A transgenic approach for controlling Lygus in cotton

Abstract

Lygus species of plant-feeding insects have emerged as economically important pests of cotton in the United States. These species are not controlled by commercial Bacillus thuringiensis (Bt) cotton varieties resulting in economic losses and increased application of insecticide. Previously, a Bt crystal protein (Cry51Aa2) was reported with insecticidal activity against Lygus spp. However, transgenic cotton plants expressing this protein did not exhibit effective protection from Lygus feeding damage. Here we employ various optimization strategies, informed in part by protein crystallography and modelling, to identify limited amino-acid substitutions in Cry51Aa2 that increase insecticidal activity towards Lygus spp. by >200-fold. Transgenic cotton expressing the variant protein, Cry51Aa2.834_16, reduce populations of Lygus spp. up to 30-fold in whole-plant caged field trials. One transgenic event, designated MON88702, has been selected for further development of cotton varieties that could potentially reduce or eliminate insecticide application for control of Lygus and the associated environmental impacts.

Characterization of the Activity Spectrum of MON 88702 and the Plant-Incorporated Protectant Cry51Aa2.834_16

“…hesperus and L . lineolaris are consistent with the results reported in Gowda et al, [31] where lethal effects of the Cry51Aa2.834_16 protein were reported for each of these species respectively.…”

“…This modified Cry51Aa2 protein, designated Cry51Aa2.834_16, has 96.44% sequence identity with the wild type Bt Cry51Aa2 [25], and shares structural similarities with the Cry35 protein expressed in DAS 59122 [28–30]. The modifications introduced into Cry51Aa2 resulting in Cry51Aa2.834_16 increased biological activity against hemipteran pests in the genus Lygus are described in detail in Gowda et al, [31]. Wide scale cultivation and use of commercialized biotechnology-derived crops expressing Bt Cry proteins, including Cry35, have revealed no instances of adverse impacts to non-target organisms (NTOs), and extensive reviews of the safety of various plant-incorporated Cry proteins are available [32, 33].…”

The Cotton Boll: The Relationship of Species and Genotype with Temporal Development of Boll Wall Thickness

“…Recently, genetically modified cotton lines with insecticidal activity against phytophagous hemipteran insect pests of cotton, namely Lygus hesperus Knight and L. lineolaris, were identified (Baum et al, 2012;Gowda et al, 2016), as previous transgenic cotton did not express toxicity towards these hemipteran pest species or related stink bug species. Interestingly, Gowda et al (2016) used DP 393 (G. hirsutum) and in this current study among G. hirsutum entries evaluated, DP 393 possessed the thinnest boll walls at 1 d after flowering (Table 3).…”

“…DP 393 continued to consistently exhibit the thinnest boll walls or second thinnest wall at later ages (Tables 4 and 5). Although the toxin was expressed in higher amounts within cotton squares (Gowda et al, 2016), the toxin was also expressed in the boll walls; the internal contents of the boll were not evaluated. Thus, this presents an interesting scenario where, if insect mortality is achieved by lygus bugs ingesting the boll wall tissue, thicker boll walls may be preferable to allow these smaller pest insects (which possess discrete capability to breach the boll wall) to ingest more of the toxin-containing boll tissue.…”

“…Although the toxin was expressed in higher amounts within cotton squares (Gowda et al, 2016), the toxin was also expressed in the boll walls; the internal contents of the boll were not evaluated. It is unknown whether Gowda et al (2016) considered the boll wall thickness of DP 393 during the development of their genetically modified cotton entry, but our findings lend credence to perhaps considering wall thickness in the development of transgenic entries. It is unknown whether Gowda et al (2016) considered the boll wall thickness of DP 393 during the development of their genetically modified cotton entry, but our findings lend credence to perhaps considering wall thickness in the development of transgenic entries.…”