Department of Biology, University of Massachusetts Dartmouth , Dartmouth, MA, USA.
Front Plant Sci. 2014 Dec 10;5:690. doi: 10.3389/fpls.2014.00690. eCollection 2014.
Fucoid zygotes use environmental vectors, including sunlight, to initiate a growth axis a few hours after fertilization. The first division is then transversely oriented by the growth axis, producing daughter cells of distinct fates. The tip growing rhizoid cell gives rise to the holdfast, anchoring the alga to the intertidal substratum, while the opposite thallus cell mainly generates the photosynthetic and reproductive stipe and fronds. Elaboration of this simple growth axis thus establishes the basic body plan of the adult; and elucidating the mechanisms responsible for formation of the growth axis is paramount to understanding fucoid morphogenesis. Recent studies have culminated in a model whereby sunlight, and perhaps other environmental cues, activate the signaling protein Rac1 at the rhizoid pole. Here it sets in motion nucleation of a patch of actin filaments that in turn, targets ions, proteins, and cellular processes to the future growth site. At germination, Rac1 initiates morphogenesis by inducing transformation of the patch of actin filaments to a structure that delivers vesicles to the growing tip, and a few hours later orients the spindle and cytokinetic plate.
紫菜受精卵利用环境载体，包括阳光，在受精后几个小时内启动生长轴。然后，第一次分裂被生长轴横向定向，产生具有不同命运的子细胞。顶端生长的假根细胞产生固着器，将藻类固定在潮间带基质上，而相反的叶状体细胞主要产生光合作用和生殖茎和叶片。这种简单生长轴的形成建立了成年体的基本体型；阐明负责生长轴形成的机制对于理解紫菜形态发生至关重要。最近的研究提出了一个模型，即阳光，也许还有其他环境线索，在假根端激活信号蛋白 Rac1。在这里，它启动了肌动蛋白丝斑块的成核，反过来，将离子、蛋白质和细胞过程靶向到未来的生长部位。在萌发时，Rac1 通过诱导肌动蛋白丝斑块转化为将囊泡输送到生长尖端的结构，从而启动形态发生，几个小时后，它使纺锤体和胞质分裂板定向。
