| Tomato is a significant industry of vegetable production in our country,which has become an important producer and exporter of tomato products in the world.Facility cultivation techniques are widely adopted in large areas,leading to a great concern on various diseases of viruses,fungi and bacteria.This restricts the sustainable development of the tomato industry.Bacterial wilt is a devastating disease in tomato cultivation,causing a serious problem in southern China,especially in Fujian Province.The soil-born Ralstonia solanacearum is responsible for tomato bacterial wilt,and invades into xylem through root wounds.After that,it replicates very quickly in xylem and causes the wilt and death of tomatoes.R.solanacearum infection shows suppression effect on root development,accompanied by a decrease in auxin synthesis.It has been reported that the type III secretion system of R.solanacearum plays an important role in Arabidopsis root development.In this study,the tomato plant was used to study the suppression effect of R.solanacearum on root development.The mutant strains stored in our laboratory were used to analyze the potential mechanism of inhibiting tomato root development;a co-relationship between root development and variety resistance was additionally studied.The main research progress of this thesis are as follows:(1)The type III secretion system mutant Δhrp B showed enhanced inhibitory effect on root development in the susceptible tomato variety Hongyangli.The average root length of the tomato seedlings receiving water treatment control was 4.3 cm long at 5 days after inoculation.In contrast,the average root length of the wild type-treated tomato seedlings was only 1.6 cm.The average root length of tomato treated with hrp B mutant was 1.2 cm.The hrp B gene mutant promoted the inhibitory effect on tomato root development.To examine whether the inhibition is related to the type III secretion system,the roots of Hongyangli were treated with NADH ubiquinone oxidoreductase F subunit mutant Δnuo F and oxidoreductase mutant ΔRSc0454.The results showed that the inhibition rate for each mutant is close to 50%,similar with wild type.(2)To explore the relationship between inhibition rate and variety resistance,the resistant variety Zhongshusihao was selected for experiment.Although the R.solanacearum strains used here were able to inhibit the root development of Zhongshusihao,the inhibition rate is significantly lower than that of the susceptible Hongyangli.Different inhibition efficiency was found between resistant Zhongshusihao and the susceptible Hongyangli.This suggested that R.solanacearum shows great inhibitory effect on susceptible tomato varieties,and weaker on the resistant varieties.(3)The inhibitory effect on root development reflects the situation within 5 days after inoculation,which belongs to the early stage of R.solanacearum infection.In order to understand the late infection stage in Zhongshusihao and Hongyangli,Δhrp B,Δnuo F,and ΔRSc0454 were labeled with GFP so as to study the diffusion rate in tomato tissue by means of stem inoculation.The results showed that R.solanacearum strains showed distinctive difference in spreading in the stems of susceptible Hongyangli and resistant Zhongshusihao.In either Hongyangli or Zhongshusihao,wild-type GMI1000 was spread the fastest.Followed by Δhrp B,ΔRSc0454 and Δnuo F moved the slowest.(4)In order to understand the special effect of hrp B on root inhibition,transcriptome was conducted to study the differentially expressed genes in Hongyangli inoculated with wild-type GMI1000,Δhrp B and the complemented CΔhrp B.In the tomato roots inoculated with Δhrp B,72 genes were down-regulated and 12 genes were up-regulated.The down-regulated genes included 4 genes related to ethylene signaling,3transcriptional regulators,and 2 receptor genes.Among the up-regulated12 genes,some of them are involved in cell cycle control and ion transport. |
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