Evolutionary tinkering of the expression of PDF1s suggests their joint effect on zinc tolerance and the response to pathogen attack

Multigenic families of Plant Defensin type 1 (PDF1) have been described in several species, including the model plant Arabidopsis thaliana as well as zinc tolerant and hyperaccumulator A. halleri. In A. thaliana, PDF1 transcripts (AtPDF1) accumulate in response to pathogen attack following synergic activation of ethylene/jasmonate pathways. However, in A. halleri, PDF1 transcripts (AhPDF1) are constitutively highly accumulated. Through an evolutionary approach, we investigated the possibility of A. halleri or A. thaliana species specialization in different PDF1s in conveying zinc tolerance and/or the response to pathogen attack via activation of the jasmonate (JA) signaling pathway. The accumulation of each PDF1 from both A. halleri and A. thaliana was thus compared in response to zinc excess and MeJA application. In both species, PDF1 paralogues were barely or not at all responsive to zinc. However, regarding the PDF1 response to JA signaling activation, A. thaliana had a higher number of PDF1s responding to JA signaling activation. Remarkably, in A. thaliana, a slight but significant increase in zinc tolerance was correlated with activation of the JA signaling pathway. In addition, A. halleri was found to be more tolerant to the necrotrophic pathogen Botrytis cinerea than A. thaliana. Since PDF1s are known to be promiscuous antifungal proteins able to convey zinc tolerance, we propose, on the basis of the findings of this study, that high constitutive PDF1 transcript accumulation in A. halleri is a potential way to skip the JA signaling activation step required to increase the PDF1 transcript level in the A. thaliana model species. This could ultimately represent an adaptive evolutionary process that would promote a PDF1 joint effect on both zinc tolerance and the response to pathogens in the A. halleri extremophile species

Crop-model assisted phenomics and genome-wide association study for climate adaptation of indica rice. 2. Thermal stress and spikelet sterility

Low night and high day temperatures during sensitive reproductive stages cause spikelet sterility in rice. Phenotyping of tolerance traits in the field is difficult because of temporal interactions with phenology and organ temperature differing from ambient. Physiological models can be used to separate these effects. A 203-accession indica rice diversity panel was phenotyped for sterility in ten environments in Senegal and Madagascar and climate data were recorded. Here we report on sterility responses while a companion study reported on phenology. The objectives were to improve the RIDEV model of rice thermal sterility, to estimate response traits by fitting model parameters, and to link the response traits to genomic regions through genome-wide association studies (GWAS). RIDEV captured 64% of variation of sterility when cold acclimation during vegetative stage was simulated, but only 38% when it was not. The RIDEV parameters gave more and stronger quantitative trait loci (QTLs) than index variables derived more directly from observation. The 15 QTLs identified at P<1 × 10−5 (33 at P<1 × 10−4) were related to sterility effects of heat, cold, cold acclimation, or unexplained causes (baseline sterility). Nine annotated genes were found on average within the 50% linkage disequilibrium (LD) region. Among them, one to five plausible candidate genes per QTL were identified based on known expression profiles (organ, stage, stress factors) and function. Meiosis-, development- and flowering-related genes were frequent, as well a stress signaling kinases and transcription factors. Putative epigenetic factors such as DNA methylases or histone-related genes were frequent in cold-acclimation QTLs, and positive-effect alleles were frequent in cold-tolerant highland rice from Madagascar. The results indicate that epigenetic control of acclimation may be important in indica rice genotypes adapted to cool environments. (Résumé d'auteur

Polymorphism in Gag Gene Cleavage Sites of HIV-1 Non-B Subtype and Virological Outcome of a First-Line Lopinavir/Ritonavir Single Drug Regimen

Virological failure on a boosted-protease inhibitor (PI/r) first-line triple combination is usually not associated with the detection of resistance mutations in the protease gene. Thus, other resistance pathways are being investigated. First-line PI/r monotherapy is the best model to investigate in vivo if the presence of mutations in the cleavage sites (CS) of gag gene prior to any antiretroviral treatment might influence PI/r efficacy. 83 patients were assigned to initiate antiretroviral treatment with first-line lopinavir/r monotherapy in the randomised Monark trial. We compared baseline sequence of gag CS between patients harbouring B or non-B HIV-1 subtype, and between those who achieved viral suppression and those who experienced virological failure while on LPV/r monotherapy up to Week 96. Baseline sequence of gag CS was available for 82/83 isolates; 81/82 carried at least one substitution in gag CS compared to HXB2 sequence. At baseline, non-B subtype isolates were significantly more likely to harbour mutations in gag CS than B subtype isolates (p<0.0001). Twenty-three patients experienced virological failure while on lopinavir/r monotherapy. The presence of more than two substitutions in p2/NC site at baseline significantly predicted virological failure (p = 0.0479), non-B subtype isolates being more likely to harbour more than two substitutions in this specific site. In conclusion, gag cleavage site was highly polymorphic in antiretroviral-naive patients harbouring a non-B HIV-1 strain. We show that pre-therapy mutations in gag cleavage site sequence were significantly associated with the virological outcome of a first-line LPV/r single drug regimen in the Monark trial

Spatially resolved quantitative chemical distribution of proteins incorporated in mesoporous calcium phosphates

International audienceThe development of bone tissue regeneration calls for biomaterials able to release biologically active substances in a controlled manner afterimplantation. In this context, mesoporous calcium phosphates are of major interest. In this work, hydroxyapatite powders with an interconnected nanoporosity were prepared. Their ability to incorporate and to release proteins was tested with the use of cytochrome C. Adsorption isotherm in solution was obtained by titration of the supernatant by UV absorption and showed a fast adsorption capacity, while the desorption experiments showed a prolonged release capability of thebiomaterial. To determine the spatial distribution of the proteins at the biointerface of the porous ceramic, an original methodology was developed. Highly sensitive Particles Induced X-ray Emission coupled to Rutherford Backscattering Spectroscopy (PIXE-RBS) was used to obtain quantitative chemical mappings of hydroxyapatite powders at the micrometer scale. Iron naturally presents in cytochrome C was used as their marker. Quantitative chemical maps of Ca, P and Fe show concentrations gradients of proteins from the centre to the periphery of the materials. In the tested hydroxyapatite, the proteins incorporation start at 10 μm from the powder surface and the majority of proteins is located in the centre. Thanks to this method we are able to determine quantitatively the proteins distribution in the bioceramics. In our case, the behaviour of proteins at the biointerface give very good outlooks for the controlled release of specific protein in the body for future experiments

Plant nitrogen supply affects Arabidopsis thaliana susceptibility to Botrytis cinerea and reveals novel virulence functions

International audienceBotrytis cinerea is a nectrotrophic plant pathogen that leads to important economic losses in many crops. B. cinerea has a large arsenal of virulence, including the production of cell wall degrading enzymes, reactive oxygen species and toxins. B. cinerea has a wide host range and plant resistance to this pathogen is quantitative. Nitrogen (N) is a major limiting factor of plant growth and soils frequently lack sufficient N. Large quantities of N fertilizers are used worldwide and have an impact on crop disease. However, the variety of effects observed indicate that there is a complex relationship linking N availability to plant disease. We showed previously that high N supply increases the susceptibility of A. thaliana to B. cinerea (Fagard et al., 2014, J. Exp Bot 65: 5643-5656). A transcriptomic approach of B. cinerea-infected A. thaliana plants grown in low or high N has enabled us to identify both fungal and plant genes for which expression is affected by the plant’s N status. Characterization of corresponding fungal knock-out mutants led to the identification of novel B. cinerea virulence genes, including a GST. On the plant side, we identified the jasmonate signaling pathway as a key player in the modulation of A. thaliana susceptibility by N supply. Our current working model is that N availability for plants primarily affects the outcome of plant-pathogen interactions through its effect on plant defense and pathogen virulence gene expression