Arabidopsis ABCG28 is required for the apical accumulation of reactive oxygen species in growing pollen tubes

First author: Thanh Ha Thi Do; Affiliations: Pohang University of Science and Technology (浦项科技大学): Pohang, Korea

Corresponding author: Youngsook Lee

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 AtABCG28 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 AtABCG28 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.

尖端富集的活性氧物质ROS积累与花粉管的生长息息相关，因此对于植物的受精作用是非常重要的。然而，尖端生长的细胞是如何建立起这种特异性的ROS定位还不清楚。多胺被认为在尖端生长过程中作为ROS过氧化氢的前体发挥作用。ABC转运体AtABCG28可能调控ROS的状态，因为该蛋白含有多个半胱氨酸残基，这种是参与ROS内稳态蛋白的特征。本文中，作者发现AtABCG28基因特异性在成熟花粉粒和花粉管中表达。AtABCG28定位于花粉管内分泌小泡中，这类分泌小泡会特异性朝尖端方向移动并最终与花粉管尖端质膜融合。AtABCG28敲除突变体导致花粉管生长的缺陷，并且多胺和ROS在生长中的花粉管尖端不再积累，表现出完全的雄性不育；另外在根毛中异源表达该基因会恢复ROS在尖端的积累，增强在高PH环境下的生长，而正常条件下高PH环境能够抑制ROS的积累和尖端生长。此外，AtABCG28的功能有可能保护花粉管不受多胺的毒害，并且将多胺运输到正在生长的尖端，用于整合到正在扩张的细胞壁中。

通讯：Youngsook Lee (http://pcb.postech.ac.kr)

个人简介：1978年，首尔国立大学，学士；1980年，首尔国立大学，硕士；1988年，康涅狄格大学，博士;1988-1990年，哈佛大学，博士后。

研究方向： 1. 植物ABC转运体； 2. 植物砷转运机制； 3. 微藻的胁迫响应。

doi: https://doi.org/10.1073/pnas.1902010116

Journal: PNAS

Published date: May 31, 2019