Role of UV-damaged DNA-binding protein-1 (DDB1) in early response to Pseudomonas syringae pv. tomato DC3000 infection in tomato

Diseases caused by pathogens are one of the most important stress factors that affect crop yield and quality and plants have evolved a complex network of responses to infection. Tomato UV-damaged DNA-binding protein-1 (DDB1) has been implicated in playing a role in resistance against Agrobacterium infection. However, the effect of DDB1 protein on plant disease resistance is still largely unknown. Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) is an important pathogen of tomato and has been used as a model for testing disease susceptibility. In this work, we compared the sensitivity to Pst DC3000 among wild-type seedlings AC(+), DDB1-deficient mutants (hp1) and DDB1 over-expression (DDB1-OE) seedlings. Results showed that the hp1 mutant is more susceptible to Pst DC3000, whereas the resistance was increased in the DDB1-OE seedlings. Hydrogen peroxide, the key component of the plant defence response and the corresponding cell death phenotype were compromised in the hp1 mutant and enhanced in the DDB1-OE plants. Consistent with that, salicylic acid production and PR1a1 gene expression were positively regulated by the DDB1 gene upon infection with Pst DC3000 at 24h after inoculation. Other pathogenesis-related genes (Gras2, Lrr22, Pti5, Wrky28 and mitogen-activated protein kinase 3) were also induced in the DDB1-OE plants but compromised to different degrees in the hp1 mutant. Overall, this study suggests that DDB1 plays a regulatory role in tomato defence responses likely through modulating SA-associated signalling pathways.