Christensen C A, Subramanian S, Drews G N
Department of Biology, University of Utah, 257 South 1400 E, Salt Lake City, Utah, 84112-0840, USA.
Dev Biol. 1998 Oct 1;202(1):136-51. doi: 10.1006/dbio.1998.8980.
The female gametophyte (embryo sac or megagametophyte) plays a critical role in sexual reproduction of angiosperms. It is the structure that produces the egg cell and central cell which, following fertilization, give rise to the seed's embryo and endosperm, respectively. In addition, the female gametophyte mediates a host of reproductive processes including pollen tube guidance, fertilization, and the induction of seed development. Several major events occur during megagametogenesis, including syncitial nuclear divisions, cellularization, nuclear migration and fusion, and cell death. While these events have been described morphologically, the molecules regulating them in the female gametophyte are largely unknown. We discuss a genetic screen based on reduced seed set and segregation distortion to identify mutations affecting megagametogenesis and female gametophyte function. We report on the isolation of four mutants (fem1, fem2, fem3, and fem4) and show that the four mutations map to different locations within the genome. Additionally, we show that the fem1 and fem2 mutations affect only the female gametophyte, while the fem3 and fem4 mutations affect both the female and male gametophyte. We analyzed female gametophyte development in these four mutants as well as in the gfa2, gfa3, gfa4, gfa5, and gfa7 mutants. We found that the fem2, fem3, gfa4, and gfa5 mutants abort development at the one-nucleate stage, while the fem1, fem4, gfa2, gfa3, and gfa7 mutants are affected in processes later in development such as polar nuclei fusion and cellularization. The establishment of a genetic screen to identify mutants and the development of a rapid procedure for analyzing mutant phenotypes represent a first step in the isolation of molecules that regulate female gametophyte development and function.
雌配子体（胚囊或大配子体）在被子植物的有性生殖中起着关键作用。它是产生卵细胞和中央细胞的结构，受精后，分别发育成种子的胚和胚乳。此外，雌配子体介导了许多生殖过程，包括花粉管引导、受精以及种子发育的诱导。在大配子发生过程中会发生几个主要事件，包括合胞体核分裂、细胞化、核迁移和融合以及细胞死亡。虽然这些事件已经从形态学上进行了描述，但在雌配子体中调节它们的分子在很大程度上仍然未知。我们讨论了一种基于结实率降低和分离畸变的遗传筛选方法，以鉴定影响大配子发生和雌配子体功能的突变。我们报告了四个突变体（fem1、fem2、fem3和fem4）的分离，并表明这四个突变位于基因组内的不同位置。此外，我们表明fem1和fem2突变仅影响雌配子体，而fem3和fem4突变同时影响雌配子体和雄配子体。我们分析了这四个突变体以及gfa2、gfa3、gfa4、gfa5和gfa7突变体中的雌配子体发育。我们发现，fem2、fem3、gfa4和gfa5突变体在单核阶段停止发育，而fem1、fem4、gfa2、gfa3和gfa7突变体在发育后期的过程中受到影响，如极核融合和细胞化。建立用于鉴定突变体的遗传筛选方法以及开发用于分析突变体表型的快速程序，是分离调节雌配子体发育和功能分子的第一步。
