Horticultural Sciences Department, University of Florida, Gainesville, Florida 32611, USA.
Plant Cell. 2011 Dec;23(12):4280-97. doi: 10.1105/tpc.111.092163. Epub 2011 Dec 2.
Endosperm and embryo development are coordinated via epigenetic regulation and signaling between these tissues. In maize (Zea mays), the endosperm-embryo signals are not known, but endosperm cellularization is a key event for embryos to form shoots and roots. We screened seed mutants for nonautonomous functions in endosperm and embryo development with genetically nonconcordant seeds and identified the recessive mutant rough endosperm3 (rgh3). The wild-type Rgh3 allele is required in the endosperm for embryos to develop and has an autonomous role in embryo and seedling development. Endosperm cell differentiation is defective in rgh3. Results from endosperm cell culture indicate that rgh3 mutants remain in a proliferative state through mid-seed development. Rgh3 encodes the maize U2AF(35) Related Protein (URP), an RNA splicing factor involved in both U2 and U12 splicing. The Rgh3 allele produces at least 19 alternative splice variants with only one isoform encoding a full-length ortholog to URP. The full-length RGH3α isoform localizes to the nucleolus and displays a speckled pattern within the nucleoplasm, and RGH3α colocalizes with U2AF(65). A survey of alternatively spliced transcripts found that, in the rgh3 mutant, a fraction of noncanonical splicing events are altered. Our findings suggest that differentiation of maize endosperm cell types is necessary for embryos to develop. The molecular cloning of Rgh3 suggests that alternative RNA splicing is needed for cell differentiation, development, and plant viability.
胚乳和胚胎的发育是通过这些组织之间的表观遗传调控和信号协调的。在玉米（Zea mays）中，胚乳-胚胎信号尚不清楚，但胚乳细胞化是胚胎形成茎和根的关键事件。我们使用遗传上不一致的种子筛选胚乳和胚胎发育中非自主性功能的种子突变体，并鉴定出隐性突变体粗糙胚乳 3（rgh3）。野生型 Rgh3 等位基因在胚乳中是胚胎发育所必需的，并且在胚胎和幼苗发育中具有自主性作用。rgh3 胚乳细胞分化缺陷。胚乳细胞培养的结果表明，rgh3 突变体在种子发育中期仍保持增殖状态。Rgh3 编码玉米 U2AF（35）相关蛋白（URP），这是一种参与 U2 和 U12 剪接的 RNA 剪接因子。Rgh3 等位基因产生至少 19 种替代剪接变体，只有一种同工型编码全长 URP 同源物。全长 RGH3α 同工型定位于核仁，并在核质中显示出斑点图案，并且 RGH3α 与 U2AF（65）共定位。对替代剪接转录本的调查发现，在 rgh3 突变体中，一部分非典型剪接事件发生改变。我们的研究结果表明，玉米胚乳细胞类型的分化对于胚胎发育是必要的。Rgh3 的分子克隆表明，替代 RNA 剪接对于细胞分化、发育和植物活力是必要的。
