[Effect of heterologous expression of malic enzyme gene on photosynthetic carbon fixation and lipid accumulation in tobacco leaves].

Microalgae possess high photosynthetic efficiency, robust adaptability, and substantial biomass, serving as excellent biological resources for large-scale cultivation. Malic enzyme (ME), a ubiquitous metabolic enzyme in living organisms, catalyzes the decarboxylation of malate to produce pyruvate, CO, and NAD(P)H, playing a role in multiple metabolic pathways including energy metabolism, photosynthesis, respiration, and biosynthesis. In this study, we identified the malic enzyme gene () and its biological functions, aiming to provide excellent target genes for the genetic improvement of higher plants. Based on the RNA-seq data from under the biofilm cultivation mode with high CO and light energy transfer efficiency and small water use, a highly expressed gene () functionally annotated as was cloned. The physicochemical properties of the -encoded protein were systematically analyzed by bioinformatics tools. The subcellular localization of SqME was determined transient transformation in leaves. The biological functions of were identified genetic transformation in , and the potential of SqME in the genetic improvement of higher plants was evaluated. The ORF of was 1 770 bp, encoding 590 amino acid residues, and the encoded protein was located in chloroplasts. SqME was a NADP-ME, with the typical structural characteristics of ME. The ME activity in the transgenic plant was 1.8 folds of that in the wild-type control. Heterologous expression of increased the content of chlorophyll a, chlorophyll b, and total chlorophyll by 20.9%, 26.9%, and 25.2%, respectively, compared with the control. The transgenic tobacco leaves showed an increase of 54.0% in the fluorescence parameter NPQ and a decrease of 30.1% in Fo compared with the control. Moreover, the biomass, total lipids, and soluble sugars in the transgenic tobacco leaves enhanced by 20.5%, 25.7%, and 9.5%, respectively. On the contrary, the starch and protein content in the transgenic tobacco leaves decreased by 22.4% and 12.2%, respectively. Collectively, the -encoded protein exhibited a strong enzymatic activity. Heterologous expressing of could significantly enhance photosynthetic protection, photosynthesis, and biomass accumulation in the host. Additionally, can facilitate carbon metabolism remodeling in the host, driving more carbon flux towards lipid synthesis. Therefore, can be applied in the genetic improvement of higher plants for enhancing photosynthetic carbon fixation and lipid accumulation. These findings provide scientific references for mining of functional genes from and application of these genes in the genetic engineering of higher plants.