Carpenter R, Coen E S
John Innes Institute, AFRC Institute of Plant Science Research, Norwich, UK.
Genes Dev. 1990 Sep;4(9):1483-93. doi: 10.1101/gad.4.9.1483.
To isolate and study genes controlling floral development, we have carried out a large-scale transposon-mutagenesis experiment in Antirrhinum majus. Ten independent floral homeotic mutations were obtained that could be divided into three classes, depending on whether they affect (1) the identity of organs within the same whorl; (2) the identity and sometimes also the number of whorls; and (3) the fate of the axillary meristem that normally gives rise to the flower. The classes of floral phenotypes suggest a model for the genetic control of primordium fate in which class 2 genes are proposed to act in overlapping pairs of adjacent whorls so that their combinations at different positions along the radius of the flower can specify the fate and number of whorls. These could interact with class 1 genes, which vary in their action along the vertical axis of the flower to generate bilateral symmetry. Both of these classes may be ultimately regulated by class 3 genes required for flower initiation. The similarity between some of the homeotic phenotypes with those of other species suggests that the mechanisms controlling whorl identity and number have been highly conserved in plant evolution. Many of the mutations obtained show somatic and germinal instability characteristic of transposon insertions, allowing the cell-autonomy of floral homeotic genes to be tested for the first time. In addition, we show that the deficiens (def) gene (class 2) acts throughout organ development, but its action may be different at various developmental stages, accounting for the intermediate phenotypes conferred by certain def alleles. Expression of def early in development is not necessary for its later expression, indicating that other genes act throughout the development of specific organs to maintain def expression. Direct evidence that the mutations obtained were caused by transposons came from molecular analysis of leaf or flower pigmentation mutants, indicating that isolation of the homeotic genes should now be possible.
为了分离和研究控制花发育的基因，我们在金鱼草中开展了大规模转座子诱变实验。获得了10个独立的花同源异型突变体，根据它们是否影响：（1）同一轮中器官的特性；（2）轮的特性以及有时轮的数量；（3）通常产生花的腋生分生组织的命运，可将这些突变体分为三类。花表型的类别提示了一个关于原基命运遗传控制的模型，其中第2类基因被认为在相邻轮的重叠对中起作用，这样它们在花半径上不同位置的组合可以确定轮的命运和数量。这些基因可能与第1类基因相互作用，第1类基因在花的垂直轴上作用不同，以产生两侧对称。这两类基因最终可能都受花起始所需的第3类基因调控。一些同源异型表型与其他物种的相似性表明，控制轮特性和数量的机制在植物进化过程中高度保守。获得的许多突变体表现出转座子插入特有的体细胞和生殖细胞不稳定性，从而首次能够测试花同源异型基因的细胞自主性。此外，我们表明，deficiens（def）基因（第2类）在整个器官发育过程中都起作用，但其作用在不同发育阶段可能不同，这就解释了某些def等位基因赋予的中间表型。def在发育早期的表达对于其后期表达并非必需，这表明其他基因在特定器官的整个发育过程中起作用以维持def的表达。所获得的突变是由转座子引起的直接证据来自对叶或花色素沉着突变体的分子分析，这表明现在应该能够分离出同源异型基因。
