Abstract
Roots display tropisms in response to environmental cues such as gravity, light, and moisture by displaying gravitropism, phototropism, and hydrotropism, respectively. Root hydrotropism is considered to have an important role for drought avoidance. However the mechanism underlying root hydrotropism is far from understanding. We previously reported MIZU-KUSSEI1 (MIZ1) as a gene required for hydrotropism, although the function of its gene product was not known. Here, we identified miz2 as a new mutant allele of GNOM, which confers ahydrotropism of Arabidopsis seedling roots. GNOM encodes a guanine-nucleotide exchange factor for ADP-ribosylation factor-type G protein. Unlike other gnom alleles, miz2 showed no apparent morphological defects or reduced gravitropism. On the other hand, brefeldin A treatment, which inhibits GNOM action, inhibited both hydrotropism and gravitropism. These results indicate that a unique GNOM-mediated vesicular trafficking plays an essential role in root hydrotropism.
