Regulation Of Tomato Resistance To Spodoptera Litura By Cytokinin And Its Glycosylation Modification

Insect pests cause huge losses to crop production and are an important factor restricting agricultural production and food security.Enhancing crop resistance to pests is crucial for reducing pesticide application and sustainable agricultural development.The defense response of plants to herbivorous insects depends on a complex regulatory network of hormone signals.The jasmonic acid（JA）signaling plays a central role in plant resistance to chewing insects by coordinating other hormone signaling pathways such as ethylene（ET）,abscisic acid（ABA）,salicylic acid（SA）,and auxin.Cytokinins（CK）are N₆substituted adenine derivatives that play an important role in regulating plant growth and development,leaf senescence,and immunity.Therefore,they are widely used as plant growth regulators.Recent studies have shown that endogenous CK are also involved in regulating plant defense responses to herbivorous insects.However,it is still unclear how exogenous and endogenous CK affect plant resistance to herbivorous insects.This study can provide reference for CK to control pests and improve crop production in the process of production practice.In this study,tomato（Solanum lycopersicum）,an important economic crop,was used as the plant material,and Spodoptera litura,a lepidoptera generalist pest,was used as the insect pest to study the effects of exogenous CK or CK signal defects on tomato defense against insect herbivores,and effects of CK and their glucosylation modification on insect resistance in tomato.The main results are as follows:（1）CK signaling was involved in regulating tomato resistance to S.litura.The weight gain of S.litura larvae feed on tomato sprayed with exogenous natural trans-zeatin（t Z）or synthetic cytokinin（BAP）was significantly higher than that of the control group sprayed only with corresponding solvents;The inhibitory effect of external application of t Z on tomato insect resistance was concentration dependent,with 100μM was the most significant;Tomato CK receptor histidine kinase Sl HK4gene is expressed in various tissues of tomato;In the Sl HK4 deficient mutant slhk4,most genes related to CK signal transduction pathway were downregulated,indicating that Sl HK4 is involved in CK signal transduction in tomato;Bioassay results showed that mutations in the Sl HK4 gene led to significantly enhanced tomato resistance to S.litura,and higher accumulation of secondary metabolites related to insect resistance such as steroidal alkaloids（SGAs）and phenolic acids（PA）in slhk4.（2）Insect herbivory by S.litura significantly changed the metabolism of endogenous CK in tomato.The results of CK metabolism in tomato leaves after simulated herbivory（WOS）treatment showed that the main active CK,including t Z,c Z,and c ZR,were significantly downregulated at 1 h of WOS treatment,while the content of inactive t ZOG increased by 20.8%and 85.6%at 1 h and 3 h of WOS treatment,respectively.In order to investigate whether O-glycosylation modification of t Z affects tomato insect resistance,hmmsearch was used to identify the genome-wide of tomato GT1s family genes,and 182 putative UDP-glucosyltransferases（UGTs）were screened;Two candidate UGT genes,UGT85A126 and UGT93Z1,were obtained by analyzing phylogenetic and herbivory-induced expression patterns;Prokaryotic expression and in vitro enzymatic experiments verify that UGT85A126can catalyze t Z to produce t ZOG.（3）In order to determine the role of UGT85A126 in regulating endogenous CK metabolism and insect resistance in tomato,tomato materials with UGT85A126 overexpression and VIGS silencing,as well as Arabidopsis materials with UGT85A126 heterologous overexpression,were constructed.The bioassay showed that the body weight gain of S.litura fed on UGT85A126 gene overexpressed tomato or Arabidopsis was significantly higher than that of the wild-type control,while there was no significant difference in insect resistance between the VIGS silenced tomato p TRV:UGT85A126 and the control p TRV1+2.The regulatory effect of UGT85A126 gene on CK metabolism and insect resistance in tomato needs further research.In summary,this study found that in tomatoes,CK signaling negatively regulates the tomato resistance to S.litura,which may depend on the CK receptor Sl HK4;Endogenous CK metabolism in tomato is significantly affected by insect herbivory,and UGT85A126 mediated active t Z-glycosylation modification may play an important role in tomato defense against S.litura.Clarifying the important role of CK and its mechanism in regulating plant defense against herbivorous insects not only helps deepen understanding of plant-insect interactions,but also provides a reference for using CK to regulate plant growth-defense balance and improve crop productivity.