School of Oceanography, University of Washington, Seattle, United States.
Molecular Engineering Graduate Program, University of Washington, Seattle, WA, Seattle, United States.
Elife. 2023 Jun 6;12:e84392. doi: 10.7554/eLife.84392.
Phytoplankton rely on diverse mechanisms to adapt to the decreased iron bioavailability and oxidative stress-inducing conditions of today's oxygenated oceans, including replacement of the iron-requiring ferredoxin electron shuttle protein with a less-efficient iron-free flavodoxin under iron-limiting conditions. Yet, diatoms transcribe flavodoxins in high-iron regions in contrast to other phytoplankton. Here, we show that the two clades of flavodoxins present within diatoms exhibit a functional divergence, with only clade II flavodoxins displaying the canonical role in acclimation to iron limitation. We created CRISPR/Cas9 knock-outs of the clade I flavodoxin from the model diatom and found that these cell lines are hypersensitive to oxidative stress, while maintaining a wild-type response to iron limitation. Within natural diatom communities, clade I flavodoxin transcript abundance is regulated over the diel cycle rather than in response to iron availability, whereas clade II transcript abundances increase either in iron-limiting regions or under artificially induced iron limitation. The observed functional specialization of two flavodoxin variants within diatoms reiterates two major stressors associated with contemporary oceans and illustrates diatom strategies to flourish in diverse aquatic ecosystems.
浮游植物依赖多种机制来适应现今富氧海洋中铁元素生物利用率降低和氧化应激诱导的环境，包括在缺铁条件下，用效率较低的无铁黄素替代需要铁的铁氧还蛋白电子穿梭蛋白。然而，硅藻在高铁区域转录黄素蛋白，而其他浮游植物则不然。在这里，我们表明硅藻中存在的两种黄素蛋白簇表现出功能上的分化，只有 II 簇黄素蛋白在适应铁限制方面表现出典型作用。我们从模式硅藻中创建了 CRISPR/Cas9 敲除的 I 簇黄素蛋白，发现这些细胞系对氧化应激高度敏感，同时对铁限制保持野生型反应。在自然硅藻群落中，I 簇黄素蛋白的转录丰度随昼夜周期而变化，而不是响应铁的可用性，而 II 簇转录丰度在缺铁区域或人工诱导铁限制时增加。在硅藻中观察到两种黄素蛋白变体的功能特化，再次强调了与现今海洋相关的两个主要胁迫因素，并说明了硅藻在多样化水生生态系统中繁荣的策略。
