Expression of aiiA gene in potato and its effect on the control of bacterial soft rot disease

Quorum sensing is a unique cell-cell communication of bacteria with production of diffusible small signal molecules such as acyl-homoserine lactones (AHLs). This phenomenon regulates the important functions including motility, antibiotic and pigment production, biofilm formation and production of virulence determinants in many bacteria. A potential aiiA homologue gene from Bacillus sp. DMS133 was PCR-amplified using specific PCR primers aiiA-7 F and aiiA-7R. To study the effect of aiiA expression in potato plant, the aiiA gene was sub-cloned into binary vector, pBI121, under the control of the constitutive CaMV35S promoter to give pBI121/aiiA. The resulting plasmid was heat/shock transformed into Agrobacterium tumefaciens LB4404 and introduced into potato explants through the node and internode culture in modified MLS medium. In bioassay, the modified genetically potato plants were inoculated with Pectobacterium carotovorum suspension at 106 CFU. The results suggested that the expression of AiiA lactonase in potato plant caused the moderate resistance against soft rot bacterium. Transgenic plants showed slightly soft rot disease symptoms at five days after inoculation, while the wild type plant showed sever symptoms. Four days after inoculation, transgenic plants still grew a healthy and without symptoms, and after this period, they showed yellowing with low growth symptoms. It seems that lactonase expression in potato causes resistance against the beginning stage of bacterial infections. However with continuing disease conditions, transgenic plants also suffered infection and the early stage symptoms (without soft rot) of disease were observed.