Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA.
Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT, 59717, USA.
Photosynth Res. 2020 Jan;143(1):81-95. doi: 10.1007/s11120-019-00689-8. Epub 2019 Nov 23.
Some terrestrial cyanobacteria acclimate to and utilize far-red light (FRL; λ = 700-800 nm) for oxygenic photosynthesis, a process known as far-red light photoacclimation (FaRLiP). A conserved, 20-gene FaRLiP cluster encodes core subunits of Photosystem I (PSI) and Photosystem II (PSII), five phycobiliprotein subunits of FRL-bicylindrical cores, and enzymes for synthesis of chlorophyll (Chl) f and possibly Chl d. Deletion mutants for each of the five apc genes of the FaRLiP cluster were constructed in Synechococcus sp. PCC 7335, and all had similar phenotypes. When the mutants were grown in white (WL) or red (RL) light, the cells closely resembled the wild-type (WT) strain grown under the same conditions. However, the WT and mutant strains were very different when grown under FRL. Mutants grown in FRL were unable to assemble FRL-bicylindrical cores, were essentially devoid of FRL-specific phycobiliproteins, but retained RL-type phycobilisomes and WL-PSII. The transcript levels for genes of the FaRLiP cluster in the mutants were similar to those in WT. Surprisingly, the Chl d contents of the mutant strains were greatly reduced (~ 60-99%) compared to WT and so were the levels of FRL-PSII. We infer that Chl d may be essential for the assembly of FRL-PSII, which does not accumulate to normal levels in the mutants. We further infer that the cysteine-rich subunits of FRL allophycocyanin may either directly participate in the synthesis of Chl d or that FRL bicylindrical cores stabilize FRL-PSII to prevent loss of Chl d.
一些陆生蓝细菌适应并利用远红（FRL；λ=700-800nm）进行放氧光合作用，这个过程被称为远红光光驯化（FaRLiP）。一个保守的、包含 20 个基因的 FaRLiP 簇编码光系统 I（PSI）和光系统 II（PSII）的核心亚基、FRL 双圆柱核心的五个藻胆蛋白亚基以及合成叶绿素（Chl）f 和可能的 Chl d 的酶。在集胞藻 PCC 7335 中构建了 FaRLiP 簇的五个 apc 基因的缺失突变体，它们都具有相似的表型。当突变体在白光（WL）或红光（RL）中生长时，细胞与在相同条件下生长的野生型（WT）菌株非常相似。然而，当在 FRL 下生长时，WT 和突变株的差异非常大。在 FRL 中生长的突变体无法组装 FRL 双圆柱核心，几乎没有 FRL 特异性藻胆蛋白，但保留 RL 型藻胆体和 WL-PSII。突变体中 FaRLiP 簇的基因转录水平与 WT 相似。令人惊讶的是，突变株的 Chl d 含量与 WT 相比大大降低（~60-99%），FRL-PSII 的水平也是如此。我们推断 Chl d 可能是组装 FRL-PSII 的必需条件，而突变体中该蛋白无法正常积累。我们进一步推断 FRL 别藻蓝蛋白的富含半胱氨酸亚基可能直接参与 Chl d 的合成，或者 FRL 双圆柱核心稳定 FRL-PSII 以防止 Chl d 的损失。
