The Mechanism Of Helicoverpa Armigera Herbivory Affecting The Light Adaptability Of Tomato

In recent years,with the global warming and the expansion of human activities,the threat of plant diseases and insect pests to agricultural production is becoming more and more serious.Vegetable is the second largest crop in China,tomato(Solanum lycopersicum)has the advantage of higher planting income than the average level of vegetable and its annual output ranks first among vegetable crops worldwide.It would contribute to monitoring yield loss and innovating prevention technologies in agricultural production to explore the effects of herbivory on tomato growth and photosynthesis.Considering that tomato grew under fluctuating light intensity,this study was carried out to investigate the effects of Helicoverpa armigera herbivory on the growth and photosynthesis of tomato under sub-high light conditions,and to illuminate the roles of cyclic electron flow(CEF),Proton Gradient Regulation 5(PGR5),jasmonate(JA)signaling and Myelocytomatosis Protein 2(MYC2)in this process.In addition,the inhibition of sub-high light on tomato herbivory resistance was discussed.The main results are as follows:1.The effects of H.armigera herbivory on the sub-high light adaptability and the CEF of tomato were preliminarily determined.H.armigera herbivory inhibited the excitation of photoprotection under sub-high light conditions,with decreased nonphotochemical quenching(NPQ)and CEF,as well as degraded photosynthetic pigments and anthocyanin.As a result,it led to the intensified photoinhibition of photosystem II(PSII)and photosystem I(PSI)which was characterized by decreased PSII maximum quantum yield(Fv/Fm),PSII efficient quantum yield [Y(II)] and PSI reaction center P700 maximum oxidation level(ΔP700max),PSI efficient quantum yield [Y(I)],and finally restrained the growth and photosynthesis of tomato.Meanwhile,we found that the inhibition of H.armigera herbivory on CEF was related to PGR and NAD(P)H dehydrogenase complex(NDH)pathways.2.We found that PGR5 and CEF were involved in the inhibition process of tomato photoprotection caused by H.armigera herbivory under sub-high light conditions.Compared with wild type(WT)plants,pgr5 mutants showed inhibited CEF and failed to stimulate NPQ under sub-high light conditions,causing severe photoinhibition and even photobleaching with the photosynthetic parameters significantly decreased,such as net photosynthetic rate(Pn),Fv/Fm,Y(II),ΔP700max and Y(I).Furthermore,H.armigera herbivory did not intensify the photoinhibition degree of pgr5 mutants.3.We found that JA signaling and the transcription factor MYC2 were involved in the process of the CEF inhibition caused by H.armigera herbivory in tomato.Under both normal light and sub-high light conditions,JA signaling insensitive mutants jai1 and myc2 showed improved CEF when suffering H.armigera herbivory compared with WT plants.Further study showed that JA signaling inhibited CEF by influencing the gene expression of PGR5,PGR5 Like A1(PGRLA1),PGR5 Like A2(PGRLA2)and Orange Ripening(ORR),while MYC2 only had influence on PGR5 and ORR.Yeast one-hybrid analysis and dual-luciferase expression assays revealed that MYC2 bound to the promotor of PGR5 and negatively regulated its transcription.4.The mechanism of sub-high light suppressing the herbivory resistance of tomato was preliminarily explored.Sub-high light inhibited the herbivory resistance of tomato by blocking JA biosynthesis,showing as the decreased content of JA and jasmonoylisoleucine(JA-Ile),as well as the lower transcription levels of JA synthetic genes Lipoxygenase D(LOXD)and 12-oxo-phytodienoic Acid Reductase 3(OPR3).It led to the results that the gene expression of JA signaling induced protein Protease Inhibitor(PI-1,PI-2)and Threonine Deaminase(TD)was inhibited,and caused the body size and weight of H.armigera increased.Further study found that this process can be restored after the light intensity returning to normal.However,under sub-high light conditions,the increase of salicylic acid(SA)content and Non-expresser of Pathogenesis-related Genes 1(NPR1)transcription level were observed,implying that the antagonism between SA and JA might be involved in this process.In summary,our study revealed that H.armigera herbivory inhibited CEF through JA signaling,thus further impaired photoprotection,leading to photoinhibition and ultimately affecting the growth and photosynthesis of tomato under sub-high light conditions.Furthermore,the roles of PGR5 and MYC2 in this process were clarified.Finally,we explored the mechanism of sub-high light suppressing the herbivory resistance of tomato.