Role And Mechanism Of Photorespiration In Defense Against Pseudomonas Syringae In Solanum Lycopersicum

Tomato (Solarium lycopersicum L.)is one of the largest cultivation area of vegetable varieties, the global tomato production at 2010 reached146 million tons. However the pests and diseases are important biological stresses which limit the growth, quality and yield in green house. Bacterial diseases can be some of the most serious and destructive diseases. Most common, bacterial spot disease occurred by Pseudomonas syringae pv.tomato strain DC3000 which causes symptoms in tomato leaves, stems, flowers, petioles and fruits occurred widely in Liaoning, Fujian, Inner Mongolia, Xinjiang, Guangxi, Hebei, Gansu, Jilin province in China, leading to 5%-75% of the yield loss. The study of pathogen-resistant mechanism in plant has been regarded as an important role in enhancement of plant resistance to pathogen and the reducing of chemical fungicides utilization. Recent researches demonstrated that photorespiration played an important role in regulation of photoinhibition, amino acid content and response to stresses. In this study, tomato cultivar Zheza 205(Solarium lycopersicum L. cv. Zheza 205) was used to explore the effect of photorespiration on Pst DC3000 infection and further study the mechanism involved. The results were as follows.1. Tomato cultivar Zheza 205(Solanum lycopersicum L. cv. Zheza 205) was used to study the effect of spraying photorespiration inhibitor on tomato against Pst DC3000. Different concentrations of photorespiration inhibitors NaHSO3 and INH were sprayed as treatment on tomato plants and photorespiration, glycolate oxidase activity (GOX)and FV/FM were consequently measured. INH treatment significantly reduced GOX activity and photorespiration without affecting normal growth of plants, therefore 0.2g/L was selected as the dose of INH treatment. Compared to plant pretreated with water, Pst DC3000 resulted in significantly higher susceptibility and more symptoms including more dead cells, higher electrolyte leakage and CFU in INH pretreated plants. Meanwhile, H2O2 pretreatment remarkably alleviated symptoms of Pst DC3000. INH plus H2O2 treatment could recover the resistance to the similar level as water pretreated plants. The results of H2O2 content, the SA-related gene expression, antioxidant genes expression indicated that H2O2 generated during photorespiration as a signal substance may play a role in the defense to Pst DC3000.2. The effect of photorespiration on tomato against Pst DC3000 and mechanisms involved was further studied. Glycolate oxidase (GOX) which is a key genes in photorespiratory pathway, serine:glyoxylate aminotransferase(SGT) and Serine hydroxymethyltransferase (SHMT) were silenced hiring tomato virus-induced gene silence (VIGS) system, and H2O2 were sprayed on genes silenced plants as pretreatment as well as water. In water pretreated plants, more severe symptoms including elevated CFU and electrolyte leakage was observed in all three lines of gene silenced plants as compared with TRV:0 plants. Meanwhile H2O2 pretreatment led to the up-regulation of genes encoding antioxidant enzymes and involved in SA signaling as well as the elevation of resistance to Pst DC3000 in GOX silenced plants, but no noteworthy changes of the same index in SGT or SHMT silenced plants. These results indicated that H2O2 may mediate resistance to Pst DC3000 in GOX silenced plants, whereas SGT and SHMT may modulate the resistance via affecting SA accumultion.3. Tobacco transient expression system was hired to probe in the role of tomato GOX, SGT, SHMT in defense against Pst DC3000. The vector carrying GOX, SGT, SHMT was conducted. The protein expression was examined via western blot at 36 hours post the infiltration of agrobacterium in tobacco fully expanded leaves. Results showed that as compared to EV plants, increased resistance to Pst DC3000 exhibted in all three lines of protein transiently expressed tobacco plants post water pre-injected but not in H2O2 pretreated plants. Compared to water injected plants, significantly increased susceptibility was only observed in GOX transiently expressed plants, not in SGT, SHMT transiently expressed plants after the injection of H2O2 scavenger dimethylthiourea (DMTU). Our data implied that H2O2 may be involved in GOX mediated defense against Pst DC3000 of transient expression plants, whereas other pathways of modulating the resistance may exist in the SGT and SHMT silenced plants.