Transcriptome Analysis Of Synechococcus Elongatus PCC 7942 Glyceroglycolipid Metabolism In Response To Phosphate Starvation

Glyceroglycolipids,which are the major component in photosynthetic membrane,have many potential applications in various aspects.Monogalactosyl diacylglycerol(MGDG),digalactosyl diacylglycerol(DGDG)and sulfoquinovosyl diacylglycerol(SQDG)are the three main glyceroglycolipids in photosynthetic membrane.Microalgae is a suitable chassis for glyceroglycolipid production because of abundant glyceroglycolipid,simple structure and mature genetic engineering platform.The synthesis of glyceroglycolipid in microalgae is closely related to environmental factors,but the response mechanism is still unclear.Meanwhile,there are still some limitations in current researches on the metabolism of glyceroglycolipid in microalgae.This limits the development of microalgae glyceroglycolipid utilization.In this study,changes in glyceroglycolipid accumulation and transcriptome of cyanobacteria Synechococcus elongatus PCC 7942 under phosphate starvation were studied,and the response mechanism of glyceroglycolipid metabolism under phosphate starvation was preliminarily proposed.In S.elongatus PCC 7942,the total glyceroglycolipid content increased up to 7% of the dry cell weight,and the MGDG/DGDG ratio decreased from4:1 to 5:3 under phosphate starvation on day 12,resulting from decreased MGDG and increased DGDG and SQDG.However,the transcription levels of MGDG and DGDG synthase genes showed no significant differences,and the transcription levels of SQDG synthase genes were significantly down-regulated.Transcriptomic analysis revealed that the glyceroglycolipid regulation was mainly based on the ratio of MGDG/DGDG for maintaining the glyceroglycolipid homeostasis on day 12 under phosphate starvation.To provide adequate precursors for glyceroglycolipid accumulation,the synthesis of glycosyl in glyceroglycolipid was enhanced at the transcription level,and the transcription level of phosphoglucomutase gene(pgm,Synpcc7942?0156)was significantly up-regulated.However,to restore the damaged glyceroglycolipid homeostasis,the transcription levels of UDPsulfoquinovose synthase gene(sqd B,Synpcc7942?0578)and SQDG synthase gene(sqd X,Synpcc7942?0579)were gradually decreased,which contributed to the MGDG/DGDG ratio increasing back to 2:1 on day 15.Meanwhile,12 transcription regulators were differentially expressed under phosphate starvation.Transcriptomic analysis also suggested that not only the transcription-level regulation but also the post-transcriptional or posttranslational regulation played important roles in glyceroglycolipid metabolism under phosphate starvation on day 12.Moreover,the most enriched GO term of differentially expressed genes was for GTP-binding proteins under phosphate starvation,which may be related to signal transduction in glyceroglycolipid metabolism.The above results showed that the changes in glyceroglycolipid accumulation were an emergency strategy of S.elongatus PCC 7942 adapting to phosphate starvation.However,glyceroglycolipid homeostasis played a more important role in recovery from phosphate starvation.In addition,seven antisense vectors of differentially expressed transcription regulators were constructed.This study proposed a model for glyceroglycolipid metabolism regulation of S.elongatus PCC 7942 under phosphate starvation,and provided technical supports for further studies on glyceroglycolipid metabolism regulation.It is of great significance to elucidate glyceroglycolipid metabolic mechanism and develop glyceroglycolipid utilization in microalgae.