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Plant Physiology 149 (2): 835-840

Copyright © 2009 by the American Society of Plant Physiologists.


GNOM-Mediated Vesicular Trafficking Plays an Essential Role in Hydrotropism of Arabidopsis Roots1,[W],[OA]

Yutaka Miyazawa, Akiko Takahashi, Akie Kobayashi, Tomoko Kaneyasu, Nobuharu Fujii, and Hideyuki Takahashi*

Graduate School of Life Sciences, Tohoku University, Sendai 980–8577, Japan

Abstract: Roots respond not only to gravity but also to moisture gradient by displaying gravitropism and hydrotropism, respectively, to control their growth orientation, which helps plants obtain water and become established in the terrestrial environment. As gravitropism often interferes with hydrotropism, however, the mechanisms of how roots display hydrotropism and differentiate it from gravitropism are not understood. We previously reported MIZU-KUSSEI1 (MIZ1) as a gene required for hydrotropism but not for gravitropism, although the function of its protein was not known. Here, we found that a mutation of GNOM encoding guanine-nucleotide exchange factor for ADP-ribosylation factor-type G proteins was responsible for the ahydrotropism of Arabidopsis (Arabidopsis thaliana), miz2. Unlike other gnom alleles, miz2 showed no apparent morphological defects or reduced gravitropism. Instead, brefeldin A (BFA) treatment inhibited both hydrotropism and gravitropism in Arabidopsis roots. In addition, a BFA-resistant GNOM variant, GNM696L, showed normal hydrotropic response in the presence of BFA. Furthermore, a weak gnom allele, gnomB/E, showed defect in hydrotropic response. These results indicate that GNOM-mediated vesicular trafficking plays an essential role in hydrotropism of seedling roots.

1 This work was supported by the Program for Promotion of Basic Research Activities for Innovative Biosciences (to Y.M.), by the Japan Society for the Promotion of Science (Grants-in-Aid for Scientific Research B, no. 20370017, to H.T.; and a Research Fellowship for Young Scientists to A.K.), by the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grants-in-Aid for Scientific Research on Priority Areas, no. 19039005, to H.T.), and by the "Ground-based Research Announcement for Space Utilization," promoted by the Japan Space Forum (to H.T.).

The author responsible for the distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors ( is: Hideyuki Takahashi (hideyuki{at}

[W] The online version of this article contains Web-only data.

[OA] Open access articles can be viewed online without a subscription.

* Corresponding author; e-mail hideyuki{at}

Received for publication October 9, 2008. Accepted for publication November 30, 2008; Published online December 3, 2008.

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