Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
Development. 2010 Jul;137(14):2409-16. doi: 10.1242/dev.049320.
The four microsporangia of the flowering plant anther develop from archesporial cells in the L2 of the primordium. Within each microsporangium, developing microsporocytes are surrounded by concentric monolayers of tapetal, middle layer and endothecial cells. How this intricate array of tissues, each containing relatively few cells, is established in an organ possessing no formal meristems is poorly understood. We describe here the pivotal role of the LRR receptor kinase EXCESS MICROSPOROCYTES 1 (EMS1) in forming the monolayer of tapetal nurse cells in Arabidopsis. Unusually for plants, tapetal cells are specified very early in development, and are subsequently stimulated to proliferate by a receptor-like kinase (RLK) complex that includes EMS1. Mutations in members of this EMS1 signalling complex and its putative ligand result in male-sterile plants in which tapetal initials fail to proliferate. Surprisingly, these cells continue to develop, isolated at the locular periphery. Mutant and wild-type microsporangia expand at similar rates and the 'tapetal' space at the periphery of mutant locules becomes occupied by microsporocytes. However, induction of late expression of EMS1 in the few tapetal initials in ems1 plants results in their proliferation to generate a functional tapetum, and this proliferation suppresses microsporocyte number. Our experiments also show that integrity of the tapetal monolayer is crucial for the maintenance of the polarity of divisions within it. This unexpected autonomy of the tapetal 'lineage' is discussed in the context of tissue development in complex plant organs, where constancy in size, shape and cell number is crucial.
开花植物花药的四个小孢子囊由原基 L2 中的孢原细胞发育而来。在每个小孢子囊中，发育中的小孢子细胞被绒毡层、中层和内皮层的同心单层包围。在一个没有正式分生组织的器官中，如何建立这个由相对较少细胞组成的复杂组织阵列，人们知之甚少。我们在这里描述了 LRR 受体激酶 EXCESS MICROSPOROCYTES 1 (EMS1) 在形成拟南芥绒毡层保姆细胞单层中的关键作用。与植物不同的是，绒毡层细胞在发育的早期就被特化，随后被包括 EMS1 在内的受体样激酶 (RLK) 复合物刺激增殖。该 EMS1 信号复合物及其假定配体的成员突变导致雄性不育植物中绒毡层初始细胞不能增殖。令人惊讶的是，这些细胞继续发育，孤立在腔室的外周。突变体和野生型小孢子囊以相似的速度扩张，突变体腔室边缘的“绒毡层”空间被小孢子细胞占据。然而，在 ems1 植物中晚期表达 EMS1 会诱导少数绒毡层初始细胞增殖，从而产生功能性绒毡层，并且这种增殖会抑制小孢子细胞的数量。我们的实验还表明，绒毡层单层的完整性对于维持其内部分裂的极性至关重要。这种出乎意料的绒毡层“谱系”自主性在复杂植物器官的组织发育中进行了讨论，在这种组织中，大小、形状和细胞数量的恒定性至关重要。
