Ca2+信号转导对小球藻中性脂积累的调控机制

Ca2+ has been shown to serve as a ubiquitous intracellular second messenger in signal transduction of environmental stimuli. This characteristic gives Ca2+ an obvious research value in studying the mechanism of signal transduction in plants including microalgae under environment stress. Nitrogen starvation is confirmed to be an efficient environmental pressure to increase lipid accumulation in microalgae. However, Ca2+ signal transduction pathway in microalgae under nitrogen starvation stress has not been studied, and nothing of the regulation mechanism of Ca2+ signal transduction on lipid accumulation in microalgae yet known. By blocking the Ca2+ signal in the oil-producing Chlorella sorokiniana strain C2 separated in the wild, delayed oil droplet formation in cells under nitrogen starvation was observed, indicating that Ca2+ signal pathway might involve in the regulation of neutral lipid synthesis and/or its accumulation. To further understand the Ca2+ regulation pathway, in this study, by using C. sorokiniana C2 as a test organism, we proposed to study the accumulation pattern of neutral lipid, the function of Ca2+ and the Ca2+ associated signal element CaM during nitrogen starvation, thus to further reveal the regulation mechanism of Ca2+ signal transduction on neutral lipid synthesis and its accumulation.

Ca2+作为细胞的第二信使，起着将细胞表面的刺激信号传递给细胞内部的作用。这一特性使Ca2+在环境胁迫下包括微藻在内的植物信号转导机制这一研究领域具有良好的研究价值。缺氮被认为是一种提高微藻油脂积累的有效环境因子。然而，到目前为止，缺氮胁迫下微藻内Ca2+信号转导途径还没有相关研究，对于Ca2+信号转导对微藻油脂积累的调控机制，我们也仍然一无所知。 我们通过对一株野外分离的高产油小球藻Chlorella sorokiniana C2的研究，发现缺氮胁迫条件下阻滞Ca2+信号会延缓细胞内中性脂油滴的形成，表明Ca2+信号途径可能参与了小球藻细胞内中性脂合成和/或积累的调控。在此基础上，我们提出以C. sorokiniana C2为材料，研究缺氮胁迫下中性脂积累规律及Ca2+和相关信号元件CaM在相应Ca2+信号转导途径中的作用机理，并进一步揭示Ca2+信号转导对中性脂合成和积累的调控机制。

Ca2+作为细胞的第二信使，当细胞受到各种刺激时，通常通过胞外钙离子进入细胞或胞内钙库钙离子的释放，提高细胞质内的游离钙离子浓度，从而成为引起细胞反应的信号。缺氮被认为是一种提高微藻油脂积累的有效环境因子，但此前对于Ca2+信号转导对微藻油脂积累的调控机制还所知甚少。本项目利用首创的时间分辨荧光钙离子动态分析和非损伤微测技术等方法，证明了小球藻缺氮诱导的油脂合成过程中钙离子信号的参与，并发现细胞质内钙离子浓度的上升来源于细胞外钙离子进入细胞和细胞内钙库钙离子的释放，从而产生钙信号调控小球藻缺氮诱导的油脂合成。使用模式绿藻Chlamydomonas reinhardtii进一步验证发现钙离子对缺氮诱导的油脂合成的调控是通过钙调蛋白（calmodulin；CaM）实现的，而钙离子对于微藻缺氮诱导的油脂合成的能量调控是通过位于类囊体膜上的钙离子感知蛋白（Calcium Sensor Protein，CAS）来调节基于PGRL1 的环式电子传递活性来实现，提出缺氮胁迫显著抑制光合作用线性磷酸化和呼吸磷酸化及相应ATP生物合成的情况下，Ca2+介导的光合作用环式磷酸化为缺氮诱导的微藻油脂生物合成过程提供能量。基于以上研究结果，首次提出了微藻缺氮诱导产油过程中，基于钙离子调控的环式光合磷酸化的能量平衡模型，对微藻诱导产油信号传导调控机制研究的进行了有益补充。