Influence des facteurs environnementaux sur la plasticité phénotypique et le microbiote : Étude expérimentale chez les broméliacées du genre Aechmea

Phenotypic plasticity, the ability of a genotype to produce different phenotypes in response to different environmental conditions, is a crucial mechanism for sessile organisms like plants that cannot escape their environment. The recent recognition of the role of microorganisms in plant health has led to considering them as potentially key players in plant-environment interactions, giving rise to the concept of the holobiont, the entity formed by a host and its microbial partners. The overall objective of this thesis is to explore the plasticity of plants at different levels of integration. To achieve this, we have leveraged the biological model represented by water-retaining bromeliads with two main objectives:

Firstly, to characterize the phenotypic plasticity of bromeliads along environmental gradients by adopting a classic view of plant phenotype through the measurement of morpho-anatomical and physiological traits. In this part, we addressed the phenotypic plasticity of Aechmea aquilega at inter-individual and intra-organ scales.

Secondly, we studied the phenotypic plasticity of the holobiont when exposed to different resource quantities. Plant phenotypes are strongly influenced by their microbiota, which are an integral part of the extended phenotype of the plant. In this second part, we expanded the study of plant traits by integrating the responses of microbial communities through metabarcoding approaches to better understand the holobiont system under environmental constraints. We also explored the putative role of the microbiota in transgenerational plasticity. For this purpose, we characterized transgenerational microbial fluxes and the influence of maternal environment on the phenotype and microbiota of offsprings in Aechmea mertensii.

Our results refine our understanding of resource acquisition strategies in Bromeliads of the genus Aechmea, notably highlighting the significant contribution of root nutrition to their growth and complex responses within the same leaf to variations in light intensity. In the second part, we reveal a covariation between microbial communities and ecophysiological traits of Aechmea, supporting the existence of a coordinated response of the different constituents of the holobiont (i.e., microbiota and its host) to environmental variations. Finally, we demonstrate the existence of maternal effects influencing the phenotype and microbiota of offspring.

The results of this work at the interface between microbiology and plant ecophysiology thus reveal a complex response of Aechmea plants to different environmental factors and biological scales (e.g., intra-organ, holobiont, and between generations). Phenotypic plasticity in plants appears to be the integration of various mechanisms and numerous interactions at different levels that need to be considered if we want to understand plant responses to past, present, and future environmental changes.

Composition du jury :
Marie Simonin, CR INRAE, Rapportrice
Benoit Pujol, DR CNRS, Rapporteur
Alexia Stockes, DR INRAE, Examinatrice
Marc Buée, DR INRAE, Examinateur
Céline Leroy, DR IRD, Directrice de thèse
Régis Céréghino, Pr Univ. Paul Sabatier, co-directeur de thèse