A Disordered Plant Microtubule Associated Protein Reorganizes Microtubules During Stress

Companion of Cellulose Synthase 1 (CC1) has been recently identified to maintain cellulose synthesis during salt stress in Arabidopsis. CC1 is predicted to be a multi-domain protein with an N-terminal cytosolic disordered region (CC1NTD), a transmembrane region, and a C-terminal apoplastic region based on bioinformatics and structural modeling using Alphafold2. Previously, the disordered region of CC1 was found to interact with cortical microtubules in a similar fashion to human Tau protein however the structural basis for the interaction has not been investigated. In this work we investigated the solution structure of CC1NTD and its interaction with microtubules using small-angle X-ray and neutron scattering. Size exclusion chromatography – small-angle X-ray scattering analysis reveals that CC1NTD exists as a redox-dependent equilibrium mixture of monomers and dimers. SAXS shows that there is a structural rearrangement of microtubules in the presence of CC1NTD that supports bundling of microtubules. Using contrast variation SANS at the contrast match point of the microtubules, we observed the structure of deuterated CC1NTD and showed that the protein has a regular distribution across the microtubule lattice that is consistent with a tetragonal arrangement of CC1NTD around the microtubules. Overall, our study provides insights into how a disordered plant microtubule associated protein can affect the cortical microtubule network when plants are subjected to stress. Current research is now focused on understanding the structural remodeling of microtubules during this process.