The Genetic Basis of Heterosis: Multiparental Quantitative Trait Loci Mapping Reveals Contrasted Levels of Apparent Overdominance Among Traits of Agronomical Interest in Maize (Zea mays L.)

Understanding the genetic bases underlying heterosis is a major issue in maize (Zea mays L.). We extended the North Carolina design III (NCIII) by using three populations of recombinant inbred lines derived from three parental lines belonging to different heterotic pools, crossed with each parental line to obtain nine families of hybrids. A total of 1253 hybrids were evaluated for grain moisture, silking date, plant height, and grain yield. Quantitative trait loci (QTL) mapping was carried out on the six families obtained from crosses to parental lines following the “classical” NCIII method and with a multiparental connected model on the global design, adding the three families obtained from crosses to the nonparental line. Results of the QTL detection highlighted that most of the QTL detected for grain yield displayed apparent overdominance effects and limited differences between heterozygous genotypes, whereas for grain moisture predominance of additive effects was observed. For plant height and silking date results were intermediate. Except for grain yield, most of the QTL identified showed significant additive-by-additive epistatic interactions. High correlation observed between heterosis and the heterozygosity of hybrids at markers confirms the complex genetic basis and the role of dominance in heterosis. An important proportion of QTL detected were located close to the centromeres. We hypothesized that the lower recombination in these regions favors the detection of (i) linked QTL in repulsion phase, leading to apparent overdominance for heterotic traits and (ii) linked QTL in coupling phase, reinforcing apparent additive effects of linked QTL for the other traits

Identification of quantitative trait loci controlling partial clubroot resistance in new mapping populations of Arabidopsis thaliana

To date, mechanisms of partial quantitative resistance, under polygenic control, remain poorly understood, studies of the molecular basis of disease resistance have mainly focused on qualitative variation under oligogenic control. However, oligogenic conferred resistance is rapidly overcome by the pathogen and knowledge of the relationship between qualitative and quantitative resistance is necessary to develop durably resistant cultivars. In this study, we exploited the Arabidopsis thaliana-Plasmodiophora brassicae pathosystem to decipher the genetic architecture determining partial resistance. This soil-borne pathogen causes clubroot, one of the economically most important diseases of Brassica crops in the world. A quantitative trait locus (QTL) approach was carried out using two segregating populations (F(2) and recombinant inbred lines) from crosses between the partially resistant accession Burren and the susceptible accession Columbia. Four additive QTLs (one moderate and three minor) controlling partial resistance to clubroot were identified, all the resistance alleles being derived from the partially resistant parent. In addition, four epistatic regions, which have no additive effect on resistance, were also found to be involved in partial resistance. An examination of candidate genes suggested that a potentially diverse array of mechanisms is related to the different QTLs. By fine-mapping and cloning these regions, the mechanisms involved in partial resistance will be identified

Deciphering the functional typology of resistance QTL through metabolomics

Deciphering the functional typology of resistance QTL through metabolomic

Recherche de déterminants métaboliques associés à la résistance polygénique du colza à la hernie des crucifères

Recherche de déterminants métaboliques associés à la résistance polygénique du colza à la hernie des crucifère

Arginase Induction Represses Gall Development During Clubroot Infection in Arabidopsis

International audienceArginase induction can play a defensive role through the reduction of arginine availability for phytophageous insects. Arginase activity is also induced during gall growth caused by Plasmodiophora brassicae infection in roots of Arabidopsis thalian

New insight into the Brassica napus / Plasmodiophora brassicae interaction through genetical metabolomics

New insight into the Brassica napus / Plasmodiophora brassicae interaction through genetical metabolomic

Genetic and physiological analysis of the relationship between partial resistance to clubroot and tolerance to trehalose in Arabidopsis thaliana.

In Arabidopsis thaliana the induction of plant trehalase during clubroot disease was proposed to act as a defense mechanism in the susceptible accession Col-0, which could thereby cope with the accumulation of pathogen-synthesized trehalose. In the present study, we assessed trehalose activity and tolerance to trehalose in the clubroot partially resistant accession Bur-0. We compared both accessions for several trehalose-related physiological traits during clubroot infection. A quantitative trait loci (QTLs) analysis of tolerance to exogenous trehalose was also conducted on a Bur-0xCol-0 RIL progeny. Trehalase activity was not induced by clubroot in Bur-0 and the inhibition of trehalase by validamycin treatments resulted in the enhancement of clubroot symptoms only in Col-0. In pathogen-free cultures, Bur-0 showed less trehalose-induced toxicity symptoms than Col-0. A QTL analysis identified one locus involved in tolerance to trehalose overlapping the confidence interval of a QTL for resistance to Plasmodiophora brassicae. This colocalization was confirmed using heterogeneous inbred family (HIF) lines. Although not based on trehalose catabolism capacity, partial resistance to clubroot is to some extent related to the tolerance to trehalose accumulation in Bur-0. These findings support an original model where contrasting primary metabolism-related regulations could contribute to the partial resistance to a plant pathogen

Multi-omic investigation of low-nitrogen conditional resistance to clubroot reveals Brassica napus genes involved in nitrate assimilation

International audienceNitrogen fertilization has been reported to influence the development of clubroot, a root disease of Brassicaceae species, caused by the obligate protist Plasmodiophora brassicae. Our previous works highlighted that low nitrogen fertilization induced a strong reduction of clubroot symptoms in some oilseed rape genotypes. To further understand the underlying mechanisms, the response to P. brassicae infection was investigated in two genotypes 'Yudal' and HD018 harboring sharply contrasted nitrogendriven modulation of resistance toward P. brassicae. Targeted hormone and metabolic profiling, as well as RNAseq analysis, were performed in inoculated and non-inoculated roots at 14-and 27-days post inoculation, under high and low-nitrogen conditions. Clubroot infection triggered a large increase of SA concentration and an induction of the SA gene markers expression whatever the genotype and nitrogen conditions. Overall, metabolic profiles suggested that N-driven induction of resistance was independent of SA-signaling, soluble carbohydrate and amino-acid concentrations. Low-nitrogen driven resistance in 'Yudal' was associated to the transcriptional regulation of a small set of genes, among which the induction of NRT2-and NR-encoding genes. Altogether, our results indicate a possible role of nitrate transporters and auxin signaling in the crosstalk between plant nutrition and partial resistance to pathogens

Etude de l’implication du métabolisme primaire dans la réponse à la hernie des crucifères chez le colza par une approche de métabotypage.

Etude de l’implication du métabolisme primaire dans la réponse à la hernie des crucifères chez le colza par une approche de métabotypage.Etude de l’implication du métabolisme primaire dans la réponse à la hernie des crucifères chez le colza par une approche de métabotypage

Metabotyping: A New Approach to Investigate Rapeseed (Brassica napus L.) Genetic Diversity in the Metabolic Response to Clubroot Infection

International audienceClubroot disease affects all Brassicaceae spp. and is caused by the obligate biotroph pathogen Plasmodiophora brassicae. The development of galls on the root system is associated with the establishment of a new carbon metabolic sink. Here, we aimed to deepen our knowledge of the involvement of primary metabolism in the Brassica napus response to clubroot infection. We studied the dynamics and the diversity of the metabolic responses to the infection. Root system metabotyping was carried out for 18 rapeseed genotypes displaying different degrees of symptom severity, under inoculated and noninoculated conditions at 42 days postinoculation (dpi). Clubroot susceptibility was positively correlated with clubroot-induced accumulation of several amino acids. Although glucose and fructose accumulated in some genotypes with minor symptoms, their levels were negatively correlated to the disease index across the whole set of genotypes. The dynamics of the metabolic response were studied for the susceptible genotype 'Yudal,' which allowed an "early" metabolic response (established from 14 to 28 dpi) to be differentiated from a "late" response (from 35 dpi). We discuss the early accumulation of amino acids in the context of the establishment of a nitrogen metabolic sink and the hypothetical biological role of the accumulation of glutathione and S-methylcysteine