Abstract: 【Background】In recent years, tomato diseases occur frequently in open field and protected cultivation due to the suboptimal environmental conditions. Tomato bacterial leaf spot caused by Pst (Pseudomonas syringae pv. tomato) is a common bacterial disease, which severely affects the yield and quality of tomato. Sugar is an important signaling molecule as well as nutrient substance in plants. When plants are subjected to pathogen attack, sugar not only functions as a signal to regulate the plant defense, but also provides energy for immune responses as a main carbon source. STP (sugar transport protein) family is responsible for the sugar transport, and play an important role in plant growth, development and defense.【Objective】The objective of this study is to clarify whether STP family are involved in the regulation of plant defense against bacterial leaf spot.【Method】CR (Solanum lycopersicum cv. Condine red) was used as the wild-type (WT) background in this study. The responses of STP gene family to Pst DC3000 were determined by Pst DC3000 inoculation. The SlSTP2, which was up-regulated most significantly after Pst DC3000 inoculation, was selected for futher investigation. The Slstp2 homozygous mutant and overexpression materials were generated. To explore the role of SlSTP2 in plant defense against Pst DC3000, WT and slstp2 mutants, OE:SlSTP2 plants were inoculated with Pst DC3000, then the disease symptoms were assessed by disease-associated cell death and bacterial growth as well as the photochemical efficiency. In order to explore the potential mechanism of SlSTP2 in the disease resistance, the interacting proteins were screened by bimolecular fluorescence complementary assay. The mutant material and overexpression materials of candidate interacting protein was generated and inoculated with Pst DC3000 to investigate its role in plant defense against bacterial leaf spot. 【Result】After inoculation with Pst DC3000 on tomato plants, the expression of SlSTP1 and SlSTP2 were up-regulated. SlSTP2 was up-regulated most significantly, so it was selected for futher investigation and its mutant and overexpression material was generated. WT and Slstp2 mutants, OE:SlSTP2 plants were subjected to Pst DC3000 inoculation. Compared with WT plants, Slstp2 mutants showed significantly increased susceptibility, as evidenced by more severe disease symptoms, increased disease-associated cell death, an enhanced bacterial population and a decreased photochemical efficiency in the leaves. On the contrary, OE:SlSTP2 plants showed enhanced defense against Pst DC3000 compared to WT plants. It was further found that SlSTP2 interacted with the G protein β subunit SlAGB1 using bimolecular fluorescence complementary assay. Similar to the Slstp2 mutants, the Slagb1 mutants also showed significantly increased susceptibility to Pst DC3000 compared with WT plants, and OE: SlAGB1 plants showed enhanced defense against Pst DC3000 as OE: SlSTP2 plants.【Conclusion】SlSTP2 is significantly induced by Pst DC3000 inoculation, and positively regulates the defense against Pst DC3000 in tomato. SlSTP2 interacts with SlAGB1, which also plays a positive role in defense against bacterial leaf spot, suggesting that SlSTP2 associated with SlAGB1 regulate tomato resistance to bacterial leaf spot.

Key words: Solanum lycopersicum, sugar transport protein, SlSTP2, bacterial leaf spot, disease resistance