Abstract: According to the tomato expression database（http：//ted.bti.cornell.edu/cgi-bin/）and real-time quantitative analysis，the sugar transporter（sugars will eventually be exported transporter）gene SlSWEET12c showed the most obvious expression difference in tomato susceptible and resistant varieties. Using the tomato（Solanum lycopersicum）plant‘Zhongshu 6’as the test material，stable genetic SlSWEET12c silencing（RNAi）and overexpression（OE）plants were obtained. After further inoculation with Pseudomonas syringae（Pst DC3000），the role of SWEET12c in resisting Pst DC3000 in tomato was clarified through the analysis of bacterial growth，Fv/Fm change，soluble sugar and starch content，reactive oxygen species accumulation，defense enzyme activity and PR protein related gene expression in leaves. Compared with the wild type，the number of bacterial colonies and brown spots were significantly reduced in the leaves of RNAi-SlSWEET12c plants vaccinated with Pst DC3000，and the resistance to Pst DC3000 was enhanced，while OE-SlSWEET12c leaves became more severe，and the number of bacterial colonies and brown spots increased. RNAi-SlSWEET12c plants have significantly higher sucrose and starch content than wild type，reactive oxygen accumulation is less than wild type，the activity of defense enzymes （POD，SOD，APX）and PR protein related genes（NPR1，PR1，PR2，PR5）expression，while the sucrose and starch content of OE-SlSWEET12c plants is lower than wild type，reactive oxygen accumulation is higher than wild type，defense enzyme activity and PR protein related gene expression is significantly lower than wild type. The above results indicate that SlSWEET12c negatively regulates tomato resistance to bacterial leaf spot disease by affecting the composition of sugars in leaves.

Key words: tomato, sugar transporter, bacterial leaf spot disease, SlSWEET12c