Development of practically applicable stress-tolerant plants by transformation of stress response genes identified and characterized from microalgae

植物螯合肽（Phytochelatins，PC）是一类重要的重金属结合肽，在植物体内重金属解毒过程中发挥重要作用。本研究以绿色藻类和蓝藻为研究对象，探讨了微藻PC生物合成的调控机制。在高等植物中，众所周知，Cd是比其他重金属更有效的PC合成诱导剂。另一方面，我们观察到PC合成更强烈地诱导锌比镉在海洋绿色藻，杜氏藻。这一结果表明，杜氏藻PC合酶基因可能适用于开发实用的有毒重金属超富集植物。然而，在这项研究中，我们发现了一个基因编码的PC酶样蛋白的原核生物，念珠藻sp.PCC7120。这种蓝藻蛋白含有保守的N-末端结构域，但不是真核生物PC酶中发现的可变C-末端结构域。此外，这种蛋白质强烈催化 ...更多信息 虽然真核生物的酶可以催化PC合成的第一步，但不能催化第二步。脱落酸（阿坝）是一种已知的诱导高等植物各种逆境反应的信号分子。本研究探讨了阿坝在微藻中的作用。虽然阿坝的生物合成通常是加速暴露于各种环境压力在高等植物中，生物合成特别是加速氧化胁迫在淡水绿色鱼，衣原体。此外，外源添加阿坝特异性诱导抗氧化反应。另一方面，在蓝细菌，集胞藻，阿坝的生物合成从来没有发生在暴露于任何压力和任何响应反应不诱导阿坝。这些结果表明，阿坝生物合成途径和ABA依赖的胁迫反应系统中发现的高等植物也存在于绿色藻类，但不存在于蓝藻。少

Phytochelatins (PCs) are heavy-metal-binding peptides that play important roles in the detoxification of toxic heavy metals in higher plants. In this study, we investigated the regulation mechanism of PC biosynthesis in microalgae such as green algae and cyanobacteria. In higher plants, it is well known that Cd is a more effective inducer of PC synthesis than other heavy metals. On the other hand, we have observed PC synthesis is more strongly induced by zinc than Cd in a marine green alga, Dunaliella. This result suggests Dunaliella PC synthase gene may be applicable to develop practical hyperaccumulator for toxic heavy metals.PC and PC synthase genes have never been identified in prokaryotes. In this study, however, we found a gene encoding a PC synthase-like protein in a prokaryote, Nostoc sp.PCC7120. This cyanobacterial protein contained the conserved N-terminal domain but not the variable C-terminal domain found in eukaryotic PC synthases. Furthermore, this protein strongly cataly … More zed the first step of PC synthesis but could not catalyze the second step, although eukaryotic enzymes can catalyze both reactions. These results suggest this prokaryotic PC synthase may be a more primitive form of the eukaryotic ones.Abscisic acid (ABA) is a well known signal molecule for induction of various stress response reactions in higher plants. In this study, we investigated the function of ABA in microalgae. Although ABA biosynthesis is generally accelerated by exposure to various environmental stresses in higher plants, the biosynthesis was specifically accelerated by oxidative stress in freshwater green alga, Chlamydomonas. Furthermore, exogenously added ABA specifically induced anti-oxidant reactions. On the other hand, in a cyanobacterium, Synechocystis, ABA biosynthesis never occurred under exposure to any stresses and any response reactions were not induced by ABA. These results suggest the ABA biosynthetic pathway and ABA-dependent stress response systems found in higher plants also exist in green algae but do not exist in cyanobacteria. Less