Agrobacterium tumefaciens, a pathogen of several dicot plants is a ble to deliever a piece of $DNA$ to transform normal plant cells into a tumor and direct these cells to produce the chemicals required by the pathogen. Agrobacterium tuma faciens contains a plasmid called $Ti$-plasmid. This has a $T-DNA$ region flanked by left border and right border sequence. The $T-DNA$ gets transferred and integrates with the host plant $DNA$. This property of $Ti$-plasmid has been exploited for cloning of gene of interest and stably integrating them in the plant genes. Therefore, by using Ti-plasmid or its derivatives, recombinant plant cells with desired genes of interest stably integrated in the plant genome has been successfully produced. Agrobacterium tumefaciens transfers its genes without human efforts and so is also called as natural genetic engineer of plants.