Positional cloning of a candidate gene for resistance to the sunflower downy mildew, Plasmopara halstedii race 300.

International audienceThe resistance of sunflower to Plasmopara halstedii is conferred by major resistance genes denoted Pl. Previous genetic studies indicated that the majority of these genes are clustered on linkage groups 8 and 13. The Pl6 locus is one of the main clusters to have been identified, and confers resistance to several P. halstedii races. In this study, a map-based cloning strategy was implemented using a large segregating F2 population to establish a fine physical map of this cluster. A marker derived from a bacterial artificial chromosome (BAC) clone was found to be very tightly linked to the gene conferring resistance to race 300, and the corresponding BAC clone was sequenced and annotated. It contains several putative genes including three toll-interleukin receptor-nucleotide binding site-leucine rich repeats (TIR-NBS-LRR) genes. However, only one TIR-NBS-LRR appeared to be expressed, and thus constitutes a candidate gene for resistance to P. halstedii race 300

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

Poplar stem transcriptome is massively remodelled in response to single or repeated mechanical stimuli

Abstract Background Trees experience mechanical stimuli -like wind- that trigger thigmomorphogenetic syndrome, leading to modifications of plant growth and wood quality. This syndrome affects tree productivity but is also believed to improve tree acclimation to chronic wind. Wind is particularly challenging for trees, because of their stature and perenniality. Climate change forecasts are predicting that the occurrence of high wind will worsen, making it increasingly vital to understand the mechanisms regulating thigmomorphogenesis, especially in perennial plants. By extension, this also implies factoring in the recurring nature of wind episodes. However, data on the molecular processes underpinning mechanoperception and transduction of mechanical signals, and their dynamics, are still dramatically lacking in trees. Results Here we performed a genome-wide and time-series analysis of poplar transcriptional responsiveness to transitory and recurring controlled stem bending, mimicking wind. The study revealed that 6% of the poplar genome is differentially expressed after a single transient bending. The combination of clustering, Gene Ontology categorization and time-series expression approaches revealed the diversity of gene expression patterns and biological processes affected by stem bending. Short-term transcriptomic responses entailed a rapid stimulation of plant defence and abiotic stress signalling pathways, including ethylene and jasmonic acid signalling but also photosynthesis process regulation. Late transcriptomic responses affected genes involved in cell wall organization and/or wood development. An analysis of the molecular impact of recurring bending found that the vast majority (96%) of the genes differentially expressed after a first bending presented reduced or even net-zero amplitude regulation after the second exposure to bending. Conclusion This study constitutes the first dynamic characterization of the molecular processes affected by single or repeated stem bending in poplar. Moreover, the global attenuation of the transcriptional responses, observed from as early as after a second bending, indicates the existence of a mechanism governing a fine tuning of plant responsiveness. This points toward several mechanistic pathways that can now be targeted to elucidate the complex dynamics of wind acclimation

Acclimation of Populus to wind: kinetic of the transcriptomic response to single or repeated stem bending

National audienc

Strategy for infering gene regulatory network from kinetic expression with unfavorable data-to-variables ratio.

absen

Molecular characterization of the sucrose transporter HbSUT6 in relation with rubber production in laticiferous cells

The rubber synthesis in latex cells requires sucrose. These particular cells are heterotrophic ones and are apoplastically connected to other tissues. Such features imply that the rubber yield may depend on the latex cell efficiency to absorb and to use the imported sucrose. This study investigates the sucrose transporters as key genes for rubber biosynthesis involved in the ethylene-stimulated rubber yield. Seven putative sucrose transporters had been isolated from a latex-derived cDNA library of PB 217. Expression profiling of these sucrose transporters under ethylene stimulation in PB 217 underlined the role of one sucrose transporter: HbSUT1B (Hevea brasiliensis Sucrose Transporter 6) (Dusotoit-Coucaud et al., 2007). This paper reports the next stage in HbSUT1B, molecular characterisation. Its expression in different parts of the rubber tree was studied. It was preferentially expressed in leaves and bark. This result was completed by in-situ hybridisation experiments. In addition, promoter cloning and analysis revealed some clues for the wounding regulation of HbSUT1B. The HbSUT1B expression was analysed in response to different treatments in latex or bark tissues. HbSUT1B was considerably up-regulated by hormones and wounding in bark but not in latex. This regulation appeared to be tissue-specific

Secondary growth regulation by strains induced by wind: from stem structure to gene expression

Mechanical signals are important factors controlling plants growth and development. External mechanical loadings, such as wind, lead to a decrease of primary growth, an increase of secondary growth, modifications of stem mechanical properties and biomass reallocation to roots (Telewski, 2006, Badel et al., 2015). Integrative approaches combining physical/modeling/kinematics at plant and organ levels demonstrated that strain-sensing (deformation) are involved in the process of mechanoperception (Moulia et al., 2011; Coutand et al., 2009). These results allowed the development of an integrative biomechanical model called S3m which postulates that mechanoperception is proportional to local strain and volume of the considered tissue (Moulia et al., 2011). In this study, we tested this biomechanical model at tissue level by studying the relation between local strain intensity, secondary growth and genes expression

Response of Grapevine Defenses to UV—C Exposure

International audienceThe defense potential of a tolerant American Vitis rupestris cultivar (Rupestris du Lot) and a susceptible European Vitis vinifera cultivar (Chardonnay) in response to UV-C irradiation was investigated. The expression of eight defense-related genes coding for enzymes of the phenylpropanoid pathway (phenylalanine ammonia lyase and stilbene synthase), the octadecanoid pathway (lipoxygenase), and pathogenesis-related proteins (class I and III chitinases, ß-1,3-glucanase, class 6 pathogenesis-related protein, and class 10 pathogenesis-related protein) was followed by real-time reverse transcription polymerase chain reaction (RT-PCR). Phenolic compound accumulation was monitored by microscopic observation. Accumulation of resveratrol, a major grapevine phytoalexin, was evaluated by HPLC, and chitinase and ß-1,3-glucanase enzyme activities were measured. Both grapevine species responded to UV-C treatment by enhancement of defense mechanisms. Intensity of some defense responses was correlated with tolerance to diseases, as previously described for stilbene accumulation: the tolerant species responded more intensely to UV-C exposure than the susceptible one. UV-C irradiation is a practical and reproducible method for inducing grapevine defense responses and can be useful in determining the defense potential of grapevine cultivars

Molecular Characterisation of the Sucrose Transporter HbSUT1B in Relation to Rubber Production in Latex Cells

The rubber synthesis in latex cells requires sucrose. These particular cells are heterotrophic ones and are apoplastically connected to other tissues. Such features imply that the rubber yield may depend on the latex cell efficiency to absorb and to use the imported sucrose. This study investigates the sucrose transporters as key genes for rubber biosynthesis involved in the ethylene-stimulated rubber yield. Seven putative sucrose transporters had been isolated from a latex-derived cDNA library of PB 217. Expression profiling of these sucrose transporters under ethylene stimulation in PB 217 underlined the role of one sucrose transporter: HbSUT1B (Hevea brasiliensis Sucrose Transporter 6) (Dusotoit-Coucaud et al., 2007). This paper reports the next stage in HbSUT1B, molecular characterisation. Its expression in different parts of the rubber tree was studied. It was preferentially expressed in leaves and bark. This result was completed by in-situ hybridisation experiments. In addition, promoter cloning and analysis revealed some clues for the wounding regulation of HbSUT1B. The HbSUT1B expression was analysed in response to different treatments in latex or bark tissues. HbSUT1B was considerably up-regulated by hormones and wounding in bark but not in latex. This regulation appeared to be tissue-specific