Soybean (Glycine max) plants genetically modified to express resistance to glyphosate: can they modify airborne signals in tritrophic interactions?

Abstract

Upon herbivory, plants activate complex biochemical pathways that result in an array of defense responses including the emission of a novel blend of volatile organic compounds (VOCs). These compounds mediate the recruitment of predators and parasitoids that exert biological control of the attacking herbivore. Genetic manipulation of a particular trait to improve agricultural plant varieties may affect other traits as a result of possible pleiotropy or insertional mutations, which in turn can affect the interaction of the plant with other organisms. Changes in herbivore-induced VOC emissions are known to occur in transgenic plants engineered to express resistance to insects (mainly Bt-plants), not only as a result of modified insect behavior but also as a result of altered resource allocation. Transgenic glyphosate-resistant plants express a variant of the enzyme EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) that is insensitive to the herbicide glyphosate. This enzyme is essential in metabolic routes that result in the synthesis of amino acids and secondary metabolites. We addressed whether the constitutive and Anticarsia gemmatalis-induced emissions of VOCs from a transgenic soybean line differ from those of the isoline, and whether changes may interfere in the foraging behavior of the predatory bug Podisus nigrispinus. Analyses showed that both herbivory and genotype influenced VOC emissions. In addition, the genotype affected the herbivore-induced VOC emission. Larger emissions were measured in the transgenic line than the non-transgenic line upon herbivory. The bioassays showed that P. nigrispinus significantly discriminated only between the odors of undamaged and damaged plants of the non-transgenic line. No preference was observed for herbivore-damaged plants of any of the two lines over the other. The results from this study suggest that despite a greater emission of volatiles the predators are less able to discriminate between herbivore-damaged and undamaged transgenic plants. This condition does not necessarily increase the preference of the predator for damaged non-transgenic plants over transgenic plants. This study opens possibilities for new studies of chemical ecology in tritrophic systems to assess the effect of transgenic glyphosate-resistant plants.

Ongoing ecological and evolutionary consequences by the presence of transgenes in a wild cotton population

“…larger fruit and seed sets) compared to their wild relatives 4 , 5 . It has been suggested that the over-expression of the epsps gene is responsible for these compensation effects on plant fitness, in view of the biotic and abiotic stressors that activate the shikimate pathway 5 , 15 . Further investigation to find out if this is the case for W cp4-epsps cotton is currently being developed under natural conditions.…”

“…cry and cp4-epsps ). Such differences have been associated with defence mechanisms and/or main metabolic pathways involved in plant growth, development, and reproduction, such as the shikimate or the octadecanoid pathways 15 , 16 . As a consequence, the quantity and quality of metabolic products are modified, compromising not only plant performance but also their interactions with insects, bacteria, and soil fungi 17 .…”

Effects of Bacillus thuringiensis Genetic Engineering on Induced Volatile Organic Compounds Emission in Maize and the Attractiveness to a Parasitic Wasp

“…When infested by the leafminer species Phyllonorycter blancardella (Fabricius), the GM apple plants with a scab resistance gene emitted less ( E,E )-α-farnesene than did their conventional equivalents (Vogler et al, 2010). A transgenic soybean cultivar expressing a glyphosate-resistant gene released a few volatile compounds in a higher amount than did its conventional isoline when the plants were damaged by the soybean looper Chrysodeixis includes (Walker) or the velvetbean caterpillar Anticarsia gemmatalis Hübner (Strapasson et al, 2016a,b). As a result, the herbivore-damaged GM soybean plants were more attractive to the larval parasitoid Meteorus rubens (Nees) than the conventional isoline (Strapasson et al, 2016a).…”

“…As a result, the Bt maize line more likely releases several volatile compounds in a lower amount than does its non- Bt isoline due to deficiency of resources when the plants are induced by caterpillar regurgitant (Turlings et al, 2005). However, after genetic transformations, some inducible VOCs, such as terpenoids, have actually increased (Strapasson et al, 2016b). One possible explanation is that the newly biosynthesized protein (responsible for herbicide tolerance in this case) has affected or is involved in the plant hormone-mediated defensive pathway, which responds to produce some VOCs (Strapasson et al, 2016a).…”

Current knowledge and future research perspectives on cassava (Manihot esculenta Crantz) chemical defenses: An agroecological view

“…While the first strategy would deprive the plant of part of its natural defenses and possibly result in the larger pesticide inputs, the second would not. Furthermore, genetic manipulation of plants can result in pleiotropic effects or mutations, affecting other plant traits, including those involved in defense (Strapasson et al, 2016). Contradictory as it may sound, South American Indians prefer to grow plants with larger amounts of cyanogenic glycosides (Wilson and Dufour, 2002).…”