Tanikawa Riko, Sakaguchi Haruna, Ishikawa Toshiki, Hihara Yukako
Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan.
Department of Biochemistry and Molecular Biology, Faculty of Science, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama, 338-8570, Japan.
Plant Cell Physiol. 2025 Jan 29;66(1):15-22. doi: 10.1093/pcp/pcae137.
Recently, acyl plastoquinol (APQ) and plastoquinone-B (PQ-B), which are fatty acid esters of plastoquinol and plastoquinone-C respectively, have been identified as the major neutral lipids in cyanobacteria. In Synechocystis sp. PCC 6803, Slr2103 having homology with the eukaryotic enzyme for triacylglycerol (TAG) synthesis, diacylglycerol acyltransferase 2 (DGAT2), was identified as responsible for the synthesis of these plastoquinone-related lipids. On the other hand, TAG synthesis in cyanobacteria remains controversial due to the low accumulation level within cyanobacterial cells together with the high contamination level from the environment. In this study, to quantify more precisely and elucidate the relationship between the accumulation of neutral lipids and the presence or absence of DGAT2-like genes, plastoquinone-related lipids and TAG were analyzed directly from total lipids of six cyanobacterial species with different sets of genes encoding DGAT2-like proteins belonging to two distinct subclades. The results showed that the synthesis of these neutral lipids is highly dependent on clade A DGAT2-like proteins under the culture conditions used in this study, although accumulation level of TAG was quite low. In contrast to APQ highly abundant in saturated fatty acids, the fatty acid composition of TAG was species-specific and partly reflected the total lipid composition. Gloeobacter violaceus PCC 7421, which lacks a DGAT2-like gene, accumulated APQ with a high proportion of C18:0, suggesting APQ synthesis by an unidentified acyltransferase.
最近，酰基质体醌醇（APQ）和质体醌-B（PQ-B），分别是质体醌醇和质体醌-C的脂肪酸酯，已被鉴定为蓝藻中的主要中性脂质。在集胞藻属PCC 6803中，与真核生物三酰甘油（TAG）合成酶二酰甘油酰基转移酶2（DGAT2）具有同源性的Slr2103被确定为负责这些质体醌相关脂质的合成。另一方面，由于蓝藻细胞内TAG积累水平低以及环境污染水平高，蓝藻中TAG的合成仍存在争议。在本研究中，为了更精确地量化并阐明中性脂质积累与DGAT2样基因的存在与否之间的关系，直接从六种蓝藻的总脂质中分析了质体醌相关脂质和TAG，这六种蓝藻具有属于两个不同亚分支的不同组编码DGAT2样蛋白的基因。结果表明，在本研究使用的培养条件下，这些中性脂质的合成高度依赖于A类DGAT2样蛋白，尽管TAG的积累水平相当低。与富含饱和脂肪酸的APQ相反，TAG的脂肪酸组成具有物种特异性，部分反映了总脂质组成。缺乏DGAT2样基因的紫球藻PCC 7421积累了高比例C18:0的APQ，这表明APQ是由一种未鉴定的酰基转移酶合成的。
