Division of Integrative Bioscience and Biotechnology, POSTECH, 37673 Pohang, Republic of Korea.
Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg, Denmark.
Proc Natl Acad Sci U S A. 2019 Jun 18;116(25):12540-12549. doi: 10.1073/pnas.1902010116. Epub 2019 May 31.
Tip-focused accumulation of reactive oxygen species (ROS) is tightly associated with pollen tube growth and is thus critical for fertilization. However, it is unclear how tip-growing cells establish such specific ROS localization. Polyamines have been proposed to function in tip growth as precursors of the ROS, hydrogen peroxide. The ABC transporter AtABCG28 may regulate ROS status, as it contains multiple cysteine residues, a characteristic of proteins involved in ROS homeostasis. In this study, we found that was specifically expressed in the mature pollen grains and pollen tubes. AtABCG28 was localized to secretory vesicles inside the pollen tube that moved toward and fused with the plasma membrane of the pollen tube tip. Knocking out resulted in defective pollen tube growth, failure to localize polyamine and ROS to the growing pollen tube tip, and complete male sterility, whereas ectopic expression of this gene in root hair could recover ROS accumulation at the tip and improved the growth under high-pH conditions, which normally prevent ROS accumulation and tip growth. Together, these data suggest that AtABCG28 is critical for localizing polyamine and ROS at the growing tip. In addition, this function of AtABCG28 is likely to protect the pollen tube from the cytotoxicity of polyamine and contribute to the delivery of polyamine to the growing tip for incorporation into the expanding cell wall.
活性氧（ROS）在花粉管生长过程中具有重要作用，但其在花粉管顶端的特异性定位机制仍不清楚。多胺作为 ROS（过氧化氢）的前体，被认为参与了顶端生长。ABC 转运蛋白 AtABCG28 可能通过调控 ROS 稳态而参与了顶端生长，因为它包含多个半胱氨酸残基，这是参与 ROS 动态平衡的蛋白质的特征。本研究发现，AtABCG28 特异性表达于成熟花粉粒和花粉管中。AtABCG28 定位于花粉管内的分泌小泡中，这些小泡向花粉管顶端的质膜移动并与之融合。敲除 基因导致花粉管生长缺陷，多胺和 ROS 无法定位到花粉管顶端，花粉完全不育，而在根毛中异位表达该基因则可以恢复 ROS 在顶端的积累，并改善在高 pH 条件下的生长，因为高 pH 通常会阻止 ROS 积累和顶端生长。这些数据表明，AtABCG28 对于多胺和 ROS 在生长顶端的定位至关重要。此外，AtABCG28 的这一功能可能有助于保护花粉管免受多胺的细胞毒性，并将多胺输送到生长顶端以整合到扩展的细胞壁中。
