The role of the MAP65 family in microtubule lattice regulation

• Applicant: Dr. Mariana Romeiro Motta
• Subject Area: Plant Biochemistry and Biophysics ; Biophysics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545084341

External and internal mechanical cues guide the development of all organisms. Cells must recognize these cues through mechanosensing and respond appropriately. Key to mechanosensing in plants are cortical microtubules (MTs), which indirectly shape the cell wall and usually align with the predicted maximal tension direction in different tissues. MTs are also more stable under tension in vitro and have been proposed to be tension sensors. However, this hypothesis needs additional experimental evidence. While attention has been paid to the dynamic ends of MTs for decades, there is increasing interest in the MT lattice, which is now known to influence MT mechanical properties and dynamics. Nevertheless, the interplay between MT lattice regulation, mechanosensing and the associated molecular pathways is unknown. In Laura Aradilla Zapata’s group, I found that MAP65 promotes tubulin incorporation into the MT lattice and a previously unknown MT nucleation mechanism along existing lattices in vitro. These two new roles of MAP65 prompted me to reconsider the function of this protein class in the organization of MTs in cells. Olivier Hamant’s group developed a single-cell system using artificial microwells in which mechanical characteristics of the cellular environment can be precisely modified, representing an opportunity to study mechanosensing in plant cells without the influence of the surrounding tissue. Stefan Diez, a planned host for this project, is an expert in microfabrication and in vitro cytoskeletal reconstitution. In this multi-team synergistic project, I will test the hypothesis that MAP65 quickly stabilizes and amplifies MTs under tension and is thus involved in the response of plant cells to tensile stress. I will (1) characterize the function of the MAP65 family in regulating the MT lattice in vitro, (2) transfer the knowledge gained in vitro to plant cells, (3) test the function of MAP65 in MT reorganization upon a change in surface tension using Hamant’s system, and (4) test the function of MAP65 in MT self-organization in motor-coated cell-sized compartments. I aim to unravel how MAP65-mediated MT lattice regulation and surface tension guide the MT array and consequently anisotropic growth. This work goes beyond plant biology and will have significant implications in cell biology of different eukaryotes, since the new MAP65-mediated MT nucleation mechanism seems to be conserved in the human homolog PRC1.

• DFG Programme: WBP Position