Résultat de la recherche
Lateral root formation in "Arabidopsis thaliana" and "Brachypodium distachyon": comparison of spatial accommodating responses
Roots are essential for anchoring plants to the soil and for the uptake of water and nutrients. Root branching significantly enhances the morphological adaptability of the root system in response to various biotic and abiotic factorsDespite significant findings in recent decades within the LR context, there remain major questions about the role of the endodermis during the emergence of the LRP. Our research has identified two important groups of auxin-mediated enzymatic components (GDSL-type esterase/lipase proteins - GELPs) that regulate suberin polymerization and likely its degradation. Additionally, we have demonstrated that developmental plasticity of the endodermis is necessary for normal LR emergence. Higher order mutants, almost completely lacking suberization in the endodermis, were highly sensitive to stress conditions. The wild grass Brachypodium distachyon, with its small genome, short life cycle, and small stature, is suitable for genetic transformation and has been developed as a model organism for both laboratory and field studies. However, it presents considerable challenges for studying LRs in their early developmental stages. We adapted a clearing method that significantly reduces clearing time, is compatible with various fluorescence dyes, and allows deep imaging of early cell divisions in the LRP. Using this toolkit, we were able to systematically categorize each LRP stage similar to what is used in Arabidopsis. We also demonstrated that, unlike in Arabidopsis, in Brachypodium the endodermis reactivates the cell cycle during LR formation. Moreover, we could show that the LRP appears to modify its Casparian strips to allow the emergence of the new organ. Surprisingly, the auxin reporter DR5 was not detected in early stages of LR formation, which does not necessarily imply that auxin is not involved in the initiation steps since we observed expression of auxin transporters during LR initiation events. We employed a root tip excision (RTE) method to synchronize LR development in Brachypodium, revealing distinct responses between accessions Bd21 and Bd21-3. In the latter accession, LRs appeared to be delayed in their emergence towards the nutrient medium along the root axis compared to Bd21. Additionally, osmotic stresses and hormonal treatments significantly reduced LR number and size in Bd21-3. Histological analyses suggested that the observed challenges in LRP emergence could be caused by early lignification of the exodermis in Bd21-3, unlike Bd21, where a delayed lignification was associated with facilitated LRP emergence. Integrating RTE with RNA-seq analysis of selected time points revealed a rapid induction of genes with a predicted function in cell-wall modification following the synchronized LR formation. Further studies, such as single-cell sequencing, will be essential to investigate the genetic programs underlying cell wall remodelling during LRP emergence in Brachypodium. In conclusion, we believe that this thesis contributed to advance our understanding of LR development in a wild grass, particularly emphasizing the pivotal role of the endodermis and its interactions with hormonal pathways and suberin dynamics.