Glucosinolates and Their Hydrolysis Products in Arabidopsis thaliana Influence Performance and Feeding Choice of Pieris rapae and Spodoptera exigua

Glucosinolates and their hydrolysis products, found in plants of the order Brassicales, are well-known for their defensive properties against insect herbivores. Arabidopsis thaliana (Col-0) genetic lines with mutations that modify the type of glucosinolates (i.e. myb28myb29 and cyp79B2cyp79B3 are deficient in the production of aliphatic and indolyl glucosinolates, respectively) make it possible to test for the specific effects of these secondary chemicals on insect herbivores. The Pad3 mutant (deficient in camalexin), which has a role in resistance to pathogens, was also tested. Likewise, the effects of different glucosinolate hydrolysis products can be evaluated using genetically modified (GM) lines of the wild type Col-0 ecotype, which naturally produces isothiocyanates. These GM lines include the nitrile-producing 35S: ESP and the double knockout tgg1tgg2, which virtually lacks hydrolysis products. In both no-choice and choice experiments, the crucifer specialist Pieris rapae was virtually unaffected by differences in the type of glucosinolates or hydrolysis products. In contrast, the generalist insect Spodoptera exigua had statistically significant increases in pupae/adult weight and faster developmental times when reared on mutants deficient in the production of aliphatic and indolyl glucosinolates and their hydrolysis products. There were no differences in the performance of either insect species when reared on wild type Col-0 or Pad3. Results from feeding choice trials showed that Pieris rapae had no statistically significant preference for any of the genetic lines. In contrast, Spodoptera exigua had a significant feeding preference for the double mutant tgg1tgg2. This study provides evidence that variation in the type of glucosinolates and their hydrolysis products can influence insect performance and feeding choices, and that responses are species-specific.

Developing multifunctional crops by engineering Brassicaceae glucosinolate pathways

Glucosinolates(GSLs),found mainly in species of the Brassicaceae family,are one of the most well-studied classes of secondary metabolites.Produced by the action of myrosinase on GSLs,GSL-derived hydrolysis products(GHPs)primarily defend against biotic stress in planta.They also significantly affect the quality of crop products,with a subset of GHPs contributing unique food flavors and multiple therapeutic benefits or causing disagreeable food odors and health risks.Here,we explore the potential of these bioactive functions,which could be exploited for future sustainable agriculture.We first summarize our accumulated understanding of GSL diversity and distribution across representative Brassicaceae species.We then systematically discuss and evaluate the potential of exploited and unutilized genes involved in GSL biosynthesis,transport,and hydrolysis as candidate GSL engineering targets.Benefiting from available information on GSL and GHP functions,we explore options for multifunctional Brassicaceae crop ideotypes to meet future demand for food diversification and sustainable crop production.An integrated roadmap is subsequently proposed to guide ideotype development,in which maximization of beneficial effects and minimization of detrimental effects of GHPs could be combined and associated with various end uses.Based on several use-case examples,we discuss advantages and limitations of available biotechnological approaches that may contribute to effective deployment and could provide novel insights for optimization of future GSL engineering.