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1、Ti-质粒与植物基因组的相互作用蒋舜媛董霞任昶2002-10-08DNA重排研究进展专题WhatisTi-plasmid?Ti-plasmid,——（shortfortumor-inducingplasmid）isalarge(150~200kb)double-strandedcircularDNAplasmidinasoilbacteriumcalledAgrobacteriumtumefaciens,whichcauseswhatisknownasproducesuncontrolledgrowths(tumors,orga
2、lls),normallyatthebase(crown)oftheplant.Ti-plasmidisthekeytothistumorproduction.Figure1.Intheprocessofcausingcrowngalldisease,thebacteriumAgrobacteriumtumefaciensinsertsapartofitsTiplasmid—aregioncalled T-DNA—intoachromosomeofthehostplant.Figure2.Simplifiedrepresenta
3、tionofthemajorregionsoftheTiplasmidofA.tumefaciens.TheT-DNA,wheninsertedintothechromosomalDNAofthehostplant,directsthesynthesisofnopaline,whichisthenutilizedbythebacteriumforitsownpurposes.T-DNAalsodirectstheplantcelltodivideinanuncontrolledmanner,producingatumor.Str
4、uctureofTi-plasmidT-DNA区毒性区(Vir-region,vir)质粒复制起点(Originofreplication,ori)质粒结合转移位点(Transferfunctionsite,tra)冠瘿碱分解位点(ocsornos)TwotypesofTi-plasmidOCSplasmid(octopine)pTiAch5,pTiA6NC,pTiB653,pTiAg162NOSplasmid(nopaline)pTiT37,pTiT38土壤农杆菌-植物DNA转移体系步骤植物敏感细胞和土壤农杆菌相互作用土壤农杆
5、菌的毒性区基因被激活T-DNA的切割和T复合物生成T复合物由土壤农杆菌经植物细胞膜进入植物细胞T-DNA整合到植物染色体上Figure1.Intheprocessofcausingcrowngalldisease,thebacteriumAgrobacteriumtumefaciensinsertsapartofitsTiplasmid—aregioncalled T-DNA—intoachromosomeofthehostplant.InteractionofAgrobacteriumTi-plasmidDNAandplant
6、cells植物敏感细胞和土壤农杆菌相互作用植物受伤产生大量对土壤农杆菌感染敏感的细胞受伤细胞产生一些低分子量的酚类物质可明显刺激土壤农杆菌Ti质粒上毒性区表达乙酰丁香酮（AS），α-羟基乙酰丁香酮Ti质粒毒性区基因激活及T-DNA复合物生成InsertpictureIntegrationofT-DNAintothechromosomeofhostplantT-DNA整合到植物染色体上首先在植物靶DNA上出现一个缺刻(nick)随着DNA解链，宿主细胞的5’—3’外切酶活性使缺刻扩大成裂口(gap)T-DNA侵入裂口，末端与靶DN
7、A单链上的少数核苷酸配对形成异源二倍体；T-DNA悬挂在外侧的末端被切割除去，T-DNA与靶DNA末端相连；靶DNA上链出现缺刻，以整合后的T-DNA下链为模板合成T-DNA的第二条链，完成整合过程。ReferencesviaNCBITheinteractionofAgrobacteriumTi-plasmidDNAandplantcells(1980)Transgeneintegrationinaspen:structuresofintegrationsitesandmechanismofT-DNAintegration.(2
8、002)HowdoestheT-DNAofAgrobacteriumtumefaciensfinditswayintotheplantcellnucleus?(1993)T-DNAintegration:amodeofillegitimaterecombinat
