Stanford University, Department of Biology, 385 Serra Mall, Stanford, CA 94305-5020, USA.
Dev Biol. 2011 Feb 1;350(1):32-49. doi: 10.1016/j.ydbio.2010.11.005. Epub 2010 Nov 9.
One fundamental difference between plants and animals is the existence of a germ-line in animals and its absence in plants. In flowering plants, the sexual organs (stamens and carpels) are composed almost entirely of somatic cells, a small subset of which switch to meiosis; however, the mechanism of meiotic cell fate acquisition is a long-standing botanical mystery. In the maize (Zea mays) anther microsporangium, the somatic tissues consist of four concentric cell layers that surround and support reproductive cells as they progress through meiosis and pollen maturation. Male sterility, defined as the absence of viable pollen, is a common phenotype in flowering plants, and many male sterile mutants have defects in somatic and reproductive cell fate acquisition. However, without a robust model of anther cell fate acquisition based on careful observation of wild-type anther ontogeny, interpretation of cell fate mutants is limited. To address this, the pattern of cell proliferation, expansion, and differentiation was tracked in three dimensions over 30 days of wild-type (W23) anther development, using anthers stained with propidium iodide (PI) and/or 5-ethynyl-2'-deoxyuridine (EdU) (S-phase label) and imaged by confocal microscopy. The pervading lineage model of anther development claims that new cell layers are generated by coordinated, oriented cell divisions in transient precursor cell types. In reconstructing anther cell division patterns, however, we can only confirm this for the origin of the middle layer (ml) and tapetum, while young anther development appears more complex. We find that each anther cell type undergoes a burst of cell division after specification with a characteristic pattern of both cell expansion and division. Comparisons between two inbreds lines and between ab- and adaxial anther florets indicated near identity: anther development is highly canalized and synchronized. Three classical models of plant organ development are tested and ruled out; however, local clustering of developmental events was identified for several processes, including the first evidence for a direct relationship between the development of ml and tapetal cells. We speculate that small groups of ml and tapetum cells function as a developmental unit dedicated to the development of a single pollen grain.
动植物之间的一个根本区别在于动物存在生殖系，而植物则不存在。在有花植物中，性器官（雄蕊和心皮）几乎完全由体细胞组成，其中一小部分体细胞会转变为减数分裂；然而，减数分裂细胞命运获得的机制是一个长期存在的植物学之谜。在玉米（Zea mays）花药小孢子囊中，体细胞组织由四个同心细胞层组成，这些细胞层围绕并支持生殖细胞在减数分裂和花粉成熟过程中的发育。雄性不育是指缺乏有活力的花粉，这是开花植物中的一种常见表型，许多雄性不育突变体在体细胞和生殖细胞命运获得方面存在缺陷。然而，如果没有基于对野生型花药个体发生的仔细观察来建立健全的花药细胞命运获得模型，那么对细胞命运突变体的解释就会受到限制。为了解决这个问题，我们使用碘化丙啶（PI）和/或 5-乙炔基-2'-脱氧尿苷（EdU）（S 期标记）对 W23 型野生型（W23）花药发育 30 天的过程进行了三维跟踪，对花粉进行了染色，并用共聚焦显微镜对花粉进行了成像。花药发育的普遍谱系模型声称，新的细胞层是通过短暂的前体细胞类型中协调、定向的细胞分裂产生的。然而，在重建花药细胞分裂模式时，我们只能确认中层（ml）和绒毡层的起源是这样的，而早期的花药发育似乎更加复杂。我们发现，每个花药细胞类型在特化后都会经历一次细胞分裂爆发，具有特征性的细胞扩张和分裂模式。两个近交系之间以及背腹侧花药小花之间的比较表明，几乎是相同的：花药发育高度定型和同步。对三种经典的植物器官发育模型进行了测试和排除；然而，确定了几个过程中发育事件的局部聚类，包括 ml 和绒毡层细胞发育之间直接关系的第一个证据。我们推测，ml 和绒毡层细胞的小群作为一个发育单位，专门用于单个花粉粒的发育。
