Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan; Faculty of Education, Wakayama University, Wakayama 640-8510, Japan.
Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
J Plant Physiol. 2018 May-Jun;224-225:137-143. doi: 10.1016/j.jplph.2018.03.014. Epub 2018 Mar 29.
In Arabidopsis, a central regulator of copper (Cu) homeostasis is the transcription factor SQUAMOSA promoter binding protein-like7 (SPL7). Under Cu deficiency, SPL7 induces the expression of miR398, which suppresses the expression of the genes CSD1 and CSD2, which encode cytosolic and chloroplastic isoforms of Cu/Zn superoxide dismutase, respectively. Consequently, the limited Cu is preferentially assigned to plastocyanin, which is essential for photosynthetic electron transport. Consistent with this function of miR398 related to photosynthesis, its expression is strongly induced in leaves. In this study, however, we showed that SPL7 was transcribed mainly around the vasculature in roots, where Cu levels were likely sensed. To test the possible long-distance signaling of Cu availability from roots to shoots, we conducted a series of grafting experiments using spl7 mutant and wild-type (WT) plants. Expression of Cu-responsive microRNAs and the resulting suppression of CSD1 and CSD2 mRNAs were observed in leaves only when the aerial part was from WT plants, in which a low level of SPL7 was transcribed also in the vascular tissues. Although local sensing of Cu was disturbed in the spl7 mutant, the Cu level was not affected in the shoots. SPL7 is expressed in specific cell layers in both roots and shoots and locally senses Cu availability, transmitting the information to surrounding cells.
在拟南芥中，铜（Cu）稳态的中央调节剂是转录因子 SQUAMOSA 启动子结合蛋白样 7（SPL7）。在 Cu 缺乏时，SPL7 诱导 miR398 的表达，后者抑制编码胞质和叶绿体同工型 Cu/Zn 超氧化物歧化酶的基因 CSD1 和 CSD2 的表达。因此，有限的 Cu 优先分配给质体蓝素，质体蓝素是光合作用电子传递所必需的。与 miR398 与光合作用相关的功能一致，其表达在叶片中强烈诱导。然而，在本研究中，我们表明 SPL7 主要在根的脉管周围转录，Cu 水平可能在那里被感知。为了测试 Cu 可用性从根部到地上部的可能长距离信号传递，我们使用 spl7 突变体和野生型（WT）植物进行了一系列嫁接实验。当空中部分来自 WT 植物时，仅在叶片中观察到 Cu 反应性 microRNAs 的表达及其对 CSD1 和 CSD2 mRNAs 的抑制，其中在血管组织中也转录了低水平的 SPL7。尽管 spl7 突变体中局部 Cu 感应受到干扰，但地上部的 Cu 水平不受影响。SPL7 在根和地上部的特定细胞层中表达，并局部感知 Cu 的可用性，将信息传递给周围细胞。
