Abstract：
Glaucophytes, an enigmatic group of freshwater algae, occupy a pivotal position within the Archaeplastida, providing insights into the early evolutionary history of plastids and their host cells. These algae possess unique plastids, known as cyanelles that retain certain ancestral features, enabling a better understanding of the plastid transition from cyanobacteria. In this study, we investigated the role of ethylene, a potent hormone used by land plants to coordinate stress responses, in the glaucophyte alga Cyanophora paradoxa. We demonstrate that C. paradoxa produces gaseous ethylene when supplied with exogenous 1-aminocyclopropane-1-carboxylic acid (ACC), the ethylene precursor in land plants. In addition, we show that cells produce ethylene natively in response to abiotic stress, and that another plant hormone, abscisic acid (ABA), interferes with ethylene synthesis from exogenously supplied ACC, while positively regulating reactive oxygen species (ROS) accumulation. ROS synthesis also occurred following abiotic stress and ACC treatment, possibly acting as a second messenger in stress responses. A physiological response of C. paradoxa to ACC treatment is growth inhibition. Using transcriptomics, we reveal that ACC treatment induces the upregulation of senescence-associated proteases, consistent with the observation of growth inhibition. This is the first report of hormone usage in a glaucophyte alga, extending our understanding of hormone-mediated stress response coordination into the Glaucophyta, with implications for the evolution of signaling modalities across Archaeplastida.
摘要：
蓝藻植物,一群神秘的淡水藻类，在古细菌中占据着举足轻重的地位，提供有关质体及其宿主细胞的早期进化史的见解。这些藻类拥有独特的质体，被称为青色，保留某些祖先特征，可以更好地了解蓝细菌的质体过渡。在这项研究中,我们研究了乙烯的作用，陆地植物用来协调应激反应的强效激素，在蓝藻藻类中。我们证明，当供应外源1-氨基环丙烷-1-羧酸（ACC）时，C.paradoxa会产生气态乙烯，陆地植物中的乙烯前体。此外,我们表明，细胞本身产生乙烯响应非生物胁迫，还有另一种植物激素，脱落酸（ABA），干扰从外源供应的ACC合成乙烯，同时正向调节活性氧（ROS）的积累。ROS合成也发生在非生物胁迫和ACC处理后，可能在应激反应中充当第二信使。对ACC处理的C.paradoxa的生理反应是生长抑制。使用转录组学，我们揭示了ACC处理诱导衰老相关蛋白酶的上调，与生长抑制的观察结果一致。这是关于在一种蓝藻植物中使用激素的第一份报告，将我们对激素介导的应激反应协调的理解扩展到Glaucophyta，对整个古细菌的信号传导方式的演变具有重要意义。
