Keywords: 
• hpaXm /
• transgenic tobacco /
• hypersensitive response（HR） /
• TMV resistance

Abstract: HpaXm,cloned and identified from Xanthomonas citri subsp. malvacearum,is a new class of harpin proteins. Tobacco（ Nicotiana tobacum‘Xanthi nc’） was transformed with HpaXm through Agrobacterium-mediation,and the resultant transgenic tobacco plants were subjected to molecular identification and protein activity assay to study the effect of the endogenous expression of hpaXm in the transgenic tobacco. The target gene and the 35 S promoter sequences were detected by PCR,and the target genes sequences were detected by Southern Blot hybridization in the genome from the T1 line positive transgenic plants,indicating that the hpaXm gene had already been integrated into the recipient genomes. Reverse transcriptase PCR indicated that the transferred genes were expressed normally in the transgenic plants. Soluble proteins extracted from plants which had been transformed with hpaXm could stimulate hypersensitive response on tobacco leaves,indicating that hpaXm expressed in transgenic tobacco plants are bioactive. Although the endogenous expression of hpaXm failed to make a large area visible necrotic spots,but the phenomenon of micro-allergic reactions was observed after trypan blue staining. Constitutive expression of hpaXm in transgenic tobaccos conferred defense responses to TMV. The study would provide a scientific basis to explore the biological characteristics of transgenic plants induced by hpaXm.