University of Cologne, Cologne Biocentre, Botanical Institute, Zülpicher Str. 47 b, 50674 Cologne, Germany.
University of Innsbruck, Department of Botany, Functional Plant Biology, Sternwartestrasse 15, 6020 Innsbruck, Austria.
Plant Cell Physiol. 2017 Dec 1;58(12):2067-2084. doi: 10.1093/pcp/pcx136.
Desiccation tolerance is commonly regarded as one of the key features for the colonization of terrestrial habitats by green algae and the evolution of land plants. Extensive studies, focused mostly on physiology, have been carried out assessing the desiccation tolerance and resilience of the streptophytic genera Klebsormidium and Zygnema. Here we present transcriptomic analyses of Zygnema circumcarinatum exposed to desiccation stress. Cultures of Z. circumcarinatum grown in liquid medium or on agar plates were desiccated at ∼86% relative air humidity until the effective quantum yield of PSII [Y(II)] ceased. In general, the response to dehydration was much more pronounced in Z. circumcarinatum cultured in liquid medium for 1 month compared with filaments grown on agar plates for 7 and 12 months. Culture on solid medium enables the alga to acclimate to dehydration much better and an increase in desiccation tolerance was clearly correlated to increased culture age. Moreover, gene expression analysis revealed that photosynthesis was strongly repressed upon desiccation treatment in the liquid culture while only minor effects were detected in filaments cultured on agar plates for 7 months. Otherwise, both samples showed induction of stress protection mechanisms such as reactive oxygen species scavenging (early light-induced proteins, glutathione metabolism) and DNA repair as well as the expression of chaperones and aquaporins. Additionally, Z. circumcarinatum cultured in liquid medium upregulated sucrose-synthesizing enzymes and strongly induced membrane modifications in response to desiccation stress. These results corroborate the previously described hardening and associated desiccation tolerance in Zygnema in response to seasonal fluctuations in water availability.
脱水耐性通常被认为是绿藻定居陆地生境和陆地植物进化的关键特征之一。已进行了大量集中于生理学的研究，以评估丝状绿藻 Klebsormidium 和 Zygnema 的脱水耐性和恢复力。在这里，我们介绍了暴露于脱水胁迫下的 Zygnema circumcarinatum 的转录组分析。在约 86%相对空气湿度下，将在液体培养基或琼脂平板上培养的 Z. circumcarinatum 进行脱水，直到 PSII 的有效量子产量 [Y(II)] 停止。通常，与在琼脂平板上培养 7 个月和 12 个月的丝状体相比，在液体培养基中培养 1 个月的 Z. circumcarinatum 对脱水的反应更为明显。在固体培养基上培养使藻类能够更好地适应脱水，并且脱水耐性的增加与培养年龄的增加明显相关。此外，基因表达分析表明，在液体培养物中进行脱水处理时，光合作用受到强烈抑制，而在琼脂平板上培养 7 个月的丝状体中则检测到较小的影响。否则，两个样本均显示出应激保护机制的诱导，如活性氧物种清除（早期光诱导蛋白、谷胱甘肽代谢）和 DNA 修复，以及伴侣蛋白和水通道蛋白的表达。此外，在液体培养基中培养的 Z. circumcarinatum 上调了蔗糖合成酶，并在响应脱水胁迫时强烈诱导了膜修饰。这些结果证实了先前描述的 Zygnema 对季节性水分供应变化的硬化和相关脱水耐性。
