Robust crop resistance to broadleaf and grass herbicides provided by aryloxyalkanoate dioxygenase transgenes

Abstract

Engineered glyphosate resistance is the most widely adopted genetically modified trait in agriculture, gaining widespread acceptance by providing a simple robust weed control system. However, extensive and sustained use of glyphosate as a sole weed control mechanism has led to field selection for glyphosate-resistant weeds and has induced significant population shifts to weeds with inherent tolerance to glyphosate. Additional weed control mechanisms that can complement glyphosate-resistant crops are, therefore, urgently needed. 2,4-dichlorophenoxyacetic acid (2,4-D) is an effective lowcost, broad-spectrum herbicide that controls many of the weeds developing resistance to glyphosate. We investigated the substrate preferences of bacterial aryloxyalkanoate dioxygenase enzymes (AADs) that can effectively degrade 2,4-D and have found that some members of this class can act on other widely used herbicides in addition to their activity on 2,4-D. AAD-1 cleaves the aryloxyphenoxypropionate family of grass-active herbicides, and AAD-12 acts on pyridyloxyacetate auxin herbicides such as triclopyr and fluroxypyr. Maize plants transformed with an AAD-1 gene showed robust crop resistance to aryloxyphenoxypropionate herbicides over four generations and were also not injured by 2,4-D applications at any growth stage. Arabidopsis plants expressing AAD-12 were resistant to 2,4-D as well as triclopyr and fluroxypyr, and transgenic soybean plants expressing AAD-12 maintained field resistance to 2,4-D over five generations. These results show that single AAD transgenes can provide simultaneous resistance to a broad repertoire of agronomically important classes of herbicides, including 2,4-D, with utility in both monocot and dicot crops. These transgenes can help preserve the productivity and environmental benefits of herbicide-resistant crops.herbicide resistance | weed management | genetically modified crops |

Safeners recruit multiple signalling pathways for the orchestrated induction of the cellular xenobiotic detoxification machinery in Arabidopsis

“…The wide adoption of this technology, particularly of glyphosateresistant crops, concomitant with the extensive use of the corresponding herbicide (Roundup), led to the recent emergence of herbicide-resistant weeds. The long-term availability of the technology is thus at risk, prompting the quest for different solutions (Behrens et al 2007;Wright et al 2010). As an alternative to biotechnological approaches, herbicide antidotes or safeners are used to protect crop plants from herbicide injury.…”

Resistance of Enlist™(AAD-12) Cotton to Glufosinate

“…Expression of the AAD-12 protein in transgenic crops has been shown to provide tolerance to the herbicide 2,4-D by catalyzing the conversion of 2,4-D to 2,4-dichlorophenol (DCP), a herbicidally inactive compound, through an Fe(II)/α-keto acid-dependent dioxygenase reaction ( Figure 37 and Figure 38) (Müller et al, 1999;Westendorf et al, 2002;Westendorf et al, 2003;Wright et al, 2009;Wright et al, 2010). (Roberts, 1998).…”

“…Some common hard to control weed species that could become "weed shifts" in U.S. cotton are listed in Table 39, with pigweed and morning glory most commonly reported by cotton growers (Duke and Powles, 2008b;Owen, 2008;Prince et al, 2012). Dow AgroSciences LLC 2,4-D Resistance 2,4-D has been used continually and widely for over 70 years, and reports of resistance have been rare (Wright et al, 2010;Greene and Reid, 2012). The earliest documented reports of herbicide resistant weeds were for resistance to 2,4-D in wild carrot (Daucus carota) (observed in 1952 but not reported until 1957) and spreading dayflower (Commelina diffusa) in 1957 (Heap, 2011).…”

“…AAD-12 has enantiomeric selectivity for the (S)-enantiomers of the chiral phenoxy acid herbicides (e.g., dichlorprop and mecoprop), but does not catalyze degradation of the (R)-enantiomers. It is the R-enantiomers in this class of chemistry that are herbicidally active; Dow AgroSciences LLC therefore AAD-12 does not provide tolerance to commercially-available chiral phenoxy acid herbicides (Wright et al, 2010).…”

“…The wild-type aryloxyalkanoate dioxygenase (AAD-12) protein coding sequence was derived from Delftia acidovorans, a gram-negative soil bacterium (Wright et al, 2010). The wild-type AAD-12 amino acid sequence and the DAS-8191Ø-7 cotton AAD-12 amino acid sequence (encoded by the plant-optimized aad-1 gene (see section 3.4.1)) are greater than 99% identical, differing only by a single amino acid addition, alanine (A), at position number two ( Figure 36).…”