Cell division is a highly important process for growth and development. The orientation of cell division, as well as the different rules regulating division plane positioning, has been a wide question in plant biology. The pre-prophase band (PPB) is a plant-specific structure positioned and predicting the position of the future division plane, appearing right before mitosis. The PPB is notably formed by cortical microtubules (CMTs), forming a ring around the cell. However, the dynamics of the CMTs, and their transitioning process towards forming the PPB has not been studied in detail. Tensile stress has been shown to play a role in the organization of interphasic CMTs, as well as the orientation of the cell division plane. This project aims to study the transition of CMTs from interphase to PPB, using the stem as a model, where the tension is both highly directional and stable. We noticed a transient re-organization of the microtubules array between the highly aligned interphasic array, and the PPB stage. During this stage, the microtubules are organized in a radial array, losing their anisotropy. We could link this “radial step” with a pre-mitotic increase in cytoplasmic microtubules, around two to three hours before the formation of the PPB. The trm678 mutant is a PPB-deficient mutant, and displays a longer and clearer “radial step”. The variability in daughter cells ratio is also highly reduced in the mutant, compared to the wild type, and the pre-mitotic accumulation of cytoplasmic microtubules much higher. With these observations, we propose that the “radial step” is a crucial step for the formation of the PPB, and reflects the internal accumulation of microtubules. This could help shield transiently the cell from external mechanical cues, and therefore allow a symmetry, in terms of volume, between the two daughter cells. To go further in the investigation of the role of the “radial step”, we studied the behavior of microtubules in other systems. Notably, using protoplasts and callus, tobacco leaves, and developing lateral roots.
Gratuit