Schwartz Brian, Yeung Edward, Meinke David
Department of Botany, Oklahoma State University, Stillwater, OK 74078, USA
Department of Biological Sciences, The University of Calgary, Calgary, Alberta T2N 1N4, Canada
Development. 1994 Nov;120(11):3235-45. doi: 10.1242/dev.120.11.3235.
The suspensor is the first differentiated structure produced during plant embryogenesis. In most angiosperms, the suspensor functions early in development to provide nutrients and growth regulators to the embryo proper. In Arabidopsis, the suspensor undergoes programmed cell death at the torpedo stage and is not present in mature seeds. We have identified at least 16 embryo-defective mutants of Arabidopsis that exhibit an enlarged suspensor phenotype at maturity. In this report, we focus on seven abnormal suspensor mutants, which define three genetic loci (sus1, sus2 and sus3). Recessive mutations at each of these loci disrupt morphogenesis in the embryo proper and consistently result in the formation of a large suspensor. Defects in the embryo proper appear by the globular stage of development; abnormalities in the suspensor are detected soon after at the heart stage. Storage protein and lipid bodies, which normally accumulate only in the embryo proper late in embryogenesis, are present in both the arrested embryo proper and enlarged suspensor. Therefore, cell differentiation in the embryo proper can proceed in the absence of normal morphogenesis, and the suspensor can be transformed into a structure with features normally restricted to the embryo proper. These observations are consistent with a model in which normal development of the embryo proper limits growth and differentiation of the suspensor. Altered development of the embryo proper in mutant seeds leads indirectly to proliferation of suspensor cells and expression of properties characteristic of the embryo proper. Ultimately, growth of the transformed suspensor is limited by the same genetic defect that disrupts development of the embryo proper. The availability of multiple alleles of sus1 and sus2, including T-DNA tagged alleles of each, will facilitate the cloning of these essential genes and molecular analysis of interactions between the embryo proper and suspensor early in development.
胚柄是植物胚胎发生过程中产生的第一个分化结构。在大多数被子植物中，胚柄在发育早期发挥作用，为胚体提供营养和生长调节因子。在拟南芥中，胚柄在鱼雷期经历程序性细胞死亡，成熟种子中不存在。我们已经鉴定出至少16个拟南芥胚胎缺陷突变体，它们在成熟时表现出胚柄增大的表型。在本报告中，我们重点研究了7个异常胚柄突变体，它们定义了3个基因位点（sus1、sus2和sus3）。这些位点上的隐性突变破坏了胚体的形态发生，并始终导致形成大的胚柄。胚体的缺陷在发育的球形期出现；胚柄的异常在心脏期后不久就被检测到。通常仅在胚胎发育后期的胚体中积累的贮藏蛋白和脂质体，在停滞的胚体和增大的胚柄中都存在。因此，胚体中的细胞分化可以在没有正常形态发生的情况下进行，并且胚柄可以转化为具有通常仅限于胚体特征的结构。这些观察结果与一个模型一致，即胚体的正常发育限制了胚柄的生长和分化。突变种子中胚体发育的改变间接导致胚柄细胞的增殖和胚体特征性质的表达。最终，转化胚柄的生长受到破坏胚体发育的相同遗传缺陷的限制。sus1和sus2的多个等位基因的可用性，包括每个基因的T-DNA标签等位基因，将有助于克隆这些必需基因，并对发育早期胚体和胚柄之间的相互作用进行分子分析。
