BACKGROUND Upon water uptake and release of seed dormancy, embryonic plant cells expand, while being mechanically constrained by the seed coat. Cortical microtubules (CMTs) are key players of cell elongation in plants: their anisotropic orientation channels the axis of cell elongation through the guidance of oriented deposition of load-bearing cellulose microfibrils in the cell wall. Interestingly, CMTs align with tensile stress, and consistently, they reorient upon compressive stress in growing hypocotyls. How CMTs first organise in germinating embryos is unknown, and their relation with mechanical stress has not been investigated at such an early developing stage. RESULTS Here, we analysed CMT dynamics in dormant and non-dormant Arabidopsis seeds by microscopy of fluorescently tagged microtubule markers at different developmental time points and in response to abscisic acid and gibberellins. We found that CMTs first appear as very few thick bundles in dormant seeds. Consistently, analysis of available transcriptome and translatome datasets show that limiting amounts of tubulin and microtubule regulators initially hinder microtubule self-organisation. Seeds imbibed in the presence of gibberellic acid or abscisic acid displayed altered microtubule organisation and transcriptional regulation. Upon the release of dormancy, CMTs then self-organise into multiple parallel transverse arrays. Such behaviour matches the tensile stress patterns in such mechanically constrained embryos. This suggests that, as CMTs first self-organise, they also align with shape-derived tensile stress patterns. CONCLUSIONS Our results provide a scenario in which dormancy release in the embryo triggers microtubule self-organisation and alignment with tensile stress prior to germination and anisotropic growth.

中文翻译：

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拟南芥种子萌发过程中的微管自组织。


背景技术在吸收水分和释放种子休眠后，胚胎植物细胞扩张，同时受到种皮的机械约束。皮质微管（CMT）是植物细胞伸长的关键参与者：它们的各向异性方向通过引导细胞壁中承重纤维素微纤维的定向沉积来引导细胞伸长的轴。有趣的是，CMT 与拉应力一致，并且一致地，它们在生长的下胚轴中根据压应力重新定向。 CMT 在萌芽胚胎中最初如何组织尚不清楚，并且在如此早期的发育阶段尚未研究它们与机械应力的关系。结果在这里，我们通过显微镜观察不同发育时间点的荧光标记微管标记以及对脱落酸和赤霉素的反应，分析了休眠和非休眠拟南芥种子的 CMT 动态。我们发现，CMT 在休眠种子中首先以很少的粗束形式出现。对可用转录组和翻译组数据集的分析一致表明，微管蛋白和微管调节剂的数量有限最初会阻碍微管自组织。在赤霉酸或脱落酸存在下吸收的种子表现出微管组织和转录调控的改变。休眠状态解除后，CMT 会自组织成多个平行的横向阵列。这种行为与这种机械约束胚胎中的拉伸应力模式相匹配。这表明，当 CMT 首先自组织时，它们也与形状衍生的拉伸应力模式保持一致。 结论我们的结果提供了一种情况，其中胚胎中的休眠释放触发微管自组织并在发芽和各向异性生长之前与拉应力对齐。