ABSTRACT The linker of nucleoskeleton and cytoskeleton (LINC) complex is an essential multi-protein structure spanning the eukaryotic nuclear envelope. The LINC complex functions to maintain nuclear architecture, positioning, and mobility, along with specialized functions in meiotic prophase and chromosome segregation. Members of the LINC complex were recently identified in maize, an important scientific and agricultural grass species. Here we characterized Maize LINC KASH AtSINE-like2, MLKS2, which encodes a highly conserved SINE-group plant KASH protein with characteristic N-terminal armadillo repeats (ARM). Using a heterologous expression system, we showed that actively expressed GFP-MLKS2 is targeted to the nuclear periphery and colocalizes with F-actin and the endoplasmic reticulum, but not microtubules in the cell cortex. Expression of GFP-MLKS2, but not GFP-MLKS2ΔARM, resulted in nuclear anchoring. Genetic analysis of transposon-insertion mutations, mlks2-1 and mlks2-2, showed that the mutant phenotypes were pleiotropic, affecting root hair nuclear morphology, stomatal complex development, multiple aspects of meiosis, and pollen viability. In male meiosis, the mutants showed defects for bouquet-stage telomere clustering, nuclear repositioning, perinuclear actin accumulation, dispersal of late prophase bivalents, and meiotic chromosome segregation. These findings support a model in which the nucleus is connected to cytoskeletal F-actin through the ARM-domain, predicted alpha solenoid structure of MLKS2. Functional conservation of MLKS2 was demonstrated through genetic rescue of the misshapen nuclear phenotype of an Arabidopsis (triple-WIP) KASH mutant. This study establishes a role for the SINE-type KASH proteins in affecting the dynamic nuclear phenomena required for normal plant growth and fertility. Abbreviations: FRAP: Fluorescence recovery after photobleaching; DPI: Days post infiltration; OD: Optical density; MLKS2: Maize LINC KASH AtSINE-like2; LINC: Linker of nucleoskeleton and cytoskeleton; NE: Nuclear envelope; INM: Inner nuclear membrane; ONM: Outer nuclear membrane

中文翻译：

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MLKS2 是一种 ARM 结构域和 F-肌动蛋白相关 KASH 蛋白，在气孔复合体发育和减数分裂染色体分离中发挥作用


摘要 核骨架和细胞骨架连接体（LINC）复合物是跨越真核细胞核膜的重要多蛋白结构。 LINC 复合体的功能是维持核结构、定位和移动性，以及减数分裂前期和染色体分离的特殊功能。最近在玉米（一种重要的科学和农业草种）中发现了 LINC 复合体的成员。在这里，我们表征了玉米 LINC KASH AtSINE-like2（MLKS2），它编码高度保守的 SINE 族植物 KASH 蛋白，具有特征性的 N 端犰狳重复序列 (ARM)。使用异源表达系统，我们发现活跃表达的 GFP-MLKS2 靶向核周边，并与 F-肌动蛋白和内质网共定位，但不与细胞皮质中的微管共定位。 GFP-MLKS2（而非 GFP-MLKS2ΔARM）的表达导致核锚定。转座子插入突变mlks2-1和mlks2-2的遗传分析表明，突变体表型是多效性的，影响根毛核形态、气孔复合体发育、减数分裂和花粉活力的多个方面。在雄性减数分裂中，突变体表现出花束阶段端粒聚集、核重新定位、核周肌动蛋白积累、后期二价体分散和减数分裂染色体分离的缺陷。这些发现支持了一个模型，其中细胞核通过 ARM 结构域与细胞骨架 F-肌动蛋白连接，预测了 MLKS2 的 α 螺线管结构。通过对拟南芥（三重 WIP）KASH 突变体的畸形核表型进行遗传拯救，证明了 MLKS2 的功能保守性。 这项研究确定了 SINE 型 KASH 蛋白在影响正常植物生长和育性所需的动态核现象中的作用。缩写：FRAP：光漂白后的荧光恢复； DPI：渗透后天数； OD：光密度； MLKS2：玉米 LINC KASH AtSINE-like2； LINC：核骨架和细胞骨架的连接体； NE：核膜； INM：内核膜； ONM：外核膜