The chlorophyll content and structure can be regulated by long-chain acyl-CoA synthetase, BnLACS9, by stimulating triacylglycerol metabolism in Brassica napus

Background: Chlorophyll is a very important pigment involved in photosynthesis, while plant Acyl-CoA biosynthesis is derived from plastid-localized fatty acids (FAs). Until now, the regulation of Acyl-CoA pathway for chlorophyll biosynthesis is still unknown. Results: Here, we identified a Long-chain Acyl-CoA Synthetase (LACS) gene BnLACS9 from Brassica napus . BnLACS9 complemented a LACS-deficient yeast strain YB525 , which indicated BnLACS9 have the LACS function. BnLACS9 was localized in chloroplast outer envelope (OE), while mainly expressed in young leaves and flowers. Overexpression of BnLACS9 in Nicotiana benthamiana lead to the contents of total CoA and MGDG increased significantly. In B. napus with overexpression of BnLACS9 , the number of the chloroplast grana lamellae and the content of chlorophyll, as well as the MGDG and DGDG contents, were all increased compared to wide-type. The net photosynthetic rate, dry weight of the whole plant and oil content of seeds were significantly increased accompanied by the increased of chlorophyll content. Transcriptome analysis revealed that overexpression of BnLACS9 upgraded the pathway of acyl-CoA biosynthesis and further upgraded the enzymes in glycolipids synthesis pathway, while acyl-CoA was the substrate for glycolipids synthesis. The increased glycolipids, especially MGDG and DGDG, accelerated the formation of the chloroplast grana lamellae, which increased the number of chloroplast thylakoid grana lamella and further leading to increased chlorophyll content. Conclusion: In the present study, we demonstrated that BnLACS9 played a crutial role in glycolipids and chlorophyll biosynthesis in B. napus . The result also provides a new direction and basis theoretical for the improvement of agronomic traits of plants.