Cultivar-Specific Interactions of Soybean with Rhizobium fredii Are Regulated by the Genotype of the Root

Rhizobium fredii USDA257 forms nitrogen-fixing nodules on soybean cultivar Peking, but not on cultivar McCall. This pattern of nodulation persists when McCall and Peking seedlings are cultivated together in plastic growth pouches. Reciprocal grafting experiments confirm that the root genotype, and not that of the shoot, regulates such cultivar specificity. When Peking roots are grafted onto McCall seedlings, the nodulation responses of roots similarly remain unaffected. Transposon-mutant 257DH4, which is derived from USDA257, can form nitrogen-fixing nodules on McCall. Such nodulation is blocked by the presence of USDA257 in the inoculum. Grafting experiments indicate that blocking is not due to a translocatable inhibitor produced by McCall roots or triggered by their interaction with USDA257. Thus, neither freely diffusible nor graft-transmissible substances are involved in cultivar-specific interactions of soybean with R. fredii and its derivatives.     

Molecular characterisation of wild populations and landraces of common bean from northwestern Argentina

Abstract

Information on the variability of wild bean populations and landraces is essential to set conservation strategies and design breeding programmes aimed at enlarging the genetic base of commercial beans. Nineteen Argentinean common bean landraces and wild populations were characterised and their diversity was analysed by means of inter‐simple sequence repeat (ISSR) markers and seed proteins. Populations were successfully identified as belonging to the Andean gene pool of origin by phaseolin electrophoresis, whereas ISSR markers revealed high levels of inter‐ and intra‐population variability. Four of 10 primers produced polymorphic and reproducible DNA profiles, which were used to generate UPGMA (unweighted pair group method with arithmetical averages) and NJ (neighbour‐joining) trees. ISSR markers revealed a high level of variability both within wild bean populations and landraces. Genetic variability of wild samples was associated with their geographic distribution. By contrast, landraces were clustered, at least to some degree, based on their seed colour and shape, showing no clear discrimination among sites. The results presented here suggest that, to a certain extent, hybridisation between wild beans and landraces occurs in the wild, a hypothesis that needs to be tested through further analyses.     

Cladosporium cladosporioides LPSC 1088 Produces the 1,8-Dihydroxynaphthalene-Melanin-Like Compound and Carries a Putative pks Gene

Cladosporium cladosporioides is a dematiaceous fungus with coloured mycelia and conidia due to the presence of dark pigments. The purpose of this study was to characterize the dark pigments synthetized by Cladosporium sp. LPSC no. 1088 and also to identify the putative polyketide synthase (pks) gene that might be involved in the pigment biosynthesis. Morphological as well as molecular features like the ITS sequence confirmed that LPSC 1088 is Cladosporium cladosporioides. UV-visible, Fourier Transform Infrared (FTIR) and Electron Spin Resonance (ESR) spectroscopy analysis as well as melanin inhibitors suggest that the main dark pigment of the isolate was 1,8 dihydroxynaphthalene (DHN)-melanin-type compound. Two commercial fungicides, Difenoconazole and Chlorothalonil, inhibited fungal growth as well as increased pigmentation of the colonies suggesting that melanin might protect the fungus against chemical stress. The pigment is most probably synthetized by means of a pentaketide pathway since the sequence of a 651?bp fragment, coding for a putative polyketide synthase, is highly homologous to pks sequences from other fungi.     

Noah’s arks in the XXI century. A typology of seed banks

In recent decades, seed banks have spread out worldwide as essential institutions for biodiversity preservation, like new Noah’s arks. However, little is known about the diversity of practices that are involved in them. The aim of this study is to reconstruct the dynamics of operation of the different seed banks, developing a typology of them worth providing. As sources for that aim, in-depth interviews to seed banks referents, documents and other materials related to seed banks have been used. First, we describe three stages which seed conservation has undergone until it became modern seed banks. The impact of the Convention on Biological Diversity and its debate context are considered. We analyze the knowledge involved in seed banks which turn them into more than just seeds reservoirs. Afterwards, we study how seed banks are used. From the functioning of seed banks and their objectives, we have identified three bank profiles: assistentialist, productivist and preservationist profiles. Finally, we analyze a series of cases that allow us to show the type of seed banks we have proposed. Policy implications are discussed.     

Effect of night temperature and photoperiod on growth,nodulation and nitrogen fixation inLotus tenuis

Summary Lotus tenuis was inoculated withRhizobium spp. and grown at three different night temperatures (17, 21 and 27°C) and at two different photoperiods for each temperature: short days (SD) of 8-h light and long days (LD) of 16-h light. Night temperature exerted a stronger effect on dry-matter partitioning than of total dry-matter accumulation. Leaf area increased under LD though less N per leaf area was found. A greater number of leaves under SD might be linked to a day-length effect upon apical dominance and hence on branching, thus resulting in a greater crown growth. Nodulation and nitrogen fixation was greater under SD though specific nodule activity was the same regardless of the environmental conditions of growth. It can be concluded that the best planting time forLotus tenuis would be in the autumn when the days are shortening and the temperature is lower.

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Effet de la température nocturne et de la photo-période sur la croissance nodulaire et la fixation d'azote chez Lotus tenuis

Résumé Lotus tenuis a été inoculé avecRhizobium spp. et mis à croître aux trois températures nocturnes, de 17, 21, et 27°C et à deux photo-périodes pour chaque température: des jours courts (SD) de 8 heures de lumière et des jours longs (LD) de 16 heures de lumière. La température nocturne exerce un effet davantage marqué sur la répartition de la matière sèche que sur l'accumulation totale de la matière sèche. La surface foliaire augmente dans le cas des LD bien que l'on trouve moins d'azote par unité de surface foliaire. Dans le cas des SD, de plus grands nombres de feuilles pourraient être liés à un effet de longueur de jours sous dominance apicale, c'est-à-dire en banchement, résultant donc dans la croissance d'une plus grande couronne. La nodulation et la fixation d'azote sont plus grandes dans le cas des SD bien que l'activité spécifique des nodules soit la même, indépendamment des conditions environnementales de croissance. On peut en conclure que le meileur moment de plantation pourLotus tenuis serait l'automne lorsque les jours raccourcissent et que la température est plus basse.

     

Nodulation of Soybean by a Transposon-Mutant of Rhizobium fredii USDA257 Is Subject to Competitive Nodulation Blocking by Other Rhizobia

Rhizobium fredii USDA257 fails to nodulate the improved soybean [Glycine max (L.)Merr.] cultivar McCall in plastic growth pouches. Mutant 257DH4, which was derived from USDA257 by transposon mutagenesis, forms nitrogen fixing nodules under these conditions. If USDA257 is present in inocula containing the mutant, most infections are arrested prior to organization of the nodule meristem, and nodule number is reduced by 95%. The improved cultivars Essex, Harosoy, Hodgson 78, and Viçoja, as well as a supernodulating mutant of Williams, respond like McCall to inoculation with such mixtures of bacteria. Nodulation blocking on McCall can be elicited by rhizobia other than USDA257, provided that they meet two criteria: Blocking strains must themselves be able to induce cortical cells of McCall to divide, and such divisions must proceed to the stage of nodule meristem formation. Nodulation by the mutant remains sensitive to a challenge inoculation with USDA257 for only the first 6 to 12 hours after inoculation. Nodulation blocking involving mutant 257DH4 thus appears to be a rapid, generalized process.     

Genetic diversity of fast-growing rhizobia that nodulate soybean ( Glycine max L. Merr)

The fast-growing Rhizobium sp. strain NGR234, isolated from Papua New Guinea, and 13 strains of Sinorhizobium fredii, isolated from China and Vietnam, were fingerprinted by means of RAPD, REP, ERIC and ARDRA. ERIC, REP and RAPD markers revealed a considerable genetic diversity among fast-growing rhizobia. Chinese isolates showed higher levels of diversity than those strains isolated from Vietnam. ARDRA analysis revealed three different genotypes among fast-growing rhizobia that nodulate soybean, even though all belonged to a subcluster that included Sinorhizobium saheli and Sinorhizobium meliloti. Among S. fredii rhizobia, two strains, SMH13 and HH303, might be representatives of other species of nitrogen-fixing organisms. Although restriction analysis of the nifD–nifK intergenic DNA fragment confirmed the unique nature of Rhizobium sp. strain NGR234, several similarities between Rhizobium sp. strain NGR234 and S. fredii USDA257, the ARDRA analysis and the full sequence of the 16S rDNA confirmed that NGR234 is a S. fredii strain. In addition, ARDRA analysis and the full sequence of the 16S rDNA suggested that two strains of rhizobia might be representatives of other species of rhizobia.     

Molecular cloning and characterization of a sym plasmid locus that regulates cultivar-specific nodulation of soybean by Rhizobium fredii USDA257

Rhizobium fredii strain USDA257 produces nitrogen-fixing nodules on primitive soybean cultivars such as Peking but fails to nodulate agronomically improved cultivars such as McCall. Transposonmutant 257DH4 has two new phenotypes: it nodulates McCall, and its ability to do so is sensitive to the presence of parental strain U5DA257, i.e. it is subject to competitive nodulation blocking. We have isolated a cosmid containing DNA that corresponds to the site of transposon insertion in 257DH4 and have localized Tn5 on an 8.0 kb EcoRI fragment. The 5596 bp DNA sequence that surrounds the insertion site contains seven open reading frames. Five of these, designated nolBTU, ORF4, and nolV, are closely spaced and of the same polarity. nolWand nolX are of the opposite polarity. The initiation codon for nolW lies 155bp upstream from that of nolB, and it is separated from nolXby 281 bp. The predicted NolT and NolW proteins have putative membrane-spanning regions. The N-terminus of the hypothetical NolW protein also has limited homology to NodH of Rhizobium meliloti, but none of the deduced protein sequences has significant homology to known nodulation gene products. Site-directed mutagenesis with mudll1734 confirms that inactivation of nolB, nolT, nolU, nolV, nolW, or nolX extends host range for nodulation to McCall soybean. This phenotype could not be genetically dissected from sensitivity to competitive nodulation blocking. Expression of nolBTU anti nolX is induced as much as 30-fold by flavonoid signal molecules, even though these genes lack nod-box promoters. Histochemical staining of McCall roots inoculated with nolB–, nolU–, or nolX–lacZ fusions verifies that these genes are expressed continuously from preinfection to the stage of the functional nodule. Although a nolU–ORF4–nolV clone hybridizes to a single 8.0 kb EcoRI fragment from 10 strains of R. fredii and broad-host-range Rhizobium sp. NGR234, hybridizing sequences are not detectable in other rhizobia.