Mutational and tissue culture analysis of regulatory mechanism in rice embryogenesis

到目前为止，我们已经鉴定了150个影响水稻胚胎发生的单隐性突变。表型特征使它们能够被分成七个组。1.球体早期致死性；2.基底区缺失；3.OGAN缺失；4.胚胎大小改变；5.器官位置异常；6.器官形态异常；7.单次章动时异常表型。这一分类表明在胚胎发生过程中至少有五个调节过程：1.模式形成，2.器官分化的决定，3.胚胎大小的调节，4.器官位置的调节，5.器官的形态发生。在每个过程中，都会检测到两种类型的基因；一种在整个胚胎中发挥作用，另一种在特定器官中发挥局部作用。本研究还揭示了胚胎大小受到两种方式的控制。当胚乳特异基因突变导致胚乳缩小时，盾片变大而不影响地上部和根的大小。另一方面，到目前为止已发现的胚胎特异基因调节每个器官的大小。我们分离到一个克隆，该克隆在胚胎诱导培养基上培养7天的愈伤组织中特异表达。该克隆在合子胚中表达，但在芽、根或花中不表达。另一个克隆在胚性诱导和不定芽诱导中普遍表达，而在愈伤组织诱导中不表达。这两个克隆将在胚胎发育和器官分化中发挥重要作用。

To date, we have identified 150 single, recessive mutations affecting embryogenesis in rice. Phenotypic characterization enabled them to be categorized into seven groups. 1. lethality at the early globular stage, 2. deletion of basal region, 3. deletion of ogans, 4. modified embryo size, 5. abnormal organ position, 6. abnormal mprphology of organs, and 7. variable abnormal phenotypes in spite of single nutation. This categorization indicates at least five regulatory processes are operating during embryogenesis : 1. pattern formation, 2. determination of organ differentiation, 3. regulation of embryo size, 4. regulation of organ position, and 5. morphogenesis of organs. In each process, two types of genes are detected ; one functioning in the whole embryo and the other functioning locally, in a specific organ. The present study also revealed that embryo size was controlled in two ways. When endosperm is reduced by the mutation of endosperm-specific gene, scutellum becomes giant without affecting shoot and root sizes. On the other hand, embryo-specific genes thus far identified regulate every organ size.We have isolated a clone which was expressed specifically in the callus cultured for seven days on a embryo-inducing medium. This clone is expressed in zygotic embryo but not in shoots, roots or flowers. another clone is expressed commonly in embryo-inducing medium and adventitious bud-inducing medium, but not callus-inducing medium. These two clones would play important roles in embryogenesis and organ differentiation.