在吸收水分和释放种子休眠后,植物胚胎细胞扩增,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:它们的各向异性取向通过引导细胞壁中承载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与拉伸应力对齐,并且始终如一,它们在生长下胚轴的压缩应力下重新定向。尚不清楚CMT如何首次组织发芽的胚胎,在如此早期的发展阶段,它们与机械应力的关系尚未得到研究。
这里,我们通过荧光标记的微管标记在不同发育时间点以及对脱落酸和赤霉素的响应显微镜分析了休眠和非休眠拟南芥种子中的CMT动力学。我们发现,在休眠种子中,CMT最初表现为很少的粗束。始终如一,对可用的转录组和翻译组数据集的分析表明,有限数量的微管蛋白和微管调节因子最初阻碍了微管自组织。在赤霉素或脱落酸存在下吸收的种子显示出改变的微管组织和转录调节。休眠释放后,然后,CMT自组织成多个平行的横向阵列。这种行为与这种机械约束的胚胎中的拉伸应力模式相匹配。这表明,作为CMT第一次自组织,它们也与形状衍生的拉伸应力模式一致。
我们的结果提供了一个场景,其中胚胎中的休眠释放触发了微管自组织,并在发芽和各向异性生长之前与拉伸应力对齐。
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.
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.
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.