Abstract:In order to study the function of TasA gene of biocontrol bacteria Bacillus CQBS03 which was isolated from citrus leaf and had bacteriostasis activity to Xanthomonas citri citri, the full-length DNA sequence encoding TasA gene was amplified from Bacillus CQBS03 genomic DNA by PCR. After that, we constructed the prokaryotic expression vector pEASY-E1/TasA and expressed in Escherichia coli BL21. The antagonism of the expression fused protein to X.citri citri was tested with filter paper-petri dish method. The sequencing result showed that full-length DNA sequence of TasA gene included a complete ORF of 786 base pairs, (GenBank accession number JQ309841), which encoded 261 amino acid residues. The TasA gene of CQBS03 had a high sequence similarity with TasA gene of Bacillus amyloliquefaciens (as high as 99.75%). A 31 kD fused protein was obtained from mutant E.coli BL21-pEASY-E1/TasA cells. Fused protein of TasA gene purified by Ni-NTA chromatography revealed obvious antibacterial activities to X.citri citri, and the diameter of antagonism zone reached 11.5 mm after 72 hours. The results proved that the TasA gene was one of the most efficient antagonism function genes of bacteria CQBS03, and it can be used in citrus canker biocontrol.