The diversity of soil microbial communities matters when legumes face drought

The cultivation of legumes shows promise for the development of sustainable agriculture, but yield instability remains one of the main obstacles for its adoption. Here, we tested whether the yield stability (i.e., resistance and resilience) of pea plants subjected to drought could be enhanced by soil microbial diversity. We used a dilution approach to manipulate the microbial diversity, with a genotype approach to distinguish the effect of symbionts from that of microbial diversity as a whole. We investigated the physiology of plants in response to drought when grown on a soil containing high or low level of microbial diversity. Plants grown under high microbial diversity displayed higher productivity and greater resilience after drought. Yield losses were mitigated by 15% on average in the presence of high soil microbial diversity at sowing. Our study provides proof of concept that the soil microbial community as a whole plays a key role for yield stability after drought even in plant species living in relationships with microbial symbionts. These results emphasize the need to restore soil biodiversity for sustainable crop management and climate change adaptation.

Independent Regulation of Symbiotic Nodulation by the SUNN Negative and CRA2 Positive Systemic Pathways

Plant systemic signaling pathways allow the integration and coordination of shoot and root organ metabolism and development at the whole-plant level depending on nutrient availability. In legumes, two systemic pathways have been reported in the Medicago truncatula model to regulate root nitrogen-fixing symbiotic nodulation. Both pathways involve leucine-rich repeat receptor-like kinases acting in shoots and proposed to perceive signaling peptides produced in roots depending on soil nutrient availability. In this study, we characterized in the M. truncatula Jemalong A17 genotype a mutant allelic series affecting the Compact Root Architecture2 (CRA2) receptor. These analyses revealed that this pathway acts systemically from shoots to positively regulate nodulation and is required for the activity of carboxyl-terminally encoded peptides (CEPs). In addition, we generated a double mutant to test genetic interactions of the CRA2 systemic pathway with the CLAVATA3/EMBRYO SURROUNDING REGION peptide (CLE)/Super Numeric Nodule (SUNN) receptor systemic pathway negatively regulating nodule number from shoots, which revealed an intermediate nodule number phenotype close to the wild type. Finally, we showed that the nitrate inhibition of nodule numbers was observed in cra2 mutants but not in sunn and cra2 sunn mutants. Overall, these results suggest that CEP/CRA2 and CLE/SUNN systemic pathways act independently from shoots to regulate nodule numbers.

Co-inoculation of a Pea Core-Collection with Diverse Rhizobial Strains Shows Competitiveness for Nodulation and Efficiency of Nitrogen Fixation Are Distinct traits in the Interaction

Pea forms symbiotic nodules with Rhizobium leguminosarum sv. viciae (Rlv). In the field, pea roots can be exposed to multiple compatible Rlv strains. Little is known about the mechanisms underlying the competitiveness for nodulation of Rlv strains and the ability of pea to choose between diverse compatible Rlv strains. The variability of pea-Rlv partner choice was investigated by co-inoculation with a mixture of five diverse Rlv strains of a 104-pea collection representative of the variability encountered in the genus Pisum. The nitrogen fixation efficiency conferred by each strain was determined in additional mono-inoculation experiments on a subset of 18 pea lines displaying contrasted Rlv choice. Differences in Rlv choice were observed within the pea collection according to their genetic or geographical diversities. The competitiveness for nodulation of a given pea-Rlv association evaluated in the multi-inoculated experiment was poorly correlated with its nitrogen fixation efficiency determined in mono-inoculation. Both plant and bacterial genetic determinants contribute to pea-Rlv partner choice. No evidence was found for co-selection of competitiveness for nodulation and nitrogen fixation efficiency. Plant and inoculant for an improved symbiotic association in the field must be selected not only on nitrogen fixation efficiency but also for competitiveness for nodulation.

Comparative Genome-Wide-Association Mapping Identifies Common Loci Controlling Root System Architecture and Resistance to Aphanomyces euteiches in Pea

Combining plant genetic resistance with architectural traits that are unfavorable to disease development is a promising strategy for reducing epidemics. However, few studies have identified root system architecture (RSA) traits with the potential to limit root disease development. Pea is a major cultivated legume worldwide and has a wide level of natural genetic variability for plant architecture. The root pathogen Aphanomyces euteiches is a major limiting factor of pea crop yield. This study aimed to increase the knowledge on the diversity of loci and candidate genes controlling RSA traits in pea and identify RSA genetic loci associated with resistance to A. euteiches which could be combined with resistance QTL in breeding. A comparative genome wide association (GWA) study of plant architecture and resistance to A. euteiches was conducted at the young plant stage in a collection of 266 pea lines contrasted for both traits. The collection was genotyped using 14,157 SNP markers from recent pea genomic resources. It was phenotyped for ten root, shoot and overall plant architecture traits, as well as three disease resistance traits in controlled conditions, using image analysis. We identified a total of 75 short-size genomic intervals significantly associated with plant architecture and overlapping with 46 previously detected QTL. The major consistent intervals included plant shoot architecture or flowering genes (PsLE, PsTFL1) with putative pleiotropic effects on root architecture. A total of 11 genomic intervals were significantly associated with resistance to A. euteiches confirming several consistent previously identified major QTL. One significant SNP, mapped to the major QTL Ae-Ps7.6, was associated with both resistance and RSA traits. At this marker, the resistance-enhancing allele was associated with an increased total root projected area, in accordance with the correlation observed between resistance and larger root systems in the collection. Seven additional intervals associated with plant architecture overlapped with GWA intervals previously identified for resistance to A. euteiches. This study provides innovative results about genetic interdependency of root disease resistance and RSA inheritance. It identifies pea lines, QTL, closely-linked markers and candidate genes for marker-assisted-selection of RSA loci to reduce Aphanomyces root rot severity in future pea varieties.

Effects of faba beans with different concentrations of vicine and convicine on egg production, egg quality and red blood cells in laying hens

The faba bean (Vicia faba L.) is a potential source of proteins for poultry, mainly for laying hens whose protein requirements are lower than those of other birds such as growing broilers and turkeys. However, this feedstuff contains anti-nutritional factors, that is, vicine (V) and convicine (C) that are already known to reduce laying hen performance. The aim of the experiment reported here was to evaluate the effects of a wide range of dietary V and C concentrations in laying hens. Two trials were performed with laying hens fed diets including 20% or 25% of faba bean genotypes highly contrasting in V+C content. In Trial 1, faba beans from two tannin-containing cultivars, but with high or low V+C content were dehulled in order to eliminate the tannin effect. In addition to the contrasting levels of V+C in the two cultivars, two intermediate levels of V+C were obtained by mixing the two cultivars (70/30 and 30/70). In Trial 2, two isogenic zero-tannin faba bean genotypes with high or low V+C content were used. In both trials, a classical corn-soybean diet was also offered to control hens. Each experimental diet was given to 48 laying hens for 140 (Trial 1) or 89 (Trial 2) days. Laying performance and egg quality were measured. The redox sensitivity of red blood cells (RBCs) was assessed by measuring hemolysis and reduced glutathione (GSH) concentration in these cells. Egg weight was significantly reduced by the diets containing the highest concentrations of V+C (P<0.0001) in Trial 1 and slightly reduced (P<0.10) in Trial 2, but only weak linear relationships between egg weight and dietary V+C concentration were established. No negative effect of V+C level was observed for egg quality parameters. In contrast, certain parameters (i.e. Haugh units, yolk color) were improved by feeding low V+C diets (P<0.05). Hemolysis of RBCs was higher in hens fed high V+C diets. A decrease in GSH concentration in RBCs of hens fed the highest levels of V+C was observed. Faba bean genotypes with low concentrations of V+C can therefore be used in laying hen diets up to 25% without any detrimental effects on performance levels or egg characteristics, without any risk of hemolysis of RBCs.

A SNP-based consensus genetic map for synteny-based trait targeting in faba bean (Vicia faba L.)

Faba bean (Vicia faba L.) is a globally important nitrogen-fixing legume, which is widely grown in a diverse range of environments. In this work, we mine and validate a set of 845 SNPs from the aligned transcriptomes of two contrasting inbred lines. Each V. faba SNP is assigned by BLAST analysis to a single Medicago orthologue. This set of syntenically anchored polymorphisms were then validated as individual KASP assays, classified according to their informativeness and performance on a panel of 37 inbred lines, and the best performing 757 markers used to genotype six mapping populations. The six resulting linkage maps were merged into a single consensus map on which 687 SNPs were placed on six linkage groups, each presumed to correspond to one of the six V. faba chromosomes. This sequence-based consensus map was used to explore synteny with the most closely related crop species, lentil and the most closely related fully sequenced genome, Medicago. Large tracts of uninterrupted colinearity were found between faba bean and Medicago, making it relatively straightforward to predict gene content and order in mapped genetic interval. As a demonstration of this, we mapped a flower colour gene to a 2-cM interval of Vf chromosome 2 which was highly colinear with Mt3. The obvious candidate gene from 78 gene models in the collinear Medicago chromosome segment was the previously characterized MtWD40-1 gene controlling anthocyanin production in Medicago and resequencing of the Vf orthologue showed a putative causative deletion of the entire 5' end of the gene.

Genetic diversity and trait genomic prediction in a pea diversity panel

BACKGROUND

Pea (Pisum sativum L.), a major pulse crop grown for its protein-rich seeds, is an important component of agroecological cropping systems in diverse regions of the world. New breeding challenges imposed by global climate change and new regulations urge pea breeders to undertake more efficient methods of selection and better take advantage of the large genetic diversity present in the Pisum sativum genepool. Diversity studies conducted so far in pea used Simple Sequence Repeat (SSR) and Retrotransposon Based Insertion Polymorphism (RBIP) markers. Recently, SNP marker panels have been developed that will be useful for genetic diversity assessment and marker-assisted selection.

RESULTS

A collection of diverse pea accessions, including landraces and cultivars of garden, field or fodder peas as well as wild peas was characterised at the molecular level using newly developed SNP markers, as well as SSR markers and RBIP markers. The three types of markers were used to describe the structure of the collection and revealed different pictures of the genetic diversity among the collection. SSR showed the fastest rate of evolution and RBIP the slowest rate of evolution, pointing to their contrasted mode of evolution. SNP markers were then used to predict phenotypes -the date of flowering (BegFlo), the number of seeds per plant (Nseed) and thousand seed weight (TSW)- that were recorded for the collection. Different statistical methods were tested including the LASSO (Least Absolute Shrinkage ans Selection Operator), PLS (Partial Least Squares), SPLS (Sparse Partial Least Squares), Bayes A, Bayes B and GBLUP (Genomic Best Linear Unbiased Prediction) methods and the structure of the collection was taken into account in the prediction. Despite a limited number of 331 markers used for prediction, TSW was reliably predicted.

CONCLUSION

The development of marker assisted selection has not reached its full potential in pea until now. This paper shows that the high-throughput SNP arrays that are being developed will most probably allow for a more efficient selection in this species.

Unexpectedly low nitrogen acquisition and absence of root architecture adaptation to nitrate supply in a Medicago truncatula highly branched root mutant

To complement N2 fixation through symbiosis, legumes can efficiently acquire soil mineral N through adapted root architecture. However, root architecture adaptation to mineral N availability has been little studied in legumes. Therefore, this study investigated the effect of nitrate availability on root architecture in Medicago truncatula and assessed the N-uptake potential of a new highly branched root mutant, TR185. The effects of varying nitrate supply on both root architecture and N uptake were characterized in the mutant and in the wild type. Surprisingly, the root architecture of the mutant was not modified by variation in nitrate supply. Moreover, despite its highly branched root architecture, TR185 had a permanently N-starved phenotype. A transcriptome analysis was performed to identify genes differentially expressed between the two genotypes. This analysis revealed differential responses related to the nitrate acquisition pathway and confirmed that N starvation occurred in TR185. Changes in amino acid content and expression of genes involved in the phenylpropanoid pathway were associated with differences in root architecture between the mutant and the wild type.

Genetic diversity in European Pisum germplasm collections

The distinctness of, and overlap between, pea genotypes held in several Pisum germplasm collections has been used to determine their relatedness and to test previous ideas about the genetic diversity of Pisum. Our characterisation of genetic diversity among 4,538 Pisum accessions held in 7 European Genebanks has identified sources of novel genetic variation, and both reinforces and refines previous interpretations of the overall structure of genetic diversity in Pisum. Molecular marker analysis was based upon the presence/absence of polymorphism of retrotransposon insertions scored by a high-throughput microarray and SSAP approaches. We conclude that the diversity of Pisum constitutes a broad continuum, with graded differentiation into sub-populations which display various degrees of distinctness. The most distinct genetic groups correspond to the named taxa while the cultivars and landraces of Pisum sativum can be divided into two broad types, one of which is strongly enriched for modern cultivars. The addition of germplasm sets from six European Genebanks, chosen to represent high diversity, to a single collection previously studied with these markers resulted in modest additions to the overall diversity observed, suggesting that the great majority of the total genetic diversity collected for the Pisum genus has now been described. Two interesting sources of novel genetic variation have been identified. Finally, we have proposed reference sets of core accessions with a range of sample sizes to represent Pisum diversity for the future study and exploitation by researchers and breeders.

Genetic dissection of nitrogen nutrition in pea through a QTL approach of root, nodule, and shoot variability

Pea (Pisum sativum L.) is the third most important grain legume worldwide, and the increasing demand for protein-rich raw material has led to a great interest in this crop as a protein source. Seed yield and protein content in crops are strongly determined by nitrogen (N) nutrition, which in legumes relies on two complementary pathways: absorption by roots of soil mineral nitrogen, and fixation in nodules of atmospheric dinitrogen through the plant-Rhizobium symbiosis. This study assessed the potential of naturally occurring genetic variability of nodulated root structure and functioning traits to improve N nutrition in pea. Glasshouse and field experiments were performed on seven pea genotypes and on the 'Cameor' x 'Ballet' population of recombinant inbred lines selected on the basis of parental contrast for root and nodule traits. Significant variation was observed for most traits, which were obtained from non-destructive kinetic measurements of nodulated root and shoot in pouches, root and shoot image analysis, (15)N quantification, or seed yield and protein content determination. A significant positive relationship was found between nodule establishment and root system growth, both among the seven genotypes and the RIL population. Moreover, several quantitative trait loci for root or nodule traits and seed N accumulation were mapped in similar locations, highlighting the possibility of breeding new pea cultivars with increased root system size, sustained nodule number, and improved N nutrition. The impact on both root or nodule traits and N nutrition of the genomic regions of the major developmental genes Le and Af was also underlined.

Differentiation of symbiotic cells and endosymbionts in Medicago truncatula nodulation are coupled to two transcriptome-switches

The legume plant Medicago truncatula establishes a symbiosis with the nitrogen-fixing bacterium Sinorhizobium meliloti which takes place in root nodules. The formation of nodules employs a complex developmental program involving organogenesis, specific cellular differentiation of the host cells and the endosymbiotic bacteria, called bacteroids, as well as the specific activation of a large number of plant genes. By using a collection of plant and bacterial mutants inducing non-functional, Fix(-) nodules, we studied the differentiation processes of the symbiotic partners together with the nodule transcriptome, with the aim of unravelling links between cell differentiation and transcriptome activation. Two waves of transcriptional reprogramming involving the repression and the massive induction of hundreds of genes were observed during wild-type nodule formation. The dominant features of this "nodule-specific transcriptome" were the repression of plant defense-related genes, the transient activation of cell cycle and protein synthesis genes at the early stage of nodule development and the activation of the secretory pathway along with a large number of transmembrane and secretory proteins or peptides throughout organogenesis. The fifteen plant and bacterial mutants that were analyzed fell into four major categories. Members of the first category of mutants formed non-functional nodules although they had differentiated nodule cells and bacteroids. This group passed the two transcriptome switch-points similarly to the wild type. The second category, which formed nodules in which the plant cells were differentiated and infected but the bacteroids did not differentiate, passed the first transcriptome switch but not the second one. Nodules in the third category contained infection threads but were devoid of differentiated symbiotic cells and displayed a root-like transcriptome. Nodules in the fourth category were free of bacteria, devoid of differentiated symbiotic cells and also displayed a root-like transcriptome. A correlation thus exists between the differentiation of symbiotic nodule cells and the first wave of nodule specific gene activation and between differentiation of rhizobia to bacteroids and the second transcriptome wave in nodules. The differentiation of symbiotic cells and of bacteroids may therefore constitute signals for the execution of these transcriptome-switches.

Adaptation of Medicago truncatula to nitrogen limitation is modulated via local and systemic nodule developmental responses

Adaptation of Medicago truncatula to local nitrogen (N) limitation was investigated to provide new insights into local and systemic N signaling. The split-root technique allowed a characterization of the local and systemic responses of NO(3)(-) or N(2)-fed plants to localized N limitation. (15)N and (13)C labeling were used to monitor plant nutrition. Plants expressing pMtENOD11-GUS and the sunn-2 hypernodulating mutant were used to unravel mechanisms involved in these responses. Unlike NO(3)(-)-fed plants, N(2)-fixing plants lacked the ability to compensate rapidly for a localized N limitation by up-regulating the N(2)-fixation activity of roots supplied elsewhere with N. However they displayed a long-term response via a growth stimulation of pre-existing nodules, and the generation of new nodules, likely through a decreased abortion rate of early nodulation events. Both these responses involve systemic signaling. The latter response is abolished in the sunn mutant, but the mutation does not prevent the first response. Local but also systemic regulatory mechanisms related to plant N status regulate de novo nodule development in Mt, and SUNN is required for this systemic regulation. By contrast, the stimulation of nodule growth triggered by systemic N signaling does not involve SUNN, indicating SUNN-independent signaling.

Analysis and modeling of the integrative response of Medicago truncatula to nitrogen constraints

An integrative biology approach was conducted in Medicago truncatula for: (i) unraveling the coordinated regulation of NO3-, NH4+ and N(2) acquisition by legumes to fulfill the plant N demand; and (ii) modeling the emerging properties occurring at the whole plant level. Upon localized addition of a high level of mineral N, the three N acquisition pathways displayed similar systemic feedback repression to adjust N acquisition capacities to the plant N status. Genes associated to these responses were in contrast rather specific to the N source. Following an N deficit, NO3- fed plants maintained efficiently their N status through rapid functional and developmental up regulations while N(2) fed plants responded by long term plasticity of nodule development. Regulatory genes associated with various symbiotic stages were further identified. An ecophysiological model simulating relations between leaf area and roots N retrieval was developed and now furnishes an analysis grid to characterize a spontaneous or induced genetic variability for plant N nutrition.

A Medicago truncatula mutant hyper-responsive to mycorrhiza and defective for nodulation

One key strategy for the identification of plant genes required for mycorrhizal development is the use of plant mutants affected in mycorrhizal colonisation. In this paper, we report a new Medicago truncatula mutant defective for nodulation but hypermycorrhizal for symbiosis development and response. This mutant, called B9, presents a poor shoot and, especially, root development with short laterals. Inoculation with Glomus intraradices results in significantly higher root colonisation of the mutant than the wild-type genotype A17 (+20% for total root length, +16% for arbuscule frequency in the colonised part of the root, +39% for arbuscule frequency in the total root system). Mycorrhizal effects on shoot and root biomass of B9 plants are about twofold greater than in the wild-type genotype. The B9 mutant of M. truncatula is characterised by considerably higher root concentrations of the phytoestrogen coumestrol and by the novel synthesis of the coumestrol conjugate malonyl glycoside, absent from roots of wild-type plants. In conclusion, this is the first time that a hypermycorrhizal plant mutant affected negatively for nodulation (Myc(++), Nod (-/+) phenotype) is reported. This mutant represents a new tool for the study of plant genes differentially regulating mycorrhiza and nodulation symbioses, in particular, those related to autoregulation mechanisms.

Rhizobium leguminosarum bv. viciae genotypes interact with pea plants in developmental responses of nodules, roots and shoots

The variability of the developmental responses of two contrasting cultivars of pea (Pisum sativum) was studied in relation to the genetic diversity of their nitrogen-fixing symbiont Rhizobium leguminosarum bv. viciae. A sample of 42 strains of pea rhizobia was chosen to represent 17 genotypes predominating in indigenous rhizobial populations, the genotypes being defined by the combination of haplotypes characterized with rDNA intergenic spacer and nodD gene regions as markers. We found contrasting effects of the bacterial genotype, especially the nod gene type, on the development of nodules, roots and shoots. A bacterial nod gene type was identified that induced very large, branched nodules, smaller nodule numbers, high nodule biomass, but reduced root and aerial part development. The plants associated with this genotype accumulated less N in shoots, but N concentration in leaves was not affected. The results suggest that the plant could not control nodule development sustaining the energy demand for nodule functioning and its optimal growth. The molecular and physiological mechanisms that may be involved are discussed.

Developmental genes have pleiotropic effects on plant morphology and source capacity, eventually impacting on seed protein content and productivity in pea

Increasing pea (Pisum sativum) seed nutritional value and particularly seed protein content, while maintaining yield, is an important challenge for further development of this crop. Seed protein content and yield are complex and unstable traits, integrating all the processes occurring during the plant life cycle. During filling, seeds are the main sink to which assimilates are preferentially allocated at the expense of vegetative organs. Nitrogen seed demand is satisfied partly by nitrogen acquired by the roots, but also by nitrogen remobilized from vegetative organs. In this study, we evaluated the respective roles of nitrogen source capacity and sink strength in the genetic variability of seed protein content and yield. We showed in eight genotypes of diverse origins that both the maximal rate of nitrogen accumulation in the seeds and nitrogen source capacity varied among genotypes. Then, to identify the genetic factors responsible for seed protein content and yield variation, we searched for quantitative trait loci (QTL) for seed traits and for indicators of sink strength and source nitrogen capacity. We detected 261 QTL across five environments for all traits measured. Most QTL for seed and plant traits mapped in clusters, raising the possibility of common underlying processes and candidate genes. In most environments, the genes Le and Afila, which control internode length and the switch between leaflets and tendrils, respectively, determined plant nitrogen status. Depending on the environment, these genes were linked to QTL of seed protein content and yield, suggesting that source-sink adjustments depend on growing conditions.

CAPs markers to assist selection for low vicine and convicine contents in faba bean (Vicia faba L.)

The antinutritional factors (ANFs) present in Vicia spp. seeds are a major constraint to the wider utilization of these crops as grain legumes. In the case of faba bean (Vicia faba L.), a breeding priority is the absence vicine and convicine (v-c); responsible for favism in humans and for the reduced animal performance or low egg production in laying hens. The discovery of a spontaneous mutant allele named vc-, which induces a 10-20 fold reduction of v-c contents, may facilitate the process. However, the high cost and difficulty of the chemical detection of v-c seriously restricts the advances in breeding-selection. To identify random amplified polymorphic DNA (RAPD) markers linked to this gene, we have analysed an F(2 )population derived from a cross between a line with high v-c content (Vf6) and the vc- genotype (line 1268). Quantification of v-c was done by spectrophotometry on the parents and the F(2 )population (n = 136). By using bulked segregant analysis (BSA), two RAPD markers linked in coupling and repulsion phase to the allele vc- were identified and further converted into sequence characterized amplified regions (SCARs). Amplification of SCARS was more consistent, although the initial polymorphism between pools was lost. To recover the polymorphisms several approaches were explored. Restriction digestion with HhaI (for SCAR SCH01(620)) and RsaI (for SCAR SCAB12(850)) revealed clear differences between the parental lines. The simultaneous use of the two cleavage amplified polymorphism (CAP) markers will allow the correct fingerprinting of faba bean plants and can be efficiently used in breeding selection to track the introgression of the vc- allele to develop cultivars with low v-c content and improved nutritional value.

Genetic and genomic analysis of legume flowers and seeds

New tools, such as ordered mutant libraries, microarrays and sequence based comparative maps, are available for genetic and genomic studies of legumes that are being used to shed light on seed production, the objective of most arable farming. The new information and understanding brought by these tools are revealing the biological processes that underpin and impact on seed production.

The Medicago truncatula SUNN gene encodes a CLV1-like leucine-rich repeat receptor kinase that regulates nodule number and root length

Four Medicago truncatula sunn mutants displayed shortened roots and hypernodulation under all conditions examined. The mutants, recovered in three independent genetic screens, all contained lesions in a leucine-rich repeat (LRR) receptor kinase. Although the molecular defects among alleles varied, root length and the extent of nodulation were not significantly different between the mutants. SUNN is expressed in shoots, flowers and roots. Although previously reported grafting experiments showed that the presence of the mutated SUNN gene in roots does not confer an obvious phenotype, expression levels of SUNN mRNA were reduced in sunn-1 roots. SUNN and the previously identified genes HAR1 (Lotus japonicus) and NARK (Glycine max) are orthologs based on gene sequence and synteny between flanking sequences. Comparison of related LRR receptor kinases determined that all nodulation autoregulation genes identified to date are the closest legume relatives of AtCLV1 by sequence, yet sunn, har and nark mutants do not display the fasciated clv phenotype. The M. truncatula region is syntenic with duplicated regions of Arabidopsis chromosomes 2 and 4, none of which harbor CLV1 or any other LRR receptor kinase genes. A novel truncated copy of the SUNN gene lacking a kinase domain, RLP1, is found immediately upstream of SUNN and like SUNN is expressed at a reduced level in sunn-1 roots.

Characterisation of new symbiotic Medicago truncatula (Gaertn.) mutants, and phenotypic or genotypic complementary information on previously described mutants

From a pool of Medicago truncatula mutants--obtained by gamma-irradiation or ethyl methanesulfonate mutagenesis--impaired in symbiosis with the N-fixing bacterium Sinorhizobium meliloti, new mutants are described and genetically analysed, and for already reported mutants, complementary data are given on their phenotypic and genetic analysis. Phenotypic data relate to nodulation and mycorrhizal phenotypes. Among the five new mutants, three were classified as [Nod+ Fix- Myc+] and the mutations were ascribed to two loci, Mtsym20 (TRV43, TRV54) and Mtsym21 (TRV49). For the two other new mutants, one was classified as [Nod-/+ Myc+] with a mutation ascribed to gene Mtsym15 (TRV48), and the other as [Nod- Myc-/+] with a mutation ascribed to gene Mtsym16 (TRV58). Genetic analysis of three previously described mutants has shown that [Nod-/+ Myc+] TR74 mutant can be ascribed to gene Mtsym14, and that [Nod-/+ Myc-/+] TR89 and TRV9 mutants are ascribed to gene Mtsym2 (dmi2). Using a detailed analysis of mycorrhizal phenotype, we have observed a delayed typical arbuscular mycorrhizal formation on some mutants that present thick lens-shaped appressoria. This phenotype was called [Myc-/+] and mutants TR25, TR26, TR89, TRV9, P1 and Y6 were reclassified as [Myc-/+]. Mutant P1 was reclassified as [Nod-/+] because of a late nodulation observed on roots of this mutant.

A putative Ca2+ and calmodulin-dependent protein kinase required for bacterial and fungal symbioses

Legumes can enter into symbiotic relationships with both nitrogen-fixing bacteria (rhizobia) and mycorrhizal fungi. Nodulation by rhizobia results from a signal transduction pathway induced in legume roots by rhizobial Nod factors. DMI3, a Medicago truncatula gene that acts immediately downstream of calcium spiking in this signaling pathway and is required for both nodulation and mycorrhizal infection, has high sequence similarity to genes encoding calcium and calmodulin-dependent protein kinases (CCaMKs). This indicates that calcium spiking is likely an essential component of the signaling cascade leading to nodule development and mycorrhizal infection, and sheds light on the biological role of plant CCaMKs.

Shoot control of root development and nodulation is mediated by a receptor-like kinase

In legumes, root nodule organogenesis is activated in response to morphogenic lipochitin oligosaccharides that are synthesized by bacteria, commonly known as rhizobia. Successful symbiotic interaction results in the formation of highly specialized organs called root nodules, which provide a unique environment for symbiotic nitrogen fixation. In wild-type plants the number of nodules is regulated by a signalling mechanism integrating environmental and developmental cues to arrest most rhizobial infections within the susceptible zone of the root. Furthermore, a feedback mechanism controls the temporal and spatial susceptibility to infection of the root system. This mechanism is referred to as autoregulation of nodulation, as earlier nodulation events inhibit nodulation of younger root tissues. Lotus japonicus plants homozygous for a mutation in the hypernodulation aberrant root (har1) locus escape this regulation and form an excessive number of nodules. Here we report the molecular cloning and expression analysis of the HAR1 gene and the pea orthologue, Pisum sativum, SYM29. HAR1 encodes a putative serine/threonine receptor kinase, which is required for shoot-controlled regulation of root growth, nodule number, and for nitrate sensitivity of symbiotic development.

Mapping of the nodulation loci sym9 and sym10 of pea ( Pisum sativum L.)

Several mutants defective in the nodulation process during rhizobial or endomycorrhizal endosymbiosis of pea have been identified previously. We have integrated the map positions of two such nodulation mutations, sym9 and sym10, into the molecular map of pea by applying molecular-marker techniques combined with bulked segregant analysis (BSA). Lines P2 and P54 were found to carry alleles of sym9, line P56 carried an allele of sym10. F2 populations were derived from crosses of P2, P54 and P56, to JI281 and JI15, two of the parental lines that have been used previously to generate a molecular map of pea. sym9 was located on linkage group IV by AFLP-BSA analysis and subsequently mapped by RFLP in both F2 populations, P2 x JI281 and P54 x JI281. RFLP-BSA analysis was applied to assign sym10 to linkage group I. The RFLP marker locus, chs2, co-segregates with sym10 in the F2 population of P56 x JI15.

Combinatorial variation in coding and promoter sequences of genes at the Tri locus in Pisum sativum accounts for variation in trypsin inhibitor activity in seeds

Cultivars of Pisum sativum that differ with respect to the quantitative expression of trypsin/chymotrypsin inhibitor proteins in seeds have been examined in terms of the structure of the corresponding genes. The patterns of divergence in the promoter and coding sequences are described, and the divergence among these exploited for the development of facile DNA-based assays to distinguish genotypes. Quantitative effects on gene expression may be attributed to the overall gene complement and to particular promoter/coding sequence combinations, as well as to the existence of distinct active-site variants that ultimately influence protein activity. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00438-002-0667-4.

Cerebral blood flow and neurological outcome in the preterm infant

Cerebral blood flow (CBF) studies have provided some insight into pathophysiological mechanisms of cerebral damage in newborn children; their value in predicting brain damage, however, remains elusive. The purpose of our study was to evaluate the role of CBF measurements in predicting developmental outcome in preterm neonates at 18 months. Preterm babies with a gestational age of less than 34 weeks and a birth weight of less than 1500 g (n = 71) were enrolled in the study. CBF was measured by the noninvasive intravenous 133Xe method on three different occasions. We classified our measurements into three groups: depending on the time when performed group 1: between 2 and 36 h (n = 52); group 2: between 36 and 108 h (n = 44); group 3: between 108 and 240 h (n = 41). At the age of 18 months neurodevelopment testing was performed according to the Bayley mental and motor scales. Surviving infants had a higher mean CBF over the three groups than non surviving children (15.2 +/- 3.5 ml/100 g brain tissue/min vs 13.0 +/- 2.1 ml/100 g brain tissue/min, P < 0.05). There was no correlation of CBF with mental or motor development in our study population in either of the three groups.

CONCLUSION

In preterm infants basal CBF is higher in surviving than in non surviving infants, but there is no correlation of resting CBF and later neurological outcome.

Sleep state changes associated with cerebral blood volume changes in healthy term newborn infants

In order to assess the possible effects of sleep states on cerebral haemodynamics in healthy term infants, we measured cerebral oxyhaemoglobin, deoxyhaemoglobin and total haemoglobin concentration using near infrared spectroscopy. Thirty-seven sleep state changes in seventeen infants (gestational age: 37 to 41 4/7 weeks), aged between two and eight days were continuously registrated during 1-3 h. Transcutaneous PaO2, PaCO2, arterial O2 saturation and heart rate were simultaneously recorded and sleep states were clinically defined. There was a close relationship between sleep state changes and changes in total cerebral haemoglobin concentration, which increased from active to quiet sleep and decreased from quiet to active sleep. Changes in total cerebral haemoglobin were due, in the most part, to changes in the cerebral oxyhaemoglobin concentration. In conclusion, sleep states influence the cerebral haemoglobin concentration. Studies on cerebral haemodynamics should take sleep state into account in term newborn infants.

Effect of nursing in the head elevated tilt position (15 degrees) on the incidence of bradycardic and hypoxemic episodes in preterm infants

OBJECTIVE

We investigated whether nursing in the head elevated tilt position (HETP), compared with the horizontal position, has any effect on the incidence of bradycardic and hypoxemic episodes in preterm infants.

METHODS

Twelve spontaneously breathing preterm infants with idiopathic recurrent apnea were studied in a randomized controlled crossover trial. Nine infants were treated with aminophylline. Each spent a total of 24 hours in the horizontal prone position and a total of 24 hours in HETP (prone, 15 degrees). The position was changed in random order every 6 hours. Thoracic impedance, heart rate, and arterial oxygen saturation were recorded continuously. The frequency of isolated hypoxemia (arterial saturation <80%), of isolated bradycardia (heart rate <90 beats per minute), and of mixed events was analyzed and compared without knowledge of the allocated position.

RESULTS

In total, there were significantly fewer bradycardic and/or hypoxemic episodes (28.2%) in HETP compared with the horizontal position (mean difference, 13.35 episodes/24 hours; 95% confidence interval [CI]: 5.9- 20.8). The decrease was largest for isolated hypoxemic episodes (48.5%; mean difference, 11.74 episodes/24 hours; 95% CI: 6.1-17.4). Isolated bradycardic episodes (mean difference, 2.27 episodes/24 hours; 95% CI: -0.78-5.31) and mixed events were not decreased significantly in HETP.

CONCLUSIONS

Nursing in a moderately tilted position (15 degrees) reduces hypoxemic events in preterm infants. This intervention is easy to apply, quickly reversible, and can be combined with drugs such as aminophylline.

Continuous noninvasive measurement of cerebral arterial and venous oxygen saturation at the bedside in mechanically ventilated neonates

OBJECTIVES

To test the practicablity of a new spectrophotometric method using pulse oximetric techniques in combination with special filters for the noninvasive determination of cerebral arterial and venous oxygen saturation and oxygen extraction in neonatal intensive care unit patients. The spectrophotometer used three different wavelengths at a sampling rate of 100 Hz.

DESIGN

Clinical evaluation of a new method and comparison with previously published data.

SETTING

Design and construction of the special spectrophotometer at the Biomedical Engineering Laboratory of the Swiss Federal Institute of Technology. Measurements in the neonatal intensive care unit of the University Hospital, Zurich, Switzerland.

PATIENTS

Convenience sample of 15 clinically stable newborn infants, who were mechanically ventilated and receiving supplemental oxygen. Median gestational age was 29 5/7 wks (range 26 3/ 7 to 36 0/7), median birth weight was 1555 g (720 to 2500), median postnatal age was 4 days (1 to 10).

INTERVENTIONS

The emitter and receiver were placed on the forehead near the sagittal sinus, between 2 and 2.8 cm apart, and the pulsating light attenuations (arterial and venous pulse waves) were recorded.

MEASUREMENTS AND MAIN RESULTS

Arterial and venous pulse waves were satisfactory in 10 of 15 infants. Mean cerebral arterial oxygen saturation was 89.9 +/- 5.4% (SD), mean cerebral venous oxygen saturation was 73.0 +/- 8.9%, and mean cerebral oxygen extraction was 16.9 +/- 11.7%. A linear regression analysis demonstrated a significant correlation between mean PCO2 and venous oxygen saturation (slope 1.0%/torr, p < .05) and between mean PCO2 and cerebral oxygen extraction (slope -1.3%/torr, p < .05).

CONCLUSION

This new method has the potential for monitoring continuously, noninvasively, and simultaneously cerebral arterial and venous oxygen saturation and oxygen extraction in mechanically ventilated preterm infants.

Loss of CO2 reactivity of cerebral blood flow is associated with severe brain damage in mechanically ventilated very low birth weight infants

BACKGROUND

Early detection of pathophysiological factors associated with permanent and severe brain damage in preterm infants requiring intensive care is a major issue in neonatal neurology. The aim of this study was to investigate if an abnormal CO2 reactivity of cerebral blood flow in high risk very low birth weight infants is associated with severe brain injury demonstrated at autopsy or by neurodevelopment examination at 18 months.

METHODS

The CO2 reactivity of cerebral blood flow (xenon-133) was measured in 18 mechanically ventilated, severely ill, very low birthweight infants (gestational age 26-32 weeks, birthweight: 630-1360 g) during the first 36 hours of life. Cerebral outcome was assessed on autopsy findings (n = 8) or at the age of 18 months using Bayley developmental scales (n = 10).

RESULTS

Eight infants with normal development at 18 months (within mean +/- 2.5 SD of reference group) and two infants with normal cerebral autopsy findings had a median CO2 reactivity of 24.4%/kPa CO2 (interquartile range 14.7-41.2). Two infants with abnormal development (> 2.5 SD below mean) and six infants with hypoxic-ischaemic encephalopathy at autopsy has a median CO2 reactivity of 3.4%/kPa CO2 (interquartile range 8.0-11.7).

CONCLUSION

In mechanically ventilated very low birthweight infants low CO2 reactivity of cerebral blood flow (below 10%/kPa CO2) during the first 36 hours of life was associated with poor neurodevelopmental outcome or hypoxic-ischaemic encephalopathy at autopsy. Loss of CO2 reactivity may play a role in the pathogenesis of hypoxic ischaemic encephalopathy. It is a candidate for predicting early severe brain damage in preterm infants requiring intensive care and for controlling the effect of early interventions.

Body proportionality in growth-retarded VLBW infants

The aim of this study was to investigate how intrauterine growth retardation affects body proportions in VLBW infants. The cohort consisted of 135 surviving and 80 deceased preterm infants weighing less than 1250 grams at birth. Gestational age varied between 24 and 36 weeks (mean age 29.7 and 27.5 weeks, respectively). Birth weight was more than 2 SD below the mean birth standard values in 32% of the surviving, and in 27% of the deceased infants. Reduction of weight, length and head circumference at birth was analysed using Z scores based on Swedish birth standards. Z scores of weight, length and head circumference were highly correlated in the surviving and the deceased infants (r = 0.78 to 0.94 and 0.65 to 0.97, respectively). Length was significantly more affected by growth retardation than weight. Weight and head circumference were proportionately reduced. Intrauterine growth retardation influences body proportions in VLBW infants differently than in larger preterm and term infants.

Diagnostic and prognostic value of cerebral 31P magnetic resonance spectroscopy in neonates with perinatal asphyxia

The impact of depressed neonatal cerebral oxidative phosphorylation for diagnosing the severity of perinatal asphyxia was estimated by correlating the concentrations of phosphocreatine (PCr) and ATP as determined by magnetic resonance spectroscopy with the degree of hypoxic-ischemic encephalopathy (HIE) in 23 asphyxiated term neonates. Ten healthy age-matched neonates served as controls. In patients, the mean concentrations +/- SD of PCr and ATP were 0.99 +/- 0.46 mmol/L (1.6 +/- 0.2 mmol/L) and 0.99 +/- 0.35 mmol/L (1.7 +/- 0.2 mmol/L), respectively (normal values in parentheses). [PCr] and [ATP] correlated significantly with the severity of HIE (r = 0.85 and 0.9, respectively, p < 0.001), indicating that the neonatal encephalopathy is the clinical manifestation of a marred brain energy metabolism. Neurodevelopmental outcome was evaluated in 21 children at 3, 9, and 18 mo. Seven infants had multiple impairments, five were moderately handicapped, five had only mild symptoms, and four were normal. There was a significant correlation between the cerebral concentrations of PCr or ATP at birth and outcome (r = 0.8, p < 0.001) and between the degree of neonatal neurologic depression and outcome (r = 0.7). More important, the outcome of neonates with moderate HIE could better be predicted with information from quantitative 31P magnetic resonance spectroscopy than from neurologic examinations. In general, the accuracy of outcome predictability could significantly be increased by adding results from 31P magnetic resonance spectroscopy to the neonatal neurologic score, but not vice versa. No correlation with outcome was found for other perinatal risk factors, including Apgar score.

Cd(II) complexes with phthalic acids: solution study and crystal structure of cadmium(II) phthalate hydrate

The acid–base properties of phthalic acid (H2L) have been determined by simultaneous spectroscopic, potentiometric, and polarographic measurements. Stability constants of the complexes CdHL+, CdL, CdL22−, CdL34−, CdH−2L24− and their distribution versus pH were determined at 25 °C and ionic strength in 0.1 M NaNO3. The advantages of each method are pointed out in such a way as to describe more precisely the interactions between cadmium and phthalic acid over a wide range of ligand and metal concentrations. The crystal structure of the [CdL] complex has been established by single-crystal X-ray diffraction. Cd(C8H4O4)•H2O is orthorhombic, space group Pbca, a = 23.463(5), b = 9.293(2), c = 7.730(1) Å, Z = 8, and ρ = 2.323 g cm−3. The structure was refined to a final R value of 0.054 for 3231 unique reflections with I > 3σ(I). The crystal is a three-dimensional polymeric network in which the Cd atom is seven-coordinated. The first ligand coordinates in a bidentate carboxylate (O,O′) mode (Cd—O = 2.372(5) and 2.445(5) Å); a second ligand is part of a seven-membered ring formed with its two carboxylate groups (Cd—O = 2.317(5) and 2.341(5) Å); two other phthalic ligands make one coordination bond (Cd—O = 2.255(5) and 2.449(5) Å) while the seventh bond is a water molecule (Cd—O = 2.333(6) Å). Key words: crystal structure, cadmium complexes, phthalic acid complexes.

[Prenatal and perinatal infections--problems for the practicing pediatrician: group B streptococci, varicella, toxoplasmosis]

A practical approach is reported for the care of the neonate born to a mother infected/colonized during pregnancy by group B streptococcus, varicella-zoster virus or Toxoplasma gondii. Starting from clinical situations, an attempt is made to work out evidence based recommendations using an overview of the current literature. GROUP B STREPTOCOCCI: Relevant factors for the treatment of infants born to colonized mothers are clinical symptoms, gestational age, additional risk factors (such as premature rupture of membranes or maternal fever) and intrapartum antibiotics. Postnatal antibiotic prophylaxis and laboratory screens failed the test of controlled trials. Transfer to a neonatology unit is recommended for symptomatic term and all preterm infants. Asymptomatic term infants should be carefully monitored during the first 48 hours for signs of respiratory, circulatory or thermoregulatory compromise. VARICELLA: In the case of maternal varicella near term, delaying delivery for one week will lower the risk of severe neonatal varicella. The postnatal administration of varicella-zoster-immunoglobulin to the neonate is supported by some (if limited) evidence from the literature in the case of maternal eruption between 7 days before and 2 days after delivery. In newborns of mothers with eruption appearing later immunoglobulin is often recommended, though no supporting clinical evidence is available. There are no data to justify the use of immunoglobulin after exposure during pregnancy in order to prevent pneumonia in the pregnant patient, but there are preliminary indications that its application could lower the risk of congenital varicella syndrome (2% between 13 and 20 weeks). The use of immunoglobulin in very low birth weight infants after nosocomial exposure is generally recommended but efficacy data are lacking. TOXOPLASMOSIS: The practical approach depends on clinical findings in the newborn and laboratory results during pregnancy and after birth. Examination of the newborn should include fundoscopy, cranial sonography and, in cases of documented infection, lumbar puncture. Serology from cord blood comprises assays for IgG, IgM and if possible IgA/IgE. If available, demonstration of the parasite by culture or PCR can be helpful. All infants with documented congenital toxoplasmosis should be treated for a minimum of 12 months. In the case of suspected toxoplasmosis the child should be treated as long as the suspicion persists. The prognosis after consequential therapy is less bleak than previously reported for untreated children even in seriously symptomatic patients.

Regional differences of cerebral blood flow in the preterm infant

The purpose of our study was to evaluate the regional distribution of the resting cerebral blood flow (CBF) pattern in preterm neonates. Sixty-eight preterm babies with a gestational age of less than 34 weeks and a birth weight of less than 1500 g were enrolled into the study. The CBF was measured by the noninvasive intravenous 133Xenon method at three different times. Depending on the age we classified our measurements into three groups. Group 1: measurement between 2-36 h (n = 46). Group 2: measurement between 36-108 h (n = 39). Group 3: measurement between 108-240 h (n = 41). In all three groups CBF was significantly lower in the occipital region than in the frontal and parietal regions (group 1: frontal region 12.8 +/- 3.5 ml/100 g/min, parietal region 12.8 +/- 3.9 ml/100 mg/min, and occipital region 11.6 +/- 3.18 ml/100 g/min; group 2: frontal region 15.4 +/- 4.2 ml/100 g/min, parietal region 15.3 +/- 4.1 ml/100 g/min, and occipital region 13.4 +/- 3.5 ml/100 g/min; group 3: frontal region 14.6 +/- 3.6 ml/100 g/min, parietal region 14.6 +/- 3.2 ml/100 g/min, and occipital region 12.8 +/- 2.7 ml/100 g/min.). CBF did not differ between the left and the right hemispheres in either of the three measured regions. No gradient was found in infants between 108 h and 240 h of age with periventricular leukomalacia and periventricular haemorrhage. CONCLUSION. In preterm neonates the antero-posterior gradient of CBF is already present. Periventricular leukomalacia as well as periventricular haemorrhage may affect the regional regulation of CBF.

Sucrose reduces pain reaction to heel lancing in preterm infants: a placebo-controlled, randomized and masked study

In term infants sucrose given by mouth has been reported to reduce duration of crying after a heel prick. This study was designed primarily to investigate the effect of sucrose administered orally immediately before heel lancing on the nociceptive reaction in preterm infants as assessed by change in heart rate and duration of crying. A secondary objective was to document changes in cerebral blood volume during acute pain. We used a randomized, masked, placebo-controlled, crossover trial in a neonatal intermediate care unit in a level 3 perinatal center. The patients studied were 16 preterm infants; birth weight, 900-1900 g; gestational wk, 27-34; corrected postmenstrual age at time of investigation, 33-36 wk. Each infant was assessed twice receiving 2 mL of sucrose 50% or 2 mL of distilled water in random order immediately before heel lance. Heart rate, thoracic movements, and transcutaneous blood gases were monitored continuously. Crying during the procedure was documented by a video-camera. A change in cerebral blood volume was assessed by near-infrared spectroscopy. We found the heart increased by a mean of 35 beats/min (bpm) after sucrose and 51 bpm after placebo (median difference 16 bpm, interquartile range 1-30 bpm, p = 0.005). Infants cried 67% of time after sucrose and 88% after placebo (median difference 10%, interquartile range 3-33%, p = 0.002). Cerebral blood volume decreased in 5 of 14 infants after sucrose and in 6 of 14 infants after placebo (difference not significant).