Comparative cytogenomics reveals genome reshuffling and centromere repositioning in the legume tribe Phaseoleae

The tribe Phaseoleae (Leguminosae; Papilionoideae) includes several legume crops with assembled genomes. Comparative genomic studies indicated the preservation of large genomic blocks in legumes. However, the chromosome dynamics along its evolution was not investigated in the tribe. We conducted a comparative genomic analysis using CoGe Synmap platform to define a useful genomic block (GB) system and to reconstruct the ancestral Phaseoleae karyotype (APK). We defined the GBs based on orthologous genes between Phaseolus vulgaris and Vigna unguiculata genomes (n = 11), then searched for these GBs in different genome species belonging to the Phaseolinae (P. lunatus, n = 11) and Glycininae (Amphicarpaea edgeworthii, n = 11 and Spatholobus suberectus, n = 9) subtribes, and in the outgroup (Medicago truncaluta, n = 8). To support our in silico analysis, we used oligo-FISH probes of P. vulgaris chromosomes 2 and 3 to paint the orthologous chromosomes of the non-sequenced Phaseolinae species (Macroptilium atropurpureum and Lablab purpureusi, n = 11). We inferred the APK with n = 11, 22 GBs (A to V) and 60 sub-GBs. We hypothesized that the main rearrangements within Phaseolinae involved nine APK chromosomes, with extensive centromere repositioning resulting from evolutionary new centromeres (ENC) in the Phaseolus lineage. We demonstrated that the A. edgeworthii genome is more reshuffled than the dysploid S. suberectus genome, in which we could reconstructed the main events responsible for the chromosome number reduction. The development of the GB system and the proposed APK provide useful tools for future comparative genomic analyses of legume species.

Macroptilium atropurpureum (siratro).

Macroptilium atropurpureum is a perennial herb widely cultivated across tropical and subtropical regions of the world as a forage crop, a soil and pasture improver and for ground cover. It is native to tropical America and has been introduced across Africa, Asia, the Caribbean, Australia and many islands in Oceania. Outside its native distribution range, and in some areas inside its native range, this species is a weed of disturbed sites, roadsides, secondary forests and ungrazed areas. It can form dense stands along forest margins and can also smother native shrubs, grasses and young trees. It has a deep-rooting system and can tolerate extreme drought conditions. Currently, M. atropurpureum is listed as invasive in Hawaii, the Dominican Republic, India, Australia and many islands in Oceania including, Fiji, Palau and Tonga.

Distribución potencial de dos especies de leguminosas en la microcuenca Tula, México

Macroptilium atropurpureum (DC.) Urb y Vicia sativa L. son dos especies forrajeras con potencial para la rehabilitación de suelos que toleran la sequía, compiten con plantas indeseadas y fijan nitrógeno. Sin embargo, se desconoce su distribución potencial en México y las zonas convenientes para introducirlas. El objetivo del presente trabajo fue evaluar la distribución geográfica potencial de M. atropurpureum y V. sativa, en la microcuenca Tula, México mediante el modelo de nicho ecológico BIOCLIM, para determinar sus zonas de óptimo crecimiento, con fines de rehabilitación de suelos. Para la modelación, se utilizaron 15 variables bioclimáticas, así como 19 registros de presencia de la especie V. sativa y 219 de M. atropurpureum, obtenidos de las bases de datos REMIB y MEXU. Los resultados de la modelación indicaron que los modelos, para M. atropurpureum y V. sativa, tienen una buena capacidad de predicción, de acuerdo con los valores obtenidos del Área Bajo la Curva, AUC, con 0.801 y 0.967, respectivamente. La distribución potencial de la especie V. sativa osciló de bajo a muy bajo, 96% de la superficie de la microcuenca; mientras que 97% de la superficie para M. atropurpureum fue muy baja y registraron una regular supervivencia con 70% y 66%, respectivamente, en la validación experimental en campo. Debido al bajo potencial de distribución y su regular supervivencia, la introducción de las dos especies no se consideró una opción para la rehabilitación de suelos en la microcuenca Tula.

Structure of the unusual Sinorhizobium fredii HH103 lipopolysaccharide and its role in symbiosis

Rhizobia are soil bacteria that form important symbiotic associations with legumes, and rhizobial surface polysaccharides, such as K-antigen polysaccharide (KPS) and lipopolysaccharide (LPS), might be important for symbiosis. Previously, we obtained a mutant of Sinorhizobium fredii HH103, rkpA, that does not produce KPS, a homopolysaccharide of a pseudaminic acid derivative, but whose LPS electrophoretic profile was indistinguishable from that of the WT strain. We also previously demonstrated that the HH103 rkpLMNOPQ operon is responsible for 5-acetamido-3,5,7,9-tetradeoxy-7-(3-hydroxybutyramido)-l-glycero-l-manno-nonulosonic acid [Pse5NAc7(3OHBu)] production and is involved in HH103 KPS and LPS biosynthesis and that an HH103 rkpM mutant cannot produce KPS and displays an altered LPS structure. Here, we analyzed the LPS structure of HH103 rkpA, focusing on the carbohydrate portion, and found that it contains a highly heterogeneous lipid A and a peculiar core oligosaccharide composed of an unusually high number of hexuronic acids containing β-configured Pse5NAc7(3OHBu). This pseudaminic acid derivative, in its α-configuration, was the only structural component of the S. fredii HH103 KPS and, to the best of our knowledge, has never been reported from any other rhizobial LPS. We also show that Pse5NAc7(3OHBu) is the complete or partial epitope for a mAb, NB6-228.22, that can recognize the HH103 LPS, but not those of most of the S. fredii strains tested here. We also show that the LPS from HH103 rkpM is identical to that of HH103 rkpA but devoid of any Pse5NAc7(3OHBu) residues. Notably, this rkpM mutant was severely impaired in symbiosis with its host, Macroptilium atropurpureum.

Composición química y digestibilidad de cuatro leguminosas tropicales mexicanas

En México, las propiedades nutricionales de las leguminosas tropicales no se conocen ampliamente. Por tanto, el objetivo del presente estudio fue evaluar el valor nutricional de Arachis pintoi, Clitoria ternatea, Macroptilium atropurpureum y Stylosanthes guianensis. Se evaluaron, proteína cruda (PC), fibra cruda (FC), extracto etéreo (EE), cenizas (CEN), fibra detergente ácido (FDA), fibra detergente neutro (FDN), lignina cruda (LC), digestibilidad in vitro de la materia seca (DIVMS) y digestibilidad in situ de la MS (DISMS). Las muestras se colectaron en las parcelas experimentales del INIFAP, estado de Veracruz, México. Las evaluaciones se realizaron en el Departamento de Zootecnia, Universidad Autónoma Chapingo. Cada especie se evaluó, con tres repeticiones y cada repetición se consideró la unidad experimental, resultando doce observaciones por variable. Las medias se separaron mediante la prueba de Tukey (p< 0.05). Arachis pintoi mostró los porcentajes más altos de PC (25.2%), CEN (9%), DIVMS (83.2%) y DISMS (88.0%) y los valores más bajos de FDN (32.8%), FDA (26.9%) y LC (5.5%). Macroptilium atropurpureum mostró los porcentajes más bajos de PC, DIVMS, DISMS y CEN (6.4%) y los valores altos de FDN (50.9%), FDA (37.6%) y LC (11.8%). Las otras leguminosas mostraron valores intermedios o bajos de todas las variables. Por tanto, con base en la composición química y la digestibilidad in vitro e in situ de la materia seca, Arachis pintoi fue la especie con el mejor valor nutricional.

MORPHOPHYSIOLOGY OF RHIZOBIA ISOLATED FROM NATIVE FORAGE OF FABACEAE OF THE CAATINGA

ABSTRACT The rhizobia found in Fabaceae plants of the Caatinga may have potential as fodder in the semiarid region, thus increasing the availability of feed for animal production in this region. This study aimed to characterize the morphophysiology of rhizobia strains of the forage species Mimosa tenuiflora (Jurema preta), Macroptilium atropurpureum (Siratro), and Desmanthus pernambucanus (Jureminha). The soil used as the substrate was collected at specific locations in the municipalities of Sertânia, Arcoverde, and São Bento do Una, state of Pernambuco. The characterization of rhizobial colonies included growth period, diameter, elevation, transparency, exopolysaccharides production, and color. In addition, salinity, temperature, and pH tolerance tests of the native rhizobia were conducted. Evaluation of cultures showed that the isolates formed colonies with flat elevation, moderate production of exopolysaccharides, coloration varying from cream to white, and a smooth surface. Physiological tests of abiotic stress resistance showed that the native species isolated from M. tenuiflora were more resistant when grown in soils from the municipality of Sertânia and isolates from M. atropurpureum and D. pernambucanus had high resistance to high temperatures, regardless of place of farming. It can be concluded that native rhizobia from the Semiarid region of Pernambuco show resistance to stress caused by high temperatures, salinity variation, and pH. These characteristics are influenced by soil and the botanical species in symbiosis with the rhizobia.

Semillas de siratro (Macroptilium atropurpureum) sometidas a escarificación química y térmica

Las leguminosas forrajeras, en general representan alto valor proteico; sin embargo, presentan limitaciones para su establecimiento debido a la latencia de las semillas. En función de ello, se evaluó la germinación de la semilla de Macroptilium atropurpureum, luego de recibir escarificación química con ácido sulfúrico al 96% en inmersión durante tres minutos, inmersión en agua caliente a 80ºC durante cinco minutos, en agua potable al ambiente durante 24 horas y un testigo (sin tratar). Se aplicó un diseño completamente aleatorizado con 15 repeticiones cada uno. Las variables cuantificadas fueron rendimiento de semillas, germinación y supervivencia de plántulas. Se encontraron 73000 semillas viables y 3% de impurezas por cada kilogramo de semilla recolectado. Las semillas tratadas con ácido sulfúrico fueron las que presentaron un mejor porcentaje de germinación y supervivencia (80 y 75.56%); seguida por las tratadas con agua a 80ºC (75.56 y 73.34%). La escarificación de semillas de leguminosas debe ser un procedimiento imprescindible, mismo que debe hacerse con un ácido sulfúrico concentrado por cuanto se encontraron los mejores resultados en germinación de semillas y supervivencia de plántulas

Loss of NifQ Leads to Accumulation of Porphyrins and Altered Metal-Homeostasis in Nitrogen-Fixing Symbioses

Symbiotic nitrogen fixation between legumes and rhizobia involves a coordinated expression of many plant and bacterial genes as well as finely tuned metabolic activities of micro- and macrosymbionts. In spite of such complex interactions, symbiotic proficiency remains a resilient process, with host plants apparently capable of compensating for some deficiencies in rhizobia. What controls nodule homeostasis is still poorly understood and probably varies between plant species. In this respect, the promiscuous Sinorhizobium (Ensifer) fredii strain NGR234 has become a model to assess the relative contribution of single gene products to many symbioses. Here, we describe how a deletion in nifQ of NGR234 (strain NGRΔnifQ) makes nodules of Vigna unguiculata, V. radiata, and Macroptilium atropurpureum but not of the mimisoid tree Leucaena leucocephala, purple-red. This peculiar dark-nodule phenotype did not necessarily correlate with a decreased proficiency of NGRΔnifQ but coincided with a 20-fold or more accumulation of coproporphyrin III and uroporphyrin III in V. unguiculata nodules. Porphyrin accumulation was not restricted to plant cells infected with bacteroids but also extended to the nodule cortex. Nodule metal-homeostasis was altered but not sufficiently to prevent assembly and functioning of nitrogenase. Although the role of NifQ in donating molybdenum during assembly of nitrogenase cofactor FeMo-co makes it essential in free-living diazotrophs, our results highlight the dispensability of NifQ in many legume species.