Fitness costs associated with evolved herbicide resistance alleles in plants

Predictions based on evolutionary theory suggest that the adaptive value of evolved herbicide resistance alleles may be compromised by the existence of fitness costs. There have been many studies quantifying the fitness costs associated with novel herbicide resistance alleles, reflecting the importance of fitness costs in determining the evolutionary dynamics of resistance. However, many of these studies have incorrectly defined resistance or used inappropriate plant material and methods to measure fitness. This review has two major objectives. First, to propose a methodological framework that establishes experimental criteria to unequivocally evaluate fitness costs. Second, to present a comprehensive analysis of the literature on fitness costs associated with herbicide resistance alleles. This analysis reveals unquestionable evidence that some herbicide resistance alleles are associated with pleiotropic effects that result in plant fitness costs. Observed costs are evident from herbicide resistance-endowing amino acid substitutions in proteins involved in amino acid, fatty acid, auxin and cellulose biosynthesis, as well as enzymes involved in herbicide metabolism. However, these resistance fitness costs are not universal and their expression depends on particular plant alleles and mutations. The findings of this review are discussed within the context of the plant defence trade-off theory and herbicide resistance evolution

The Molecular Basis of Imidazolinone Herbicide Resistance in Arabidopsis Thaliana Var. Columbia.

Acetolactate synthase (ALS) is a key regulatory enzyme in the biosynthetic pathway of leucine, isoleucine, and valine. ALS is inhibited by four classes of structurally unrelated herbicides viz. sulfonylureas, imidazolinones, triazolopyrimidines, and pyrimidyl-oxy-benzoate. To understand the molecular basis of imidazolinone resistance, the ALS gene was isolated from an imazapyr-resistant mutant GH90 of Arabidopsis thaliana (Haughn and Somerville, 1990. Plant Physiol. 92:1081-1085). DNA sequence analysis of the mutant gene demonstrated a single point mutation from G to A at the 1958th nucleotide of the ALS coding sequence (Sathasivan et al., 1990. Nucl. Acids Res. 18:2188). This would result in serine to asparagine substitution at the 653rd amino acid, near the carboxyl terminal of matured ALS. The mutant ALS gene was introduced into tobacco using Agrobacterium-mediated transformation. The presence of the introduced ALS gene was confirmed by a southern hybridization analysis of transgenic plant DNA. Imidazolinone resistance of transformed calli and leaves of transgenic plants was 100 fold greater than that of wild type. The level of resistance of the ALS activity in vitro correlated with the amount of resistance in the leaves of transgenic plants. These results demonstrated that the single amino acid substitution from serine to asparagine at the 653rd amino acid near the carboxyl terminus of ALS is the molecular basis of imidazolinone herbicide resistance

Identification of a herbicide-resistant biotype of Echinochloa crus-galli in Ukraine

Ukraine is one of the world’s guarantors of food security and has the potential to further increase agricultural production. However, the vast majority of herbicides used on crops are acetolactate synthase (ALS) inhibitors, which poses a threat of herbicide-resistant weed species. The emergence and spread of herbicide-resistant weed biotypes can significantly increase the cost of growing crops to the point of loss of profitability. Herbicide resistance in barnyardgrass (Echinochloa crus-galli var. crus-galli) has been studied in long-term field and greenhouse experiments. Resistance of E. crus-galli to the ALS herbicide triazolopyrimidine derivative ‒ penoxsulam was identified. Expressed resistance was observed in weed plants grown from seeds collected under production conditions in Kherson region in 2015–2016 and 2020–2021. Cross resistance was observed for imidazolinone and sulfonylurea derivatives. It should be noted that the level of cross resistance to ALS herbicides was slightly higher for plants derived from weed seeds harvested in 2020–2021 compared to those harvested in 2015–2016. The introduction of a herbicidal composition of a herbicide mixture ‒ an inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD) (an enzyme in plants in the chain of carotenoid synthesis) ‒ mesotrione with an ALS-inhibitor (nicosulfuron) allowed effective control of the weed, which indicates the absence of multiple resistance to herbicides ‒ inhibitors of carotenoid synthesis. The high efficiency of E. crus-galli control was established by the application of herbicides ‒ inhibitors of fatty acid synthesis (graminicides). The highest level of efficiency in the experiments was observed with the application of fluazifop-butyl and somewhat less ‒ with pinoxaden. A tendency to reduce phytotoxicity to barnyardgrass from the south of Ukraine was observed with the introduction of tepraloxydim and quizalofop-ethyl. A lower level of phytotoxicity of fenoxaprop-p-ethyl on E. crus-galli should be noted compared to the effect of pinoxaden. No multiple resistance was observed with glyphosate (5-enolpyruvylshikimate-3-phosphate synthase inhibitor) and reglone (photosystem I inhibitor), allowing control of vegetative weeds at the beginning and end of the growing season. It has been established that monocot weed species have significantly increased their presence and harmfulness in agrophytocenoses in Ukraine and in the world since the 1950s with the widespread introduction of selective dicotyledonous species control with aryloxyphenoxyacetic, propionic and benzoic acid derivatives. This trend has been maintained until recently ‒ barnyardgrass is one of the dominant weed species in modern agrophytocenoses of Ukraine. Therefore, the identification of the ALS-resistant biotype of barnyardgrass complicates weed control in the following crops in rotations in the southern regions of the country: in maize crops with cross resistance to nicosulfuron, in sunflower ‒ to imidazolinones (imazamox, imazapyr), and also makes it impossible to use penoxsulam in rice production. Traditionally, the use of synthetic auxins, phenoxyacetic acid derivatives, etc. is used to control ALS-resistance. However, in Kherson region of Ukraine, already in the third year of application of rinskor (florpyrauxifen-benzyl), some weed plants were found on rice fields affected by ALS-resistant barnyardgrass, which recovered after the use of synthetic auxin. Therefore, the control of ALS-resistance (penoxsulam, etc.) in E. crus-galli with the application florpyrauxifen-benzyl in the Kherson region of Ukraine is already limited. An obvious and economically feasible preventive measure against the emergence of resistant weed biotypes is the implementation of GAP (Good Agricultural Practice, FAO) approaches: in particular, the use of high quality seeds without weed impurities, increasing the proportion of agrotechnical weed control measures, restoring and expanding crop rotations with mandatory rotation of herbicides with different modes of action, introducing dicotyledonous/leguminous crops into rotations, and using herbicides with different modes of action in crops separately or in mixtures. At the same time, agrotechnical measures and the preservation of biodiversity in agrophytocenoses should be the main factor in controlling resistance in weeds. The use of herbicides and their mixtures with different modes of action is of secondary importance. The identification of highly damaging ALS-resistant E. crus-galli in southern Ukraine indicates the insufficient effectiveness of weed control exclusively with herbicides with a single mechanism of action and requires a significant revision of the principles of crop rotation and ways of weed control in the country to maintain high levels of profitability and productivity of agrophytocenoses. Solving this problem is urgent for the preservation of Ukraine's potential as one of the guarantors of global food security

Characterization of acetolactate synthase resistance in common sunflower (Helianthus annuus)

Herbicides that inhibit acetolactate synthase (ALS) have been important weed management tools for nearly 20 years. In recent years, resistance to ALS inhibiting herbicides has increased. In 1996, a population of common sunflower near Howard, South Dakota was suspected to be resistant to chlorimuron and imazethapyr, both ALS-inhibiting herbicides. Whole-plant ALS enzyme assays and herbicide dose response experiments concluded that cross resistance between chlorimuron and imazethapyr was present in the Howard common sunflower population. The percentages of resistant to sensitive individuals within the resistant population also indicated that the resistant population was not homogeneously resistant to either herbicide. Herbicide penetration and translocation experiments showed that resistant plants absorbed approximately 44% and 36% less 14C-chlorimuron and 14C-imazethapyr, respectively, compared to sensitive plants. Translocation of 14C did not vary. An alanine to valine substitution at amino acid position 204 of the ALS gene was found in six of seven clones from resistant plants. A frame shift occurred in Region B of the ALS gene, suggesting that multiple copies exist in the genome. Gene flow experiments suggested that resistance is due to a semi-dominant, nuclear-encoded ALS gene

Green foxtail (Setaria viridis) resistance to acetolactate synthase inhibitors

Des sétaires vertes (Setaria viridis) présumées résistantes aux inhibiteurs de l'acétolactate synthase (ALS) ont été identifiées en 1999 au Wisconsin, É.-U., dans un champ de soja (Glycine max) issu d'un semis direct. La résistance aux herbicides imidazolinone et sulfonylurée a été caractérisée au niveau de la plante entière et de celui des enzymes. Ces sétaires vertes au stade trois à quatre feuilles étaient respectivement 1020, 53 et 6,5 fois plus résistantes à l'imazethapyr, à l'imazamox et au nicosulfuron que les sétaires sensibles. L'ALS in vivo était respectivement 1300 et 1,7 fois plus résistante à l'imazethapyr et au nicosulfuron. Ces résultats laissent supposer que ce groupe de sétaires vertes était très résistant à l'imazethapyr et à l'imazamox, et que la résistance est associée à un enzyme ALS insensible.Green foxtail (Setaria viridis) plants putatively resistant to acetolactate synthase (ALS) inhibitors were identified in a Wisconsin USA no-tillage soybean (Glycine max) field in 1999. Resistance to imidazolinone and sulfonylurea herbicides was characterized at the whole-plant level and enzyme level. Three- to four-leaf stage green foxtail plants were 1020, 53, and 6.5-fold resistant to imazethapyr, imazamox, and nicosulfuron, respectively, compared to susceptible plants. In vivo ALS was 1300 and 1.7-fold resistant to imazethapyr and nicosulfuron, respectively. These results suggested that this green foxtail accession was highly resistant to imazethapyr and imazamox, and that resistance was associated with an insensitive ALS enzyme

Association Genetics for Agronomic Traits in Rice and Cloning of ALS Herbicide Resistant Genes from Coreopsis Tinctoria Nutt

We have evaluated the potential of discriminant analysis (DA) to detect candidate markers associated with twelve economically important traits in a large population of unrelated U.S. and Asian inbred lines of rice. Associated marker alleles detected by DA mapped within the same genetic intervals when compared with previous traditional QTL mapping experiments that evaluated progeny derived from various controlled crosses. New markers identified by DA suggest that the procedure can also uncover relevant genetic regions not possible by standard genetic tests. With the same dataset, we also compared different modern regression approaches for selecting molecular markers associated with the twelve agronomic traits. These methods included stepwise forward regression (SFR), least angle regression (LAR) and least absolute shrinkage and selection operator (LASSO) selection. The epistatic model based on stepwise forward regression did successfully identify several interacting loci that explained a relatively high proportion of the observed variation for all the twelve agronomically important traits. Moreover, the loci identified by the epistatic model mapped within previously known QTL regions that underscores the genetic basis of the selected markers. It was concluded that stepwise forward regression with consideration for population structure, epistatic interactions, and missing data (multiple imputation) was a robust method, compared to the general linear model, to identify markers associated with complex agronomic traits. Acetolactate synthase (ALS), also known as acetohydroxy acid synthase (AHAS), which catalyzes the first step in the biosynthesis of the branched-chain amino acids valine, leucine and isoleucine in plants, is a target of five herbicide groups, including sulfonylurea and imidazolinone. A recently discovered group of Coreopsis tinctoria Nutt. mutants from the field showed high levels of resistance to both sulfonylurea and imidazolinone herbicides. In this study the mutants were compared by chemical, genetic, and molecular analyses with “normal” or wild-type Coreopsis. A phylogenetic analysis revealed that the ALS gene can serve as a useful molecular tool for evaluating evolutionary relationships among plant species. Due to pending patent applications by the Louisiana State University Agricultural Center and restrictions of patent applications, specific results from this research cannot be presented in this dissertation

Integrativna ekspresija gena za glukoamilazu u soju pivskoga kvasca Saccharomyces pastorianus

The recombinant brewer’s yeast Saccharomyces pastorianus strain was constructed byintroducing the ilv2:GLA fragment released from pMGI6, carrying glucoamylase gene (GLA) and using the yeast α-acetolactate synthase gene (ILV2) as the recombination sequence. The strain was able to utilise starch as the sole carbon source, its glucoamylase activity was 6.3 U/mL and its α-acetolactate synthase activity was lowered by 33.3 %. The introduced GLA gene was integrated at the recipient genomic ILV2 gene, one copy of ILV2 gene was disrupted and the other copy remained intact. Primary wort fermentation test confirmed that the diacetyl and residual sugar concentration in the wort fermented by the recombinant strain were reduced by 65.6 and 34.2 % respectively, compared to that of the recipient strain. Under industrial operating conditions, the maturation time of beer fermented by the recombinant strain was reduced from 7 to 4 days, there were no significant differences in the appearance and mouthfeel, and the beer satisfied the high quality demands. That is why the strain could be used in beer production safely.Uvođenjem ilv2:GLA isječka iz pMGI6, kao nosioca gena za glukoamilazu (GLA) i uporabom rekombinacijske sekvencije gena za α-acetolaktat sintazu (ILV2), konstruiran je rekombinantni soj pivskoga kvasca Saccharomyces pastorianus. Utvrđeno je da soj može koristiti škrob kao jedini izvor ugljika, da aktivnost glukoamilaze iznosi 6,3 U/mL, a da je aktivnost α-acetolaktat sintaze smanjena za 33,3 %. Uvedeni gen GLA, integriran u gen primatelja ILV2, raskinuo je jednu kopiju gena ILV2, dok je druga kopija ostala nepromijenjena. Prvi test fermentacije sladovine potvrdio je da je fermentacijom s pomoću rekombinantnog soja koncentracija diacetila smanjena za 65,6 %, a koncentracija ostatka šećera za 34,2 % u usporedbi sa sojem primatelja. U industrijskim uvjetima zrenje piva fermentiranog s pomoću rekombinantnog soja smanjeno je sa 7 na 4 dana, pri čemu nema značajne razlike u izgledu i okusu, te je ono zadovoljilo visoke zahtjeve. Stoga se ovaj soj može sigurno upotrijebiti u proizvodnji piva

Growth enhancement and drought tolerance of hybrid poplar upon inoculation with endophyte consortia

With increasing effects of global climate change, there is a strong interest in developing biofuels from trees such as poplar (Populus sp.) that have high C sequestration rates and relatively low chemical inputs. Using plant-microbe symbiosis to maximize plant growth and increase host stress tolerance may play an important role in improving the economic viability and environmental sustainability of poplar as a feedstock. Based on our previous research, a total of ten endophyte strains were selected as a consortium to investigate the effects of inoculation on commercial hardwood cuttings of Populus deltoides x P. nigra clone OP-367. After one and a half months of growth under non-stress conditions followed by one month under water stress, there was substantial growth promotion with improved leaf physiology of poplar plants in response to the endophyte inoculation. Furthermore, inoculated plants demonstrated reduced damage by reactive oxygen species (ROS) indicating a possible mechanism for symbiosis-mediated drought tolerance. Production of important phytohormones by these endophytes and identification of microbial genes involved in conferring drought tolerance suggests their potential roles in the modulation of the plant host stress response.Fil: Khan, Zareen. University of Washington; Estados UnidosFil: Rho, Hyungmin. University of Washington; Estados UnidosFil: Firrincieli, Andrea. Università degli Studi della Tuscia; ItaliaFil: Hung, Shang Han. University of Washington; Estados UnidosFil: Luna, Maria Virginia. Universidad Nacional de Rio Cuarto. Facultad de Cs.exactas Fisicoquimicas y Naturales. Instituto de Investigaciones Agrobiotecnologicas. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigaciones Agrobiotecnologicas.; ArgentinaFil: Masciarelli, Oscar Alberto. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Ciencias Naturales; ArgentinaFil: Kim, Soo-Hyung. University of Washington; Estados UnidosFil: Doty, Sharon L.. University of Washington; Estados Unido

Use of Acetolactate Synthase-Inhibiting Herbicides in Inzen Grain Sorghum (Sorghum bicolor L. Moench ssp. bicolor)

Grain sorghum is typically grown as a rotational crop in Arkansas because of its many benefits, one being the effective control of Palmer amaranth through the use of atrazine. However, limited options exist for postemergence (POST) control of weedy grasses within the crop. Inzen™ grain sorghum is the result of a nicosulfuron resistant weedy sorghum biotype cross-bred with a commercial line of grain sorghum. Inzen™ allows for safe use of over-the-top applications of nicosulfuron within the crop. Nicosulfuron is an acetolactate synthase (ALS)-inhibiting herbicide, which has historically been used in corn for control of weedy grasses. Experiments were conducted in 2016 and 2017 to (1) evaluate the tolerance of Inzen™ grain sorghum to various herbicides in Weed Science Society of America Group 2 ALS-inhibiting herbicides, (2) evaluate weed control programs utilizing nicosulfuron, and (3) determine the sensitivity of conventional grain sorghum to low rates of nicosulfuron and glufosinate. Results indicate Inzen™ grain sorghum was tolerant to ALS-inhibiting herbicides evaluated when applied directly to the soil prior to crop emergence (PRE). When ALS-inhibiting herbicides were applied to Inzen™ grain sorghum at the V4 growth stage, a high level of resistance was observed to all herbicides, with the exception of bispyribac-Na, which resulted in 20% visible injury and a 35% yield reduction. Additionally, weed control programs utilizing S-metolachlor preemergence and nicosulfuron + atrazine applied POST resulted in a yield increase along with acceptable control of both Palmer amaranth and johnsongrass. Finally, conventional grain sorghum appeared to be most sensitive to low rates of nicosulfuron and glufosinate at V8, flagleaf, or heading growth stages. Yield reductions of up to 96% were observed from rates of nicosulfuron equivalent to 1/10X of a labeled use rate. Nomenclature: Inzen; atrazine; byspyribac; glufosinate; nicosulfuron; S-metolachlor; johnsongrass, Sorghum halepense L. Pers.; Palmer amaranth, Amaranthus palmeri S. Wats.; corn, Zea mays L.; grain sorghum, Sorghum bicolor L. Moench ssp. bicolo