Integrative analysis of acquired thermotolerance in developmentally arrested Arabidopsis seedlings. Implication of energy metabolism

In the context of climate change, the increased frequency and intensity of heat waves will likely have a negative impact on plant physiology, due to the structural destabilization of proteins and membranes caused by high temperatures. As part of this thesis, we developed and characterized an original experimental setup in which Arabidopsis thaliana seedlings are arrested in their development because of mineral starvation. These seedlings exhibit a high metabolic plasticity, especially for energy metabolism, which allows them to survive in a steady state for weeks. Then, we performed an integrative analysis of the processes that allow these seedlings to survive an otherwise lethal heat stress (43°C, 2 h), thanks to a priming treatment at a nonlethal temperature (38°C, 2 h). Priming protects the energy metabolism and permits the recovery of organelle dynamics after stress. At the transcriptional level, primed seedlings overexpress many chaperone proteins and genes involved in photosynthesis, and in the regulation of the expression of mitochondrial and plastidial genomes. At the protein level, the accumulation of HSPs and other stress proteins favour seedling recovery, whereas in the absence of acclimation, heat shock provokes the decrease of ribosomal proteins and the accumulation of proteins implicated in protein degradation. This study highlights the relevance of multi-scale analysis to decipher mechanisms of stress response in plants

Arabidopsis seedlings display a remarkable resilience under severe mineral starvation using their metabolic plasticity to remain self-sufficient for weeks

During the life cycle of plants, seedlings are considered vulnerable because they are at the interface between the highly stress tolerant seed embryos and the established plant, and must develop rapidly, often in a challenging environment, with limited access to nutrients and light. Using a simple experimental system, whereby the seedling stage of Arabidopsis is considerably prolonged by nutrient starvation, we analysed the physiology and metabolism of seedlings maintained in such conditions up to 4 weeks. Although development was arrested at the cotyledon stage, there was no sign of senescence and seedlings remained viable for weeks, yielding normal plants after transplantation. Photosynthetic activity compensated for respiratory carbon losses, and energy dissipation by photorespiration and alternative oxidase appeared important. Photosynthates were essentially stored as organic acids, while the pool of free amino acids remained stable. Seedlings lost the capacity to store lipids in cytosolic lipid droplets, but developed large plastoglobuli. Arabidopsis seedlings arrested in their development because of mineral starvation displayed therefore a remarkable resilience, using their metabolic and physiological plasticity to maintain a steady state for weeks, allowing resumption of development when favourable conditions ensue