American Society of Plant Biologists
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Minisymposium 13: Tropisms

Abs # M1304: Hydrotropism in lateral roots and its possible contribution to drought avoidance in Arabidopsis thaliana

Presenter: Iwata, Satoru       Contact Presenter
AuthorsIwata, Satoru  (A)   Miyazawa, Yutaka  (A)   Takahashi, Hideyuki  (A)  
Affiliations: (A): Tohoku University Graduate School of Life Sciences

Plants have evolved numerous abilities to adapt to the surroundings they come across. For an example, roots of terrestrial plants show hydrotropism in response to water potential gradients, which makes roots bend towards area of high water potential. We previously identified MIZU-KUSSEI1 (MIZ1) and MIZ2 as genes essential for hydrotropism of primary roots in Arabidopsis. MIZ1 encodes an unknown protein and is expressed at the root cap where the moisture gradient is sensed. MIZ2 encodes a guanine exchange factor for ADP-ribosylation factor, known as GNOM. Because water availability is an important factor for sustaining plant lives, it is assumed that root hydrotropism contributes to plant water acquisition under water-limited conditions. However, the role of hydrotropism in nature is not proven yet. Considering that the vast root system responsible for acquisition of water is mainly comprised of lateral roots, whether lateral roots respond to water potential gradient is a matter of great importance to understand the role of hydrotropism in plant drought avoidance. In the present study, we established an experimental system for the study of hydrotropism in Arabidopsis lateral roots and analyzed its characteristics. We found that lateral roots of Arabidopsis exhibited hydrotropism as primary roots did. The degree of hydrotropism fluctuated irrespective of the lengths of lateral roots, and there was no obvious correlation between the degree of hydrotropism and the length of lateral root. In addition, expressions of a pMIZ1::GUS fusion gene were found at the root tips of lateral roots. This GUS activity was observed irrespective of the length of lateral roots, which is in agreement with the results indicating that hydrotropic response is independent of lateral root length. Furthermore, we found that lateral roots of neither miz1 nor miz2 mutants exhibited hydrotropism at all. When moisture gradients were established in the soil, more lateral roots were distributed to the moistened region in the wild type but not miz1 mutant. These observations demonstrate that lateral roots of Arabidopsis are capable of responding to water potential gradients, and that this hydrotropic response is regulated by MIZ1 and MIZ2. Also, our studies demonstrate that hydrotropism of lateral roots plays a role in root system development and thereby contributes to plant drought avoidance under water-limited conditions.

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