Eysholdt-Derzsó Emese, Sauter Margret
Plant Developmental Biology and Plant Physiology, University of Kiel, 24118 Kiel, Germany.
Plant Developmental Biology and Plant Physiology, University of Kiel, 24118 Kiel, Germany
Plant Physiol. 2017 Sep;175(1):412-423. doi: 10.1104/pp.17.00555. Epub 2017 Jul 11.
When plants encounter soil water logging or flooding, roots are the first organs to be confronted with reduced gas diffusion resulting in limited oxygen supply. Since roots do not generate photosynthetic oxygen, they are rapidly faced with oxygen shortage rendering roots particularly prone to damage. While metabolic adaptations to low oxygen conditions, which ensure basic energy supply, have been well characterized, adaptation of root growth and development have received less attention. In this study, we show that hypoxic conditions cause the primary root to grow sidewise in a low oxygen environment, possibly to escape soil patches with reduced oxygen availability. This growth behavior is reversible in that gravitropic growth resumes when seedlings are returned to normoxic conditions. Hypoxic root bending is inhibited by the group VII ethylene response factor (ERFVII) RAP2.12, as seedlings show exaggerated primary root bending. Furthermore, overexpression of the ERFVII member inhibits root bending, suggesting that primary root growth direction at hypoxic conditions is antagonistically regulated by hypoxia and hypoxia-activated ERFVIIs. Root bending is preceded by the establishment of an auxin gradient across the root tip as quantified with DII-VENUS and is synergistically enhanced by hypoxia and the auxin transport inhibitor naphthylphthalamic acid. The protein abundance of the auxin efflux carrier PIN2 is reduced at hypoxic conditions, a response that is suppressed by RAP2.12 overexpression, suggesting antagonistic control of auxin flux by hypoxia and ERFVII. Taken together, we show that hypoxia triggers an escape response of the primary root that is controlled by ERFVII activity and mediated by auxin signaling in the root tip.
当植物遭遇土壤积水或洪涝时，根系是最先面临气体扩散减少从而导致氧气供应受限的器官。由于根系不能产生光合氧气，它们很快就会面临氧气短缺，使根系特别容易受到损害。虽然对低氧条件的代谢适应（可确保基本能量供应）已得到充分表征，但根系生长和发育的适应受到的关注较少。在本研究中，我们表明低氧条件会导致初生根在低氧环境中侧向生长，可能是为了逃离氧气可利用性降低的土壤区域。这种生长行为是可逆的，因为当幼苗回到常氧条件时，重力生长会恢复。低氧根系弯曲受到VII组乙烯反应因子（ERFVII）RAP2.12的抑制，因为幼苗表现出夸张的初生根弯曲。此外，ERFVII成员的过表达抑制根系弯曲，这表明低氧条件下初生根的生长方向受到低氧和低氧激活的ERFVII的拮抗调节。根系弯曲之前会在根尖建立生长素梯度，这通过DII-VENUS定量，并且低氧和生长素运输抑制剂萘基邻苯二甲酸协同增强这种梯度。生长素外流载体PIN2的蛋白质丰度在低氧条件下降低，这种反应被RAP2.12过表达所抑制，这表明低氧和ERFVII对生长素通量具有拮抗控制作用。综上所述，我们表明低氧触发了初生根的逃逸反应，该反应由ERFVII活性控制并由根尖中的生长素信号介导。
