Changes In Glucosinolate Concentrations And Differentially Expressed Genes In Response To Spodoptera Exigua (H(?)bner) In Brassica Juncea

Glucosinolates(GS)are a typical class of defense compounds in cruciferous plants.Under the action of transporters,glucosinolates in the plant form a non-uniform distribution,and the more vulnerable parts accumulate higher glucosinolates concentrations.Specific glucosinolate components are important insect-resistant traits in Brassica juncea,and degradation products of the glucosinolates in mustard elicit lethal effects on larvae.However,the patterns of variability in glucosinolate content and the defense response mechanism mediated by glucosinolates in B.juncea eaten by pests has yet to be reported.In this study,We detected the glucosinolate content and composition of Brassica juncea in different tissues,either at different growth stages,or in dieffernt position of leaves,the physiological and ecological significance of the distribution of glucosinolate in B.juncea was briefly discussed.In addition,the resistance mechanism mediated by glucosinolates in mustard consumed by the omnivorous pest beet armyworm Spodoptera exigua(Hübner)was investigated.The main results of this study are as follows:(1)There were significant differences in the glucosinolate content and composition in B.juncea root and leaf.The total glucosinolate composition in the leaves decreased gradually during the growth from cotyledon stage to the 16-leaf stage,however,there was not significantly different in total glucosinolate composition after the 8-leaf stage.Sinigrin was the main glucosinolate in the B.juncea leaves.In contrast,total glucosinolate composition in the roots increased gradually during the growth from cotyledon stage to 16-leaf stage.Gluconasturtiin was detected in the roots but not found in the leaves,and gluconasturtiin in roots was the highest content of glucosinolate in the 8-leaf stage,and sinigrin in roots is the highest content of glucosinolate in the12-leaf and 16-leaf stage.(2)The analysis of the glucosinolate composition in different leaf positions of 9-leaf leaf stege showed that the higher glucosinolate composition in the more fresh leaves.(3)Total glucosinolates composition were not apparently changed after 1 h of feeding,but increased significantly after 24 h feeding by the insects(by 24.7%)(P < 0.05).Aliphatic and indole glucosinolates were enhanced after 24 h feeding by 22.1% and 239.4%,respectively.Sinigrin which accounts for about 96.0% of the total glucosinolates(P < 0.05)increased by 20.08% in the 24 h group(P < 0.05).Gluconapin also increased significantly after feeding.We found that all of indole glucosinolates were significantly increased except for 4OHI3 M after 1 h of feeding,with the increase of I3 M being the largest.(4)Transcriptome analysis revealed 20.7,20.6,and 20.0 million clean reads from the three samples(CK,1 h,and 24 h).A total of 60,948 unigenes were assembled from the clean reads and 40,580 unigenes were annotated on the basis of the similarity to those genes documented in seven databases.The expression of 53 genes related to glucosinolate synthesis,degradation,and transport was almost completely upregulated.The expression levels of genes related to the signal hormones JA,ET,and SA involved in plant defense also increased.JA genes were significantly upregulated at 1 h post treatment,and the response intensity of these genes was significantly higher than that of ET and SA genes at 1 and 24 h post treatment.Our experiments provided a basis for further studies on the mechanism of gluocosinolatemediated insect resistance and the function of key genes related to glucosinolate metabolism in plants.