Institute of Molecular Biophysics, The Florida State University, Tallahassee, FL 32306-4370, USA.
BMC Plant Biol. 2010 Dec 8;10:269. doi: 10.1186/1471-2229-10-269.
The nuclear envelope that separates the contents of the nucleus from the cytoplasm provides a surface for chromatin attachment and organization of the cortical nucleoplasm. Proteins associated with it have been well characterized in many eukaryotes but not in plants. SUN (Sad1p/Unc-84) domain proteins reside in the inner nuclear membrane and function with other proteins to form a physical link between the nucleoskeleton and the cytoskeleton. These bridges transfer forces across the nuclear envelope and are increasingly recognized to play roles in nuclear positioning, nuclear migration, cell cycle-dependent breakdown and reformation of the nuclear envelope, telomere-led nuclear reorganization during meiosis, and karyogamy.
We found and characterized a family of maize SUN-domain proteins, starting with a screen of maize genomic sequence data. We characterized five different maize ZmSUN genes (ZmSUN1-5), which fell into two classes (probably of ancient origin, as they are also found in other monocots, eudicots, and even mosses). The first (ZmSUN1, 2), here designated canonical C-terminal SUN-domain (CCSD), includes structural homologs of the animal and fungal SUN-domain protein genes. The second (ZmSUN3, 4, 5), here designated plant-prevalent mid-SUN 3 transmembrane (PM3), includes a novel but conserved structural variant SUN-domain protein gene class. Mircroarray-based expression analyses revealed an intriguing pollen-preferred expression for ZmSUN5 mRNA but low-level expression (50-200 parts per ten million) in multiple tissues for all the others. Cloning and characterization of a full-length cDNA for a PM3-type maize gene, ZmSUN4, is described. Peptide antibodies to ZmSUN3, 4 were used in western-blot and cell-staining assays to show that they are expressed and show concentrated staining at the nuclear periphery.
The maize genome encodes and expresses at least five different SUN-domain proteins, of which the PM3 subfamily may represent a novel class of proteins with possible new and intriguing roles within the plant nuclear envelope. Expression levels for ZmSUN1-4 are consistent with basic cellular functions, whereas ZmSUN5 expression levels indicate a role in pollen. Models for possible topological arrangements of the CCSD-type and PM3-type SUN-domain proteins are presented.
核膜将细胞核内容物与细胞质分隔开，为染色质附着和皮质核质的组织提供了一个表面。与其相关的蛋白质在许多真核生物中得到了很好的描述，但在植物中却没有。SUN（Sad1p/Unc-84）结构域蛋白位于核内膜中，与其他蛋白质一起发挥作用，在核骨架和细胞骨架之间形成物理连接。这些桥将力传递穿过核膜，并越来越多地被认为在核定位、核迁移、核膜在细胞周期中的有丝分裂和减数分裂过程中的破裂和重建、端粒引导的核重组以及核融合中发挥作用。
我们从玉米基因组序列数据的筛选开始，发现并鉴定了一组玉米 SUN 结构域蛋白。我们鉴定了五个不同的玉米 ZmSUN 基因（ZmSUN1-5），它们分为两类（可能起源于古代，因为它们也存在于其他单子叶植物、双子叶植物甚至苔藓植物中）。第一个（ZmSUN1、2），在这里被指定为典型的 C 端 SUN 结构域（CCSD），包括动物和真菌 SUN 结构域蛋白基因的结构同源物。第二个（ZmSUN3、4、5），在这里被指定为植物普遍存在的中 SUN 3 跨膜（PM3），包括一个新的但保守的结构变体 SUN 结构域蛋白基因类。基于微阵列的表达分析显示，ZmSUN5 mRNA 在花粉中优先表达，但在其他组织中表达水平较低（每十亿 50-200 个）。描述了一个全长 cDNA 的克隆和表征 PM3 型玉米基因，ZmSUN4。ZmSUN3、4 的肽抗体被用于 Western-blot 和细胞染色实验，以显示它们在核周的表达和浓缩染色。
玉米基因组编码并表达至少五种不同的 SUN 结构域蛋白，其中 PM3 亚家族可能代表一类新的蛋白质，在植物核膜中可能具有新的和有趣的作用。ZmSUN1-4 的表达水平与基本的细胞功能一致，而 ZmSUN5 的表达水平表明其在花粉中的作用。提出了 CCSD 型和 PM3 型 SUN 结构域蛋白可能的拓扑排列模型。
