Analysis of molecular mechanism for root hydrotropism that plays a role in plant adaptation to drought conditions

我们试图通过分析MIZ1和MIZ2在亲水性中起重要作用的功能来揭示拟南芥根系亲水性的分子机制。首先，我们获得了MIZ1(MIZ1OEs)的过表达基因，并对其表型进行了分析。我们发现，MIZ1OEs表现出更强的向水性，侧根形成减少。这些现象可能是由于MIZ1OEs生长素含量降低所致。此外，MIZ2突变对MIZ1的过度表达具有上位性。将MIZ1-GFP导入miz1突变体中，补充了突变体的表型，并在皮层细胞和侧根冠细胞中检测到高水平的GFP。MIZ1-GFP被分成可溶性蛋白质组分和内质网(ER)膜组分，在胞质侧结合到ER膜的表面。此外，我们还通过免疫沉淀法和LC-MS/MS分析成功地分离出了与MIZ1结合的蛋白质。此外，我们还获得了miz1和miz2抑制子的突变体。本研究表明，光和ABA信号独立地整合到MIZ1的表达中，并调节亲水性。证明了MIZ1调控的侧根亲水性在土壤根系发育中起着重要作用，有助于避免干旱，从而在水分限制条件下获得更好的成活率和产量。

We attempted to reveal molecular mechanism of hydrotropism in Arabidopsis roots by analyzing the functions of MIZ1 and MIZ2 that play essential roles in hydrotropism. First, we generated the overexpressors of MIZ1 (MIZ1OEs)and analyzed their phenotypes. We found that MIZ1OEs showed an enhanced hydrotropism and a reduced lateral root formation. These phenomena likely resulted form the decreased level of auxin content in MIZ1OEs. Also, it was shown that the miz2 mutation is epistatic to MIZ1 overexpression. MIZ1-GFP introduced into miz1 mutant complemented the mutant phenotype and was detected at high levels in cortical cells and lateral root cap cells. MIZ1-GFP was fractionated into a soluble protein fraction and an endoplasmic reticulum (ER)membrane fraction, where it was bound to the surface of the ER membrane at the cytosolic side. Furthermore, we succeeded in isolating proteins that bind MIZ1 by immunoprecipitation method and LC-MS/MS analysis. In addition, we obtained mutants of suppressors of both miz1 and miz2. This study showed that light and ABA signaling are independently integrated into MIZ1 expression and regulate hydrotropism. Then, we demonstrated that the MIZ1-regulated hydrotropism of lateral roots plays an important role in root system development in soil and contributes to drought avoidance, which results in better survival and yield under the water-limited conditions.