Boscq Samuel, Billoud Bernard, Charrier Bénédicte
Morphogenesis of Macroalgae, Laboratory of Integrative Biology of Marine Models, UMR8227, Station Biologique de Roscoff, CNRS-Sorbonne University, Place Georges Teissier, 29680 Roscoff, France.
Plants (Basel). 2024 May 13;13(10):1341. doi: 10.3390/plants13101341.
Brown algae are multicellular organisms that have evolved independently from plants and animals. Knowledge of the mechanisms involved in their embryogenesis is available only for the , , and , which are brown algae belonging to three different orders. Here, we address the control of cell growth and cell division orientation in the embryo of , a brown alga belonging to the order Laminariales, which grows as a stack of cells through transverse cell divisions until growth is initiated along the perpendicular axis. Using laser ablation, we show that apical and basal cells have different functions in the embryogenesis of this alga, with the apical cell being involved mainly in growth and basal cells controlling the orientation of cell division by inhibiting longitudinal cell division and thereby the widening of the embryo. These functions were observed in the very early development before the embryo reached the 8-cell stage. In addition, the growth of the apical and basal regions appears to be cell-autonomous, because there was no compensation for the loss of a significant part of the embryo upon laser ablation, resulting in smaller and less elongated embryos compared with intact embryos. In contrast, the orientation of cell division in the apical region of the embryo appears to be controlled by the basal cell only, which suggests a polarised, non-cell-autonomous mechanism. Altogether, our results shed light on the early mechanisms of growth rate and growth orientation at the onset of the embryogenesis of , in which non-cell-specific cell-autonomous and cell-specific non-cell-autonomous processes are involved. This complex control differs from the mechanisms described in the other brown algal embryos, in which the establishment of embryo polarity depends on environmental cues.
褐藻是多细胞生物，它们独立于植物和动物进化而来。目前仅对属于三个不同目级别的褐藻（分别为[具体名称1]、[具体名称2]和[具体名称3]）的胚胎发生机制有所了解。在此，我们研究了海带目褐藻[具体名称4]胚胎中细胞生长和细胞分裂方向的控制机制。该褐藻通过横向细胞分裂形成细胞堆叠进行生长，直到沿垂直轴开始生长。利用激光消融技术，我们发现顶端细胞和基部细胞在这种褐藻的胚胎发生中具有不同功能，顶端细胞主要参与生长，基部细胞通过抑制纵向细胞分裂从而控制胚胎变宽来调控细胞分裂方向。这些功能在胚胎发育到8细胞阶段之前的早期发育过程中就已观察到。此外，顶端和基部区域的生长似乎是细胞自主的，因为激光消融后胚胎大部分细胞缺失并没有得到补偿，与完整胚胎相比，消融后的胚胎更小且伸长程度更低。相反，胚胎顶端区域的细胞分裂方向似乎仅由基部细胞控制，这表明存在一种极化的、非细胞自主的机制。总之，我们的研究结果揭示了[具体名称4]胚胎发生起始阶段生长速率和生长方向的早期机制，其中涉及非细胞特异性的细胞自主过程和细胞特异性的非细胞自主过程。这种复杂的控制机制不同于其他褐藻胚胎中所描述的机制，在其他褐藻胚胎中胚胎极性的建立依赖于环境线索。
