SOMATIC EMBRYOGENESIS - A MODEL FOR EARLY DEVELOPMENT IN HIGHER-PLANTS
SOMATIC EMBRYOGENESIS - A MODEL FOR EARLY DEVELOPMENT IN HIGHER-PLANTS
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DOI：
10.1105/tpc.5.10.1411
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发表时间：
1993-10-01
期刊：
影响因子：
11.6
通讯作者：
ZIMMERMAN, JL
中科院分区：
文献类型：
--
作者：
ZIMMERMAN, JL
通过体细胞胚胎发生过程，从培养物中未分化的体细胞产生形态和发育正常的胚胎以及实际上整个植物的能力，在植物界中是独一无二的。自从35年前首次描述从胡萝卜愈伤组织细胞产生体细胞胚以来（Steward et al.，1958），这种独特的发育潜力已被认为是从细胞培养系统再生植物的重要途径，也被认为是研究植物胚胎发生中的早期调控和形态发生事件的潜在模型。在过去的5到10年里，通过体细胞胚胎发生，可以从细胞培养中再生为完整植株的物种数量激增。文献包含数百篇参考文献，描述了从多种农艺学和园艺学上重要的植物实现体细胞胚发育所需的具体操作。虽然这显然是体细胞胚胎发生过程中的一个极其重要的应用，但它不是本文的重点。相反，这篇评论将集中在体细胞胚胎发生作为一个模型系统的使用，了解在高等植物的生命中最早的发育事件所需的基因表达的调控：受精卵发育成成熟的胚胎。受精和随后的胚胎发育通常发生在母体组织的深处。早期胚很小，被胚乳细胞和母体细胞包围。虽然胚胎发育的形态学描述已被广泛记录，通过显微镜，早期胚胎发生的分子和生化分析已大大阻碍了这种物理上的不便。因此，我们对高等植物早期胚胎发生所必需的基因知之甚少，对它们的调控更是知之甚少。这是开始补救最近密集的努力，以遗传学鉴定基因所需的早期胚胎发生的模式系统，如拟南芥和玉米（见西方和原田，1993年，这个问题），许多有趣的突变体已被确定，可能提供进入分子分析的主要形态发生事件在胚胎发生。这些分析将大大增强的细胞，组织和发育阶段特异性标记的重要事件的细胞分化和建立的主要组织系统的植物，发生在胚胎发生早期的可用性。此外，一旦已经鉴定出胚胎发生所必需的基因，则其调控的后续分析将通过适当的体外模型系统的可用性而大大促进，所述体外模型系统在组织数量或可及性方面不受限制。体细胞胚胎系统就是这样一个模型系统。本文综述了体细胞胚胎发生的过程，并讨论了体细胞胚胎作为研究植物胚胎发育早期事件的潜在模型的优势和局限性。
The ability to produce morphologically and developmentally normal embryos and, indeed, whole plants from undifferentiated somatic cells in culture, through the process of somatic embryogenesis, resides uniquely within the plant kingdom. Since the initial description of somatic embryo production from carrot callus cells more than 35 years ago (Steward et al., 1958), this unique developmental potential has been recognized both as an important pathway for the regeneration of plants from cell culture systems and as a potential model for studying early regulatory and morphogenetic events in plant embryogenesis. The last 5 to 10 years have witnessed an explosion in the number of species that can now be regenerated from cell culture into whole plants through somatic embryogenesis. The literature contains hundreds of references describing the specific manipulations required to effect somatic embryo development from a variety of agronomically and horticulturally important plants. Although this is obviously an extremely important application of the process of somatic embryogenesis, it is not the focus of this review. Rather, this review will focus on the use of somatic embryogenesis as a model system for understanding the regulation of gene expression required for the earliest developmental events in the life of a higher plant: the development of the fertilized zygote into a mature embryo. The events of fertilization and subsequent embryo development normally occur deep within maternal tissues. The early embryo is minute and is surrounded by both endosperm and maternal cells. Although the morphological description of embryo development has been extensively recorded through microscopy, molecular and biochemical analyses of early embryogenesis have been hampered significantly by this physical inaccessibility. As a consequence, we know very little about the genes that are necessary for early embryogenesis in higher plants and even less about their regulation. This is beginning to be remedied by recent intensive efforts to genetically identify genes required for early embryogenesis in model systems such as Arabidopsis and maize (see West and Harada, 1993, this issue); many interesting mutants have been identified that may provide entry points into molecular analyses of major morphogenetic events in embryogenesis. These analyses would be greatly enhanced by the availability of cell, tissue, and developmental stage-specific markers of important events in the differentiation of cells and the establishment of the major tissue systems of the plant, which occur early in embryogenesis. In addition, once genes have been identified that are essential for embryogenesis, the subsequent analysis of their regulation would be greatly facilitated by the availability of an appropriate in vitro model system that is not limited in tissue quantity or accessibility. The somatic embryo system represents just such a model system. This review will summarize the process of somatic embryogenesis and will address the strengths and limitations of somatic embryos as potential models for studying early events in plant embryo development.