Endo Kaichiro, Kobayashi Koichi, Wada Hajime
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-8902 Japan.
Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-8902 Japan
Plant Cell Physiol. 2016 Dec;57(12):2461-2471. doi: 10.1093/pcp/pcw159. Epub 2016 Sep 11.
Anionic lipids, sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), are major classes of the thylakoid membrane lipids in cyanobacteria and plant chloroplasts. PG is essential for growth and photosynthesis of cyanobacteria, algae and plants, but the requirement for SQDG differs even among cyanobacterial species. Although SQDG and PG can compensate each other in part presumably to maintain proper balance of anionic charge in lipid bilayers, the functional relationship of these lipids is largely unknown. In this study, we inactivated the sqdB gene, encoding a UDP-sulfoquinovose synthase and involved in SQDG biosynthesis, in Thermosynechococcus elongatus BP-1. In wild-type cells, PG accounted for only approximately 3.5 mol% of total membrane lipids, but its content was substantially increased along with complete loss of SQDG in the sqdB mutant. Under phosphate (Pi)-sufficient conditions, the growth rate and PSII activity were slightly lower in sqdB than in wild-type cells. In addition, the formation of PSI trimers and PSII dimers and energy transfer in phycobilisomes were perturbed in the mutant. Under Pi-deficient conditions, the growth of sqdB cells was severely impaired, with a decrease in PSII activity. PG supplementation could partially rescue the defective growth and PSII activity of Pi-deficient sqdB cells but fully recovered the impaired growth of the pgsA mutant of T. elongatus, which is deficient in PG biosynthesis. These data suggest that SQDG has a specific role in the growth and photosynthesis of T. elongatus, which cannot be complemented by PG, particularly under Pi-deficient conditions.
阴离子脂质，磺基喹喔啉二酰基甘油（SQDG）和磷脂酰甘油（PG），是蓝细菌和植物叶绿体类囊体膜脂质的主要类别。PG对于蓝细菌、藻类和植物的生长及光合作用至关重要，但即使在蓝细菌物种之间，对SQDG的需求也有所不同。尽管SQDG和PG可能在一定程度上相互补偿，以维持脂质双层中阴离子电荷的适当平衡，但这些脂质的功能关系在很大程度上尚不清楚。在本研究中，我们使编码UDP-磺基喹喔啉合酶且参与SQDG生物合成的sqdB基因在嗜热栖热菌BP-1中失活。在野生型细胞中，PG仅占总膜脂质的约3.5摩尔％，但其含量在sqdB突变体中随着SQDG的完全丧失而大幅增加。在磷酸盐（Pi）充足的条件下，sqdB突变体的生长速率和PSII活性略低于野生型细胞。此外，突变体中PSI三聚体和PSII二聚体的形成以及藻胆体中的能量转移受到干扰。在Pi缺乏的条件下，sqdB细胞的生长严重受损，PSII活性降低。补充PG可以部分挽救Pi缺乏的sqdB细胞的生长缺陷和PSII活性，但能完全恢复嗜热栖热菌中缺乏PG生物合成的pgsA突变体受损的生长。这些数据表明，SQDG在嗜热栖热菌的生长和光合作用中具有特定作用，而PG无法替代，特别是在Pi缺乏的条件下。
