Oryzalexin S biosynthesis:a cross-stitched disappearing pathway  

作　　者：Le Zhao Richard Oyagbenro Yiling Feng Meimei Xu Reuben J.Peters 

机构地区：[1]Roy J.Carver Department of Biochemistry,Biophysics and Molecular Biology,Iowa State University,Ames,IA,50011,USA

出　　处：《aBIOTECH》2023年第1期1-7,共7页生物技术通报（英文版）

基　　金：The authors thank Prof.Robert Coates(Univ.Illinois,ret.)for an authentic standard of oryzalexin S.This work was supported by Grants from the NIH(GM131885)and USDA(2020-67013-32557)to R.J.P.

摘　　要：Rice produces many diterpenoid phytoalexins and,reflecting the importance of these natural products in this important cereal crop plant,its genome contains three biosynthetic gene clusters(BGCs)for such metabolism.The chromosome 4 BGC(c4BGC)is largely associated with momilactone production,in part due to the presence of the initiating syn-copalyl diphosphate(CPP)synthase gene(OsCPS4).Oryzalexin S is also derived from syn-CPP.However,the relevant subsequently acting syn-stemarene synthase gene(OsKSL8)is not located in the c4BGC.Production of oryzalexin S further requires hydroxylation at carbons 2 and 19(C2 and C19),presumably catalyzed by cytochrome P450(CYP)monooxygenases.Here it is reported the closely related CYP99A2 and CYP99A3,whose genes are also found in the c4BGC catalyze the necessary C19-hydroxylation,while the closely related CYP71Z21 and CYP71Z22,whose genes are found in the recently reported chromosome 7 BGC(c7BGC),catalyze subsequent hydroxylation at C2α.Thus,oryzalexin S biosynthesis utilizes two distinct BGCs,in a pathway cross-stitched together by OsKSL8.Notably,in contrast to the widely conserved c4BGC,the c7BGC is subspecies(ssp.)specific,being prevalent in ssp.japonica and only rarely found in the other major ssp.indica.Moreover,while the closely related syn-stemodene synthase OsKSL11 was originally considered to be distinct from OsKSL8,it has now been reported to be a ssp.indica derived allele at the same genetic loci.Intriguingly,more detailed analysis indicates that OsKSL8(j)is being replaced by OsKSL11(OsKSL8i),suggesting introgression from ssp.indica to(sub)tropical japonica,with concurrent disappearance of oryzalexin S production.

关 键 词：Biosynthetic gene clusters PHYTOALEXINS DITERPENOIDS Rice evolution 

分 类 号：O62[理学—有机化学]