Periodic Reporting for period 2 - LIPIDEV (Lipid gradients and the dynamics of the plant endomembrane system: from the nano- to the developmental scales)
Periodo di rendicontazione: 2023-04-01 al 2024-09-30
Anionic lipids are critical for membrane organization and signaling in eukaryotes, including animals and plants. The dogma is that they accumulate in distinct membranes, thereby recruiting a unique set of lipid-binding proteins to each compartment. In turn, these proteins regulate trafficking and signaling activities on these compartments. However, it is increasingly recognized that anionic lipid distribution is not organelle-specific. In particular, we uncovered the presence of anionic lipids concentration gradients between the membranes of various compartments in plant cells. We further found that these cellular lipid gradients are dynamically regulated during cell differentiation and rapid responses to auxin, one of the major regulators of plant growth and architecture. In this project, we ask how lipid gradients are generated at the level of the cell but also at the organ scale and in response to specific stimuli. From there, we address the function of anionic lipids and lipid gradients in cell and tissue homeostasis.
During the first half of the project, we made significant progress on the mechanism underlying the formation of lipid gradients. We found that membrane contact sites are critical sites for the establishment of lipid gradients. This is true at the level of the cell but also at the tissue scale, which we did not anticipate initially. We also found that anionic lipid feedback on the formation of membrane contact sites, thereby regulating the establishment of their own patterns. Using a microfluidic based system and high-resolution time-lapse imaging, we uncovered that not only auxin, but also regulatory peptides, can rapidly impact anionic lipids subcellular accumulation. Finally, we analyzed the function of anionic lipids in the formation of signaling nanodomains at the plasma membrane and their impact on signal specificity. Here, we found that different anionic lipids are critical for the formation of Rho GTPase-containing nanodomains. However, we also uncovered the existence of anionic lipid-independent mechanisms that we will investigate during the second reporting period.
One of the breakthrough outcomes of this project so far is our results on plasmodesmata. Indeed, in collaboration with the group of Emmanuelle Bayer (Bordeaux), we showed that plasmodesmata act as unconventional membrane contact sites regulating inter-cellular molecular exchange in plants. The highlights of this study are: i) Plasmodesmata are unconventional ER/PM tubular contact sites sitting at cell-cell interface, ii) Plasmodesmata act as control valves, adjusting the ER-PM contacts to modulate cytosolic flow, iii) MCTPs and PI4P tethering elements act as valve-size controllers and iv) MCTP/PI4P tethers function independently of callose levels to regulate cell-to-cell diffusion