Use of Multicopy Transposons Bearing Unfitness Genes in Weed Control: Four Example Scenarios

Abstract

We speculate that multicopy transposons, carrying both fitness and unfitness genes, can provide new positive and negative selection options to intractable weed problems. Multicopy transposons rapidly disseminate through populations, appearing in approximately 100% of progeny, unlike nuclear transgenes, which appear in a proportion of segregating populations. Different unfitness transgenes and modes of propagation will be appropriate for different cases: (1) outcrossing Amaranthus spp. (that evolved resistances to major herbicides); (2) Lolium spp., important pasture grasses, yet herbicide-resistant weeds in crops; (3) rice (Oryza sativa), often infested with feral weedy rice, which interbreeds with the crop; and (4) self-compatible sorghum (Sorghum bicolor), which readily crosses with conspecific shattercane and with allotetraploid johnsongrass (Sorghum halepense). The speculated outcome of these scenarios is to generate weed populations that contain the unfitness gene and thus are easily controllable. Unfitness genes can be under chemically or environmentally inducible promoters, activated after gene dissemination, or under constitutive promoters where the gene function is utilized only at special times (e.g. sensitivity to an herbicide). The transposons can be vectored to the weeds by introgression from the crop (in rice, sorghum, and Lolium spp.) or from planted engineered weed (Amaranthus spp.) using a gene conferring the degradation of a no longer widely used herbicide, especially in tandem with an herbicide-resistant gene that kills all nonhybrids, facilitating the rapid dissemination of the multicopy transposons in a weedy population.

Ambient insect pressure and recipient genotypes determine fecundity of transgenic crop‐weed rice hybrid progeny: Implications for environmental biosafety assessment

“…). Therefore, effective methods for mitigating the fitness advantages of the insect‐resistant transgenes in weedy/wild rice populations should be considered to reduce such an undesired impact (Gressel and Levy ; Gressel ).…”

“…Such evolution may translate into increased weed problems or other undesirable ecological impacts (Lu and Snow 2005;Lu and Yang 2009;Ellstrand et al 2013). Therefore, effective methods for mitigating the fitness advantages of the insect-resistant transgenes in weedy/wild rice populations should be considered to reduce such an undesired impact (Gressel and Levy 2014;Gressel 2015). Ambient insect pressure and genotypes of weedy rice parents determines the fecundity change from transgenes…”

Integrated pest management and weed management in the United States and Canada

“…The research that supports this weed management concept was based on fields with Lolium rigidum populations that did not have multiple herbicide resistance, and a herbicide treatment was used to augment the mechanical destruction of the weed seeds by the machine. However, viable weed seeds are returned to the seedbank after the procedure in potentially high enough numbers to have a limited impact on residual weed seedbank population densities, unless the tactic is supplemented by herbicides . In the case of weed populations with multiple herbicide resistance, effective herbicides may not be available, resulting in minimal impact on the weed seed population density by the mechanical practice.…”

“…However, viable weed seeds are returned to the seedbank after the procedure in potentially high enough numbers to have a limited impact on residual weed seedbank population densities, unless the tactic is supplemented by herbicides. 83 In the case of weed populations with multiple herbicide resistance, effective herbicides may not be available, resulting in minimal impact on the weed seed population density by the mechanical practice. Importantly, this technology has not been evaluated on dicotyledonous HR weeds, which are problems in US agriculture.…”

Focus on Weed Control

“…The natural world is well versed in waging chemical warfare on plants in the form of allelochemicals and phytotoxins, and here the authors propose that some of these agents are interesting new leads for herbicides. Using a completely different strategy, it is proposed that multicopy transposons carrying unfitness genes could be used to help control weeds by reducing their competiveness against crops (Gressel and Levy, 2014). Four potential scenarios are described relating to different weeds, with the introduced transposons only activated under conditions induced by selective environmental conditions or by spraying with specific agrochemicals.…”