Over 160 years ago, scientists made the first microscopic observations of angiosperm pollen. Unlike in animals, male meiosis in angiosperms produces a haploid microspore that undergoes one asymmetric division to form a vegetative cell and a generative cell. These two cells have distinct fates: the vegetative cell exits the cell cycle and elongates to form a tip-growing pollen tube; the generative cell divides once more in the pollen grain or within the growing pollen tube to form a pair of sperm cells. The concept that male germ cells are less active than the vegetative cell came from biochemical analyses and pollen structure anatomy early in the last century and is supported by the pollen transcriptome data of the last decade. However, the mechanism of how and when the transcriptional repression in male germ cells occurs is still not fully understood. In this review, we provide a brief account of the cytological and metabolic differentiation between the vegetative cell and male germ cells, with emphasis on the role of temporary callose walls, dynamic nuclear pore density, transcription repression, and histone variants. We further discuss the intercellular movement of small interfering RNA (siRNA) derived from transposable elements (TEs) and reexamine the function of TE expression in male germ cells.

160多年前，科学家首次对被子植物花粉进行了显微观察。与动物不同，被子植物中的雄性减数分裂产生单倍体小孢子，该单倍体小孢子经过一个不对称分裂形成营养细胞和生殖细胞。这两个细胞有不同的命运：营养细胞退出细胞周期并伸长形成尖端生长的花粉管。生殖细胞在花粉粒中或生长中的花粉管中再次分裂，形成一对精子细胞。雄性生殖细胞的活性低于营养细胞的概念来自上世纪初的生化分析和花粉结构解剖，最近十年的花粉转录组数据支持了这一观点。然而，关于如何以及何时发生雄性生殖细胞转录抑制的机制仍未完全了解。在这篇综述中，我们简要介绍了营养细胞和雄性生殖细胞之间的细胞学和代谢分化，重点是暂时性ose壁，动态核孔密度，转录抑制和组蛋白变体的作用。我们进一步讨论小分子干扰RNA（siRNA）从转座因子（TEs）衍生的细胞间运动，并重新检查男性生殖细胞中TE表达的功能。