Biology Department, Colorado State University, Fort Collins, Colorado 80523, USA.
Plant Physiol. 2011 Nov;157(3):1300-12. doi: 10.1104/pp.111.183350. Epub 2011 Sep 22.
Plastocyanin, which requires copper (Cu) as a cofactor, is an electron carrier in the thylakoid lumen and essential for photoautotrophic growth of plants. The Cu microRNAs, which are expressed during Cu deprivation, down-regulate several transcripts that encode for Cu proteins. Since plastocyanin is not targeted by the Cu microRNAs, a cofactor economy model has been proposed in which plants prioritize Cu for use in photosynthetic electron transport. However, defects in photosynthesis are classic symptoms of Cu deprivation, and priorities in Cu cofactor delivery have not been determined experimentally. Using hydroponically grown Populus trichocarpa (clone Nisqually-1), we have established a physiological and molecular baseline for the response to Cu deficiency. An integrated analysis showed that Cu depletion strongly reduces the activity of several Cu proteins including plastocyanin, and consequently, photosynthesis and growth are decreased. Whereas plastocyanin mRNA levels were only mildly affected by Cu depletion, this treatment strongly affected the expression of other Cu proteins via Cu microRNA-mediated transcript down-regulation. Polyphenol oxidase was newly identified as Cu regulated and targeted by a novel Cu microRNA, miR1444. Importantly, a spatiotemporal analysis after Cu resupply to previously depleted plants revealed that this micronutrient is preferentially allocated to developing photosynthetic tissues. Plastocyanin and photosynthetic electron transport efficiency were the first to recover after Cu addition, whereas recovery of the other Cu-dependent activities was delayed. Our findings lend new support to the hypothesis that the Cu microRNAs serve to mediate a prioritization of Cu cofactor use. These studies also highlight poplar as an alternative sequenced model for spatiotemporal analyses of nutritional homeostasis.
质体蓝素需要铜 (Cu) 作为辅助因子，是类囊体腔中的电子载体，对植物的光合作用生长至关重要。在 Cu 缺乏时表达的 Cu 微 RNA 下调了几个编码 Cu 蛋白的转录本。由于质体蓝素不是 Cu 微 RNA 的靶标，因此提出了一种辅因子经济模型，其中植物优先将 Cu 用于光合作用电子传递。然而，光合作用缺陷是 Cu 缺乏的典型症状，并且 Cu 辅因子传递的优先级尚未通过实验确定。我们使用水培生长的 Populus trichocarpa（克隆 Nisqually-1）为 Cu 缺乏的反应建立了生理和分子基线。综合分析表明，Cu 耗尽强烈降低了几种 Cu 蛋白的活性，包括质体蓝素，因此光合作用和生长减少。虽然 Cu 耗竭仅轻度影响质体蓝素 mRNA 水平，但这种处理强烈影响了其他 Cu 蛋白的表达，这是通过 Cu 微 RNA 介导的转录本下调实现的。多酚氧化酶被新鉴定为 Cu 调节的，受新型 Cu 微 RNA miR1444 靶向调控。重要的是，对先前耗尽的植物进行 Cu 再供应后的时空分析表明，这种微量元素优先分配给正在发育的光合组织。Cu 补充后，质体蓝素和光合作用电子传递效率是第一个恢复的，而其他依赖 Cu 的活性的恢复则延迟。我们的研究结果为 Cu 微 RNA 有助于介导 Cu 辅因子使用的优先级的假设提供了新的支持。这些研究还强调了杨树作为营养动态平衡时空分析的替代测序模型。
