Genetic Strain Research Center, National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan.
Dev Biol. 2011 Mar 1;351(1):208-16. doi: 10.1016/j.ydbio.2010.12.006. Epub 2010 Dec 10.
The floral meristem is the homeostatic source of floral organs in angiosperms. In rice, after stamen and carpel differentiation, the floral meristem is terminated and exhausted to produce an ovule. To elucidate underlying mechanisms controlling the continuous process from floral meristem termination to ovule formation, we investigated two rice mutants showing abnormalities in ovule formation. In the weak mutant of the lonely guy gene, responsible for cytokinin activation to maintain the floral meristem, ovule formation was abolished inside the normally developing carpel. The loss-of-function of the OsMADS13 gene, encoding a MADS-box transcription factor, resulted in the replacement of ovule with extra carpels. The in situ expression of tissue-specific markers in both mutants revealed that a lateral region of the terminating floral meristem adjacent to the site of carpel initiation exclusively differentiated the ovule and is apparently distinct from the remainder of the floral meristem, in contrast to previous assumptions. Our findings also suggest that primordial germ cells are initiated independently of ovule formation, but dependently on the presence of active cytokinin. We propose a novel pattern of ovule formation in angiosperms, in which the ovule is a lateral organ finally differentiated from the terminating floral meristem in rice.
花分生组织是被子植物花器官的同源结构来源。在水稻中，雄蕊和心皮分化后，花分生组织终止并耗尽，产生胚珠。为了阐明控制花分生组织终止到胚珠形成的连续过程的潜在机制，我们研究了两个在胚珠形成方面表现出异常的水稻突变体。在负责细胞分裂素激活以维持花分生组织的孤单基因的弱突变体中，胚珠形成被取消在正常发育的心皮内。编码 MADS 框转录因子的 OsMADS13 基因的功能丧失导致胚珠被额外的心皮取代。在两个突变体中的组织特异性标记的原位表达揭示，终止的花分生组织的一个侧向区域紧邻心皮起始的部位，专门分化出胚珠，与之前的假设明显不同，与花分生组织的其余部分明显不同。我们的研究结果还表明，原始生殖细胞的起始独立于胚珠的形成，但依赖于活性细胞分裂素的存在。我们提出了被子植物中一种新的胚珠形成模式，其中胚珠是最终从水稻终止的花分生组织中分化出来的侧生器官。
