Key message

In vitro embryo development is highly plastic; embryo cell fate can be re-established in tissue culture through 17 different pathways.

Abstract

In most angiosperms, embryo development from the single-celled zygote follows a defined pattern of cell divisions in which apical (embryo proper) and basal (root and suspensor) cell fates are established within the first cell divisions. By contrast, embryos that are induced in vitro in the absence of fertilization show a less regular initial cell division pattern yet develop into histodifferentiated embryos that can be converted into seedlings. We used the Brassica napus microspore embryogenesis system, in which the male gametophyte is reprogrammed in vitro to form haploid embryos, to identify the developmental fates of the different types of embryogenic structures found in culture. Using time-lapse imaging of LEAFY COTYLEDON1-expressing cells, we show that embryogenic cell clusters with very different morphologies are able to form haploid embryos. The timing of surrounding pollen wall (exine) rupture is a major determinant of cell fate in these clusters, with early exine rupture leading to the formation of suspensor-bearing embryos and late rupture to suspensorless embryos. In addition, we show that embryogenic callus, which develops into suspensor-bearing embryos, initially expresses transcripts associated with both basal- and apical-embryo cell fates, suggesting that these two cell fates are fixed later in development. This study reveals the inherent plasticity of in vitro embryo development and identifies new pathways by which embryo cell fate can be established.

中文翻译：

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甘蓝型油菜小孢子胚胎培养物中胚胎发生结构的实时成像突出了诱导全能细胞的发育可塑性。

关键信息

体外胚胎发育具有很高的可塑性。胚胎细胞的命运可以通过17种不同的途径在组织培养中重建。

抽象

在大多数被子植物中，单细胞合子的胚胎发育遵循确定的细胞分裂模式，其中在最初的细胞分裂中建立了顶端（固有的胚胎）和基底（根和悬垂）细胞的命运。相比之下，在没有受精的情况下在体外诱导的胚显示出较不规则的初始细胞分裂模式，但发育成可以分化为幼苗的组织分化胚。我们使用了甘蓝型油菜小孢子胚胎发生系统，其中雄配子体在体外被重新编程以形成单倍体胚，以鉴定培养物中发现的不同类型胚发生结构的发育命运。使用LEAFY COTYLEDON1的延时成像表达细胞，我们表明具有非常不同形态的胚发生细胞簇能够形成单倍体胚。花粉壁（外壁）破裂的时机是这些簇中细胞命运的主要决定因素，外壁早期破裂导致带有悬臂的胚胎形成，而后期破裂导致无悬臂的胚胎。另外，我们显示了发育成具有悬浮物的胚的胚性愈伤组织最初表达与基础和顶端胚细胞命运相关的转录本，表明这两种细胞命运在以后的发展中是固定的。这项研究揭示了体外胚胎发育的固有可塑性，并确定了建立胚胎细胞命运的新途径。