Role And The Underlying Mechanism For Tomato Mitochondrial α-KGDH-E2 In Defense Against Leaf Speck Disease

In recent years,the disease area of vegetable crop gradually increased and the damage greatly weakened the economic value and then threated the country’s agricultural production safety.Bacterial leaf spot is one of the important bacterial diseases in tomato,which usually leads to 10%～30%reduction of vegetable crops and even more than 50%reduction of vegetable crops.Therefore,it is of great significance to analyze the response of vegetable to bacterial leaf spot and the defense mechanism which can explore the path of environment-friendly disease-resistance regulation.In recent years,studies have suggested that mitochondrial respiration plays a role in plant disease resistance,but the mechanism is far from clear.In this paper,the response of Sla-kGDH E2 to tomato bacterial leaf spot(P.syringae pv.tomato DC3000)was studied in the tomato mitochondrial TCA cycle by using tomato(Solarium lycopersicum),and we also used the methods of gene silencing and gene overexpression to explore the role and mechanism of signal transduction in leaf spot infection.The main findings are as follows:1.The responses of mitochondrial respiration and its related genes in leaf speck disease were studied.The transcript levels of TCA cycle and mitochondrial electron transfer in tomato leaves were studied after inoculation with Pst DC3000.The contents of salicylic acid(SA)and the lipoylated level of Sla-kGDH E2 protein in tomato leaves were studied.The results showed that the α-KGDH gene in the TCA cycle gene was down-regulated,the A OX gene was up-regulated and the expression of SA gene and its resistance gene were significantly increased after inoculation with Pst DC3000.It is presumed that Sla-kGDH E2 may play a role in the process of tomato defense Pst DC3000.2.The effect of mitochondrial α-KGDH-E2 on defense leaf speck disease and its relationship with alternation electron transport and salicylic acid resistance pathways were studied.The silencing of α-KGDH-E2 and AOX gene and the overexpression of tobacco plants were carried out.After inoculation with Pst DC3000,the silencing of Slα-kGDH E2 and the co-silencing of Slα-kGDH E2/AOX gene plants had more significant defense compared with TRV:0 plants.the AOX-silenced plants had no significant difference compared with the TRV:0 plants.Similarly,the overexpressing of the Slα-kGDH E2 plants significantly increased the resistance to Pst DC3000 compared to the control plants.The results showed that SA could not further enhance the disease resistance of the Slα-kGDH E2 silencing plants,but it could eliminate the disease resistance of the Slα-kGDH E2 overexpressing plants.The results showed that the expression of Slα-kGDH E2 subunit was inhibited by SA.Therefore,it is thought that SA may prevent Pst DC3000 infection by inhibiting the activity of Slα-kGDH E2 subunit,but the pathway of AOX didn’t take part in this resistance process.3.Further studies on the regulation and function of mitochondrial a-KGDH-E2 protein in defense against leaf speck disease were carried out.In this chapter,the key gene LIP2,which regulates the lipoylation of Slα-kGDH E2 subunit,was silenced and the lipoylated level of Sla-kGDH E2 protein was significantly decreased after LIP2 and Slα-kGDH E2 gene silencing plants were inoculated with Pst DC3000.The resistance to Pst DC3000 were significantly enhanced in the plants LIP2 silencing plants and Slα-kGDH E2/LIP2 co-silencing plants.The contents of oxidized protein and ROS in these plants were also significantly decreased post-inoculation with Pst DC3000.Therefore,it is thought that the lipoylation of LIP2 gene to Slα-kGDH E2 subunit may be involved in the path of defense of tomato against Pst DC3000.