Mechanism Of Priming Of Tomato Resistance To Spodoptera Litura By β-Ocimene

Insects herbivory is an important factor restricting agricultural production and food security.Currently,agricultural production is suffering from the dual impacts of expanding the distribution of pests and increasing pesticide resistance caused by climate change.It is urgent to find ways to control crop pests using the unique defense characteristics of plants to achieve pesticide reduction and sustainable agricultural development.Herbivorous insect attacks can induce plants to produce herbivore-induced plant volatiles(HIPVs),which are typically mixtures of compounds derived from multiple biosynthetic pathways,mainly including terpenes,green leaf volatiles,and aromatic compounds,and may participate as physiological regulators in regulating plant growth and stress response.Previous studies have shown that volatile terpenes can prime resistance in healthy plants to herbivorous insects.However,the mechanism of terpene primed insect resistance in important crops such as tomato is still unclear.In this study,tomato(Solanum lycopersicum),an important economic crop,was used as the main plant,and Spodoptera litura(S.litura),a lepidoptera generalist pest,was used as the main insect.To study identification of effective terpene volatiles that prime insect resistance in tomato.Relationship between insect resistance induced by β-ocimene and various phytohormone signaling pathways in tomato.The main conclusions are as follows:(1)Infection with S.litura significantly altered the HIPVs metabolic profile of tomato.In order to identify HIPVs that can trigger insect resistance in healthy tomatoes,volatiles released from healthy tomatoes and tomatoes infected with S.litura for 24 and 48 hours were collected in headspace.Compared with the control,multiple monoterpenes and sesquiterpenes specifically induced by S.litura infection were detected by GC-MS analysis.Through OPLS-DA analysis,five volatile terpenes,including β-ocimene(βoci),myrcene,phellandrene,limonene and linalool,were selected that were significantly induced to release by the infection of S.litura.In addition,q PCR results showed that the key enzyme genes involved in the synthesis of related terpenes,such as TPS7,TPS25,and TPS5,were significantly induced by S.litura.(2)βoci exposure can significantly prime tomato resistance to S.litura.Using a dispenser to simulate the release rate of terpenes induced by insect pests in tomato,it was found that the effect of βoci on priming insect resistance in tomato was the most significant,and the primed insect resistance in tomato was maintained at least for 10 days after 24 hours ofβoci pre-exposure;In addition,βoci exposure treatment can prime insect resistance in most tomato varieties to varying degrees,such as ’cv.Castlemart’(CM),’cv.Moneymaker’(MM)and Micro-Tom(MT),but it cannot prime resistance in ’cv.Ailsa Craig’(AC),indicating that the insect resistance primed by βoci in tomato is related to the genetic background of tomato.(3)The insect resistance primed by βoci depends on the jasmonic acid(JA)signaling pathway in tomato.Quantitative analysis of phytohormones showed that compared to plants exposed to the corresponding solvent control,βoci exposure significantly promoted the accumulation of JA and JA-isoleucine(JA-Ile)contents in tomato leaves during 6 and 12 hours of infection by S.litura,while the contents of salicylic acid(SA)and abscisic acid(ABA)were not significantly promoted or inhibited;Similarly,q RTPCR results showed that the key genes involved in JA biosynthesis,LOXD and AOS,were significantly induced during 1 and 3 hours by S.litura infection after pretreatment with βoci pre-exposure.Using βoci preexposure to participate in phytohormone signaling pathway defects such as JA,ethylene(ET),SA,and ABA,it was found that in the JA synthesis defect mutant spr8,the insect resistance of tomato primed by βoci preexposure basically disappeared compared to the corresponding background wild type CM tomato;In the ET signal deficient mutant slein2-1 and the SA content deficient 35S::Nah G tomato,the insect resistance primed byβoci pre-exposure was inhibited to some extent.The above results suggest that JA plays a central regulatory role in βoci primed tomato insect resistance,while ET and SA may participate in fine-tuning of βoci-primed defense.In summary,this study found that in tomato,infestation by S.liturasignificantly alters the metabolic profile of volatiles in tomato.Among them,βoci specifically induced by insect herbivory can effectively prime defense to S.litura in healthy tomato,and this primed defense mainly depends on the JA signal pathway and may involve the synergistic regulation of ET and SA signaling pathways.Clarifying the important role of terpene volatiles βoci in priming insect resistance in tomato not only helps to deepen understanding of the role of HIPVs in regulating plantinsect interactions,but also provides a reference for the application of HIPVs in green control of crop pests and improving crop productivity.