The present study aimed at the preparation of monoclonal antibody against the recombinant PthA-NLS and the isolation of the relative ScFv(single chain variable fragment) genes,providing the possibility to better understand the pathogenesis mechanism via PthA,and developing proper construct for future experimentation to obtain citrus plants resistant to canker disease by transformation and plant antibody techniques.The recombinant polypeptide PthA-NLS was injected into Balb/c mice to produce monoclonal antibody.Total RNA was isolated from the hybridoma cell line 3D10H2 which secreted antiPthA-NLS McAb,and the variable region genes were amplified with specific primers by RT-PCR and SOE-PCR(splicing by overlap extension),and then the ScFv gene was isolated.The recombinant ScFv gene was cloned into pGEM-T and pET32a(+) vector.The later plasmid was transferred into E.coli BL21(DE3) and the expression of the recombinant protein was induced.Three cell lines producing monoclonal antibody against PthA-NLS were acquired and named 1C8H1,2D12B6,and 3D8A10.The recombinant ScFv gene of about 750 bp was constructed.The sequencing results showed that the ScFv gene consists of a 360 bp heavy chain,a 342 bp light chain,and a 45 bp linker region.The recombinant fusion ScFv protein was expressed by IPTG induction,and a 44.5 kDa of recombinant fusion protein was obtained.In conclusion,we obtained three cell lines stably producing monoclonal antibody specifically bound to PthA-NLS,and the relative ScFv gene was constructed and successfully expressed in E.coli.These results may play an important role in further understanding the pathogenesis mechanism and in the development of possible citrus resistant to canker disease by genetic transformation and plant antibiobody. The present study aimed at the preparation of monoclonal antibodies against the recombinant PthA-NLS and the isolation of the relative ScFv (single chain variable fragment) genes, providing the possibility to better understand the pathogenesis mechanism via PthA, and developing proper construct for future experimentation to obtain citrus plants resistant to canker disease by transformation and plant antibody techniques. The recombinant polypeptide PthA-NLS was injected into Balb / c mice to produce monoclonal antibody. Total RNA was isolated from the hybridoma cell line 3D10H2 which secreted antiPthA-NLS McAb, and the variable region genes were amplified with specific primers by RT-PCR and SOE-PCR (splicing by overlap extension), and then the ScFv gene was isolated. The recombinant ScFv gene was cloned into pGEM-T and pET32a (+) vector. The later plasmid was transferred into E. coli BL21 (DE3) and the expression of the recombinant protein was induced. Thh cell lines producing monoclonal antibody again st PthA-NLS were acquired and named 1C8H1, 2D12B6, and 3D8A10. The recombinant ScFv gene of about 750 bp was constructed. The sequencing results showed that the ScFv gene consists of a 360 bp heavy chain, a 342 bp light chain, and a 45 bp linker region. The recombinant fusion ScFv protein was expressed by IPTG induction, and a 44.5 kDa of recombinant fusion protein was obtained. In conclusion, we obtained three cell lines stably competent monoclonal antibody specifically bound to PthA-NLS, and the relative ScFv gene was constructed and successfully expressed in E. coli. These results may play an important role in further understanding the pathogenesis mechanism and in the development of possible citrus resistant to canker disease by genetic transformation and plant antibiobody.