In flowering plants, production of functional gametophytes is prerequisite for the double fertilization that leads to successful proliferation. Pollen grains as male gametophytes in Arabidopsis thaliana are uniquely patterned with two sperm cells inside a vegetative cell. To better understand the genetic regulation underlying pollen development, we morphologically screened DAPI-stained mature pollen in a mutant population generated using an activation tagging vector in this study. As a result, we identified two independent lines, AL318 and AL434, exhibiting similar mutant phenotypes regarding nucleus number and pollen pattern. Genetic analysis showed that the two mutants are maintained in heterozygotes but not in homozygotes, due to highly reduced genetic transmission from both sexes. Developmental analysis revealed that mutant microspores at the polarized stage either completely fail to enter pollen mitosis I, or abnormally divide with altered division asymmetry, resulting in mature pollen without the male germline. We found that these defects arise from genetic lesions in the AUG2 and AUG4 genes, members of the augmin complex that mediates microtubule (MT)-dependent MT nucleation in a broad range of species. Collectively, our study provides genetic evidence that the augmin complex plays a critical role in mitotic entry and proper execution for pollen mitosis I, broadening the spectrum of augmin function during sexual reproduction in Arabidopsis.

在开花植物中，功能配子体的产生是导致成功增殖的双重受精的前提。花粉粒作为拟南芥中的雄配子体，在营养细胞内部具有两个精子细胞，具有独特的图案。为了更好地了解花粉发育的遗传调控，我们在本研究中使用激活标记载体在突变种群中形态学筛选了DAPI染色的成熟花粉。结果，我们确定了两条独立的线AL318和AL434，在核数和花粉模式方面表现出相似的突变表型。遗传分析表明，由于两个性别的遗传传递大大减少，这两个突变体保留在杂合子中，而不是纯合子。发育分析表明，处于极化阶段的突变体微孢子要么完全不能进入花粉有丝分裂I，要么由于分裂不对称性的改变而异常分裂，导致没有雄性种系的成熟花粉。我们发现这些缺陷是由AUG2和AUG4的遗传损伤引起的基因，是在广泛的物种中介导微管（MT）依赖性MT成核的Augmin复合物的成员。总的来说，我们的研究提供了遗传学证据，表明在混合花粉有丝分裂I中，augmin复合物在有丝分裂进入和正确执行中起关键作用，从而扩大了拟南芥有性生殖过程中augmin功能的范围。