Hong S K, Kitano H, Satoh H, Nagato Y
Faculty of Agriculture, University of Tokyo, Japan.
Development. 1996 Jul;122(7):2051-8. doi: 10.1242/dev.122.7.2051.
It is unclear how embryo size is genetically regulated in plants. Since cereals have a large persisting endosperm, it is expected that embryo size is affected by endosperm development. Nine single recessive mutations, four reduced embryo mutations representing three loci, REDUCED EMBRYO1, REDUCED EMBRYO2 and REDUCED EMBRYO3, four giant embryo mutations derived from a single locus GIANT EMBRYO, and one endospermless mutation endospermless1-2 were analyzed. Every reduced embryo mutation caused reduction of all the embryonic organs including apical meristems and the enlargement of the endosperm. The giant embryo mutants have a reduced endosperm and an enlarged scutellum. However, shoot and radicle sizes were not affected. All the reduced embryo and giant embryo mutations did not largely affect postembryonic development. Accordingly, the expression of genes analyzed are seed-specific. In reduced embryo and giant embryo mutations, abnormalities were detected in both embryo and endosperm as early as 2 days after pollination. endospermless1-1 resulted in an early loss of endosperm, yielding a giant embryo, suggesting that embryo growth was physically limited by the endosperm. A double mutant between giant embryo-2 and club-shaped embryo1-1, which has a normal endosperm and a minute undifferentiated embryo, resulted in a club-shaped embryo1-1 embryo and a reduced endosperm of giant embryo-2, indicating that GIANT EMBRYO regulates the endosperm development. Double mutants between giant embryo-2 and three reduced embryo mutants exhibited the reduced embryo phenotype in both embryo and endosperm, suggesting that reduced embryo mutations cause the enlarged endosperm. Further, a double mutant of reduced embryo3 and endospermless1-1 showed the enlarged embryo in endospermless seed. This confirms that reduced embryo3 does not regulate embryo size but enlarges endosperm size. Together with the results of the other double mutant analysis, REDUCED EMBRYO1, REDUCED EMBRYO2, REDUCED EMBRYO3 and GIANT EMBRYO are concluded to regulate endosperm development.
目前尚不清楚植物中胚胎大小是如何受到基因调控的。由于谷类植物有一个持续存在的大胚乳，因此预计胚胎大小会受到胚乳发育的影响。对九个单隐性突变进行了分析，其中四个是代表三个位点的胚体减小突变，即胚体减小1、胚体减小2和胚体减小3，四个是源自单个位点巨型胚的巨型胚突变，以及一个无胚乳突变无胚乳1-2。每一个胚体减小突变都会导致包括顶端分生组织在内的所有胚胎器官减小，以及胚乳增大。巨型胚突变体的胚乳减小，盾片增大。然而，茎和胚根的大小不受影响。所有胚体减小和巨型胚突变在很大程度上都不影响胚后发育。因此，所分析基因的表达具有种子特异性。在胚体减小和巨型胚突变中，早在授粉后2天就在胚胎和胚乳中检测到了异常。无胚乳1-1导致胚乳早期消失，产生一个巨型胚，这表明胚的生长受到胚乳的物理限制。巨型胚-2和具有正常胚乳和微小未分化胚胎的棒状胚1-1之间的双突变体，产生了棒状胚1-1胚胎和巨型胚-2的减小胚乳，这表明巨型胚调节胚乳发育。巨型胚-2和三个胚体减小突变体之间的双突变体在胚胎和胚乳中均表现出胚体减小的表型，这表明胚体减小突变会导致胚乳增大。此外，胚体减小3和无胚乳1-1的双突变体在无胚乳种子中表现出增大的胚。这证实了胚体减小3不调节胚胎大小，而是增大胚乳大小。结合其他双突变分析的结果，可以得出结论，胚体减小1、胚体减小2、胚体减小3和巨型胚调节胚乳发育。
