Dataset For Melogno PNAS2023-20470

Although the formation of new walls during plant cell division tends to follow maximal tensile stress direction, analyses of individual cells over time reveal a much more variable behavior. The origin of such variability, as well as the exact role of interphasic microtubule behavior before cell division have remained mysterious so far. To approach this question, we took advantage of the Arabidopsis stem, where the tensile stress pattern is both highly anisotropic and stable. Although cortical microtubules generally align with maximal tensile stress, we detected a specific time window, ca. 3 hours before cell division, where cells form a radial pattern of cortical microtubules. This microtubule array organization preceded preprophase band formation, a transient cortical microtubule array predicting the position of the future division plane. It was observed under different growth conditions, and was not related to cell geometry or polar auxin transport. Interestingly, this cortical radial pattern correlated with the well-documented increase of cytoplasmic microtubule accumulation before cell division. This radial organization was prolonged in cells of the <i>trm678</i> mutant, where cortical microtubules are unable to form a preprophase band. Whereas division plane orientation in <i>trm678</i> is noisier, we found that cell division symmetry was in contrast less variable between daughter cells. We propose that this “radial step” reflects a trade-off in robustness for two essential cell division attributes: symmetry and orientation. This involves a “reset” stage in G2, where an increased cytoplasmic microtubule accumulation transiently disrupts cortical microtubules alignment with tissue stress.

尽管植物细胞分裂过程中新细胞壁的形成通常遵循最大拉伸应力方向，但对单个细胞的时序追踪分析却揭示出其行为具有显著更高的变异性。迄今为止，此类变异性的来源，以及细胞分裂前间期微管（interphasic microtubule）行为的确切作用，仍属未解之谜。为解答这一问题，我们选取拟南芥（Arabidopsis）茎秆作为研究模型——其拉伸应力模式兼具高度各向异性与稳定性。尽管皮层微管（cortical microtubules）通常会与最大拉伸应力方向对齐，但我们观测到一个特定的时间窗口：即在细胞分裂前约3小时，细胞会形成皮层微管的放射状排列模式。这种微管阵列结构早于早前期带（preprophase band）的形成——早前期带是一种可预测未来分裂平面位置的短暂皮层微管阵列。该现象在多种生长条件下均能观测到，且与细胞几何形态或极性生长素运输无关。有趣的是，这种皮层放射状排列与已有充分文献记载的细胞分裂前细胞质微管（cytoplasmic microtubule）积累量上升现象相关。在trm678突变体（trm678）的细胞中，该放射状排列的持续时间显著延长——该突变体的皮层微管无法形成早前期带。尽管trm678突变体的分裂平面取向噪声更高，但我们发现其子细胞间的细胞分裂对称性反而变异性更低。我们提出，这一“放射状阶段”反映了细胞分裂两项核心属性——对称性与取向——在鲁棒性上的权衡。该过程涉及G2期的“重置”阶段：此时细胞质微管积累量的增加会暂时性破坏皮层微管与组织应力的对齐状态。