论文题目：Foraging for water by MIZ1-mediated antagonism between root gravitropism and hydrotropism
论文作者：Zhang, Yuzhou; Bao, Zhulatai; Smoljan, Adrijana; Liu, Yifan; Wang, Huihui; Friml, Jiri
论文摘要：
Root system integrates multiple environmental cues, chiefly gravity and soil humidity, to anchor plants in soil and forage for water. While the mechanism of auxin-mediated root gravitropism is comparably well-understood, the root's capability to grow toward moist soil for water uptake and drought avoidance, termed root hydrotropism, remains largely mysterious. Here, we provide key insights into the mechanism of hydrotropic growth and assign a role to the master regulator of hydrotropism, MIZU-KUSSEI 1 (MIZ1). We show that efficient hydrotropism requires the attenuation of antagonistically acting gravitropism, which is inhibited under drought conditions. Drought stress interferes with subcellular trafficking and the lateral mobility of PIN auxin transporters, which are polarly localized at the root cell plasma membranes. This leads to defects in PIN2 polarity and gravity-induced polarization of PIN3, ultimately inhibiting gravity-induced auxin redistribution and root bending. The miz1 mutant is defective in all these regulations, and in support of MIZ1's action on PINs, pin mutations rescue the hydrotropic defects in the miz1 mutant. These observations identify a mechanism for how drought via MIZ1 attenuates gravitropism to promote root hydrotropism for efficient water foraging under drought conditions.
根系可以整合多种环境线索，主要是重力和土壤湿度，来帮助植物固定于土壤并寻找土壤水分。虽然生长素介导的根向重力弯曲机制相对较为清楚，但根部向湿润土壤生长以吸收水分来避免干旱的能力（称为根部水分趋向性）仍然不明确。研究发现向水性生长关键调节基因 MIZU-KUSSEI 1 （ MIZ1 ）可通过一种目前未知的机制来调控植物对水分的搜寻能力。首先向重力性与向水性生长属于拮抗关系，干旱通过减弱根向重力性应答反应，从而提高了根向水性生长能力。干旱胁迫干扰了生长素转运蛋白PIN的亚细胞转运和在细胞膜上的侧向移动速度，导致PIN2在细胞中的极性发生改变以及和重力诱导条件下PIN3极性产生缺陷，最终抑制了重力刺激下生长素的重新分布，从而抑制了植物的向重力性生长。 miz1 突变体中干旱对PIN的调控存在缺陷，证明了MIZ1对PIN蛋白的调控作用。同时遗传学进一步证明 pin 突变体可以回复 miz1 突变体的水向性缺陷表型。这些实验结果表明干旱通过MIZ1减弱向重力性应答来促进根的水向性生长，从而帮助植物在干旱条件下高效的寻找水分。
论文链接：www.pnas.org/doi/10.1073/pnas.2427315122