PIAF Thesis 2020 :

• Modeling the effects of tree canopy structure on the availability of water, nutrients and microclimate

Contacts : philippe.malagoli@uca.fr, philippe.balandier@inrae.fr, marc.saudreau@inrae.fr

Tree canopy structure has a clear influence on resource availability (light, water, nitrogen) in natural or cultivated tree ecosystems. This structure induces emergent meteorological and microclimatic properties that can influence functional interactions between different plant strata (Gaudio et al., 2017). To optimize and predict the evolution of different functions of these tree ecosystems (microclimate, production, resource use efficiency) it is necessary to take into account these multi-stratum interactions. The hypothesis tested would be that there is (are) a tree structure(s) (neither too open nor too closed, tiered) that allow to optimize these different functions under different assumptions of climate forcing. The idea is, based on one or two case studies in the field, to parameterize and validate a model in order to test in silico the effect of different tree structures with increasing levels of complexity. The thesis will rely on the modelling platform Capsis, already used by the team and in which candidate multistratum models already exist but require development.

Gaudio N, Gendre X, Saudreau M, Seigner V, Balandier P. 2017. Agricultural and Forest Meteorology, 237-238: 71-79.

• Study of the dynamics of the transcriptional and post-transcriptional response of Black Poplar to water deficiency

Contacts : philippe.label@inrae.fr, aurelie.gousset@uca.fr, Boris.Fumanal@uca.fr

Future climate change modelling predicts global warming in Western Europe associated with an increase in the frequency and severity of extreme weather events. In this context, exploring the response of plants to water scarcity is of great importance in terms of maintaining production and even the survival of individuals in their natural range.

Black poplar is a model for the study of woody plants by the scientific community (rapid growth, sequenced and annotated genome, etc.). An initial study carried out at UMR PIAF on different genotypes of contrasting black poplars (tolerant or avoidant strategy) has made it possible to identify and analyse the role of physiological plasticity in relation to their strategy for responding to drought. The aim of this thesis is to highlight the network of transcribed genes involved in the black poplar response to drought. For this purpose, transcriptomic analysis of RNA and microRNA in kinetics will be carried out on black poplar leaves of contrasting strategies subjected to progressive hydric deficiency. Particular attention will be paid to the regulatory network of genes encoding aquaporins and to the tissue localization of candidate gene expression. This study will ultimately make it possible to decipher the key molecular mechanisms of trees' response to drought.

Garavillon-Tournayre et al. 2018. Integrated drought responses of black poplar: How important is phenotypic plasticity? Physiol. Plant. 163(1):30-44

• Deciphering the processes of dehydration-induced cell mortality and their relationship to hydraulic failure.

Contacts : stephane.herbette@uca.fr, josemanuel.torresruiz@inrae.fr

Xylem hydraulic failure has been identified as a ubiquitous factor in triggering drought-induced tree mortality. It results in the blockage of water transport from roots to leaves, leading to accelerated desiccation of downstream tissues. Yet, the mechanistic link between hydraulic failure and drought-induced cellular damage is still unknown. This PhD proposal aims to elucidate this link to improve our predictions of drought-induced tree mortality, focusing on three objectives:

- Analyze the relationship between cell mortality and the plant's ability to recover from drought.

- To test the relationship between cell mortality and hydraulic failure in species with different drought resistance strategies.

- Assess the effect of drought dynamics on the different processes leading to cell death.

The PhD student will be trained in new and varied techniques to assess variation in plant hydraulic functioning, cell damage and recovery capacity in different plant species exposed to different drought conditions.

- Mantova M, Herbette S, Cochard H & Torres-Ruiz JM. 2022. Hydraulic failure and tree mortality: From correlation to causation. Trends in Plant Science.

- Lemaire C, Blackman CJ, Cochard H, Menezes-Silva PE, Torres-Ruiz JM & Herbette S. 2021. Acclimation of hydraulic and morphological traits to water deficit delays hydraulic failure during simulated drought in poplar. Tree Physiology 41, 2008-2021.

•  Root cap response to soil impedance change

Contact : valerie.legue@uca.fr

Plant roots are continuously submitted to mechanical constraints due to changing edaphic conditions (compaction, water deficit). Although the entire root is in contact with the soil, many studies have highlighted the importance of the root cap, located at the root tip, in the perception and integration of edaphic factors. Our analyses of root growth dynamics in a soil model suggest that the cap is a key zone in the perception of mechanical signals (Roué et al., 2020). The objective of this thesis is to decipher the transduction mechanisms in response to an axial force in Arabidopsis roots. We propose to take an interdisciplinary approach by combining physical and biological approaches. In a first step, we will finely analyze the deformation of root apex cells using 3D images using a light sheet microscope (SPIM for Selective Plane Illumination Microscopy), available in the laboratory. Then, we will target the key actors involved in deformation-induced transduction mechanisms. Our studies will focus on ROS and jasmonates. In plants, a number of mechanosensitive ion channels have been identified including the MSL, OSCAR, MCA and more recently PIEZZO channel families for which we will focus on phenotyping mutants.

Roué J., et al, 2020. Root cap size and shape influence responses to the physical strength of the growth medium in Arabidopsis thaliana primary roots. J. Exp. Bot., 71, 126–137. https://hal.archives-ouvertes.fr/hal-02394664.