Objective
1. Generate glucosinolate-free B. napus lines
2. Eliminate myrosinase from canola leaf tissue to generate myrosinase-free lines
3. Verify the genetic modifications through molecular and biochemical analyses
4. Assay the impact of glucosinolates and/or their breakdown products on canola’s response to flea beetles
Project Description
Flea beetles pose a significant threat to canola production causing extensive damage to young seedlings and leading to substantial yield losses. Current flea beetle management strategies rely heavily on neonicotinoid insecticides; however, concerns over their environmental impact have led to regulatory restrictions, including bans in Europe. In addition, striped flea beetles appear to have a natural resistance to neonicotinoids, thus any change in insect population dynamics could be problematic. Considering constantly changing public opinions, the long-term sustainability of neonicotinoid use in Canada could be uncertain, thus posing an urgent demand for alternative pest control strategies. Despite their agricultural significance, key aspects of flea beetle biology and ecology remain poorly understood, which hinder the development of other sustainable control strategies.
One under explored area is the role of glucosinolates, a class of secondary metabolites unique to Brassicaceae family members. Glucosinolates can be hydrolyzed by myrosinase to produce toxic chemicals, such as isothiocyanates (ITCs), thiocyanates, and nitriles. The important roles of glucosinolates and their hydrolysis products during plants’ defense against generalist herbivores have been well documented. However, flea beetles are specialist insects feeding on a narrow host plant range that is restricted to the Brassicaceae family, but do not feed on plants which do not contain glucosinolates, which suggests that glucosinolates are feeding and/or oviposition stimulants for such specialist insects. As specialist herbivores, flea beetles have adapted to these toxic glucosinolates and their hydrolysis products, for example horseradish flea beetle can sequester intact glucosinolates and use their endogenous myrosinase to defend themselves against predators. Thus, flea beetles could not only tolerate these glucosinolates but may also use glucosinolates for their host plant recognition and feeding stimulation. Interestingly, another oilseed crop from the Brassicaceae family, Camelina sativa, has shown almost complete immunity to flea beetles. A comprehensive comparison of the pre-feeding behaviors of adult flea beetles on host plant B. napus versus non-host plant C. sativa suggested that the flea beetle resistance of C. sativa might result from the absence of stimulatory volatile phytochemicals. This speculation was further supported by our own preliminary data (ADF project #20200180), where we could trigger flea beetle feeding by applying a glucosinolate hydrolysis product to C. sativa leaves. Notably, canola quality B. napus accumulates varying levels of glucosinolates in its leaves, while it was recently shown that there are no detectable glucosinolates in C. sativa leaves, with glucosinolates contained to the roots only. Despite mounting evidence suggesting that glucosinolates may play a kairomonal role in insect-plant interactions, it remains unclear whether intact glucosinolates or their hydrolysis products serve as key feeding cues for flea beetles. This knowledge gap has direct implications for breeding canola with enhanced flea beetle resistance. By generating transgenic B. napus lines that lack glucosinolates or myrosinases, we will establish a comprehensive experimental system to dissect the fundamental role of glucosinolates in flea beetle host selection and feeding behavior. This research will provide novel insights into flea beetle-plant interactions, thus supporting the development of canola varieties with improved flea beetle resistance.
