A new type IV secretion system promotes conjugal transfer in Agrobacterium tumefaciens
A new type IV secretion system promotes conjugal transfer in Agrobacterium tumefaciens
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DOI：
10.1128/jb.184.17.4838-4845.2002
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发表时间：
2002-09-01
影响因子：
3.2
通讯作者：
Nester, EW
中科院分区：
文献类型：
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作者：
Chen, LS;Chen, YC;Nester, EW
先前已在根癌农杆菌中鉴定出两个由肿瘤诱导(Ti)质粒编码的DNA转移系统。VIRB操纵子是将转移的DNA转移到植物寄主所必需的，而TRB系统编码在农杆菌细胞之间进行钛质粒的接合转移所需的功能。最近获得的农杆菌基因组序列使我们能够鉴定出与亨氏巴尔通体IV型VIRB分泌系统最相似的第三个系统。我们将该系统命名为农杆菌毒力同源物VIRB。AvhB基因座位于pAtC58上，编码至少10个蛋白(AvhB2至AvhB11)，其中7个与Ti质粒毒力相关的VIRB蛋白有很大的相似性。然而，AvhB系统不是肿瘤形成所必需的；相反，它介导了pAtC58隐蔽质粒在农杆菌细胞之间的接合转移。这种转移发生在没有钛质粒编码的VIRB和TRB系统的情况下。与VIRB系统一样，AvhB产物促进incq质粒RSF1010的配偶转移，表明这些产物组成了交配对形成系统。质粒TiC58或RSF1010的存在使pAtC58的接合转移效率分别降低10倍或1000倍。这些数据表明，农杆菌的三种DNA转移系统之间存在复杂的底物相互作用。
Two DNA transfer systems encoded by the tumor-inducing (Ti) plasmid have been previously identified in Agrobacterium tumefaciens. The virB operon is required for the transfer of transferred DNA to the plant host, and the trb system encodes functions required for the conjugal transfer of the Ti plasmid between cells of Agrobacterium. Recent availability of the genome sequence of Agrobacterium allowed us to identify a third system that is most similar to the VirB type IV secretion system of Bartonella henselae. We have designated this system avhB for Agrobacterium virulence homologue virB. The avhB loci reside on pAtC58 and encode at least 10 proteins (AvhB2 through AvhB11), 7 of which display significant similarity to the corresponding virulence-associated VirB proteins of the Ti plasmid. However, the AvhB system is not required for tumor formation; rather, it mediates the conjugal transfer of the pAtC58 cryptic plasmid between cells of Agrobacterium. This transfer occurs in the absence of the Ti plasmid-encoded VirB and Trb systems. Like the VirB system, AvhB products promote the conjugal transfer of the IncQ plasmid RSF1010, suggesting that these products comprise a mating-pair formation system. The presence of plasmid TiC58 or plasmid RSF1010 reduces the conjugal transfer efficiency of pAtC58 10- or 1,000-fold, respectively. These data suggest that complex substrate interactions exist among the three DNA transfer systems of Agrobacterium.