CEA, CNRS, Aix-Marseille University, Institute of Biosciences and Biotechnologies of Aix-Marseille (BIAM), UMR7265, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France.
Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PRP-ENV/SRTE/LECO, Cadarache, 13108 Saint-Paul-Lez-Durance, France.
Plant Physiol. 2021 Jul 6;186(3):1455-1472. doi: 10.1093/plphys/kiab168.
Fatty acid photodecarboxylase (FAP) is one of the few enzymes that require light for their catalytic cycle (photoenzymes). FAP was first identified in the microalga Chlorella variabilis NC64A, and belongs to an algae-specific subgroup of the glucose-methanol-choline oxidoreductase family. While the FAP from C. variabilis and its Chlamydomonas reinhardtii homolog CrFAP have demonstrated in vitro activities, their activities and physiological functions have not been studied in vivo. Furthermore, the conservation of FAP activity beyond green microalgae remains hypothetical. Here, using a C. reinhardtii FAP knockout line (fap), we showed that CrFAP is responsible for the formation of 7-heptadecene, the only hydrocarbon of this alga. We further showed that CrFAP was predominantly membrane-associated and that >90% of 7-heptadecene was recovered in the thylakoid fraction. In the fap mutant, photosynthetic activity was not affected under standard growth conditions, but was reduced after cold acclimation when light intensity varied. A phylogenetic analysis that included sequences from Tara Ocean identified almost 200 putative FAPs and indicated that FAP was acquired early after primary endosymbiosis. Within Bikonta, FAP was retained in secondary photosynthetic endosymbiosis lineages but absent from those that lost the plastid. Characterization of recombinant FAPs from various algal genera (Nannochloropsis, Ectocarpus, Galdieria, Chondrus) provided experimental evidence that FAP photochemical activity was present in red and brown algae, and was not limited to unicellular species. These results thus indicate that FAP was conserved during the evolution of most algal lineages where photosynthesis was retained, and suggest that its function is linked to photosynthetic membranes.
脂肪酸脱羧酶（FAP）是少数几种需要光才能进行催化循环的酶之一（光酶）。FAP 最初在微藻 Chlorella variabilis NC64A 中被鉴定出来，属于葡萄糖-甲醇-胆碱氧化还原酶家族中藻类特有的亚群。虽然来自 Chlorella variabilis 的 FAP 及其 Chlamydomonas reinhardtii 同源物 CrFAP 已经证明具有体外活性，但它们的活性和生理功能尚未在体内进行研究。此外，FAP 活性在绿藻之外的保留仍然是假设的。在这里，我们使用 C. reinhardtii FAP 敲除系（fap）表明，CrFAP 负责形成 7-十七烯，这是该藻类唯一的烃类化合物。我们进一步表明，CrFAP 主要与膜相关，并且 >90%的 7-十七烯在类囊体部分中回收。在 fap 突变体中，在标准生长条件下光合作用不受影响，但在光强度变化后的冷驯化后减少。包括 Tara Ocean 序列的系统发育分析鉴定了近 200 种推定的 FAP，并表明 FAP 在初级内共生后早期获得。在 Bikonta 内，FAP 在二次光合内共生谱系中保留，但在失去质体的谱系中不存在。来自各种藻类属（Nannochloropsis、Ectocarpus、Galdieria、Chondrus）的重组 FAP 的表征提供了实验证据，表明 FAP 的光化学活性存在于红藻和褐藻中，并且不限于单细胞物种。这些结果表明，FAP 在保留光合作用的大多数藻类谱系的进化过程中得到了保守，并且表明其功能与光合膜有关。
