Defense Response Study in Oilseed Rape (Brassica napus L.) in Response to Beet Armyworm Spodoptera exigua

Abstract

In the Brassicaceae family, a glucosinolate-myrosinase-based system exists against herbivory Glucosinolate-Myrosinase system is differentially compartmentalized but substrate glucosinolate enter in contact with the enzyme myrosinase when plant tissues are attacked by insects. The glucosinolate breakdown into a variety of biologically active toxins further deterrenting the herbivory of different chewing and sucking insect pests. The myrosinase enzyme present is in myrosin cells were genetically removed from B. napus plant during the seed development. These genetically modified myrosin cells free plants are known as MINELESS plant. Genetically modified oilseed rape (Brassica napus) was produced by removing toxic mines. Here, we evaluauted the tritrophic interaction between Brassica napus wildtype and genetically modified and polyphagous pest Spodoptera. In force feeding experiment, larval growth of S. exigua was slow and gained less weight on MINELESS seedlings as compared to wild-type seedling. Additionally, highest amount of total glucosinolate was found in MINELESS control than that of wild type control. Myrosinase activity was not affected by the S. exigua feeding on the MINELESS plants. However, reduced activity of myrosinase was observed in the wild-type seedlings. Moreover, the S. exigua induced the concentration of tryptophan derived glucosinolate (indol-3-yl-methyl, 1-methoxy-indol-3-yl-methyl) that was found slightly higher in MINELESS seedlings than on wild-type seedling. Feeding of S. exigua deregulated the level of glucosinolate hydrolysis products in both types of plants. Transcriptional data after S. exigua feeding on wildtype and MINELESS showed differential response of methyl jasmonate and glucosinolate responsive genes were observed. We also observed that after methyl jasmonate treatment, methyl jasmonate and glucosinolate responsive genes were incease in the wild-type and MINELESS seedlings showing their negative effect on the growth of S. exigua. Overall, generalist insect results are interesting by considering the function of myrosin cells and binary defense system. Further, same experiment should be performed against generalist and specialist insect herbivores of above- and below-ground.