit Conditions

Summer legume cover crops (CC) such as Crotalaria juncea, Crotalaria spectabilis, Crotalaria ochroleuca, and Cajanus cajan could offer diverse advantages for the environment and productive cropping systems. A low transpiration efficiency (TE) of CC can induce soil water content to levels that present a challenge for the subsequent crop. In a 75-day growth chamber experiment, using the natural abundance of 13C, 18O, and 15N we evaluated the TE and BNF under two soil water conditions. Our results showed that the four species tested are good candidates for their use as CC because they showed good results in terms of productivity parameters, TE, and BFN. Cajanus cajan had the highest TE, a high shoot dry matter production, and accumulated more N from BFN in the shoot than C. spectabilis, C. juncea, and C. ochroleuca. ∆18O increased under moderate water deficit and showed an inversely proportional relationship with the amount of transpired water, supporting the use of this isotopic indicator as a proxy for transpiration and stomatal conductance. For the isotopic parameters no interaction between the factors water regimen and species were found. We propose the mass ratio of nitrogen fixed by the volume of transpired water and the isotopic discrimination of 13C as useful indicators of drought fixing legumes tolerance

Phylogenetic relationships among introduced and autochthonous rhizobia nodulating Trifolium spp. in Uruguayan soils

Trifolium pratense (red clover) and T. repens (white clover) inoculated with Rhizobium leguminosarum sv. trifolii strain U204 are used to improve pastures in Uruguay. Although inoculation is a common practice in the country, there has been a progressive abandonment by farmers because they do not always see the benefits. The presence of efficient rhizobial populations may be one of the reasons why a response to inoculation is not always observed. We studied the identities and phylogenetic relationships among the clover rhizobia populating Uruguayan soils by analysis of 16S rRNA genes, ITS sequences and housekeeping (atpD, glnII, recA, rpoB) and symbiotic (nodA, nodC, nifH) genes. Strains like P3 and P33, isolated from the endemic Trifolium polymorphum, are inefficient in red and white clover. These strains clustered separately from the symbionts of these clovers. Bacteria which are efficient in red and white clovers clustered in either of two groups: one, represented by isolate 249, are likely naturalized rhizobia derived from the inoculant U204; and other included strains like U317 and N2, which share symbiotic genes with the inoculant. We hypothesize that these strains may be derived from native strains that acquired symbiotic gene from inoculant strains. These types of rhizobia are strong candidates for a second generation of clover inoculants for Uruguay.Authors are grateful to the funding of grants from FPTA-INIA 295, PEDECIBA and Udelar-CAP (Magister grant for C.T.). The support of the Estación Experimental del Zaidín-CSIC and the Spanish National Research Agency to the lab of JS (i.e., Grants BIO2014-55075-P and BIO2017-83533-P, cofinanced with FEDER funds) are greatly acknowledged.Peer Reviewe