Minisymposium 10: Tropisms
Abs #
23004: Analysis of the wav2 mutant exhibiting the strong wavy growth patter of roots
Roots of Arabidopsis thaliana seedlings begin wavy growth when agar plates are shifted from an upright position to an inclined position. After the shift to the angled position, roots bend downward according to gravity and encounter agar surface. Because the roots cannot penetrate the agar medium used, the roots continuously respond to touch stimulation in addition to gravity. wav2 is a mutant which has an enhanced root wavy growth. We think the WAV2 product plays a pivotal role in stimulus-induced curvature of roots. Here we report the phenotypes of the wav2 mutant, cloning of the WAV2 gene, and localization of the WAV2 as follows.
1) wav2 roots have larger curvature angles of wavy growth.
Roots of the wav2 mutant had larger waving angles and shorter wavelength than Ler. On the other hand, wave frequency and growth rate of roots were not significantly different between the mutant and wild type.
2) wav2 roots have larger curvature angles of stimulus-induced bending.
We examined the gravitropism and phototropism of roots of the wav2 mutant. Both curvature angles of roots were larger in wav2 mutant than in wild type. Takahashi et al. (2002, Planta 216: 203|211) also reported that wav2 mutant roots had a larger curvature angle of hydrotropism. We thus concluded that the WAV2 product plays an important role in normal bending of roots, which was induced by several stimuli but not by a specific stimulus.
3) wav2 roots displays an enhanced helical growth during wavy growth.
Root tips of wild type seedlings exhibited periodic reversion of rotation during wavy growth. Consequently, the epidermal cell layers exhibited repeated twisting from side to side. We examined the twisting manner of wav2 roots. Roots of wav2 mutant had an enhanced helical growth, especially right-handed helical growth, suggesting that WAV2 is involved in normal bending of roots through the suppression of the helical growth.
4) Gene, expression and localization of WAV2.
Map-based cloning revealed that the WAV2 encodes a novel protein with a transmembrane domain. Northern blot analysis indicated that the WAV2 gene strongly expressed in seedlings and roots. Observation of GFP fluorescence of wav2 mutant, which was transformed with a construct of a WAV2-promotor::WAV2:GFP and whose mutant phenotype was recovered, revealed that WAV2 localized in apical region of the root where root tip rotation was observed during wavy growth.
