Abstract
Plant roots sense moisture gradient and bend toward humid area. This response is called hydrotropism, and is thought to contribute to effective water uptake. However, molecular mechanisms of hydrotropism are still unclear. Through the genetic screening, we recently isolated mizu-kussei2 (miz2) mutant that lacks hydrotropic response. Fine mapping revealed that miz2 was allelic to GNOM, which encodes an ARF-GEF required for vesicle trafficking. In contrast to other gnom alleles, miz2 showed no obvious developmental defects, which suggests that gnommiz2 lack the GNOM activity specifically required for hydrotropism. In order to determine the GNOM function involved in hydrotropism, we conducted genetic analysis of miz2 mutant. Transheterozygotes of miz2 and gnomB4049 or gnomR5 showed lack of hydrotropism. In contrast, transheterozygote of miz2 and gnomemb30-1, a loss-of-function mutant of GEF activity, partially recovered hydrotropic response. These results suggest that GNOM function, other than GEF activity, might be required for expressing hydrotropism in roots.
