DataSheet_1_Ascorbate peroxidase plays an important role in photoacclimation in the extremophilic red alga Cyanidiococcus yangmingshanensis.pdf

IntroductionAcidothermophilic cyanidiophytes in natural habitats can survive under a wide variety of light regimes, and the exploration and elucidation of their long-term photoacclimation mechanisms promises great potential for further biotechnological applications. Ascorbic acid was previously identified as an important protectant against high light stress in Galdieria partita under mixotrophic conditions, yet whether ascorbic acid and its related enzymatic reactive oxygen species (ROS) scavenging system was crucial in photoacclimation for photoautotrophic cyanidiophytes was unclear.
MethodsThe significance of ascorbic acid and related ROS scavenging and antioxidant regenerating enzymes in photoacclimation in the extremophilic red alga Cyanidiococcus yangmingshanensis was investigated by measuring the cellular content of ascorbic acid and the activities of ascorbate-related enzymes.
Results and discussionAccumulation of ascorbic acid and activation of the ascorbate-related enzymatic ROS scavenging system characterized the photoacclimation response after cells were transferred from a low light condition at 20 μmol photons m–2 s–1 to various light conditions in the range from 0 to 1000 μmol photons m–2 s–1. The activity of ascorbate peroxidase (APX) was most remarkably enhanced with increasing light intensities and illumination periods among the enzymatic activities being measured. Light-dependent regulation of the APX activity was associated with transcriptional regulation of the chloroplast-targeted APX gene. The important role of the APX activity in photoacclimation was evidenced by the effect of the APX inhibitors on the photosystem II activity and the chlorophyll a content under the high light condition at 1000 μmol photons m–2 s–1. Our findings provide a mechanistic explanation for the acclimation of C. yangmingshanensis to a wide range of light regimes in natural habitats.

引言
自然生境中的嗜酸嗜热蓝型红藻（cyanidiophytes）可在多样光照条件下存活，对其长期光适应机制的探索与阐明，在后续生物技术应用中具备极高潜力。此前研究已明确，混合营养条件下抗坏血酸（ascorbic acid）是帕氏盖迪尔藻（Galdieria partita）抵御高光胁迫的关键保护因子，但光合自养型蓝型红藻的光适应过程中，抗坏血酸及其相关酶促活性氧（reactive oxygen species, ROS）清除系统是否发挥核心作用，仍有待厘清。

材料与方法
本研究以极端嗜热红藻阳明山蓝球菌（Cyanidiococcus yangmingshanensis）为研究对象，通过测定细胞内抗坏血酸含量及抗坏血酸相关酶的活性，探究了抗坏血酸及其相关ROS清除与抗氧化再生酶在其光适应过程中的重要意义。

结果与讨论
当细胞从20 μmol光子·m⁻²·s⁻¹的低光照条件转接至0~1000 μmol光子·m⁻²·s⁻¹的梯度光照条件后，抗坏血酸的积累与抗坏血酸相关酶促ROS清除系统的激活，构成了光适应响应的典型特征。在本次检测的酶活性中，抗坏血酸过氧化物酶（ascorbate peroxidase, APX）的活性随光照强度升高与光照时长延长得到了最为显著的增强。APX活性的光依赖性调控，与靶向叶绿体的APX基因的转录调控显著相关。在1000 μmol光子·m⁻²·s⁻¹的高光条件下，APX抑制剂对光系统II活性及叶绿素a含量的影响，进一步证实了APX活性在光适应过程中的关键作用。本研究结果为阳明山蓝球菌适应自然生境中广泛光照范围的现象提供了机制层面的解释。