Glyphosate Resistance in Agriculture - MBA 605
Characterizing adaptation and speciation in tiger swallowtail butterflies using transcriptome assemblies and genomic analysis.
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Ahsanullah University of Science & Technology
Strategic Management (MBA 605)
Added on 2020-03-04
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The MBA 605 Literature Review, defines herbicide resistance as the Heritable Ability of weeds to survive and reproduce in the presence of herbicide doses that are lethal to the wild type of the species. Herbicide resistance was first observed by an ornamental nursery owner in 1968.
Glyphosate Resistance in Agriculture - MBA 605
Characterizing adaptation and speciation in tiger swallowtail butterflies using transcriptome assemblies and genomic analysis.
Ahsanullah University of Science & Technology
Strategic Management (MBA 605)
Added on 2020-03-04
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The genetic basis of glyphosate resistance in the Central Valleyagricultural weed hairy fleabane (Erigeron bonariensis L.)
ABSTRACTHerbicide resistance is the heritable ability of weeds to survive and reproduce in the presence ofherbicide doses that are lethal to the wild type of the species. One mechanism of such resistanceis non-target site reduced translocation of the herbicide, in which vacuolar sequestration preventsthe chemical from spreading around the plant. Resistance of Erigeron canadensis to glyphosateis thought to involve this mechanism and it is believed that EPSPS and the ABC transportergenes M10 and M11 may be responsible for this resistance. This study therefore aims atdetermining through quantitative PCR and RNA-Seq if these genes provide the mechanism forglyphosate resistance in Erigeron bonariensis, a close relative of Erigeron canadensis, or if thereare other genes responsible for the resistance observed in this species. RNA will be extractedfrom the leaves of glyphosate treated and untreated individuals, collected from 10 sites in theCentral Valley and two control populations of Erigeron bonariensis, for quantitative real timePCR and RNA-Seq analysis. Total RNA for RNA-Seq analysis will be used in cDNA librarysynthesis and sequenced via Illumina HiSeq. Sequenced reads will be assembled de novo usingthe software Trinity, assigned to respective genes with the pipeline HTSeq, tested for differentialexpression by DESeq and functionally annotated using the NCBI nonredundant protein (Nr)database.
INTRODUCTIONMoss (2002) defines herbicide resistance as the heritable ability of weeds to survive andreproduce in the presence of herbicide doses that are lethal to the wild type of the species.Herbicide resistance was first observed by an ornamental nursery owner in 1968 (Jasieniuk at al.1996). The first recorded case of herbicide resistance was in Senecio vulgaris; seeds from theresistant biotypes were found to resist the chemicals simazine and atrazine (Pieterse 2010). In1974, herbicide resistance became a problem for corn growers (Gressel et al. 1982). Since then,more than 187 species of weeds have developed resistance against various herbicides worldwide(Pieterse 2010). The first case of herbicide resistance in California was reported in 1981 byscientists at UC-Riverside (Holt at al. 1981) and recently, more species have also evolvedresistance to various other herbicide chemicals employed by farmers in California (Malone 2014.Glyphosate herbicide (marketed by Monsanto as RoundUp®) contains N-phosphonomethyl glycine and it acts against plants by hindering aromatic amino acid synthesis(Bridges 2003). Upon application, the plant takes up glyphosate and it is remitted with otherproducts of photosynthesis to all parts of the plant. In susceptible plants, glyphosate hinders therole of the plastidine enzyme 5-enolpiruvilshikimate-3-phosphate synthase (EPSPS) important inthe prechorismate step of the shikimate pathway: normally, this enzyme works by condensingshikimate-3-phosphate and phosphoenolpyruvate into 5-enolpiruvilshikimate-3-phosphate(EPSP) with inorganic phosphate, initiating the anabolism of aromatic amino acids (Ferreira2008). Being unable to synthesize the amino acids phenylalanine, tryptophan, and tyrosineeventually kills the plant (Herman and Weaver 1999). Glyphosate has become the world’s mostcommonly used herbicide since its market introduction in 1974 (Baylis 2000). Several factorshave made it the most utilized herbicide globally: it has numerous ideal characteristics, including
its potency against an extensive variety of species (monocots and dicots), less harmful activityagainst animals than other herbicides (glyphosate targets the enzyme EPSPS that is not found inanimals), fast inactivation in the soil, and low cost (Duke and Powles 2008). Also, it has beencommonly used in recent years as a part of reduced tillage frameworks that have numerousenvironmental-based benefits and economic importance; these systems depend greatly onherbicides to control weeds (Owen 2008; Powles 2008; Shaner 2000). With the adoption ofgenetically modified glyphosate resistant crops in 1996, the already high levels of glyphosateapplication increased even more (Powles & Preston 2006). The combined effects of glyphosateover-usage in glyphosate-resistant crops and zero tillage adoption created a significantlyincreased risk of evolution of glyphosate resistance (Neve at al. 2003). Herbicide resistance isstimulated by the re-current use of herbicides with the same active chemical ingredients(LeBaron 1991), and so inevitably, glyphosate resistance has evolved in many weeds (Powles etal. 1998). Because of its ability to control numerous weeds and other features which are key tofarmers, such as low cost and reduced soil erosion, glyphosate remains the best option, andtherefore farmers are unwilling to return to the tillage system or older, more toxic herbicides(Beckie 2012).Two mechanisms that have been demonstrated to contribute to glyphosate resistance inweed species are target-site and non-target site resistance. Target site-based resistance is acondition where resistance evolves due to a gene mutation conferring a change to a target siteenzyme so that the herbicide fails to effectively inhibit the normal enzyme function (Powles andPreston 2006). The mutation may involve a specific nucleotide substitution in the coding regionproducing a different amino acid that results in structural, hydrophobicity or charge change insite of the enzyme that the herbicide targets, making it less sensitive to inhibition by the
herbicide. A few weeds such as goosegrass, have evolved weak target site mutagenesis (Lee andNgim, 2000; Dinelli et al. 2006) of the enzyme EPSPS, via a substitution mutation that replacedthe amino acid proline with serine at position 106 (Pro106-Ser). Ng et al. (2004 & 2005) alsoshowed that substitution of proline by threonine (Pro106-Thr) confers resistance glyphosateresistance to the weed goosegrass (Eleusine indica (L.) Gaertn.). The mutated EPSPS enzymehas a low affinity for glyphosate but almost normal affinity for phosphoenol pyruvate (theenzyme’s usual substrate); therefore the shikimate pathway can proceed normally, synthesizingaromatic amino acids (Gaines et al. 2010).Non-target site reduced translocation of glyphosate (Wakelin et al. 2004) preventsglyphosate from reaching all sites of the plant. According to Claus & Brehrens’ (1976) study,rapid and widespread glyphosate translocation is necessary to achieve high herbicide efficacy.There is therefore a possibility that changes in its translocation may enable resistance in plantsthat were initially susceptible to it. The study that unraveled this phenomenon was carried out inrigid ryegrass (Lolium rigidum Gaud.; Lorrraine-Colwill et al. 2002), and indicated thatresistance in at least one biotype of this species was not due to EPSPS enzyme targetmutagenesis or degradation. In the same study, it was shown that there was no significantdifference between glyphosate resistance and susceptible species in EPSPS sensitivity orexpression level or in glyphosate absorption, but the pattern of its translocation was significantlydifferent. The researchers observed that glyphosate accumulated at the lower part of the plantand to some extent in the roots in susceptible plants, while in resistant plants, it accumulated inthe tip of the leaves with a negligible amount translocated to the roots (Lorrraine-Colwill et al.2002). Welkelin et al. (2004) found the same pattern of reduced glyphosate translocation whenworking with four glyphosate resistant ryegrass populations in Australia.
Researchers investigating mechanisms of glyphosate resistance in other Loliumpopulations have not found large differences in glyphosate translocation. Perez et al. (2004)found no significant difference in glyphosate absorption and translocation between susceptibleand resistant Chilean Lolium plants. In an investigation in glyphosate resistance in CalifornianLolium, Simarmata et al. (2003) found significantly higher glyphosate concentration in treatedleaves of glyphosate resistant plants 2-3 days after treatment. Interestingly, these authorsobserved no other significant differences in glyphosate absorption or translocation betweenresistant and susceptible plants. These varying results suggest that there might be differentmechanisms responsible for glyphosate resistance in different Lolium populations. In general,most studies observed no differences in glyphosate absorption, but its translocation to the rootswas greatly reduced (Feng et al. 2004; Koger and Reddy 2005) in resistant species. Failure ofglyphosate translocation from leaves to the roots seems to be important mechanisms that lead toresistance in certain Lolium biotypes and biotypes of other weeds, including those in the genusErigeron (Conyza) (Preston 2002). Erigeron species consist of annual or short-lived perennial plants native to the Americasthat have in the recent past become cosmopolitan and invasive weeds of many crops and arablelands (Prieur-Richard et al. 2000). The genus is in the sunflower family (Asteraceae) and theweed species were formerly placed in the genus Conyza before taxonomic revision ( Baldwin,2012). Erigeron spp. are prolific seed producers: a single plant is capable of producingthousands of viable seeds (Weaver 2001) that can be widely dispersed by wind (Shields et al.2006), establishing themselves in areas previously uninfected. Erigeronspp. have become very common and problematic weedy plants in agronomiccrops around the world (Weaver 2001). This is probably because they are capable of adapting to
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