Activation of plant defence in Brassica napus L. cv. Westar and transgenic MINELESS plants after attack by Mamestra brassicae (cabbage moth)

Plants within the Brassicaceae family have a unique defence mechanism known as the “glucosinolate-myrosinase” system. Upon tissue disruption by insect herbivores, glucosinolates are hydrolysed by the enzyme myrosinase (EC 3.2.1.147) into a variety of degradation products, which can deter insect herbivory. This process has been termed as “The Mustard Oil Bomb”. Seeds of Brassica napus have been genetically modified to remove myrosinase containing myrosin cells. The modified plants have been named MINELESS due to a lack of toxic mines in seeds. This study aimed to get insights into defence responses of B. napus wild-type and MINELESS seedlings, after being challenged by larvae of the generalist herbivore Mamestra brassicae. The microarray analysis showed 494 and 159 genes to be differentially regulated after M. brassicae feeding on wild-type and MINELESS seedlings, respectively. Many of the observed transcriptional responses i B. napus and the MINELESS mutant are related to those found in Arabidopsis thaliana plants when they are exposed to insects. Mamestra brassicae larvae were maintained and propagated on wild-type (Brassica napus) and MINELESS (Brassica napus) seedling for 10 days. The 10-days old M. brassicae larvae were transferred to 6-7 days old seedlings of wild-type and MINELESS, respectively. In order to retain the larvae, pots (4 seedlings in each pot) were enclosed in cages. Controls were treated in the same way, without insects. Pots with control (non-infested) and M. brassicae infested seedlings were kept under the same conditions in greenhouse. Control and M. brassicae challenged seedlings were harvested after 24h of induction. Cages and larvae were removed and seedlings were harvested and flash frozen in liquid nitrogen. Each biological replica of untreated plants (controls) comprised 4 pots (4 seedlings in each pot), while for M. brassicae challenged seedlings, each biological replica comprised 6 pots (4 seedlings in each pot). Differences in transcriptional responses were measured by comparing genes expression of M. brassicae challenged seedlings against non-infested control seedlings.