‘Myrosin cells’ are not a prerequisite for aphid feeding on oilseed rape (Brassica napus) but affect host plant preferences

Abstract

The enzyme myrosinase (EC 3.2.3.1.147) is present in specialised myrosin cells and forms part of the glucosinolate-myrosinase system, also known as 'the mustard oil bomb', which has an important role in the defence system of cruciferous plants against insect pests. Transgenic Brassica napus MINELESS have been produced by transgenic ablation of myrosin cells. This prompted us to investigate the importance of myrosin cells in plant-aphid interactions. In order to study this, we challenged transgenic MINELESS and wild-type cultivar Westar seedlings with the aphids Brevicoryne brassicae (a specialist) and Myzus persicae (a generalist). Our study included aphid free-choice and aphid fecundity experiments. Data from these experiments showed that B. brassicae prefers wild-type seedlings and M. persicae prefers MINELESS. B. brassicae and M. persicae showed significant variation in establishment on plants regardless of whether they were wild type or MINELESS and also differed significantly in affecting plant parts. Myrosinase activity in MINELESS control seedlings was 83.6% lower than the wild-type control seedlings. Infestation with either of the two aphid species induced myrosinase levels in both wild-type and MINELESS seedlings. Infestation with M. persicae reduced the concentration of most glucosinolates while B. brassicae had the opposite effect. B. brassicae enhanced the formation of glucosinolate hydrolysis products both in wild-type and MINELESS seedlings. However, M. persicae decreased All ITC but increased 3,4ETBut NIT in wild-type seedlings. Taken together, the investigation shows that the presence of myrosin cells affects the preference of generalist and specialist aphid species for Brassica napus plants.

Plant defence responses in oilseed rape MINELESS plants after attack by the cabbage moth Mamestra brassicae

“…In this study, the total glucosinolate levels were observed to be higher in MINELESS control seedlings relative to wild-type control seedlings. Moreover, in our previous studies, we have shown the total glucosinolate levels to be higher in MINELESS control (non-infested) seeds than wild-type control seeds and seedlings ( Borgen et al , 2010 ; Ahuja et al , 2011 ; Borgen et al , 2012 ). Glucosinolates form a constitutive defence ( Wittstock and Gershenzon, 2002 ), but it is also evident that these compounds accumulate in response to wounding or herbivory ( Doughty et al , 1995 ; Bartlet et al , 1999 ; Brader et al , 2001 ; Mikkelsen et al , 2003 ).…”

“…6 ), which were 36.5- and 38.8-fold higher in the MINELESS control compared to the wild-type control. The detection of high amounts of these compounds particularly in MINELESS seedlings is interesting as we have not found these compounds before in MINELESS seeds or seedlings ( Borgen et al , 2010 ; Ahuja et al , 2011 ; Borgen et al , 2012 ). 1 MTPe has been detected in B .…”

“…On the other hand, some studies revealed induction or increases in myrosinase activity after herbivore attack by B . brassicae on wild-type and MINELESS seedlings ( Borgen et al , 2012 ) and, for example, by P . xylostella on B .…”

Semiochemical-based alternatives to synthetic toxicant insecticides for pollen beetle management

“…Transgenic OSR has been produced with low myrosinase activity (Borgen et al 2010) which consequently reduces the production of glucosinolate hydrolysis products (mainly isothiocyanates). Compared to wild-type, these low isothiocyanate releasing seedlings were more preferred in free-choice experiments by generalist aphid species but less preferred by specialist aphid species (Borgen et al 2012). However, such manipulation of plant volatile emissions can result in physiological costs to the plant (Robert et al 2013) and it is imperative that any modifications do not impair the plant's natural ability to defend itself against other generalist pests after herbivore attack (Hopkins et al 2009).…”

Presence of substitute diets alters plant resistance to specialist and generalist herbivores: a meta‐analysis

“…For example, related plants often share a similar composition of secondary metabolite, such as the glucosinolates of Brassicaceae and relatives (Spencer , Borgen et al. ). In addition, plant phylogeny may be correlated with other life‐history traits.…”