Pseudomonas syringae pv. tomato DC3000 (PstDC3000) is an important plant pathogen that infects tomatoes and Arabidopsis. Thiamine and its derivative thiamine pyrophosphate (TPP) are cofactors that play an important role in the growth and survival of many bacterial microorganisms. However, the role of thiamine-related genes has not been determined in PstDC3000. Hence, to investigate the role of TPP in growth, resistance to stresses, and virulence of PstDC3000, double and quadruple mutants of thiamine biosynthesis-related genes (thiD/E, thiS/G, and thiD/E/S/G deletion mutants) as well as a single mutant of a lipoprotein-related gene (apbE) were constructed. Our results showed that growth of the thiD/E, thiS/G, and thiD/E/S/G mutants in the mannitol-glutamate (MG) medium was significantly lower than that of the wild type (WT) and their growth could be restored to the WT level with the addition of exogenous thiamine, whereas mutation of the apbE gene did not affect its growth in vitro. While tolerance to acid, osmotic, and oxidative stresses for the double mutants was similar to the WT, tolerance to stresses for the apbE mutant was reduced as compared to the WT. In addition, all four mutants exhibited reduced virulence and growth in tomatoes. However, when the double and quadruple mutants were inoculated with exogenous thiamine, the virulence and growth rate of these mutants were restored to the WT level. These results indicated that the thiD/E, thiS/G, and thiD/E/S/G mutants exhibiting growth deficiency in planta are probably due to a lack of thiamine biosynthesis, thus reducing colonization in tomatoes. On the other hand, it is possible that the apbE mutant exhibited reduced stress tolerances, thus resulting in reduced colonization. Overall, our findings suggest that the thiamine biosynthetic (TBS) pathway plays an important role in the colonization and infection of PstDC3000. Therefore, the thiamine biosynthetic pathway could be used as the target to develop new control measures for a bacterial spot in tomatoes.

Pseudomonas syringae pv. actinidiae (Psa) is the causal agent of kiwifruit canker, a serious threat to commercial kiwifruit production worldwide. Studies of the movement path and the survival time of Psa in the host are crucial for integrated management programs. Hence, we used Psa with GFPuv gene (Psa-GFPuv) strain to investigate the movement path of Psa in leaves and branches, and the survival time of Psa in leaves under different environmental conditions. We found that the pathogen Psa spread longitudinally in the branches and leaves rather than transverse path. Additionally, the survival time of bacteria in fallen leaves under different environmental conditions were simulated by the way of Psa infecting the detached kiwifruit leaves. Psa survives the longest, up to 43 days in detached kiwifruit leaves with high humidity (above 80%) at 5 °C, and up to 32 days with low humidity (20%). At 15 °C, the Psa can survive in detached kiwifruit leaves for 20–30 days with increasing humidity. At 25 °C, it can only survive for 3 days with low humidity (20%) and 15 days with high humidity (above 80%). Furthermore, the population growth experiments showed that bacterial growth of Psa was more favorable in detached kiwifruit leaves with above 80% humidity at 5 °C. These results suggest that the survival condition of Psa in detached kiwifruit leaves is significantly affected by environmental conditions, and provide the basis for the control timing and technology of kiwifruit canker.