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

本研究通过分析在拟南芥根向水性化过程中起重要作用的MIZ 1和MIZ 2的功能，试图揭示拟南芥根向水性化的分子机制。首先，我们构建了MIZ 1的过表达子（MIZ 1 OEs）并分析了它们的表型。我们发现，MIZ 1 OEs表现出增强的向水性和减少侧根的形成。这些现象可能是由于MIZ 1 OE中生长素含量降低所致。此外，还表明miz 2突变对MIZ 1过表达具有上位性。MIZ 1-GFP导入miz 1突变体补充突变体表型，并在皮层细胞和侧根帽细胞中检测到高水平。将MIZ 1-GFP分级分离成可溶性蛋白级分和内质网（ER）膜级分，其中其在胞质侧结合到ER膜的表面。此外，我们成功地分离蛋白结合MIZ 1的免疫沉淀法和LC-MS/MS分析。此外，我们还获得了miz 1和miz 2抑制基因的突变体。这项研究表明，光和阿坝信号独立地整合到MIZ 1的表达和调节向水性。然后，我们证明了MIZ 1调节侧根的向水性在土壤中的根系发育中起着重要作用，并有助于避免干旱，从而在水分有限的条件下获得更好的存活和产量。

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.