Coarse-Grained Model of Cooperative Chloroplast Transport in Moss

Organelle motility is essential for the functioning of the eukaryotic cell. Actively modifying intracellular structures allows cells to change and adapt to different conditions. One of these cellular structures is the microtubule cytoskeleton, which is comprised of polarized filaments that function as tracks to transport cargo via molecular motors. Recent studies have revealed the importance of cooperative transport in living cells. In the moss Physcomitrella patens, reorganization of the chloroplasts is critical to adapt to changes in light quality and intensity. In this work, we performed detailed analysis of the transport of chloroplasts in protonemal moss cells, and showed that their transport is facilitated by molecular motors and the microtubule cytoskeleton. Our findings were recapitulated using coarse-grained modeling of this cargo transport over different microtubule network topologies. Our simulations include a detailed description of motor and microtubule dynamics, in the presence of thermal fluctuations. Our modeling sheds light into the molecular mechanisms at play in the photo-relocation response of chloroplasts in moss.