The maintenance of optimum conditions for growing of plants has always been in attendant by researchers. In nature each plant is attacked by the thousands of microorganisms but only small number of these microorganisms causes disease in plants. The coordination of different defensive reactions in contrast to pathogens results in stimulation of coping from many of defensive genes. One of the important group of these genes is in charge of coding the pathogens related protein. The importance of these proteins is especially because of their ability to fight on different kinds of microorganisms. Up to now, 17 groups of pathogenic proteins have been recognized in monocotyledon and dicotyledon plants. In 5th group of this II SK plus (pSK) vector and was transferred to E. coli XL1blue, E. coli MC1061. Then this gene was ligated to pBI121 vector and its cloning was done in E. coli XL1blue to increase the number of pBI121 plasmids containing TLP-3 gene and to enhance the possibility of having access to this plasmid in emergency condition. In the end the mentioned plasmid was transferred to Agrobacterium tumefaciens to transfer pBI121 plasmid containing gene to tobacco plant. After culturing the tissues of tobacco plant in MS medium, the leaves of this plant were used to cocultivating with A . tumefaciens containing pBI121. Then the explant were placed in MS medium containing 100 mg/l kanamaysin and 500 mg/l cefatoxime were used. The buds produced by callus containing the TLP-3 gene were transferred to a new medium after being separated. After enough growth of tobacco plants in in vitro condition, they were transferred to flower pot. In this stage the DNA extraction from transgenic plants was done and then the presence of TLP-3 gene in two forms of with and without signal peptide was proved through PCR test. Also RT-PCR test was don after the RNA extraction from the plants, and mRNA synthesis was confirmed the TLP-3 gene in two forms of with and without signal peptide. The extract of transgenic plants caused the TLP-3 protein power in preventing the growth of Alternaria alternata to reveal also. Doing green house researches also showed the performance of the gene containing signal peptide in prevent of pathogenic behavior of Alternaria . Key Words: Thaumatin- like gene, Signal peptide , Agrobacterium tumefaciens , Alternaria alternata.
