Could thioredoxin h be involved in early response to gravitropic stimulation of poplar stems?

The perception of gravity is essential for plant development. Trees constantly develop specialized woody tissues, termed « reaction wood » to correct inclined branch and stem growth in order to adopt an optimal position. Despite the economical impact of reaction wood occurrence and itsimportance from a developmental point of view, the perception and response to the gravitational stimulus have not been extensively studied in woody species in which primary and secondary growth occur. Using complementary approaches (proteomics, qRT-PCR, immunolocalization), we have compared straight polar stems to stems that were inclined at 35° from the vertical axis for periods of time varying from 10 min to 6 hours depending on the experiments. The proteomics approach revealed that thirty six percent of the identified proteins that were differentially expressed after gravistimulation were established as potential Thioredoxin targets. qRT-PCR indicated an early induction of Thioredoxin h expression following gravistimulation. In situ immunolocalization indicated that Thioredoxin h protein co-localized with the amyloplasts located in the endodermalcells which may be specialized in gravity perception. These investigations suggest the involvement of Thioredoxin h in the first events of signal transduction in inclined poplar stems, leading to reaction wood formation

Sunflower Hybrid Breeding: From Markers to Genomic Selection

In sunflower, molecular markers for simple traits as, e.g., fertility restoration, high oleic acid content, herbicide tolerance or resistances to Plasmopara halstedii, Puccinia helianthi, or Orobanche cumana have been successfully used in marker-assisted breeding programs for years. However, agronomically important complex quantitative traits like yield, heterosis, drought tolerance, oil content or selection for disease resistance, e.g., against Sclerotinia sclerotiorum have been challenging and will require genome-wide approaches. Plant genetic resources for sunflower are being collected and conserved worldwide that represent valuable resources to study complex traits. Sunflower association panels provide the basis for genome-wide association studies, overcoming disadvantages of biparental populations. Advances in technologies and the availability of the sunflower genome sequence made novel approaches on the whole genome level possible. Genotype-by-sequencing, and whole genome sequencing based on next generation sequencing technologies facilitated the production of large amounts of SNP markers for high density maps as well as SNP arrays and allowed genome-wide association studies and genomic selection in sunflower. Genome wide or candidate gene based association studies have been performed for traits like branching, flowering time, resistance to Sclerotinia head and stalk rot. First steps in genomic selection with regard to hybrid performance and hybrid oil content have shown that genomic selection can successfully address complex quantitative traits in sunflower and will help to speed up sunflower breeding programs in the future. To make sunflower more competitive toward other oil crops higher levels of resistance against pathogens and better yield performance are required. In addition, optimizing plant architecture toward a more complex growth type for higher plant densities has the potential to considerably increase yields per hectare. Integrative approaches combining omic technologies (genomics, transcriptomics, proteomics, metabolomics and phenomics) using bioinformatic tools will facilitate the identification of target genes and markers for complex traits and will give a better insight into the mechanisms behind the traits

Seleno-independent glutathione peroxidases - More than simple antioxidant scavengers

Glutathione peroxidases (GPXs, EC 1.11.1.9) were first discovered in mammals as key enzymes involved in scavenging of activated oxygen species (AOS). Their efficient antioxidant activity depends on the presence of the rare amino-acid residue selenocysteine (SeCys) at the catalytic site. Nonselenium GPX-like proteins (NS-GPXs) with a Cys residue instead of SeCys have also been found in most organisms. As SeCys is important for GPX activity, the function of the NS-GPX can be questioned. Here, we highlight the evolutionary link between NS-GPX and seleno-GPX, particularly the evolution of the SeCys incorporation system. We then discuss what is known about the enzymatic activity and physiological functions of NS-GPX. Biochemical studies have shown that NS-GPXs are not true GPXs; notably they reduce AOS using reducing substrates other than glutathione, such as thioredoxin. We provide evidence that, in addition to their inefficient scavenging action, NS-GPXs act as AOS sensors in various signal-transduction pathways

Study of the variability and evolution of Orobanche cumana populations infesting sunflower in different European countries

International audienc

Molecular characterization, organ distribution and stress-mediated induction of two glutathione peroxidase-encoding mRNAs in sunflower (Helianthus annuus)

International audienc

Variabilité moléculaire de populations d’Orobanche cumana de différents pays européens.

International audienc

Transgenic tomatoes showing higher glutathione peroxydase antioxidant activity are more resistant to an abiotic stress but more susceptible to biotic stresses

The function of selenium independent glutathione peroxidase (GPx) in response to biotic and abiotic stresses was investigated in transgenic tomato plants overexpressing an exogenous GPx and exhibiting a 50% increase in total GPx activity. GPx-overexpressing and control plants were challenged either by a mechanical stress or by infection with the biotrophic parasite Oidium neolycopersici or the necrotrophic parasite Botrytis cinerea. In mechanically stressed plants, internode growth was significantly less modified in GPx-overexpressing plants compared to controls. This stress resistant phenotype was not accompanied with any change in the global antioxidant response of the plants other than their increased GPx activity. Following infection by O. neolycopersici or by B. cinerea, lesion extension was increased in GPx-overexpressing plants compared with controls. These results showed that GPx overexpression provoked opposite effects in situations of biotic and abiotic challenges, suggesting a key role for this scavenger enzyme in controlling biotic and abiotic stress responses