Liu Meijing, Ding Wei, Pan Yufang, Hu Hanhua, Liu Jin
Laboratory for Algae Biotechnology & Innovation, College of Engineering, Peking University, Beijing, 100871, China.
Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.
Biotechnol Biofuels Bioprod. 2023 May 3;16(1):74. doi: 10.1186/s13068-023-02326-y.
The marine alga Nannochloropsis oceanica, an emerging model belonging to Heterokont, is considered as a promising light-driven eukaryotic chassis for transforming carbon dioxide to various compounds including carotenoids. Nevertheless, the carotenogenic genes and their roles in the alga remain less understood and to be further explored.
Here, two phylogenetically distant zeaxanthin epoxidase (ZEP) genes from N. oceanica (NoZEP1 and NoZEP2) were functionally characterized. Subcellular localization experiment demonstrated that both NoZEP1 and NoZEP2 reside in the chloroplast yet with differential distribution patterns. Overexpression of NoZEP1 or NoZEP2 led to increases of violaxanthin and its downstream carotenoids at the expense of zeaxanthin in N. oceanica, with the extent of changes mediated by NoZEP1 overexpression being greater as compared to NoZEP2 overexpression. Suppression of NoZEP1 or NoZEP2, on the other hand, caused decreases of violaxanthin and its downstream carotenoids as well as increases of zeaxanthin; similarly, the extent of changes mediated by NoZEP1 suppression was larger than that by NoZEP2 suppression. Interestingly, chlorophyll a dropped following violaxanthin decrease in a well-correlated manner in response to NoZEP suppression. The thylakoid membrane lipids including monogalactosyldiacylglycerol also correlated with the violaxanthin decreases. Accordingly, NoZEP1 suppression resulted in more attenuated algal growth than NoZEP2 suppression did under either normal light or high light stage.
The results together support that both NoZEP1 and NoZEP2, localized in the chloroplast, have overlapping roles in epoxidating zeaxanthin to violaxanthin for the light-dependent growth, yet with NoZEP1 being more functional than NoZEP2 in N. oceanica. Our study provides implications into the understanding of carotenoid biosynthesis and future manipulation of N. oceanica for carotenoid production.
海洋藻类微拟球藻是一种新兴的不等鞭毛类模式生物，被认为是一种有前景的光驱动真核底盘，可将二氧化碳转化为包括类胡萝卜素在内的各种化合物。然而，该藻类中的类胡萝卜素生成基因及其作用仍了解较少，有待进一步探索。
在此，对来自微拟球藻的两个系统发育距离较远的玉米黄质环氧化酶（ZEP）基因（NoZEP1和NoZEP2）进行了功能表征。亚细胞定位实验表明，NoZEP1和NoZEP2均位于叶绿体中，但分布模式不同。在微拟球藻中，NoZEP1或NoZEP2的过表达导致紫黄质及其下游类胡萝卜素增加，同时玉米黄质减少，与NoZEP2过表达相比，NoZEP1过表达介导的变化程度更大。另一方面，抑制NoZEP1或NoZEP2会导致紫黄质及其下游类胡萝卜素减少以及玉米黄质增加；同样，NoZEP1抑制介导的变化程度大于NoZEP2抑制介导的变化程度。有趣的是，响应NoZEP抑制，叶绿素a随着紫黄质减少而以良好的相关性下降。包括单半乳糖基二酰基甘油在内的类囊体膜脂也与紫黄质减少相关。因此，在正常光照或高光阶段，抑制NoZEP1比抑制NoZEP2导致的藻类生长衰减更明显。
这些结果共同支持，位于叶绿体中的NoZEP1和NoZEP2在将玉米黄质环氧化为紫黄质以实现光依赖生长方面具有重叠作用，但在微拟球藻中NoZEP1比NoZEP2功能更强。我们的研究为理解类胡萝卜素生物合成以及未来对微拟球藻进行类胡萝卜素生产的操作提供了启示。
