The Effects And The Mechanism Of Exogenous Resistance-related Signal Molecule On Root-knot Nematode Infection Of Tomato Plants

Facility agriculture has been an important component of modern agriculture in China during recent years, it plays fundamental role in non-staple food supply and in raising people’s living level throughout our country. However, with the increase of cultivar years, many years of planting sole crop with high financial benefit often result in widespread continuous cropping problems, one of which is that caused by root-knot nematode. According to statistics data, root-knot nematode killed20%vegetables grown in greenhouse and reduced80%productivity in north of China, thus both the quantity and quality of greenhouse vegetables production were severly affected by root-knot nematode, and this problem has been the one in urgent to be solved. Up to now, there are several methods for root-knot nematode control, such as chemical control, physical control, biological control, agronomic measure and using resistant varieties. Different methods have their advantages and disadvantages, effective and convenient means are necessary to solve these problems.Phytohormones and signaling molecules, such as jasmonic acid (JA), salicylic acid (SA) and nitrogen oxide (NO), not only play role in regulating plant growth and development, but also are important in signaling pathway of resistance to environmental stresses. In this study, tomato cultivar Zheza205(Solanum lycopersicum L. cv. Zheza205) was used to explore the alleviatory effects of exogenous JA, SA and NO on root-knot nematode infection of tomato plants and the underlying mechanism involved. Main results are listed as following:1, Using susceptible tomato cultivar Zheza205(Solanum lycopersicum L. cv. Zheza205) as the plant material, we have studied the alleviatory effect of foliar application of JA, SA and NO on root-knot nematode infection of tomato plants.36days after inoculation with RKN, we measured root-knot number, plant growth, leaf photosynthesis, chlorophyll fluorescence parameters, the electrolyte leakage and the membrane lipid per-oxidation. The results showed that foliar application of100uM JA,2000uM SA and250uM NO can relieved the damage of root-knot nematode to some extent. When compared to the RKN inoculated control plants without any chemical treatment, root-knot number, the relative electrolyte leakage, and the membrane lipid per-oxidation were significantly reduced by application of JA, SA, and NO.while the photosynthetic capacity, Fv/Fm, and plant biomass were evidently increased. The alleviatory effect of JA is more evident than that of SA and NO. Additionally, the three signal molecules, especially JA significantly increased the relative expression of Mi, which might be involved in the anti-RKN process by the three signal molecules.2, The above results indicated that exogenous JA, SA and NO have the effect of relieving the RKN-induced damage to tomato plants. In the present study, we analyzed the effect of three signal molecules’foliar application on expression of key resistant genes involved in JA, SA and NO signalling pathway and content of signal molecules in roots of tomato in response to RKN inoculation.24days after inoculation, the transcripts PⅠ Ⅱ gene in JA signaling pathway was significantly increased by both RKN inoculation and application of JA, SA and NO. By contrast, PR-1gene induction in SA pathway is only increased in the SA/M.inco treatment. Eventhough content of free SA was up-regulated in RKN-inoculated plants they are similar among JA/M.inco, NO/M.inco and M.inco alone treatments. Expression level of secondary signaling gene of NO-GSNOR and it’s important synthesis-related gene-NR and content of endogenous NO are up-regulated to some extent only in the treatment of NO/M.inco, while other treatments does not have this effect. Accordingly, we speculated that the involvement of SA and NO in resistance to RKN might be related with JA signaling pathway, and PⅠ Ⅱ gene of JA resistant pathway might play an important role in this process.3, To examine whether SA-and NO-induced resistance to RKN was related with JA signaling pathway, the endogenous NO and PⅠ Ⅱ gene were down-regulated by cPTIO, and virus-induced gene silence, respectively. Experimental results showed that scavenging NO accumulated in tomato by cPTIO does not affect the resistant effect of exogenous JA and SA on RKN infection. By contrast, when PⅠ Ⅱ gene of JA signalling pathway was inhibited by VIGS, there was a significant increase in nematode infecting tomato root and an obvious inhibition in the resistant effect of exogenous JA, SA and NO on root-knot nematode. In PⅠ Ⅱ gene silencing plants, root-knot number and photosynthesis have a similar performance among the combined treatments of JA/M.inco, SA/M.inco, NO/M.inco and M.inco alone. Root-knot number of these treatments were all significantly higher than TRV control plants. These results clearly indicated that resistant effect of JA, SA and NO alleviating root-knot nematode’s damage on tomato are related to PⅠ Ⅱ element of JA pathway.