广宿主Ti质粒virA毒力基因对窄宿主根癌农杆菌MI3—2菌株宿主范围的扩展作用

THE ROLE OF A virA GENE FROM A WIDE HOST RANGEVIRULENCE REGION ON EXPENDING OF LIMITED HOSTRANGE OF AGROBACTEMUM TUMEFACIENS STRAIN MI3-2

生物3型葡萄根癌农杆菌MI3—2有很窄的宿主范围,除了葡萄外,只对少数植物能致瘤。我们先前的研究曾观察到,MI3—2菌株的DNA与广宿主根癌农杆菌A348的PTiA6质粒毒力区virA基因座和T—DNA的tms基因不同源。本实验把含有PTiA6质粒T_L—DNA片段及毒力区各基因座(virA,B,G,c,D和E)片段的粘粒(cosmid),通过三菌接合引入MI3—2菌株,组成局部二倍体,使之与MI3—2Ti质粒中相对应的基因互补。用这种转移接合子感染植物表明,引入有T_L—DNA片段或virA基因座的MI3—2,均能使宿主范围有所扩大,并能在落地生根致瘤。本文提出了广宿主virA基因对根癌农杆菌宿主范围的作用。

Biotype 3 Agrobacterium tumefaciens strain MI3-2 from grapevine in nature is responsible for the formation of tumors on a very narrow host range of plants, particularly vitis(grapevine)cultivars. The previous work demonstrated that the DNA in MI3-2 exhibited little or no homology to a wide host range(WHR, strain A348) virA locus and auxin gene in the TL-DNA of PTiA6. In this report the cosmid clones from WHR vir region and T-DNA were mobilized into the narrow host range (LHR) strain (MI3-2) by tri-parental mating procedure, complementing the corresponding genes in merodiploid of MI3 - 2 strain, and assayed for their ability to allow tumor formation on Kalanchoe, petunia, sunflower, tomato and tobacco. The results showed that pvck232 containing the WHR TL -DNA , pvck219 and pvck257, both containing WHR virA locus, and when presented in the LHR strain, expanded host range to some of these plants and allowed tumor formation weakly on Kalanchoe leaves. Pvck225 and pvck242, which contained the PTiA6 virB, virG, virC, virD and virE, were unable to expand host range. This indicated that WHR virA locus could play an important role in expanding narrow host range of the MI3-2 strain.