Kaur Dasmeet, Moreira Diana, Coimbra Sílvia, Showalter Allan M
Department of Environmental & Plant Biology, Ohio University, Athens, OH, United States.
Molecular and Cellular Biology Program, Ohio University, Athens, OH, United States.
Front Plant Sci. 2022 Jun 14;13:935413. doi: 10.3389/fpls.2022.935413. eCollection 2022.
In flowering plants, male reproductive function is determined by successful development and performance of stamens, pollen grains, and pollen tubes. Despite the crucial role of highly glycosylated arabinogalactan-proteins (AGPs) in male gamete formation, pollen grain, and pollen tube cell walls, the underlying mechanisms defining these functions of AGPs have remained elusive. Eight partially redundant Hyp-galactosyltransferases (named GALT2-GALT9) genes/enzymes are known to initiate Hyp--galactosylation for Hyp-arabinogalactan (AG) production in . To assess the contributions of these Hyp-AGs to male reproductive function, we used a quintuple mutant for this study. Both anther size and pollen viability were compromised in the quintuple mutants. Defects in male gametogenesis were observed in later stages of maturing microspores after meiosis, accompanied by membrane blebbing and numerous lytic vacuoles. Cytological and ultramicroscopic observations revealed that pollen exine reticulate architecture and intine layer development were affected such that non-viable collapsed mature pollen grains were produced, which were devoid of cell content and nuclei, with virtually no intine. AGP immunolabeling demonstrated alterations in cell wall architecture of the anther, pollen grains, and pollen tube. Specifically, the LM2 monoclonal antibody (which recognized β-GlcA epitopes on AGPs) showed a weak signal for the endothecium, microspores, and pollen tube apex. Pollen tube tips also displayed excessive callose deposition. Interestingly, expression patterns of pollen-specific AGPs, namely AGP6, AGP11, AGP23, and AGP40, were determined to be higher in the quintuple mutants. Taken together, our data illustrate the importance of type-II AGs in male reproductive function for successful fertilization.
在开花植物中，雄性生殖功能取决于雄蕊、花粉粒和花粉管的成功发育及表现。尽管高度糖基化的阿拉伯半乳聚糖蛋白（AGPs）在雄配子形成、花粉粒和花粉管细胞壁中起着关键作用，但定义AGPs这些功能的潜在机制仍不清楚。已知八个部分冗余的Hyp-半乳糖基转移酶（命名为GALT2-GALT9）基因/酶可启动Hyp-阿拉伯半乳聚糖（AG）的Hyp-半乳糖基化反应。为了评估这些Hyp-AGs对雄性生殖功能的贡献，我们在本研究中使用了一个五重突变体。五重突变体的花药大小和花粉活力均受到影响。在减数分裂后成熟小孢子的后期阶段观察到雄配子发生缺陷，伴随着细胞膜起泡和大量裂解液泡。细胞学和超微结构观察表明，花粉外壁网状结构和内壁层发育受到影响，从而产生了无活力的塌陷成熟花粉粒，这些花粉粒没有细胞内容物和细胞核，几乎没有内壁。AGP免疫标记显示花药、花粉粒和花粉管的细胞壁结构发生了改变。具体而言，LM2单克隆抗体（识别AGPs上的β-GlcA表位）在内皮层、小孢子和花粉管顶端显示出较弱的信号。花粉管顶端还表现出过多的胼胝质沉积。有趣的是，花粉特异性AGPs，即AGP6、AGP11、AGP23和AGP40的表达模式在五重突变体中更高。综上所述，我们的数据说明了II型AGs在雄性生殖功能中对成功受精的重要性。
