Biology subjects

Pelletier, G.

Publications and source records attributed to Pelletier, G..

4 recordsLinked to original sources

bioRxiv2020

Differential alteration of plant functions by homologous fungal candidate effectors

Rust fungi are plant pathogens that cause epidemics that threaten the production of important plant species, such as wheat, soy, coffee and poplar. Melampsora larici-populina (Mlp) causes the poplar rust and encodes at least 1 184 candidate effectors (CEs), however their functions are poorly known. In this study, we used Arabidopsis plants constitutively expressing CEs of Mlp to discover processes targeted by these fungal proteins. For this purpose, we sequenced the transcriptome and used mass spectrometry to analyse the metabolome of Arabidopsis plants expressing individually one of the 14 selected CEs and of a control line. We found 2 299 deregulated genes across the experiment. Among the down-regulated genes, the KEGG pathways "MAPK signaling pathway" and "Plant-pathogen interaction" were respectively over-represented in six and five of the 14 transgenic lines. Moreover, genes related to hormone response and defense were down-regulated across all transgenic lines are. We further observed that there were 680 metabolites deregulated in at least one CE-expressing transgenic line, with highly unsaturated and phenolic compounds enriched in up-regulated metabolites and peptides enriched among down-regulated metabolites. Interestingly, we found that transgenic lines expressing unrelated CEs had correlated patterns of gene and metabolite deregulation, while expression of CEs belonging to the same family deregulated different genes and metabolites. Taken together, our results indicate that the sequence of effectors and their belonging to families may not be a good predictor of their impact on the plant. ImportanceRust fungi are plant pathogens that threaten the production of important crops, including wheat, soy, coffee and poplar. Effectors are used by pathogens to control the host, however in the case of Melampsora larici-populina, the causal agent of the poplar rust, and other rust fungi these proteins are poorly known. We used Arabidopsis plants expressing candidate effectors (CEs) of Mlp to better understand the interaction between this pathogen and its hosts. We found that expression of unrelated CEs led to similar patterns of gene and metabolite deregulation, while transgenic lines expressing CEs belonging to the same family showed different groups of different genes and metabolites deregulated. Thus, our results suggest that functional annotation of effectors based on sequence similarity may be misleading.

plant biology↗

bioRxiv2020

The value of the whole or the sum of the parts: The role of ventromedial prefrontal cortex in multi-attribute object evaluation

Everyday decision-making commonly involves assigning values to complex objects with multiple value-relevant attributes. Drawing on object recognition theories, we hypothesized two routes to multi-attribute evaluation: assessing the value of the whole object based on holistic attribute configuration or summing individual attribute-values. In two samples of healthy human participants undergoing eye-tracking and fMRI while evaluating novel pseudo-objects, we found evidence for both forms of evaluation. Fixations to, and transitions between attributes differed systematically when value of pseudo-objects was associated with individual attributes or attribute configurations. Ventromedial prefrontal cortex (vmPFC) and perirhinal cortex were engaged when configural processing was required. These results converge with our recent findings that individuals with vmPFC lesions were impaired in decisions requiring configural evaluation, but not when evaluating "the sum of the parts". This suggests that multi-attribute decision-making engages distinct evaluation mechanisms relying on partially dissociable neural substrates, depending on the relationship between attributes and value. SIGNIFICANCE STATEMENTDecision neuroscience has only recently begun to address how multiple choice-relevant attributes are brought together during evaluation and choice among complex options. Object recognition research makes a crucial distinction between individual attribute and holistic/configural object processing, but how the brain evaluates attributes and whole objects remains unclear. Using fMRI and eye-tracking, we found that the vmPFC and the perirhinal cortex contribute to value estimation specifically when it emerged from the whole objects i.e. predicted by the unique configuration of attributes, and not when value was predicted by the sum of individual attributes. This novel perspective on the interactions between subjective value and object processing mechanisms bridges an important gap between the fields of object recognition and reward-guided decision-making.

neuroscience↗

bioRxiv2018

A critical role for human ventromedial frontal lobe in value comparison based on multi-attribute configuration

Real-life decisions are often between options with multiple value-relevant attributes. Neuroeconomic models propose that the value associated with each attribute is integrated in a global value for each option. However, evidence from patients with ventromedial frontal (VMF) damage argues against a very general role for this region in value integration, suggesting instead that it contributes critically to specific value inference or comparison processes. Here, we tested value-based decision-making between artificial multi-attribute objects in 12 men and women with focal damage to VMF, compared to a healthy control group (N=24) and a control group with frontal lobe damage sparing VMF (N=12). In a configural condition, overall object value was predicted by the conjunction of two attributes, while in an elemental condition, object value could be assessed by combining the independent values of individual attributes. Patients with VMF damage were impaired in making choices when value was uniquely predicted by the configuration of attributes, but intact when choosing based on elemental attribute-values. This is evidence that VMF is critical for inferring the value of whole objects in multi-attribute choice. These findings have implications for models of value-based choice, and add to emerging views of how this region may interact with medial temporal lobe systems involved in configural object processing and relational memory.

neuroscience↗

bioRxiv2018

Ventromedial prefrontal cortex is not critical for behavior change without external reinforcement

Cue-approach training (CAT) is a novel paradigm that has been shown to induce preference changes towards items without external reinforcements. In the task the mere association of a neutral cue and a speeded button response has been shown to induce a behavioral change lasting months. This paradigm includes several phases whereby after the training of individual items, behavior change is manifested through binary choices of items with similar initial values. Neuroimaging data have implicated the ventromedial prefrontal cortex (vmPFC) during the choice phase of this task. However, it still remains unclear what are the underlying neural mechanisms during training. Here, we sought to determine whether the ventromedial frontal cortex (VMF) is critical for the non-reinforced preference change induced by CAT. For this purpose, eleven participants with focal lesions involving the VMF and 30 healthy age-matched controls performed the CAT. We found that at the individual level, a similar proportion of VMF and healthy participants showed a preference shift following CAT. The VMF group performed similarly to the healthy age-matched control group in the ranking and training phases. As a group the healthy age-matched controls exhibited a behavior change, but the VMF participants as a group did not. We did not find an association between individual lesion patterns and performance in the task. We conclude that a fully intact VMF is not critical to induce non-externally reinforced preference change and suggest potential mechanisms for this novel type of behavioral change.

neuroscience↗