In microalgae, photosynthesis provides energy and sugar phosphates for the biosynthesis of storage and structural carbohydrates, lipids, and nitrogenous proteins. The oleaginous alga Nannochloropsis salina does not preferentially partition photoassimilates among cellulose, chrysolaminarin, and lipids in response to nitrogenous nutrient deprivation. In the present study, we investigated whether genetic impairment of the cellulose synthase gene (CesA) expression would lead to protein accumulation without the accumulation of storage C polymers in N. salina. Three cesA mutants were generated by the CRISPR/Cas9 approach. Cell wall thickness and cellulose content were reduced in the cesA1 mutant, but not in cesA2 or cesA4 cells. CesA1 mutation resulted in a reduction of chrysolaminarin and neutral lipid contents, by 66.3% and 37.1%, respectively, but increased the soluble protein content by 1.8-fold. Further, N. salina cells with a thinned cell wall were susceptible to mechanical stress, resulting in a 1.7-fold enhancement of lipid extractability. Taken together, the previous and current studies strongly suggest the presence of a controlling mechanism that regulates photoassimilate partitioning toward C and N metabolic pathways as well as the cellulose metabolism as a potential target for cost-effective microalgal cell disruption and as a useful protein production platform.

中文翻译：

---

纤维素生物合成的遗传障碍增加了细胞壁的脆性，并提高了油质藻类Nannochloropsis salina的脂质提取能力。

在微藻中，光合作用提供能量和磷酸糖，用于生物合成存储和结构化碳水化合物，脂质和含氮蛋白质。含油藻类Nannochloropsis salina不会优先响应于氮素养分的缺乏而在纤维素，chrysolaminarin和脂质之间分配光同化物。在本研究中，我们调查了纤维素合酶基因（CesA）表达的遗传损伤是否会导致蛋白质积累而不在盐沼猪笼草中积累C聚合物。通过CRISPR / Cas9方法生成了3个cesA突变体。cesA1突变体的细胞壁厚度和纤维素含量降低，而在cesA2或cesA4细胞。CesA1突变导致chrysolaminarin和中性脂质含量分别降低了66.3％和37.1％，但可溶性蛋白含量却提高了1.8倍。此外，具有薄的细胞壁的盐沼猪笼草细胞容易受到机械应力，导致脂质提取能力提高了1.7倍。综上所述，先前和当前的研究强烈表明，存在一种控制机制，该机制调节光同化物向C和N代谢途径的分配以及纤维素代谢，将其作为经济高效的微藻细胞破坏的潜在目标，并作为有用的蛋白质生产平台。