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Published on April 11, 2008; 10.1104/pp.108.117341

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Received February 4, 2008
Accepted April 7, 2008

Roles of Phosphatidylinositol 3-kinase in root hair growth

Yuree Lee , Gwangbae Bak , Yunjung Choi , Wen-I Chuang , Hyung-Taeg Cho , and Youngsook Lee *

POSTECH-UZH Global Research Lab., Division of Molecular Life Sciences, POSTECH, Pohang, 790-784, Korea; and Department of Biology, Chungnam National University, Daejeon 305-764, Korea

* Corresponding author; email: ylee{at}postech.ac.kr.

The root hair is a model system for understanding plant cell tip growth. As phosphatidylinositol 3-phosphate (PtdIns(3)P) has been shown in other plant cell types to regulate factors that affect root hair growth, including reactive oxygen species (ROS) levels, cytoskeleton, and endosomal movement, we hypothesized that PtdIns(3)P is also important for root hair elongation. The enzyme that generates PtdIns(3)P, PI3K, was expressed in root hair cells of transgenic plants containing the PI3K promoter::{beta}-glucuronidase reporter construct. To obtain genetic evidence for the role of PtdIns(3)P in root hair elongation, we attempted to isolate Arabidopsis mutant plants that did not express the gene VPS34 encoding the PI3K enzyme. However, the homozygous mutant was lethal due to gametophytic defects, and heterozygous plants were not discernibly different from wild type. Alternatively, we made transgenic plants expressing the PtdIns(3)P-binding FYVE domain in the root hair cell in order to block signal transduction downstream of PtdIns(3)P. These transgenic plants had shorter root hairs and reduced hair growth rate compared to wild type plants. In addition, LY294002, a PI3K-specific inhibitor, inhibited root hair elongation, but not initiation. In LY294002-treated root hair cells, endocytosis at the stage of final fusion of the late endosomes to the tonoplast was inhibited and ROS level decreased in a dose dependent manner. Surprisingly, the LY294002 effects on ROS and root hair elongation were similar in rhd2 mutant plants, suggesting that RHD2 was not the major ROS generator in the PtdIns(3)P-mediated root hair elongation process. Collectively, these results suggest that PtdIns(3)P is required for maintenance of the processes essential for root hair cell elongation.




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