Global warming is expected to have a direct impact on plant disease patterns in agro-eco-systems. However, few analyses report the effect of moderate temperature increase on disease severity due to ...soil-borne pathogens. For legumes, modifications of root plant-microbe interactions either mutualistic or pathogenic due to climate change may have dramatic effects. We investigated the effect of increasing temperature on the quantitative disease resistance to
spp., a major soil-borne fungal pathogen, in the model legume
and the crop
. First, twelve pathogenic strains isolated from various geographical origin were characterized with regard to their
growth and pathogenicity at 20°C, 25°C and 28°C. Most of them exhibited 25°C as the optimum temperature for
parameters, and between 20°C and 25°C for pathogenicity. Second, a
strain was adapted to the higher temperature by experimental evolution,
. three rounds of UV mutagenesis and selection for pathogenicity at 28°C on a susceptible
genotype. Inoculation of monospore isolates of these mutants on resistant and susceptible
accessions revealed that at 28°C they were all more aggressive than the wild type strain, and that some had acquired the ability to cause disease on resistant genotype. Third, one mutant strain was selected for further studies of the effect of temperature increase on the response of
and
(cultivated alfalfa). The response of seven contrasted
genotypes and three alfalfa varieties to root inoculation was followed using disease severity and plant colonization, at 20°C, 25°C and 28°C. With increasing temperature, some lines switched from resistant (no symptoms, no fungus in the tissues) to tolerant (no symptoms but fungal growth into the tissues) phenotypes, or from partially resistant to susceptible. Further studies in greenhouse evidence the reduction in plant fitness due to disease in susceptible lines. We thus report that root pathogenic interactions are affected by anticipated global warming, with trends towards increased plant susceptibility and larger virulence for hot-adapted strains. New threats due to hot-adapted strains of soil-borne pathogens, with possibly wider host range and increased aggressiveness, might occur.
Oleic acid is a monounsaturated fatty acid increasing oil oxidative stability. High content of oleic acid is thus a valuable trait in oilseed crops. Sunflower (Helianthus annuus L.) normally ...accumulates linoleic acid as a major fatty acid, but a mutant expressing a high oleic phenotype form was previously obtained by chemical mutagenesis and mapped on the sunflower genome. Several studies suggest the presence of additional genes involved in the control of the high content of oleic acid, with their expression possibly depending on the genetic background. To test this hypothesis, we performed a QTL mapping of the high oleic acid trait within two independent F2 crosses involving lines with contrasting oleic acid content from the Pustovoit All-Russia Research Institute of Oil Crops (VNIIMK) collection. We applied genotyping-by-sequencing (GBS) to construct single nucleotide polymorphism-based genetic maps and performed QTL mapping using quantitative and qualitative encoding for oleic acid content. Our results support the finding that the oleic acid content in the assessed crosses is controlled by one major effect locus. However, different dominant/recessive effects of the major locus were reported for both crosses. Additionally, a possible translocation between chromosome 7 and 14 was reported in one assessed cross. We defined a set of single nucleotide polymorphism markers for each cross which could be used for marker-assisted selection.
Medicago truncatula is a model for investigating legume genetics, including the genetics and evolution of legume–rhizobia symbiosis. We used whole-genome sequence data to identify and characterize ...sequence polymorphisms and linkage disequilibrium (LD) in a diverse collection of 26 M. truncatula accessions. Our analyses reveal that M. truncatula harbors both higher diversity and less LD than soybean (Glycine max) and exhibits patterns of LD and recombination similar to Arabidopsis thaliana. The population-scaled recombination rate is approximately one-third of the mutation rate, consistent with expectations for a species with a high selfing rate. Linkage disequilibrium, however, is not extensive, and therefore, the low recombination rate is likely not a major constraint to adaptation. Nucleotide diversity in 100-kb windows was negatively correlated with gene density, which is expected if diversity is shaped by selection acting against slightly deleterious mutations. Among putative coding regions, members of four gene families harbor significantly higher diversity than the genome-wide average. Three of these families are involved in resistance against pathogens; one of these families, the nodule-specific, cysteine-rich gene family, is specific to the galegoid legumes and is involved in control of rhizobial differentiation. The more than 3 million SNPs that we detected, approximately one-half of which are present in more than one accession, are a valuable resource for genome-wide association mapping of genes responsible for phenotypic diversity in legumes, especially traits associated with symbiosis and nodulation.
Verticillium wilt is a major threat to many crops, among them alfalfa (
). The model plant
, a close relative of alfalfa was used to study the genetic control of resistance towards a new
isolate. The ...accidental introduction of pathogen strains through global trade is a threat to crop production and such new strains might also be better adapted to global warming. Isolates of
were obtained from alfalfa fields in Iran and characterized. The Iranian isolate AF1 was used in a genome-wide association study (GWAS) involving 242 accessions from the Mediterranean region. Root inoculations were performed with conidia at 25°C and symptoms were scored regularly. Maximum Symptom Score and Area under Disease Progess Curve were computed as phenotypic traits to be used in GWAS and for comparison to a previous study with French isolate V31.2 at 20°C. This comparison showed high correlation with a shift to higher susceptibility, and similar geographical distribution of resistant and susceptible accessions to AF1 at 25°C, with resistant accessions mainly in the western part. GWAS revealed 30 significant SNPs linked to resistance towards isolate AF1. None of them were common to the previous study with isolate V31.2 at 20°C. To confirm these
, the expression of nine underlying genes was studied. All genes were induced in roots following inoculation, in susceptible and resistant plants. However, in resistant plants induction was higher and lasted longer. Taken together, the use of a new pathogen strain and a shift in temperature revealed a completely different genetic control compared to a previous study that demonstrated the existence of two major QTLs. These results can be useful for
breeding programs to obtain varieties better adapted to future conditions.
The phytopathogenic bacterium Ralstonia solanacearum encodes a family of seven type III secretion system (T3SS) effectors that contain both a leucine-rich repeat and an F-box domain. This structure ...is reminiscent of a class of typical eukaryotic proteins called F-box proteins. The latter, together with Skp1 and Cullin1 subunits, constitute the SCF-type E3 ubiquitin ligase complex and control specific protein ubiquitinylation. In the eukaryotic cell, depending on the nature of the polyubiquitin chain, the ubiquitin-tagged proteins either see their properties modified or are doomed for degradation by the 26S proteasome. This pathway is essential to many developmental processes in plants, ranging from hormone signaling and flower development to stress responses. Here, we show that these previously undescribed T3SS effectors are putative bacterial F-box proteins capable of interacting with a subset of the 19 different Arabidopsis Skp1-like proteins like bona fide Arabidopsis F-box proteins. A R. solanacearum strain in which all of the seven GALA effector genes have been deleted or mutated was no longer pathogenic on Arabidopsis and less virulent on tomato. Furthermore, we found that GALA7 is a host-specificity factor, required for disease on Medicago truncatula plants. Our results indicate that the GALA T3SS effectors are essential to R. solanacearum to control disease. Because the F-box domain is essential to the virulence function of GALA7, we hypothesize that these effectors act by hijacking their host SCF-type E3 ubiquitin ligases to interfere with their host ubiquitin/proteasome pathway to promote disease.
The explosive growth of genomic data provides an opportunity to make increased use of sequence variations for phenotype prediction. We have developed a prediction machine for quantitative phenotypes ...(WhoGEM) that overcomes some of the bottlenecks limiting the current methods. We demonstrated its performance by predicting quantitative disease resistance and quantitative functional traits in the wild model plant species, Medicago truncatula, using geographical locations as covariates for admixture analysis. The method's prediction reliability equals or outperforms all existing algorithms for quantitative phenotype prediction. WhoGEM analysis produces evidence that variation in genome admixture proportions explains most of the phenotypic variation for quantitative phenotypes.
The Kazakhstan-Siberia Network for Spring Wheat Improvement (KASIB) was established in 2000, forming a collaboration between breeding and research programs through biannual yield trials. A core set ...of 142 genotypes from 15 breeding programs was selected, genotyped for 81 DNA functional markers and phenotyped for 10 agronomic traits at three sites in Kazakhstan (Karabalyk, Shortandy and Shagalaly) and one site in Russia (Omsk) in 2020-2022. The study aim was to identify markers demonstrating significant effects on agronomic traits. The average grain yield of individual trials varied from 118 to 569 g/m
. Grain yield was positively associated with the number of days to heading, plant height, number of grains per spike and 1000-kernel weight. Eight DNA markers demonstrated significant effects. The spring-type allele of the
gene accelerated heading by two days (5.6%) and was present in 80% of the germplasm. The winter allele of the
gene significantly increased grain yield by 2.7%. The late allele of the earliness marker per se,
delayed development by 1.9% and increased yield by 4.5%. Translocation of 1B.1R was present in 21.8% of the material, which resulted in a 6.2% yield advantage compared to 1B.1B germplasm and a reduction in stem rust severity from 27.6 to 6.6%. The favorable allele of
increased both kernel weight and yield by 2-3%. Four markers identified in ICARDA germplasm,
(Kukri_c3243_1065, 3B),
(TA004946-0577, 1B),
(BS00076246_51, 5A),
(wsnp_Ex_c12812_20324622, 4A), showed an improved yield in this study of 3-4%. The study recommends simultaneous validation and use of selected markers in KASIB's network.
Six Medicago truncatula genotypes differing in cadmium susceptibility were used to test the effect of this heavy metal on mineral, carbohydrate and amino acid supply in growing radicles. Cadmium ...treatment caused alteration of macronutrient (Ca and K), microelement (Fe, Zn and Cu), carbohydrate (total soluble sugars (TSS), glucose, fructose and sucrose) and free amino acid (FAAS) accumulations. These mobilization changes differed in the tested genotypes. Carbohydrates were determining to susceptible lines' growth in control condition; free amino acids enabled tolerant lines to counteract cadmium intrusion. Transcriptional changes in response to cadmium treatment were analyzed on MtMST, a gene encoding a monosaccharide transport protein. A significant down-regulation was observed in the most susceptible line TN1.11. Glucose was over-consumed in tolerant lines. Thus, glucose metabolism integrity seems essential to maintain growth under cadmium exposure. Analysis of germination medium showed solute losses at the expense of suitable mobilization to the growing embryonic axis and highlights cadmium-triggered membrane alterations. FAAS and TSS leakages were reduced in tolerant lines while monosaccharide losses were accentuated in susceptible lines. This research work gave an overview of cadmium deleterious effects on biomass mobilization and membrane integrity. Carbon metabolism is shown to be primordial to enhance early embryonic growth and nitrogen metabolism is revealed to be crucial to establish seedling growth under cadmium stress.
Chickpea (Cicer arietinum L.), the third largest produced pulse worldwide, is primarily grown on marginal soils often characterized by a phosphorus (P)-deficiency that severely hampers yields. The ...objectives of the study are to investigate the relationships between the P-acquisition, P-use efficiency (PUE) and the agronomical performances towards the developing varieties tolerant to the P-deficiency. We evaluate the impact of the P-deficiency on the growth, yield, germination and nodulation performances of seven chickpea cultivars grown in fields with a low-P soil availability, during two seasons. The adaptive mechanisms to maintain the efficiency of the physiological processes, such as the nitrogen (N)-fixing nodule function, germinability, and possibly photosynthesis, are revealed. In contrast, the large genotypic variation in the yield components, in the P and N acquisition, and in the PUE is observed, supporting the role of the nodules in the P uptake in P-deficient soils. The P-acquisition and utilization efficiencies are genetically decoupled, suggesting designing distinct breeding strategies to promote one or both PUE components. As an outcome, we identify a set of chickpea cultivars adapted to a region with a soil P scarcity, that exhibit efficient N and P metabolism and a superior productivity. This germplasm can be used in breeding programs for low-P input efficient chickpeas. This contributes to the implementation of eco-friendly farming practices while making the most of marginal soils.
Resistance mechanisms to
wilt are well-studied in tomato, cotton, and Arabidopsis, but much less in legume plants. Because legume plants establish nitrogen-fixing symbioses in their roots, resistance ...to root-attacking pathogens merits particular attention. The interaction between the soil-borne pathogen
and the model legume
was investigated using a resistant (A17) and a susceptible (F83005.5) line. As shown by histological analyses, colonization by the pathogen was initiated similarly in both lines. Later on, the resistant line A17 eliminated the fungus, whereas the susceptible F83005.5 became heavily colonized. Resistance in line A17 does not involve homologs of the well-characterized tomato
1 and
1 genes. A transcriptomic study of early root responses during initial colonization (i.e., until 24 h post-inoculation) similarly was performed. Compared to the susceptible line, line A17 displayed already a significantly higher basal expression of defense-related genes prior to inoculation, and responded to infection with up-regulation of only a small number of genes. Although fungal colonization was still low at this stage, the susceptible line F83005.5 exhibited a disorganized response involving a large number of genes from different functional classes. The involvement of distinct phytohormone signaling pathways in resistance as suggested by gene expression patterns was supported by experiments with plant hormone pretreatment before fungal inoculation. Gene co-expression network analysis highlighted five main modules in the resistant line, whereas no structured gene expression was found in the susceptible line. One module was particularly associated to the inoculation response in A17. It contains the majority of differentially expressed genes, genes associated with PAMP perception and hormone signaling, and transcription factors. An
analysis showed that a high number of these genes also respond to other soil-borne pathogens in
, suggesting a core of transcriptional response to root pathogens. Taken together, the results suggest that resistance in
line A17 might be due to innate immunity combining preformed defense and PAMP-triggered defense mechanisms, and putative involvement of abscisic acid.
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