Cell Biology and Plant Biochemistry, University of Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany.
Development. 2010 Jan;137(2):333-45. doi: 10.1242/dev.035964.
Reversible post-translational modification of numerous proteins by small ubiquitin-related modifiers (SUMOs) represents a major regulatory process in various eukaryotic cellular and developmental processes. To study the role of sumoylation during female gametophyte (FG) development in maize, we identified Zea mays genes encoding SUMO (ZmSUMO1a and ZmSUMO1b) and a diSUMO-like protein called ZmDSUL that contains two head-to-tail SUMO-like domains. Whereas ZmSUMO1a and ZmSUMO1b are almost ubiquitously expressed, ZmDSUL transcripts were detected exclusively in the egg apparatus and zygote. ZmDSUL was selected for detailed studies. ZmDSUL is processed close to the C-terminus, generating a dimeric protein that is similar to animal FAT10 and ISG15, which contain two ubiquitin-like domains. Whereas GFP fused to the ZmDSUL N-terminus was located in the cytoplasm and predominately in the nucleoplasm of some transiently transformed maize suspension cells, C-terminal GFP fusions exclusively accumulated at the nuclear surface. GFP or ZmDSUL-GFP under control of the ZmDSUL promoter first displayed GFP signals in the micropylar-most position of the FG at stage 5/6, when migration of polar nuclei and cellularization occurs. Mature FGs displayed GFP signals exclusively in the egg cell, but the strongest signals were observed shortly after fertilization and disappeared during the first asymmetric zygotic division. RNAi silencing of ZmDSUL showed that it is required for FG viability. Moreover, nuclei segregation and positioning defects occurred at stage FG 5 after mitotic nuclear divisions were completed. In summary, we report a diSUMO-like protein that appears to be essential for nuclei segregation and positioning, the prerequisite for cell specification during FG maturation.
许多蛋白质的翻译后可逆修饰是由小泛素相关修饰物（SUMO）完成的，这代表了各种真核细胞和发育过程中的主要调控过程。为了研究玉米雌性配子体（FG）发育过程中SUMO 化的作用，我们鉴定了编码 SUMO（ZmSUMO1a 和 ZmSUMO1b）和一种称为 ZmDSUL 的双 SUMO 样蛋白的玉米基因，ZmDSUL 包含两个头尾相连的 SUMO 样结构域。虽然 ZmSUMO1a 和 ZmSUMO1b 几乎普遍表达，但 ZmDSUL 转录本仅在卵器和受精卵中检测到。ZmDSUL 被选中进行详细研究。ZmDSUL 在接近 C 末端进行加工，产生二聚体蛋白，类似于动物 FAT10 和 ISG15，它们含有两个泛素样结构域。虽然 GFP 融合到 ZmDSUL N 端位于细胞质中，并且主要位于一些瞬时转化的玉米悬浮细胞的核质中，但 C 端 GFP 融合物仅在核表面积累。在 ZmDSUL 启动子控制下的 GFP 或 ZmDSUL-GFP 首先在 FG 的珠孔端位置显示 GFP 信号，此时极核迁移和细胞化发生。成熟的 FG 仅在卵细胞中显示 GFP 信号，但在 FG 阶段 5/6 时，即极核迁移和细胞化发生时，观察到最强的信号。在第一次不对称合子分裂后，信号消失。ZmDSUL 的 RNAi 沉默表明它是 FG 存活所必需的。此外，在有丝分裂核分裂完成后，FG 阶段 5 时出现核分离和定位缺陷。总之，我们报告了一种双 SUMO 样蛋白，它似乎对核分离和定位是必需的，这是 FG 成熟过程中细胞特化的前提。
