Origin, Evolution, Functional Diversitification And Expression Of The OSC Gene Family In Jilin Ginseng(Panax Ginseng C.A. Mayer)

The oxidosqualene cyclase(OSC) gene family is a super-gene family that encodes oxidosqualene cyclase catalyzing 2,3-oxidosqualene into sterol and precursors of triterpene. Therefore, the OSC gene family plays important roles in the biosynthesis of sterol and triterpene to which the major medical component of ginseng(ginsenosides) belong. This study isolated the Jilin ginseng genes of the OSC gene family from a new database consisting of Jilin ginseng 248,992 Unigenes and characterized it in origin, evolution, function and expression. 1. A total of 45 new OSC genes were isolated from the Jilin ginseng unigene database. The new OSC genes plus the 23 existing ginseng OSC genes in GenBank form the Jilin ginseng’s OSC gene family. Sixty-one genes of the OSC gene family were annotated to three enzymes, beta-Amyrin Synthase(β-AS), Cycloartenol Synthase(CAS) and Dammarenediol Synthase(DS). 2. The OSC genes of the family have been characterized in amino acid sequences. All of the OSC genes contain the conserved domain ISOPREN_C2_like superfamily and four motifs, MWCYCR(Motif1), QXXXXXW(Motif2), WVEDPN(Motif3) and DCTAE(Motif4). 3. Phylogenetic analysis revealed that the Jilin ginseng OSC gene family is ancient, with most of its members originating after the origin of the family Araliaceae, especially that of the genus Panax. 4. It is also revealed that members of the ginseng OSC gene family have been functionally diversified and participate in as many as 24 GO functions. Nineteen of them are evolved in steroid biosynthesis. 5. The expressions of OSC genes vary enormously across and within tissues or developmental stages, but they are significantly correlated, forming a co-expression network. The network is shown to dramatically vary among genotypes.These findings have, for first time, revealed the mechanisms underling the function, expression and biology of a plant gene family, and provided gene resources and knowledge essential for enhanced research and applications of the OSC gene family in ginseng.