Abstract
Roots show hydrotropism in response to moisture gradient, but its molecular mechanism remains unclear. We have identified MIZ1 as a gene essential for hydrotropism, and revealed that light plays an important role for MIZ1 expression. To understand this light-dependency of MIZ1 expression, we conducted genetic analyses using GFP-fused MIZ1 expressing plants. We found that the MIZ1-GFP signal was clearly reduced in hy5 mutant, while it was not altered in single photoreceptor mutants. It is also known that ABA treatment induces MIZ1 expression and that HY5 is also involved in ABA signaling. To test the possibility that HY5 also functions to regulate ABA-mediated MIZ1 expression, we analyzed MIZ1-GFP in ABA-treated hy5 roots. The results showed that the signal of MIZ1-GFP in ABA-treated hy5 mutant was comparable to that of wild-type. These results suggested that ABA-dependent induction of MIZ1 expression did not involve HY5-mediated signaling. Because hy5 mutant showed a reduction in hydrotropism that was recovered by ABA treatment, it is considered that environmental signals such as light and abiotic stresses induce MIZ1 expression to regulate hydrotropism of Arabidopsis roots.
