Transcriptional Analysis Of Terpenoids Metabolism In Developing Panax Ginseng Root

Panax ginseng C.A.Meyer is a perennial herb of Panax L.(Araliaceae)and it has been used as medical plant for many years.Mountain-cultivated ginsengs is planted imitatively in a natural forest environment without transplantation,scarification,irrigation,or fertilization during the periods of growth,thus suffering much severe environmental stresses as the wild ginseng.Through transcriptome analysis combined with metabolomics determination,the terpenoids metabolism among field-and mountain-cultivated ginsengs,or mountain-cultivated ginsengs in different season and ages,were analyzed.The main results are as follows:(1)The differentially expressed genes of 5-year-old field-and mountain-cultivated ginsengs were mainly distributed in the terpenoids biosynthesis pathways,which proved that morphological and physiological differences between the two types of ginsengs were attributed to the terpenoids metabolism.Among which,496 differentially expressed genes were involved in 7 major terpenoids biosynthesis pathways(terpenoid backbone biosynthesis,monoterpenoid biosynthesis,diterpenoid biosynthesis,carotenoid biosynthesis,sesquiterpenoid and triterpenoid biosynthesis,steroid biosynthesis,and ubiquinone and other terpenoid-quinone biosynthesis).It was found that the transcription levels of diterpenoid and triterpenoid biosynthesis genes were higher in field-cultivated ginseng,and the genes in sesquiterpenoid and carotenoid biosynthesis exhitied an opposite trend.Additionally,terpenoids backbones,monoterpenoids and terpenoid-quinones biosyntheses were neither obviously inclined.Our determination also revealed that there were more gibberellins and steroids,responsible for quick vegetative growth,accumulated in field-cultivated ginsengs,and enriched abscisic acid and germacrenes as well as protopanaxatriol-type ginsenosides relevant to enhanced stress-resistance in mountain-cultivated ginsengs.(2)Based on comparative transcriptomes of ginsengs sampled from August to October,it was found that the terpenoids biosynthesis pathways exhibited an obvious seasonal variation.A total of 97,182 transcripts were screened by this sequencing,among which 33,679 were identified as new transcripts,and 6,790 new genes were obtained through functional prediction.Among which,the biosyntheses of brassinosteroids(triterpenoids),germacrene(sesquiterpenoids),solavetivone(sesquiterpenoids),valencene(sesquiterpenoids)and terpinol(monoterpenoids)were more active in August;the biosyntheses of campesterol(triterpenoids),gibberellin(diterpenoids)and strigol(cartenoids)were activated while those of brassinosteroids and valencene were suppressed in September.In October,all terpenoids biosynthesis pathways were suppressed except for those of stigmasterol(triterpenoids),abscisic acid(carotenoids)and neomenthol(monoterpenoids).(3)To explore the terpenoids metabolism in ginsengs with different ages,we sequenced the transcriptomes of 5-,10-and 15-year-old ginsengs.A total of 98,671 transcripts was screened by this sequencing,among which 37,596 were identified as new transcripts,and 8,647 new genes were obtained through functional prediction.Among which,the biosyntheses of brassinosteroids,gibberellin,germacrene and neomenthol were more active in 5-year-old ginseng,while those of campesterol and solavetivone were higher expressed in 10-year-old ginseng,and all pathways were down-regulated in 15-year-old ginseng.